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The University of
Lethbridge
BIOLOGY 1020
Diversity of Life
LABORATORY MANUAL
Fall 2007
BIOLOGY 1020
Diversity of Life
Laboratory Manual
2007
Compiled and edited by:
J. Golden and K. White
Department of Biological Sciences
University of Lethbridge
Student Name:
Lab Day:
I.D. Number:
Lab Section:
Lab Time:
Instructor’s Name:
Office:
Email address:
Telephone:
Office Hours:
Lab Room:
TABLE OF CONTENTS
Laboratory Schedules
i
Emergency and Safety Information
ii
General Information
iv
Taxonomy and the Diversity of Life
1
Natural Selection and Phylogeny
9
The Protists
21
Soft-Bodied Invertebrates
31
Seedless Plants
41
Plant Anatomy
51
Seed Plants
63
Fungi
74
“Armoured” Invertebrates
81
Deuterostomes
91
Appendix I
100
Appendix II
104
Revised August 2007
i
BIOLOGY 1020
LABORATORY SCHEDULE
FALL 2007
DATE
EXERCISE
Sept. 10-14
Taxonomy
Sept. 17-21
Natural Selection & Phylogeny (2% quiz)
Sept. 24-28
Protists (2% quiz)
Oct. 1-5
Soft-bodied Invertebrates (2% quiz)
Oct. 9
Lab Exam 1: Time and Location TBA
Oct. 15-19
No labs
Oct. 22-26
Seedless Plants (3% assignment)
Oct. 29-Nov. 2
Plant Anatomy (2% quiz)
Nov. 5-9
Seed Plants (2% quiz)
Nov. 13-16
Fungi (2% quiz)
(Students in Monday sections must arrange to attend another section)
Nov. 19-23
“Armoured” Invertebrates (2% quiz and 3% assignment)
Nov. 26-30
Deuterostomes (2% quiz)
Dec. 4
Lab Exam 2: Time and Location TBA
Any questions concerning the laboratory should be directed to your lab instructor (see list below) or to Katrina
White, Biology 1020 Laboratory Coordinator (also listed below).
LAB INSTRUCTORS – CONTACT INFORMATION
Name:
Joanne Golden
Ali Krimmer
Nora Magyara
Chelsea Matisz
Julie Nielsen
Katrina White
Lab Number:
1
2
3
4
5
6
7
8
9
10
11
Office Number:
E782
C832
C732
D724
HH123
D885
Day:
Monday
Monday
Tuesday
Tuesday
Tuesday
Tuesday
Wednesday
Thursday
Thursday
Thursday
Friday
Telephone:
317-5035
317-5046
329-2105
329-2319
329-2172
329-2125
email:
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
SCHEDULED LABS: Fall, 2007
Time:
Room:
13:00-15:50
D720
13:00-15:50
C740
9:25-12:05
D720
9:25-12:05
C740
13:40-16:20
D720
13:40-16:20
C740
13:00-15:50
D720
9:25-12:05
D720
13:40-16:20
D720
13:40-16:20
C740
13:00-15:50
D720
Instructor:
Joanne Golden
Nora Magyara
Joanne Golden
Nora Magyara
Chelsea Matisz
Julie Nielsen
Joanne Golden
Ali Krimmer
Katrina White
Ali Krimmer
Katrina White
ii
GUIDELINES FOR SAFETY PROCEDURES
Students enrolled in laboratories in the Biological Sciences should be aware that there are risks of personal injury
through accidents (fire, explosion, exposure to biohazardous materials, corrosive chemicals, fumes, cuts, etc). The
guidelines outlined below are designed to:
a) minimize the risk of injury by emphasizing safety precautions and
b) clarify emergency procedures should an accident occur.
EMERGENCY NUMBERS:
City Emergency
Campus Emergency
Campus Security
Student Health Centre
9-911
2345
2603
2484 (Emergency - 2483)
THE LABORATORY INSTRUCTOR MUST BE NOTIFIED AS SOON AS POSSIBLE AFTER THE
INCIDENT OCCURS.
EMERGENCY EQUIPMENT:
Your lab instructor will indicate the location of the following items to you at the beginning of the first lab period.
•
•
•
•
•
•
•
Closest emergency exit
Closest emergency telephone and emergency phone numbers
Closest fire alarm
Fire extinguisher and explanation of use
Safety showers and explanation of operation
Eyewash facilities and explanation of operation
First aid kit
GENERAL SAFETY REGULATIONS:
•
•
•
•
•
•
•
•
Eating and drinking is prohibited in the laboratory. Keep pencils, fingers and other objects away from
your mouth. These measures are to ensure your safety and prevent accidental ingestion of chemicals or
microorganisms.
Coats, knapsacks, briefcases, etc. are to be hung on the hooks provided, stowed in the cupboards beneath
the countertops, or placed along a side designated by your instructor. Take only the absolute essentials
needed to complete the exercise with you to your laboratory bench.
Mouth pipetting is NOT permitted; pipet pumps are provided and must be used.
Always wash your hands prior to leaving the laboratory.
Students are not allowed access to the central Biology Stores area for any reason. Consult your instructor if you
require additional supplies.
Report any equipment problems to instructor immediately. Do NOT attempt to fix any of the equipment
that malfunctions during the course of the lab.
Use caution when handling chemical solutions. Consult the lab instructor for instruction regarding the
clean-up of corrosive or toxic chemicals.
Contain and wipe up any spills immediately and notify your lab instructor (see SPILLS below). Heed
any special instructions outlined in the lab manual, those given by the instructor or those written on
reagent bottles.
iii
•
Long hair must be restrained to prevent it from being caught in equipment, Bunsen burners, chemicals,
etc.
Dispose of broken glass, microscope slides, coverslips and pipets in the specially marked white and blue
boxes.
You are responsible for leaving your lab bench clean and tidy. Glassware must be thoroughly rinsed and
placed on paper toweling to dry.
•
•
SPILLS:
•
Spill of SOLUTION/CHEMICAL: While wearing gloves, wipe up the spill using paper towels and a
sponge as indicated by the lab instructor.
•
Spill of ACID/BASE/TOXIN: Contact instructor immediately. DO NOT TOUCH.
•
BACTERIA SPILLS: If necessary, remove any contaminated clothing. Prevent anyone from going near
the spill. Cover the spill with 10% bleach and leave for 10 minutes before wiping up. Discard paper
towels in biohazard bag. Discard contaminated broken glass in designated biohazard sharps container.
DISPOSAL:
•
Broken glass, microscope slides, coverslips and Pasteur pipets are placed in the upright white ‘broken
glass’ cardboard boxes.
•
Petri plates, microfuge tubes, pipet tips should be placed in the orange biohazard bags. The material in
this bag will be autoclaved prior to disposal.
•
Liquid chemicals should be disposed of as indicated by the instructor. DO NOT dispose of residual
solution in the regent bottles. In case of any uncertainty in disposal please consult the lab instructor.
HEALTH CONCERNS:
•
Students who have allergies, are pregnant, or who may have other health concerns should inform their lab
instructor so that appropriate precautions may be taken where necessary.
iv
BIOLOGY 1020 GENERAL INFORMATION
Preface:
Biology 1020 is an introductory course on organismal diversity and forms part of the core program offered by the
Department of Biological Sciences. Together with Biology 1010 (The Cellular Basis of Life), you are provided with
suitable background to continue your study of biology in the Department.
Biology 1020 is designed to provide you with a comparative study of the major lineages of organisms (focusing
mainly on the eukaryotes) from an evolutionary perspective. The primary goal of this course is thus to develop an
understanding of the evolution and general characteristics of each major taxonomic group. The laboratory
component of the course has been designed to closely complement the lecture component. You will have an
opportunity each week to examine in depth the organisms described in lecture so that concepts introduced there will
be reinforced in your laboratory.
There are two major approaches to the study of biology. The experimental approach is what most people think of as
science. The experimental technique involves the development and testing of hypotheses using what we term
“scientific method”. On the other hand, the comparative approach involves examining different organisms (or organ
systems, organs, tissues, etc.) to try to understand how they are related to the environment in which they exist.
Analysis of characteristics that may be shared with other organisms allows for the development of phylogenetic
relationships and may suggest what forces have been involved in the evolution of such traits. The laboratories in
Biology 1020 generally follow the latter approach.
Objectives:
The objectives of the laboratory for Biology 1020 are:
1.
To be able to identify the major groups of organisms based on the characteristics they possess, and to recognize
the phylogenetic relationships between them.
2.
To develop an understanding of the role of natural selection and evolution in explaining the diversity of life
observed.
3.
To gain an appreciation for the diversity of life on earth in the past, and currently.
4.
To gain practical experience in using laboratory equipment, particularly dissecting and compound light
microscopes. Microscopy is a fundamental tool in the study of biology.
v
Your Laboratory Experience:
Your attitude about the laboratories in Biology 1020 will to a great extent determine the outcome of your lab
experience. If you are interested in learning about different organisms, and why they appear the way they do, then
the laboratory should prove to be a pleasant and rewarding experience. The laboratories themselves are reasonably
unstructured; it is important that you develop the mental discipline required to work your way independently
through the exercises. The laboratories require that an appropriate amount of time and energy be spent observing
the specimens. The labs are designed to occupy the amount of time allocated to them (nearly 3 hours), and you
should plan to spend the full time in lab every week. Although some opportunities for review of materials are
available to you via our internet resources, you will not have an opportunity to reexamine specimens from labs prior
to the lab exams.
We have made every effort to incorporate live material as much as possible into these laboratories. Much of the
beauty of these organisms is lost when they are preserved or dried. However, living organisms are very expensive
and must be treated with the appropriate care and respect if all students are to have the opportunity to see them.
The same level of care should be taken when handling preserved or dried materials; in many cases, the specimens
are irreplaceable.
A few steps are required to make your lab experience go smoothly. It is worthwhile to read your manual prior to
attending lab. This ensures that you are aware of what needs to be completed during the exercise. It is useful to
bring lecture notes and your textbook to labs, as they provide you with valuable information regarding the organisms
you will examine. The textbook in particular is useful as it contains many illustrations and photographs of
organisms you will look at. Biology 1020 has an extensive set of web pages relating to laboratory materials you will
view. In the past, students have made use of these to review materials that are on display that week. More
information about our web pages is found in the next section. Finally, we have designed a series of interactive, webbased quizzes that will enable you to test your knowledge of concepts and organisms studied in each exercise.
Access to these quizzes is also explained in the next section. Your laboratory instructors are available during class
time and during their office hours to help you with any questions or problems you may have. Please consult them;
they are there to help you.
Internet Resources:
Many of the materials that you will examine in Biology 1020 labs have been placed on the internet for your use.
The same is true for many of the courses offered by the Biological Sciences Department. We strongly encourage
you to make use of this excellent resource.
To access information on the internet, you will need to access a computer on campus, or use a modem connection
from a computer you have at home. Information Technology (D547, or http://home.uleth.ca/css) can help you
establish a remote connection. The URL for the Biology 1020 web pages is:
http://classes.uleth.ca/200703/biol1020a/
From here, you can browse through any of the materials we have on the web, and visit other related sites.
vi
You may also wish to make use of the electronic mail facilities available. All students are automatically assigned an
email address upon registration. Talk to Information Technology if you are unsure about how to use email.
Dissections:
This semester, you will be introduced to the art of dissection. As with any other component of Biology 1020 labs,
we will not force you to perform the dissections, but if you choose for any reason not to participate, recognize that
you are still responsible for the material presented.
No one can tell you how to dissect; it must be learned through practice. There are, however, some helpful hints that
will improve your acquisition of dissecting skills.
1.
Dissection is not surgery. It is not your objective to put the organism back together again, so you can be less
cautious about your procedures. Generally, if particular caution is required, you will be given notice of this in
the laboratory instructions.
2.
Point #1 notwithstanding, do not take any action on your specimen without clearly understanding what you are
doing. Do not proceed through a dissection sentence by sentence, but be sure you have read the entire set of
instructions first, and preferably before coming to lab.
3.
Never cut when you can rip or tear. Most dissections involve clearing away connective tissue. Since your
ability to see the organ or structure you want to expose is limited until you have cleared such tissue away, you
cannot see clearly what you are doing. Thus, cutting may lead to accidental slicing of underlying tissues.
Connective tissue often can be pulled away with forceps, or the back end of a scalpel or forceps, or with a
dissecting needle. (Most times when you want to cut, you shouldn't; usually, cutting is necessary only to part
the integument of the specimen in order to get inside.)
4.
When pinning out a specimen in a dissecting tray, keep the heads of the pins as far to the side as possible so
they won't interfere with your work. Drive the pins fairly deeply into the wax, so they won't come out while
you are working.
Other Laboratory Considerations:
•
Always leave your microscopes as you find them (or should find them): the scanning objective in place, the
cord CAREFULLY wrapped around the lower arm and lamp housing, and the dust cover in place.
•
When you are done for the day: return all prepared slides to their proper trays, rinse and dry all glassware and
dissecting instruments after use; remove pins from specimens you are going to discard; and place discarded
SHARPS (slides, cover glasses, scalpel blades, etc.) only in containers labeled for that purpose, and clean
and dry lab benches before leaving the lab. Your cooperation in this will be appreciated by cleaning staff.
vii
Laboratory Grade Distribution And Evaluation Procedures:
Laboratory Evaluation:
The lab portion of Biology 1020 is worth 40% of your total course grade. Evaluation for the lab will be made up of
quizzes, assignments, and lab exams.
Lab Mark Break-down:
Quizzes (8 in total, worst mark dropped)
14%
Assignments (2 in total)
6%
Lab Exam 1
8%
Lab Exam 2
12%
Total
40%
Quizzes are held promptly at the beginning of each lab period. You should plan to arrive a few minutes early. You
will not have an opportunity to make up a quiz missed due to lateness.
If you miss your regular lab during the week, you will be required to provide a doctor’s note (or other official
documentation) to be excused from the quiz. You should also inform your lab instructor and arrange to attend an
alternate section to view the lab material. Unexcused quizzes will receive a grade of zero.
Lab exams will be offered in several sittings to accommodate all students’ schedules. There will be no opportunity
to make up a missed exam. Appropriate documentation must be provided to have an exam waived. Without
documentation, a missed exam will result in a grade of zero.
If a quiz or exam is missed due to a foreseeable event (e.g. upcoming surgery), documentation must be provided
before the date of the quiz or exam. If a quiz or exam is missed due to an unforeseeable emergency (e.g. sudden,
serious illness), documentation may be provided up to seven days after the quiz or exam.
1
TAXONOMY and the DIVERSITY of LIFE
Introduction
Until the 1960s, biologists classified all life into one of two kingdoms - plants and animals. In 1969, Robert
Whittaker proposed a Five Kingdom system, adding Monera (bacteria), Protista, and Fungi to the existing
Plantae and Animalia Kingdoms. More recently, molecular biology techniques such as DNA sequencing and
protein analyses have shown that this Five Kingdom model is inadequate and that Kingdom-level classification
will undergo taxonomic revisions. Kingdom Protista for example has been split into as many as 20 kingdoms
using molecular data.
It is clear that at the highest level, there are three broad groups (usually designated Domains) into which all
organisms fall – Domain Bacteria, Domian Archaea, and Domain Eukarya (Eukaryotes). Bacteria and
Archaea will largely fall outside the scope of Biology 1020. In this course, we will concentrate on the diversity
found in the Domain Eukarya and examine several clades within the former “Kingdom Protista”, as well as
organisms that fall within the traditional Kingdoms Plantae, Fungi, and Animalia.
Today, your first task will be to develop your observational skills for the purpose of “classifying” the diversity
of organisms in front of you. We will spend the better part of the lab looking at select organisms from all
groups, developing a list of characteristics that describe them, and relating them to taxonomic hierarchy. You
will also have an opportunity to use some of the tools available for taxonomic investigations.
In preparation for lab, please read pages 13, 443-451, 495-497, and 529-531 of Campbell and Reece (2005), and
Appendix I of the lab manual.
Laboratory Objectives:
At the conclusion of today’s lab, you should:
•
Be familiar with the use of a compound light microscopes: to prepare wet mount slides, and to find and focus on
a microscopic specimen
•
Be able to define and describe taxonomy, and recognize taxonomic hierarchical categories
•
Be able to recognize a few Latin binomials and suggest names for new organisms
•
Be able to use a dichotomous key to identify organisms
A. Microscopy
Throughout the Biology 1020 labs, you will be using both dissecting and compound light microscopy to view
minute details of specimens. Appendix I at the end of your lab manual details the use of both types of scopes.
Your lab instructor will lead you through the setup and use of the microscopes during today’s lab, but you
should feel free to consult Appendix I at any time during the term.
2
Use a Pasteur pipette and bulb to remove a drop of scummy pond water as directed by your lab instructor.
•
Prepare a slide for viewing under the compound scope by making a spiral of Vaseline on the slide and
putting your drop of water inside the spiral.
•
Try to include tiny bits of plant and algal material.
•
Add a cover slip and take it to your scope.
•
Examine the slide’s contents carefully, watching for movement of microscopic organisms, or for green
colouration, or any other evidence of structures.
B.
•
Try again if unsuccessful the first (or second, or third) time.
•
Sketch what you see and suggest a possible identity of your organism in the space below.
Taxonomy is the branch of biology that deals with naming and classifying the diverse forms of life. There
are three facets to taxonomy:
1.
Arrangement of organisms into groups based on shared similar characters (classification);
2.
Assignment of names to the groups (nomenclature); and
3.
Arrangement of the classification into a form, such as a dichotomous key which can be used to identify
specimens (identification). You will be introduced to the use of a dichotomous key as a tool for
identifying organisms in this lab.
I.
Classification:
On the tray at your bench and at the side benches of the lab are 30 examples of organisms from Domain
Bacteria and Domain Eukarya. The bacteria should be easy to identify in the set of organisms. Can you recall
from your high school biology what characters separate the two groups? Once you have determined the
specimens that fit in Domain Bacteria, you should put their name(s) in “Group 1” in the table below and list the
characters that define them. Next, use the remaining specimens (from Domain Eukarya) to form sets that
logically “group together”. Work with the people at your bench to complete this exercise.
•
Use attributes that are observable. (You may use your textbook to look up characteristics and traits.)
•
Examine each specimen closely, then sort it into one of about 4 or 5 groups so that all members of a
group exhibit the same characteristic. For example, group 2 may be “animals that walk on 2 legs” so
all specimens in that group will exhibit bipedalism. They may differ in skin covering or habitat
preference, but they will all walk on two legs. Ideally the members of a group will relate more closely
to one another than to organisms in other sets.
•
List the characters (=traits) you used to define each of your groups in the box at the bottom of each
column.
•
Do your colleagues agree on your final lists?
•
Check with other groups to see if they agree with your classification. Why do you agree / disagree?
3
Group 1
Group 1 Traits:
Group 2
Group 2 Traits:
Group 3
Group 4
Group 3 Traits:
Group 4 Traits:
Group 5
Group 5 Traits:
II. Nomenclature
A. Hierarchy
When considering an organism such as a dog, it is first recognized as a eukaryote (domain), then as an animal
(Kingdom), then chordate (Phylum), vertebrate (Class), mammal (Order) canine (Family) and so on. The entire
hierarchy from the most to the least inclusive is:
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
In the eighteenth century, Carolus Linnaeus assigned a two-part Latin name called a binomial to over 11,000
species of plants and animals. The system he devised is still in use today.
•
The first word designates the genus (plural, genera) to which the organism belongs, the second word is
the specific epithet, and both words together constitute the species name. By convention, these two
words are either italicized or underlined.
•
The genus name is capitalized whereas the specific epithet is not. Different species within a genus will
have the same first word in their name, but will have a different specific epithet. For example, Canus
familiaris is the scientific name for your family’s dog, and Canus lupus is the scientific name for the
grey wolf, Canus rufus for the red wolf, and Canus latrans for the coyote. All belong in the Family
4
Canidae. All are more related to each other than they are to other members of the Order Carnivora like
grizzly bears (Ursus horribilis), bobcats (Lynx rufus) and skunks (Mephitis mephitis).
The “bull’s eye” diagram below is an example of a typical hierarchical system used to classify organisms.
While this one will be complete for only Homo sapiens, most of the specimens in front of you can be placed
into at least one or more hierarchical levels. At least one specimen in your collection will fall outside of
Domain Eukarya.
•
Use the specimens from part I and place the number of each organism in the hierarchical levels so that
the group in the center is a subset of the group that surrounds it. The domestic dog, #2, is done for
you.
•
All specimens should be assigned. To get started you should go to your text and look up characters
that might define organisms in each of the hierarchical levels, then examine each of the 30 specimens
to determine if those characters are present.
•
When you are finished, your hierarchy should look something like Fig. 1-14 on p. 13 (Campbell and
Reece, 2005).
Fig. 1 Bull’s eye diagram of hierarchical levels showing nested groups for sorting 30 different organisms.
The hierarchy can also be shown as a tree similar to the diagram below. Like the bull’s eye diagram above, this tree
includes only select representatives of each of the hierarchical levels. Note that only three Kingdoms of Eukarya are
shown (Animalia, Fungi, Plantae), and the “candidate” Kingdoms of protists are joined to the base of the tree by a
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series of dashed lines. As you will see in subsequent labs, there are far more phyla, classes, orders, families, etc.
than illustrated here.
To add other groups (lines) to the tree, you first have to decide what characters your groups do or do not possess,
then connect the line to the branch where those characters might be found. For example, a salamander is a member
of Class Amphibia. It is a member of Phylum Chordata, so your line will connect somewhere to the branch
originating above Chordata. Similarly, it possesses a cranium, so the line must connect somewhere above Craniata.
However, the salamander is not a reptile or a mammal, so we know the line must join the main branch somewhere
below these two classes.
•
Complete the following exercises (use your text for characters if needed):
o
Draw and label a line on the tree where you might expect to find a) frogs, b) sharks,
o
Circle and label a group that might include c) lobsters, d) bread molds, and e) ferns.
o
Follow the lineage of Homo sapiens down from the species level to the Domain. In what
family does the species belong? In what Order, Class, and Phylum does Homo sapiens
belong?
Fig. 2 Tree diagram showing hierarchical levels in a hypothetical phylogeny of eukaryotes.
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B. What’s in a name?
When naming an organism, taxonomists usually attempt to use descriptive words that apply to the organism.
For example, Helianthus annus, is the large yellow-flowered plant that you find growing along the trail in the
coulees below the university (still flowering in September). Heli- is a Greek term for “the sun”, =anthus means
“flower”. The species epithet, annu, is Latin meaning “a year”. The plant is an annual sunflower that grows
from seeds every year.
Based on the scientific name alone, you can often predict characteristics of a species.
•
In the table below, you have been given the genus and species names of 10 organisms
•
Without referring to pictures or drawings, use the species name to predict what the organism is and
some of its characteristics
•
Start by breaking the genus and specific epithet names into component parts, i.e. root words. There
may be 2 or more root words for each.
•
Look up the meaning of each part using the list on the following page
•
Use you own words to describe what the organism might look like.
•
You have been given the type of organism for 5 of the 10 species. For the remaining organisms,
suggest what type of organism each might be.
Scientific name:
Spirogyra crassa
Type of organism
Filamentous green
algae
Agaricus bisporus
Pisaster giganteus
Amoeba proteus
Animal-like
protists
Hydra vulgaris
Aquatic animals
Volvox globator
Colonial green
algae
Lumbricus terrestris
Marchantia
Low-growing
polymorpha
green plants
Zea nicaraguensis
Cycas revoluta
Predicted description of organism:
7
Note: The basic word roots below may be used as suffixes, prefixes, or terminal roots. (G. stands for Greek,
L means Latin is the source language)
Word root
agaric
ameb
aster
bi
crass
cycad
gigan
glob
gyra
hydra
lumbric
morpha
pisc
poly
proteus
revolut
spiro
spor
terrestr
volv
vulga
zea
Source language
(G.)
(G.)
(G.)
(L.)
(L.)
(G.)
(G.)
(L.)
(L.)
(G.)
(L.)
(G.)
(L.)
(G.)
(G.)
(L.)
(L.)
(G.)
(L.)
(L.)
(L.)
(G.)
English meaning
mushroom
change
star
two, twice, double
thick
a kind of palm
giant, very large
ball, globe
round, turning
water
earthworm
form
fish
many
mythical god that could assume many forms
rolled back
a spiral, coil
spore, seed
on land
roll, turn
common
grain
What advantage would scientific names have over common names when referring to biological organisms?
III. Identification
Dichotomous keys are useful tools to help you correctly identify names of organisms. Although many picture books
and photographic atlases are available, keys provide the fastest and most reliable method of identification.
Taxonomic (=dichotomous) keys are constructed in a series of paired, mutually exclusive statements (couplets) that
divide a set of objects into smaller and smaller groups in a series of steps. At each step in the key, you are asked to
decide which statement is applicable, at which point you will be referred to another couplet, where you will again
make a choice. The process is repeated until you arrive at the name of the object.
Your instructor will demonstrate how to use a short key to 4 or 5 common objects.
Work with your classmates at your bench. Use the key provided to identify 10 of the specimens from part I.
•
To use a dichotomous key, you must follow several basic guidelines:
o Always read both choices
o Be sure you understand the meaning of the words in the couplet
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o If you come to a couplet where the choice is not clear or you do not have enough information, try
both choices. You will eventually get to a spot where it is clear whether you have chosen the
wrong couplet or that the description fits.
o Check the identity of your specimen with outside sources (your instructor)
•
Key out the set of specimens indicated by your instructor and fill in the number and species names below:
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
You will also have an opportunity to use dichotomous keys in the Fungi lab later in the semester.
9
NATURAL SELECTION AND PHYLOGENY
Background Reading:
Pages 446-448 (Ch. 22), 464-470 (Ch. 23) 497- 500 (Ch. 25) of Campbell and Reece (7th ed., 2005). The introductory portions of this lab exercise are much longer than most. You should read them carefully before coming to
lab.
A. Introduction
The theory of evolution is the basis of much of our understanding of the biological diversity we see in the world
today, and in the fossil record. In 1859, Charles Darwin published his book, The Origin of Species, which presented
the concept of natural selection. The main idea of natural selection is that a population of organisms will change
over time if individuals possessing certain heritable traits have better reproductive success than other individuals.
Populations contain a pool of variable phenotypes that have arisen through random mutations and recombination.
In certain environmental conditions, specific characteristics enhance the reproductive success and survival of an
individual bearing that favourable trait. The result is an increase in relative proportion of the advantageous
phenotype in the next generation of a population. This differential success is the mechanism of adaptive evolution.
Small-scale evolutionary changes such as gene frequencies within a population are known as microevolution. The
two main mechanisms are natural selection and genetic drift.
Darwin proposed the idea of descent with modification, which links all organisms back to some common ancestor
millions of years in the past. Over time, and through the pressures of natural selection and genetic drift, populations
became more and more dissimilar. At some point individuals in the populations are no longer capable of
reproducing with their ancestral organisms, and a new species is formed. Macroevolutionary events result in the
creation of a new species or taxonomic group, one that is distinct from the original “parent” form.
Laboratory Objectives:
Today you will build on the concept of divergent evolution that was introduced in last week’s lab. You will look at
the mechanisms that are responsible for maintaining advantageous phenotypes in a variable population. You will
also construct phylogenetic trees in order to learn about how linkages are recognized between different groups of
organisms that likely shared a common ancestor in their evolutionary history.
At the conclusion of today’s lab, you should be able to:
•
Define and describe natural selection as a mechanism of microevolution.
•
Understand the general processes that lead to changes in the gene pool of a population.
•
Define and describe phylogeny, and apply terminology associated with phylogenetic trees.
10
B. Natural Selection
Because evolution occurs over a long time period it is difficult to look at in nature. However, many of the selection
pressures are measurable and we can see the process of natural selection at work if we look at a few subsequent
populations. We know that mutations occur at random in populations and that they contribute to changes in the
genetic make-up of the population. If a mutation is advantageous, it will likely become more prevalent within the
population over time. Looking at some observations of nature and then making inferences from those observations
can help us logically break down Darwin’s theory of natural selection.
Facts Based on Observations of Nature:
•
Organisms express variations, some of which are inheritable.
•
More individuals are born than survive to reproduce.
•
Competition for resources occurs between individuals.
Inferences from Observations:
•
The characteristics of some individuals make them more able to survive and reproduce under certain
environmental conditions.
•
Environmental pressures “select” against non-adaptive traits and only individuals with adaptive traits live
long enough to pass those traits on to future generations (survival of the fittest).
Selection for mutations can be driven by a number of selection pressures. Some examples of these include
predation, competition, and environmental factors (such as temperature, precipitation, or soil quality). A trait that
makes individuals have better fitness in any of these areas may increase the chance that those traits are passed on in
future generations.
Today you will focus on how predation can be an important selecting pressure on adaptations within populations,
but you should think about how the influences you see today are important for other selection pressures as well.
Predation Simulation
As you complete the model predator-prey exercise, think about the selection pressures that are affecting which prey
are more “fit” than others in each scenario.
Protocol
1.
Work in groups of four to complete the exercise. Within your group, choose an individual to perform each
of the following tasks:
•
Recorder – records data
•
Prey monitor – counts the prey, distributes new prey, and monitors the foraging trial
•
Predator – manipulates the foraging tools to capture prey during each foraging trial.
•
Timer – times the foraging trials.
11
2.
Two habitat types are available in which to conduct the simulation. Your lab instructor will indicate which
habitat type your group should use. In this simulation there are two frog species that live in both habitats
types. You will act as a predator and forage the habitat for the frog prey in timed foraging trials.
3.
The prey monitor sets-up each foraging period by scattering the prey through the habitat. For the first
foraging period scatter 10 prey of each type (20 frogs in total). The predator will start foraging from a
random position in the habitat and work through the habitat for 10 seconds.
4.
You will conduct four timed foraging trials. Place the prey consumed by the predator in a dish labeled with
the trial number. Count the number of each prey type captured and record it in Table 1.
5.
At the end of each foraging trial, calculate the number of prey of each type that are left in the habitat
(subtract the number captured from the number you started with). Record this number under “Surviving”
in Table 1. To represent reproduction within the population, allow each prey to add another prey of the
same type to the population (e.g. if you calculated that there are five frogs of one species remaining add
five more similar frogs to the habitat). After you have reproduced all the prey, make sure you take note of
the new starting totals for the next trial. At the end of the fourth trial, do not reproduce the prey.
6.
At the beginning of each foraging period, the prey monitor will randomly scatter the newly reproduced prey
across the habitat. The predator should not watch.
7.
After you have completed all four trials, remove the remaining prey. Count the number of survivors from
each species. Calculate the total number captured from each species by summing those captured in all
trials.
8.
Repeat the procedure with a new foraging tool.
Table 1. Number of prey captured and surviving in all foraging trials. Two experiments were run using different
foraging tool in each.
Foraging
Trial #
tool
Pinchers
Species A
Start
1
Captured
Species B
Survived
Start
10
10
10
10
2
3
4
Sticky
1
stick
2
3
4
Captured
Survived
12
Fill in Table 2 to allow comparison of results with the different foraging tools. Add all the prey captured during
each four-trial foraging simulation (from Table 1) to calculate the total number captured. Compare your results with
a bench that used the other habitat type. Use their data to fill in the section labeled ‘Habitat B’ in Table 2.
Table 2. Final number of prey surviving compared to total number captured in each habitat type with each foraging
tool.
Habitat A:
Foraging Tool
Species A
Surviving
Species B
Captured
Surviving
Captured
Pinchers
Sticky stick
Habitat B:
Foraging Tool
Species A
Surviving
Species B
Captured
Surviving
Captured
Pinchers
Sticky stick
Use your data and that collected from a group working with the other habitat type to construct a graph illustrating
the total number of prey of each type captured in the two different habitats with the two different foraging tools
(graph paper will be provided for you). Think carefully about how this graph should be constructed to best show the
effect of habitat type or foraging tool on prey capturability. Consult with your instructor or classmates if you are
unsure.
Now, use your graph and your noted observations to answer the following questions that apply to your model
system, as well as to real predator-prey relationships.
1.
Look at the number of each prey type caught in the two different habitats. Does prey colour have an effect
on capturability?
2.
Did the foraging tool used affect the amount of prey collected? Explain.
13
3.
Describe any evidence shown for natural selection of particular colours over the various trials.
4.
The most obvious cases of natural selection were likely seen in the prey, however natural selection works
on predator species as well. Did any changes in your foraging behaviour occur over time? If so, what were
they and how might similar types of changes affect predator success in the wild?
5.
In this exercise, you observed how predation pressure can cause natural selection for certain traits in a prey
population. What are other naturally occurring selection pressures that could cause changes in populations
over a long term?
14
C. Phylogeny
A phylogeny is a hypothesis of evolutionary history among a set of organisms. It is most often depicted as an
evolutionary tree that shows which species are closely related and in what order related species evolved. Generally,
two species will be more different if there is a long period of time since they shared a common ancestor, and more
similar if they diverged more recently. The following exercises will introduce you to the steps used to construct a
phylogeny, and a computer program used to examine phylogenetic trees, as well as introduce some of the general
concepts and terminology used when studying phylogenetics and the process of evolution.
Remember that last week, you learned about the concept of divergent evolution, the increasing dissimilarity
between two or more populations that were originally one, which accounts for much of the species diversity we see
today. Before beginning the phylogeny exercise, we need to explain some other terms that come up frequently in
discussions of evolution:
[a] Primitive (ancestral) and advanced (derived) - A structure is primitive or ancestral if it is found in the
earliest member of an evolutionary lineage. A structure is advanced or derived if it is found in later
members of the lineage and is changed from the ancestral form.
[b] Homologous structures and analogous structures - Homologous structures are structures that are similar in
different organisms because of a shared ancestry. In its broadest sense, homologous means descended from
the same primitive structure. For example: all tetrapod forelimbs have a common structure, one bone in the
upper arm (the humerus) and two bones in the lower arm (the ulna and the radius). The forelimbs of
humans, bats and birds are homologous because they are all derived from an ancestor that had the basic
forelimb plan.
[c] Structures that perform the same function without being homologous are called analogous. Because they
perform the same function, these structures are often superficially similar in form. How do they come to
resemble one another if they were not derived from a common ancestral character? The answer lies in
convergent evolution. Species from different evolutionary lineages may have similar ecological roles, and
natural selection then shapes analogous adaptations. An example is body shape of a shark and a whale.
The similar fusiform body shape functions in efficient propulsion through an aquatic environment.
15
C-1. Phylogenetic analysis of cartoon cladisticules.
To construct a phylogeny, several steps must be followed:
•
Create a table of character data for the taxa that you are studying.
•
Determine outgroup (closely related taxon but not part of the group under study). The Outgroup
characters are used as the ancestral character state for the Ingroup.
•
Determine homologous characters (characters that are similar because of common ancestry), and
character states. A large number are needed to be sure that all available information is included in
the phylogeny. Characters are chosen because their form, or character state, differs between the
taxa under study and their common ancestor.
16
•
Fill in data matrix of characters states for all taxa. The character state shown by the outgroup is
always coded as (0), as illustrated in character 1.
The Outgroup (Joe), Ingroup (April, Mike, Tanya, Bobby, Jason, Jerry, Jane) and first two homologous
characters are already set up for you.
•
Work in pairs and identify 5 more characteristics and code the character states.
•
Fill in the table of character states for all Cladisticules.
Table 3. Data matrix of seven homologous characters for 8 cartoon cladisticules. Character states are
designated as (0) or (1) for each character. Joe is the outgroup taxon.
1. Head fused
2. Feet
to Thorax
2 toes (0)
Yes (0)
3 toes (1)
3.
4.
5.
6.
7.
No (1)
Joe (OG)
April
Mike
Tanya
Bobby
Jason
Jerry
Jane
Can you suggest additional characteristics that should have been included in the data matrix?
C-2. MacClade
Using the computer program, MacClade 3.1, you will work in pairs to construct a most parsimonious tree
depicting the phylogeny of cartoon cladisticules above. Your final task will be to construct a phylogenetic tree using
the data set of characters for vertebrates on the desktop of your computer.
In phylogenetics, parsimony relates to the number of times a character changes from one state to another. A
parsimonious tree will be the tree with the fewest number of changes (=steps). Ideally, we are also looking for a tree
with character changes appearing only once. This is a statistic called consistency index (=CI). A CI of 1.0 is more
parsimonious than a tree with a CI of 0.35. Watch for these numbers in the lower right hand corner of your
computer screen.
17
Your lab instructor will step you through the operation of the MacClade program. Please do not randomly click on
icons or get ahead of your instructor – it is easy to get ‘lost’ in this exercise.
1. Open the file called “Cladisticules”. Note your starting tree length and CI.
Starting tree length _______ steps.
Starting CI __________.
To manipulate your tree, click on a branch and drag it to a new branch. Try to group taxa that show shared derived
characters. By doing this, you are attempting to uncover monophyletic groups that are made up of an ancestral
species and all of its descendents (Fig 25-10, p. 498). Your tree length should go down and the CI should go up as
you approach the most parsimonious tree for this data set.
Final tree length _______ steps.
Final CI __________.
Draw your final tree in the space below. Indicate the evolutionary changes on the branches by placing the character
number below the group in which it appears. Do any characters appear more than once on your tree? If yes, which
one/ones?
2.
Close the “Cladisticules file by selecting “Quit” in the FILE menu. DO NOT SAVE THE CURRENT TREE.
3.
Open the file called “Vertebrates”, and construct a phylogenetic tree in the same way as you did for the
“Cladisticules” data set. Note the starting tree length and CI.
4.
Complete the table on the following page. Use your tree to find monophyletic groups including 2, 4, 5, 7 and 9
taxa. You should be able to find at least one group that is defined by two or more characters.
18
5.
Close the “Vertebrate” file by selecting “Quit” in the FILE menu. DO NOT SAVE THE CURRENT TREE.
Notes on terms used in Vertebrate phylogeny:
•
Cranium is the skull or braincase.
•
Carpals and tarsals are bones in the ankles and feet.
•
Amniotic membranes protect eggs laid on land from desiccation.
•
Diapsids have two large holes in the sides of the skull for jaw muscles to pass through.
•
Glandular skin in amphibians often secretes poisons that deter predators.
•
Fenestra is an opening in the skull.
•
Warm-blooded animals (endotherms) generate most of their heat internally.
References
Campbell, N.A. and J. B. Reece. 2005. Biology. 7th ed. Benjamin Cummings: San Francisco, CA.
Cunningham, W.P. and B. W. Saigo. 2001. Environmental Science: A Global Concern. 6th ed. McGraw Hill: New
York, NY
Mischler, B. 2005. Building the Tree of Life. National meeting of the Botanical Society of America, Austin, TX
Pough, FH, CM Janis, and JB Heiser. 1999. Vertebrate Life. 5th Ed. Prentice Hall, Upper Saddle River, NJ.
If you are interested, check out the “Tree of Life web project” at the following URL:
http://www.tolweb.org/tree/
19
Group
Taxa in group
size
2 taxa
2 taxa
4 taxa
5 taxa
(=Diagnostic characters)
____________
____________
____________
_____________
____________
____________
____________
____________
____________
____________
____________
____________
__________
7 taxa
____________
____________
____________
____________
____________
____________
__________
9 taxa
Shared derived character(s)
____________
____________
____________
____________
____________
____________
____________
____________
__________
20
Possible Exam Questions:
1.
The ancestors of hominids were quadrupeds, walking on four legs. Humans are bipedal. Is this character
derived or ancestral? Are the walking habits of chimpanzees primitive or advanced?
2.
Consider the shell of a turtle and the shell of a snail. Are they homologous or analogous? Why? What
type of evolution is this an example of?
3.
Are the wings of birds and insects homologous or analogous? Explain.
4.
The common ancestor of all the tetrapod vertebrates had four limbs with a similar skeletal structure to that
seen in many vertebrates today. Considering this, in what sense are the arms of humans homologous to the
wings of a bird?
5.
The green algal ancestors of plants existed in aquatic habitats, contained chlorophyll a and b, and had cell
walls composed mainly of cellulose. Land plants also contain chlorophyll a and b and have cell walls of
cellulose. What traits in the land plants are primitive? What trait represents divergent evolution from the
ancestral form?
21
THE PROTISTS
A. Introduction:
Protist taxonomy is currently in a state of flux. Nucleic acid sequencing and cell structure studies have given
systematists evidence that they can use to begin sorting protists into monophyletic groups. Campbell and Reece
(2005) note that some systematists have split the protists into up to 20 kingdoms to more accurately reflect the
evolutionary relationships among these organisms. You should be aware of the current state of protistan
taxonomy (see Figure 28.4 in Campbell and Reece (2005) for a nice summary), but today we will focus on
simply observing a wide diversity of protists.
Protists are the most diverse of all the eukaryotes and may exhibit a range of animal-like, fungus-like, or plantlike characteristics. These characteristics are often considered when studying protists, but it is important to
remember that they have little basis in either phylogeny or taxonomy.
The Protists are also very diverse in terms of their sexual life cycles. The life cycles are named based on when
meiosis occurs and what the products of meiosis are. You will be introduced to these in today’s lab, but you
will need to consult the information in Part B periodically throughout the rest of the semester.
You should read pages 242-243 and Chapter 28 of Campbell and Reece (2005) in preparation for this exercise.
Laboratory Objectives:
At the conclusion of today’s lab, you should be able to:
•
Recognize members of different protist “phyla”, and indicate which features define each group
•
Identify structures associated with various organisms and give their function
•
Describe the events associated with the three types of life cycles, and to relate the life cycles to the
organisms studied in today’s exercise.
Note: See Appendix 1 for information on the use of the compound microscope and preparation of wet
mount and Vaseline mount slides.
B. Life Cycles and Sexual Reproduction:
When looking at a diversity of organisms, it is essential to have some understanding of life cycles. The
information outlined for you here will prove to be useful in this exercise as well as others throughout the
remainder of the term. You should refer back to this section repeatedly over the next several weeks.
There are three basic types of life cycles (exhibiting zygotic, sporic, or gametic meiosis) that can be used to
describe all organisms (Figure 1). Each of the three cycles is similar in that (i) a haploid (n) phase alternates
with a diploid (2n) phase; (ii) to get to the haploid phase from the diploid phase, meiosis has to occur; and (iii)
to get to the diploid phase from the haploid phase, fusion of gametes (syngamy) must take place. The life
cycles differ with respect to the timing of meiosis and fertilization, and what the products of meiosis are.
22
1. Life Cycle Exhibiting Zygotic Meiosis:
Zygotic meiosis is very common in organisms like green algae and fungi. In this type of life cycle, the
organism exists for most of the cycle as a multicellular, haploid organism. This organism at some point
produces gametes via mitosis, which then unite to form a diploid zygote. The zygote undergoes a meiotic
division and haploid spores are the result. These spores germinate to produce a new multicellular gametophyte.
Hence, the only multicellular stage is the gametophyte, and meiosis takes place in the zygote to produce spores.
2. Life Cycle Exhibiting Sporic Meiosis:
Some green and brown algae, as well as the red algae and all plants exhibit life cycles with sporic meiosis. All
organisms possessing this life cycle exhibit alternation of generations, where a multicellular, haploid form of
the organism (the gametophyte) alternates with a multicellular diploid form (the sporophyte). If the two
generations appear to be identical, then the organism is said to exhibit isomorphic alternation of generations. If
the gametophyte and sporophyte stages are phenotypically distinct, then heteromorphic alternation of
generations is the result. At first glance, this life cycle may seem to be much more complicated than life cycles
with zygotic meiosis, but in reality, little has changed. The multicellular gametophyte still produces gametes
via mitosis, and these gametes will again fuse to form the zygote. However, the zygote then divides mitotically
to produce a multicellular sporophyte, rather than immediately undergoing meiosis. At some point, cells in the
multicellular sporophyte will undergo meiosis to produce spores which then germinate to form a new
multicellular gametophyte. In sporic meiosis then, there is an alternation of multicellular sporophytic and
gametophytic generations, and the products of meiosis are spores. This alternation of generations is found only
in organisms that exhibit sporic meiosis.
3. Life Cycle Exhibiting Gametic Meiosis:
Gametic meiosis is exhibited by some brown algae and all animals. In this life cycle, only the gametes are
haploid. All other stages are diploid (think of your own bodies: every cell in your body has two sets of
chromosomes, except for the eggs or sperm that you produce. These only contain one set of chromosomes).
This life cycle is also somewhat similar to a sporic meiosis life cycle. Imagine a reduction in the size of the
multicellular haploid stage to just one cell, a gamete, while the diploid stage remains large and dominant. This
is a trend that occurs in plants. The most advanced plants have very reduced gametophytes and large, dominant
sporophytes. Conversely, you can get sporic meiosis from gametic meiosis by making the product of meiosis a
spore, rather than a gamete and having the spore grow to produce a multicellular haploid stage. Thus, in
gametic meiosis, the only multicellular stage is diploid, and the products of meiosis are always gametes.
23
Figure 1: The Three Basic Types of Life Cycles. Each life cycle is distinguished based on when meiosis
occurs, and what the products of meiosis are.
24
C. The Diversity of Protists:
You will observe a variety of protist groups based on the current phylogeny given in Campbell and Reece
(2005). Protists are the oldest and most diverse of the eukaryotes. Think about this diversity as you look at the
different specimens. They are mostly microscopic unicellular organisms but there are also more complex
colonial and multicellular forms. Remember that protists probably share common ancestors with the
multicellular plants, animals, and fungi. Later on in the semester as you learn about each of these other
Kingdoms you should be able to observe characteristics in the protists that distinguish them from plants,
animals and fungi.
C-1. Kingdom Euglenozoa:
Euglenozoa consists of two major groups of protists, the euglenoids and the kinetoplastids (not observed in lab).
Members of Euglenozoa can be photosynthetic or heterotrophic (obtain food from other organisms), and
reproduce through longitudinal fission. Like many other protist groups, euglenozoans possess flagella that are
used for locomotion. Although similar to green algae, which you will observe later, in their possession of both
chlorophyll a and b, euglenoids differ in that they do not have a cell wall composed of cellulose as green algae
do, and they store their energy as paramylon rather than as starch. It is now thought that ancestral euglenoids
ingested green algae, and subsequently (by endosymbiosis) formed a stable relationship with the former green
algal chloroplasts.
Prepare a wet mount slide of the freshwater-dwelling Euglena
and examine using the 40X objective lens. Draw living
members of Euglena. Notice the flexibility of the cell wall.
This is due to the presence of a series of flexible protein strips
that, in conjunction with the cell membrane, form a structure
termed the pellicle. Watch Euglena move through the culture.
Prepare another wet mount, but add a drop of methyl cellulose to your slide. Can you see the flagella, the
chloroplasts, and the eyespot?
25
C-2. Kingdom Alveolata, Phylum Ciliophora
Current taxonomic treatments place the ciliates in a group called Alveolates, unicellular protists that have
membrane bound cavities under the cell surface. These cavities, or alveoli, are thought to help regulate the
water and ion balance between the cell and its environment. Dinoflagellates and apicomplexans are also
members of this group.
Members of the ciliate group move via cilia, minute hair-like
structures that beat against their watery environment to provide
locomotion. Cilia also serve to sweep food into the oral groove.
Prepare a Vaseline mount slide of living Stentor. Add a drop of
Methyl cellulose to your preparation, and then carefully place the
coverslip on your vaseline mount. Look for the mouth, oral
groove, and food vacuoles. There is a large macronucleus,
stretched out like a string of beads. One or more contractile
vacuoles may be seen. Sketch this protist. As well, view the
prepared slide of Stentor.
C-3. Kingdom Stramenopila:
Stramenopilans are protists that possess flagella with many hairlike projections. The group includes oomycetes,
golden algae, brown algae, and diatoms.
a. Phylum Bacillariophyta (diatoms):
Diatoms are unicellular photosynthetic algae possessing chlorophyll a and c as well as various carotenes and
xanthophylls. Their cell wall structure is distinctive, as it consists of two valves made of silica. These two valves
fit together, like a petri dish. Diatoms are either radially symmetrical (centric) or bilaterally symmetrical
(pennate).
View the demonstration slides of diatom types. Once you
locate the cells, make your observations using your 40X
objective lens. Distinguish between centric and pennate
diatoms? Can you differentiate between valve (top) and girdle
(side) views?
View the 3D images of diatoms taken with the scanning
electron microscope. Make sketches of your observations.
26
b. Phylum Phaeophyta (brown algae):
Brown algae are common in temperate marine waters, have cell walls composed of cellulose and possess
chlorophyll a and c. You will notice that superficially, the brown algae resemble plants. The similarities are
analogous because the body plan evolved independently in the brown algae and plant lineages. Unlike most
brown algae, which exhibit zygotic meiosis, Laminaria exhibits a sporic life cycle. Consult the diagram of the
Laminaria life cycle diagram Fig. 28.21, p. 562 of your text.
Examine and sketch the preserved material on display.
Note the differentiation of the thallus (body) into a
blade (flat leaflike photosynthetic region), a stipe
(stemlike support) and a holdfast (rootlike anchor).
Examine the prepared slide of a cross-section through
the blade under the 40X objective. Sporangia, located
on the surface of the blade, produce zoospores by
meiosis. Can you locate the sporangia on the slide?
Draw your observations.
C-4. Kingdom Rhodophyta (red algae):
The red algae are a group of predominantly marine organisms that lack flagellated stages in their life cycle.
They possess chlorophyll a as well as various other accessory pigments. The red algae you are looking at
today exhibits sporic meiosis, a life cycle where both haploid and diploid generations are multicellular (refer
back to Fig. 1).
Polysiphonia is a widespread marine alga with a
branching, filamentous thallus. The filaments are often
thicker than one cell. Like in other algae the cell walls
are composed of cellulose. Examine preserved material
available on demonstration and make a sketch in the
space to the right. Note the relatively simple thallus.
27
C-5. Kingdom Chlorophyta (green algae):
The Chlorophyta is an important and diverse group of protists. Much of the diversity arises in the vegetative
body form (thallus) possessed by members of this phylum, which include unicellular, colonial, filamentous, and
parenchymatous types. Members of this phylum undergo sexual life cycles with zygotic or sporic meiosis.
Many characters, including the types of pigments the individuals possess (namely chlorophyll a, b and
accessory pigments), suggest that the most likely ancestor of land plants was a member of this phylum. Three
groups are recognized, based largely on subcellular characters (we will look at two of the three).
a. Chlorophytes
This group contains most of the green algae. Typically, these organisms inhabit freshwater environments,
although some species are found in marine and terrestrial environments as well. Chlorophytes may be
unicellular, colonial, or multicellular, and many form a mutualistic association with fungi known as lichens (see
Fungi lab). All undergo sexual life cycles with zygotic meiosis.
Volvox is a good example of a highly-developed colony.
Make a wet mount from the Volvox culture provided and
observe colonies using the 40X objective. Sketch what you
see in the space to the right. Notice that the colony is a
hollow ball. The wall is composed of hundreds of flagellated
cells which cannot reproduce in isolation. Daughter colonies
form inside of and are eventually released by the large
colony.
b. Charophyceans
This group consists of unicellular, filamentous, and parenchymatous (growth in three planes) forms. Life cycles
exhibit zygotic meiosis. Charophyceans show several features that suggest they are the green algae group most
closely related to land plants. The types of cellulose- synthesizing protein in the plasma membrane, the
presence of peroxisomes, and the process of forming of new cell wall material via phragmoplasts are a few
examples of homologies.
Spirogyra is a filamentous member of this group. It is
most famous for its spiraling, ribbon-like chloroplast.
Use the culture provided to prepare a wet mount of
living Spirogyra. Examine your slide using the 40X
objective lens and sketch its distinctive appearance in
the space to the right.
28
Chara is a distinctive, multicellular green alga found
locally in fresh or brackish water. The cell walls are
heavily calcified, and give these algae a gritty texture.
Examine fresh or preserved material and note this
characteristic. Sketch the appearance of the vegetative
structure of Chara.
Examine the demonstration of reproductive structures
of Chara. Using the 10X objective lens, find and
differentiate between the spiral-shaped oogonium and
the spherical-shaped antheridium and make labeled
drawings of these structures.
C-6. Kingdom Amoebozoa:
a. Phylum Myxogastrida (plasmodial slime molds):
Members of this group play an important role as decomposers in their natural habitats, and in that respect,
resemble fungal organisms. However, they are probably most closely related to the amoeboid protists.
Slime molds are found in moist soil or rotting vegetation. Most are decomposers, although a few are pathogens
on plants. The life cycle of a plasmodial slime mold is shown on pg. 565 of your text. In their vegetative state,
these organisms exist as thin, streaming masses of protoplasm, bound by a cell membrane and containing many
nuclei, that move in amoeboid fashion. This stage is referred to as a plasmodium.
Examine and draw living material of Physarum, a
representative plasmodial slime mold. Locate the
plasmodium, the central veins of protoplasm, and evidence of
a slime sheath. Is this organism haploid or diploid? Where
are the nuclei located? Can you see evidence of cytoplasmic
streaming?
When the food supply and/or water becomes limiting, the
plasmodium stops moving and begins to form a series of
small mounds. Each mound develops into a mature
sporangium (a spore-containing sac) sitting on top of a
narrow stalk (usually). The sporangium is the site of
meiosis. Products of meiosis are spores. Are the spores
haploid or diploid? Sketch the dried Physarum
sporangia on demonstration under the dissecting
microscope.
29
b. Phylum Gymnamoeba:
Gymnamoebas are amoeboid protists that move by forming and extending a pseudopodium, at any point on
their body surfaces. The cytoplasm in these protists is differentiated into two regions: the ectoplasm is
nonflowing and more peripheral in position, while the endoplasm is more fluid and more central in position.
Examine the tip of an advancing pseudopodium for sudden bulges of ectoplasm. Note that the endoplasm
abruptly flows into the tip of the pseudopodium, then turns to the side and forms gelled ectoplasm. The plasma
membrane has adhesive properties and new pseudopodia attach to the substrate as they are formed.
Make a vaseline mount of Amoeba proteus and
examine it using the 10X objective lens,
sketching your observations to the right. Note
the plasma membrane and the disk-shaped
nucleus. You may also observe the contractile
vacuole (intermittent, round and clear and used
to rid the amoeba of water gained osmotically)
and food vacuoles.
Amoeboid locomotion: spend some time watching fluid/gel transitions at the tips of advancing pseudopodia and
at the trailing end of the organism. These transitions are based on interactions between the contractile
cytoskeletal proteins. Note that the amoeba must be in contact with a substratum to carry out effective
locomotion. See Figure 28.24 on page 564 of your text for a diagram of how the amoeba moves.
30
As you have discovered, the protists are an extremely diverse group. Use the information you have gathered
from completing this exercise, from your lecture notes, and from Campbell and Reece (2005) to complete the
following table. Note that not all boxes can be filled out for all taxa (e.g. some don’t have photosynthetic
pigments).
Taxa
Mode of
nutrition
Motile via:
Cell wall or
shell made of:
Photosynthetic
pigments
Habitat
Life Cycle
Type
Euglenozoa
Alveolata:
Ciliophora
Stramenopila:
a) Bacillariophyta
b) Phaeophyta
Rhodophyta
Chlorophyta:
a) Chlorophytes
b) Charophyceans
Amoebozoa:
a) Myxogastrida
b) Gymnamoeba
Use you observations, the information in your lab manual and the textbook or lecture notes to fill in the above
table. For each column choose from the options listed below:
Mode of nutrition: photosynthetic or heterotrophic
Motile via: flagella, cilia, streaming cytoplasm, or generally non-motile
Cell wall or shell made of: pellicle, silica, cellulose, or absent
Photosynthetic pigments: chl a, b, c or none (note some may possess more than one of the chlorophylls)
Habitat: marine, freshwater, or terrestrial
Life cycle type: asexual, gametic, sporic, or zygotic
31
KINGDOM ANIMALIA Part 1: Soft-Bodied Invertebrates
A. Introduction:
We begin our survey of the Animal Kingdom in this exercise by introducing you to many of the major phyla
(and classes for the larger phyla) of invertebrates. In addition you will learn about four major branches in the
animal phylogeny, which are used to group the animal phyla. Finally, you will examine the external and
internal anatomy of a representative annelid, the earthworm. Please read pp. 638-655, pp. 626-627 of Campbell
and Reece (2005) for background for today’s lab. Following the lab, you may find it useful to try related
activities on the CD that came with your text, to prepare for quizzes and examinations.
Laboratory Objectives:
Representative specimens (occasionally only illustrations are available) of the groups listed below are displayed
on the side and rear benches. Your goal is to become familiar with them in the following respects:
•
You should be able to place them (or specimens similar to them) into the proper phylum (for specimens in
the larger phyla (Cnidaria, Platyhelminthes and Annelida) you further should be able to place specimens
into their proper Class).
•
You should know the observable distinguishing external structures, features and characteristics of these
•
You should know what general habitats they occupy (marine, freshwater, terrestrial, parasitic).
•
You should be able to name the major branches in the animal phylogeny, the characteristics of each branch,
specimens (see the boldface terms below).
and the phyla on each branch.
•
You should be able to identify external and internal features of the earthworm and to indicate their
respective functions.
B. Survey of Invertebrates:
KINGDOM ANIMALIA
PARAZOA: Animals in the Parazoa lack true tissues and organs. Symmetry is radial or lacking. The Parazoa
contains a single phylum, Porifera.
Phylum Porifera (sponges): These sessile animals are
predominately marine organisms. Some sponges are also
found in freshwater environments. They feed by filtering
water through choanocytes (flagellated internal collar cells).
Water enters sponges through microscopic incurrent
openings, or porocytes (ostia, sing. = ostium). The simpler
species may be vase-shaped, with a single excurrent opening
(osculum, pl = oscula), but the larger and more complex
sponges are asymmetric and have numerous excurrent
oscula. Sketch and label a representative sponge.
32
Many sponges secrete glassy or calcareous skeletal structures
(spicules); some (such as the bath sponges) lack these
skeletal elements and instead have skeletons comprised of
flexible proteinaceous material (spongin). Some sponges
have both spongin and spicules. Prepared slides provide
examples of spicules and spongin. Sketch these structures.
EUMETAZOA: Animals in the Eumetazoa are composed of definite tissues and organs; symmetry may be
radial or bilateral; alimentary tract (if present) may have one opening (mouth) or two openings (mouth and
anus); bodies may be comprised of 2 (ectoderm and endoderm) or 3 (ectoderm, endoderm and mesoderm)
basic embryonic tissue types. There are two main branches in the Eumetazoa, the Radiata and the Bilateria
RADIATA: Animals from the Radiata show primary radial symmetry and generally are diploblastic
(composed of 2 main embryonic tissue layers, an outer ectoderm which forms the epidermis, and an inner
endoderm which forms the gastrodermis lining the gastrovascular cavity); the inner and outer cell layers are
separated by a thick or thin, secreted, largely or completely noncellular gelatinous matrix called the mesoglea.
There is only one opening from the gastrovascular cavity to the exterior (mouth) and the development of organs
is limited. The two phyla of the Radiata branch are the Ctenophora and the Cnidaria.
Phylum Cnidaria (hydras, jellyfishes, corals and anemones): These are all soft-bodied, radially symmetrical
animals (though some secrete internal or external skeletons) bearing tentacles around a mouth opening which
communicates with a pouch-like gastrovascular cavity. This gut communicates with the outside only via the
mouth (there is no anus). All members have stinging cells (cnidocytes) containing nematocysts, which can be
used defensively or offensively. There usually are 2 basic body forms: the sexual, motile, usually planktonic
medusa and the asexual, nonmotile, usually sessile (attached) or sedentary (slow moving), polyp. Both forms, but
especially the polyps, may be colonial. Most species are marine; some are fresh water.
Class Hydrozoa (hydrozoans) Members of this class are
usually quite small, solitary or colonial, and mostly marine
(but nearly all fresh water cnidarians are in this class). Most
species have dominant polyps (which often are colonial,
with individuals showing specialization for reproduction or
feeding), and reduced medusae. This class includes the
common freshwater Hydra and the incredibly complex
jellyfish-like marine colony, the Portuguese Man-of-War
(Physalia). Hydrozoan medusae have a velum (membrane
lining the inner edge of bell and serving to narrow the
opening through which water is ejected in jet propulsive
swimming). The velum is easily seen in Gonionemus. Draw
representative members of this class to the right.
33
Class Scyphozoa (jellyfishes) Scyphozoans show a
dominant medusa and a reduced or absent polyp.
Scyphozoan medusae show a massive development of
mesoglea and, unlike hydrozoan medusae, most lack a velum.
Sketch the Aurelia on display. Note the 4-part radial
symmetry - 4 oral arms, 4 gonads and 4 radial canals (not
easily visble) branching off the gastrovascular cavity.
Class Anthozoa (corals and anemones) Members of this
class occur in a variety of types, but two main groups
predominate: the large, solitary anemones are fleshy and
lack any calcareous exoskeleton; the corals (comprised of
enormous colonies of minute coral animals, which secrete
calcareous exoskeletons) and, in warm, clear, tropical
waters, can form reefs. The corals displayed are the
exoskeletons only. Observe the specimen in the marine tank.
Can you see the tentacles and mouth?
Make a sketch of discharged nematocysts available on
demonstration under oil immersion.
Phylum Ctenophora (comb jellies) These exclusively marine
animals are planktonic, swimming by means of 8 rows of fused
ciliated comb plates, and feeding with retractable tentacles
containing adhesive mucous-secreting cells. If you can’t find the
tentacles in the preserved specimens, they have probably been
retracted. Ctenophores are radial and diploblastic.
Name two characteristics that members of the Phylum Cnidaria and the Phylum Ctenophora have in common.
Name two diagnostic characteristics that can be used to distinguish between members of these phyla.
34
BILATERIA. Animals show primary bilateral symmetry. Organs are well developed and "organized" into
systems. A body cavity (coelom) between the gut and body wall may be absent (acoelomate), partly lined
with mesoderm (pseudocoelomate), or completely lined with mesoderm (eucoelomate). The type of coelom
was previously thought to be important to understanding the phylogeny of the Bilateria (see Fig. 32.10 p. 634,
Campbell and Reece 2005), but recent evidence suggests a different relationship among the phyla in the
Bilateria (see Fig. 32.11, p. 635, Campbell and Reece 2005). Under current thinking, there are two main
subgroups in the Bilateria, the Protostomia and the Deuterostomia.
PROTOSTOMIA: The animals in this branch display a characteristic embryology with spiral, determinate
cleavage, mesoderm arising from cells near the lip of the blastopore, coelom arising as a split in an originally
solid mass of mesoderm, and mouth arising from the embryonic blastopore. (See Fig. 32.9, p. 632, Campbell
and Reece 2005). Two branches exist within the Protostomes: the Lophotrochozoa and the Ecdysozoa.
LOPHOTROCHOZOA: The Lophotrochozoa are grouped mainly on the basis of molecular evidence.
However a few eucoelomate phyla in this group display a set of ciliated tentacles called a lophophore, while
some members of other eucoelomate phyla in this branch have a ciliated trochophore larva.
Phylum Platyhelminthes (flatworms; planarians, flukes, tapeworms) These bilateral, acoelomate animals occur
in marine, freshwater and damp terrestrial habitats. You will observe representatives of Classes Turbellaria,
Trematoda, and Cestoda. Flatworms lack an anus, and usually are hermaphroditic.
Class
Characteristics
Turbellaria
•
•
•
•
Trematoda
•
•
•
Cestoda
•
•
•
Notes / Drawing
Mostly freeliving in freshwater,
some parasitic
Carnivorous
Ciliated epidermis
Often possess light-detecting
eyespots and auricles,
distinguishing head region
Parasitic
Oral and ventral suckers for
attachment to host
Diverticulate digestive tract
Parasitic
Scolex with suckers and hooks for
attachment to host
Proglottids for egg production and
release
What are some adaptations for a parasitic lifestyle seen in the trematode and cestode specimens you
observed?
35
Phylum Rotifera Rotifers are pseudocoelomate, freeliving marine and freshwater animals that swim and feed
with an anterior ciliated corona, and break up food
particles with complex internal jaws (the mastax).
Unlike Platyhelminthes, they have a complete digestive
tract with mouth and anus. If living rotifers are on
display, watch the action of these two structures.
Phylum Annelida Members of this phylum are eucoelomate, segmented worms. The segments are usually
divided internally by transverse septa (sing. septum), membranous partitions that separate each segment. Most
annelids show evidence of cephalization (development of an anterior head, and concentration of nervous
system and sense organs there). They have closed circulatory systems (i.e. distant from the heart, the arteries
and veins are connected by capillaries), and a complete gut (mouth and anus present). Three classes, the
Polychaeta, Oligochaeta and Hirudinea, will be examined.
Class Polychaeta Members are marine. Polychaetes
have lateral, fleshy parapodia beset with numerous
setae, and well developed head appendages such as
jaws, tentacles and eyes. What function(s) do you
think parapodia serve?
Polychaetes may be tube dwellers, bottom wanderers,
or planktonic swimmers. Polychaetes include
carnivores, herbivores, omnivores and scavengers.
They are dioecious (have separate sexes). Sketch a
representative polychaete and label the parapodia.
Distinguish between setae and septa.
Class Oligochaeta Oligochaetes are largely freshwater
(small species) or terrestrial (earth-worms); they lack
parapodia, and have very few setae per segment;
earthworms have reduced heads and evidence of
cephalization. Most are scavengers, feeding on dead
organic matter, especially vegetation. Small freshwater
species feed on detritus and microorganisms. They have a
clitellum and are hermaphroditic. Sketch a typical
oligochaete in the space to the right. What is the function
of the clitellum?
36
Class Hirudinea Leeches are largely fresh water, but have
damp terrestrial members also. They lack the internal
septa, are dorsoventrally flattened, have lobed intestines
(which swell when they feed), and (like oligochaetes)
possess a clitellum and are hermaphroditic. Leeches lack
setae, which are characteristic of the other two classes.
Most leeches are intermittent ectoparasitic blood feeders,
but some are predators or scavengers. The anterior sucker
is reduced, but the posterior sucker is conspicuous. Eyes
are present. What characteristic(s) could be used to
distinguish between Hirudineans, Polychaetes and
Oligochaetes?
C. Dissection of the earthworm (Lumbricus terrestris): work in pairs.
1.
External anatomy: Examine the external anatomy of a preserved earthworm under the dissecting
microscope. Be sure you note the external features listed below, and can identify the dorsal and ventral
surfaces, the anterior and posterior ends of your specimen before beginning your dissection.
Setae: small bristle-like hairs protruding from each segment. Can be felt by drawing the worm gently
forwards and backwards over your fingers. Using the dissecting microscope, can you determine how
many setae there are in a typical segment?
Mouth: anteroventral opening to digestive tract.
Anus: posteroterminal opening of digestive tract.
Dorsal blood vessel: visible through the semi-transparent skin, as a dark line on the dorsal surface.
Clitellum: slightly swollen region at segments #32-37; is more towards the anterior end than it is to the
posterior end. Does the ventral surface of the clitellum differ from its dorsal and lateral surfaces? Can
you find evidence of setae in the region of the clitellum?
Genital pores: pair of large pores, the openings of the vas deferens. May be seen ventrally about
midway between the mouth and clitellum. Note that there are no conspicuous external appendages or
sense organs (compare this with the polychaetes observed in section B, above).
2.
Internal Anatomy: Place your worm near enough to the side of a dissecting dish so that you can observe it
under a dissecting microscope (a folded microscope dust-cover will provide good support to keep your
dissecting pan level).
•
Cut the earthworm approximately in half and make a shallow mid-dorsal incision through the body
wall from the cut through to the clitellum and on up to first segment. Proceed very carefully near the
anterior end to preserve the ganglia and nerve connections.
•
Starting posteriorly, pin out the cut edges of the body wall until you come to within a few segments of
the anterior end, gently breaking the transverse septa as you go. (It will be helpful to angle your pins
outwards, and not to leave them vertically.)
37
•
Digestive System:
Muscular pharynx: most anterior portion of the alimentary tract; it appears to have a “fuzzy”
surface due to dilator muscles extending to the body wall. Contraction of these muscles expands
the pharynx and sucks in particles of soil and detritus (source of food particles).
Esophagus: through which food passes for processing
Crop: thin-walled sac (in segments 14-15) for storage.
Gizzard: muscular organ for grinding food particles
Intestine: for chemical digestion and absorption. Undigested material is voided through the anus.
Note the "accordioned" appearance of the intestine as it passes through the septa.
•
Circulatory System:
Dorsal blood vessel: dark tube overlying the digestive tract. Earthworms have a closed circulatory
system, and blood from the capillaries of each segment collects into the dorsal blood vessel and
flows forward to the esophagus region.
Ventral blood vessel: small, yellowish tube running along underside of intestine. Sever the
intestine and fold it back to see the ventral blood vessel.
Aortic arches (or hearts): 5 pairs of vessels circling the esophagus. These vessels pump the blood
from the dorsal vessel into the ventral blood vessel and from there blood flows posteriorly into the
capillaries of the segments. Tiny capillaries in the skin of each segment serve to pick up oxygen
and discharge carbon dioxide.
•
Nervous System:
Cerebral ganglia: brain-like pair of concentrated nerves. These are in the first or second segment
on the surface of the alimentary canal, and bear connections with the nerve cord beneath.
Ventral nerve cord: thin, whitish cord located below the ventral blood vessel vessel.
Lateral nerves and ganglia: look for small nerves that run into the muscles of the body wall from
swollen regions on the ventral nerve cord.
•
Reproductive System:
Seminal vesicles: 3 large, whitish sacs, extending from segments 9 to 14 (the largest pairs are
posteriormost); sperm released from very tiny testes are released into the seminal vesicles where
they mature.
Seminal receptacles: 2 pairs of small, rounded, white sacs (segments 9 and 10) somewhat obscured
by the seminal vesicle. The receptacles receive sperm from the partner during copulation. The
remaining reproductive structures are quite difficult to locate, and will be omitted from the
dissection.
•
Excretory System:
Nephridia: one pair per segment, in region posterior to gizzard. These are excretory organs coelomic fluid enters the open end of each tubule and metabolic wastes are excreted via a pore
through the body wall while essential minerals and water are reabsorbed back into the coelomic
fluid.
Label the diagram, using the information provided above to help you.
38
Figure 1. Dorsal view of earthworm (Class Oligochaeta) internal anatomy.
39
3.
Cross Section: Obtain a prepared slide from the side bench, and examine a cross section of the earthworm
showing the setae, and identify the following structures or tissues on your slide, in comparison with the
description and illustration below.
Body wall: layer of tissues and muscle, which encloses coelom and internal organs.
Cuticle: external layer protecting skin
Epidermis: cellular layer of tissue beneath the cuticle
Circular muscles: thin layer of muscle tissue, which when contracted squeezes worm long and thin
Longitudinal muscles: thick layer of muscle tissue beneath the circular muscle, when contracted
squeezes worm short and fat. (Why are the longitudinal muscles so much more heavily developed?)
Peritoneum: very thin covering on innermost surface of the longitudinal muscles.
Setae: 4 pairs of bristle-like hairs penetrating body wall; 2 lateral pairs and 2 ventrolateral pairs.
Can you find the muscles that protract and retract the setae?
Intestine: located centrally within coelom
Typhlosole: large rod of tissue hanging suspended in the intestine, greatly increase area for
absorption in the intestine.
Lumen (of the intestine): internal cavity of the intestine; made quite narrow by the typhlosole.
Dorsal blood vessel: located above the intestine.
Ventral blood vessel: located beneath the intestine; suspended by a thin mesentery.
Ventral nerve cord: beneath the ventral blood vessel; consists of 2 large and 3 smaller fibers. The
3 smaller fibers serve to convey urgent information (e.g. CONTRACT the longitudinal muscles!)
very rapidly from one end of the worm (perhaps the end in a robin's beak) to the other end
(hopefully embedded firmly in the burrow).
Coelom: body cavity
Nephridia: in the ventral and lateral areas of the coelom.
• Surrounding the intestine, and most heavily developed dorsally, is a mass of tissue, which provides liverlike storage functions.
Label the cross section diagram with the features described above.
Figure 2. Cross-section through typhlosole of earthworm (Class Oligochaeta).
40
Based on observations made in the lab and reference to Figure 32.10 of Campbell and Reece (2005), complete the
table below:
Phylum
Body
Symmetry
Number of
Body Layers
Habitat
Lifestyle
Diagnostic
Character(s)
Porifera
Cnidaria
Ctenophora
Platyhelminthes
Rotifera
Annelida
What characteristics could you use to separate the three classes within the Phylum Cnidaria?
What characteristics could you use to separate the three classes within the Phylum Platyhelminthes?
What characteristics could you use to separate the four classes within the Phylum Mollusca?
What characteristics could you use to separate the three classes within the Phylum Annelida?
41
KINGDOM PLANTAE Part 1: SEEDLESS PLANTS
A. Introduction:
All plants share many features with their green algal (Class Charophyceae) ancestors. They possess chlorophyll
a and b, carotenoids, and xanthophylls. Their cell walls are predominantly composed of cellulose, and
photosynthetic products are stored as starch. However, in contrast to their algal predecessors, most are
terrestrial organisms.
There are many differences between water and land as environments for plant growth. In an aquatic
environment, water is available to all cells and also acts as a supportive medium. All of the oxygen, carbon
dioxide and minerals required by a photosynthetic organism are in solution and thus, most cells are capable of
photosynthesis. In terrestrial habitats, light, oxygen and carbon dioxide are readily available, but water is often
limiting, and when present, is mostly found in the soil. As a result, photosynthesis and nutrient absorption are
often separated in terrestrial photosynthetic organisms. As you examine the plant material provided for you in
today’s exercise, look for adaptations exhibited by these organisms that have enabled them to flourish in
terrestrial habitats. To help prepare for this exercise, read Chapter 29 of Campbell and Reece (2005).
Laboratory Objectives:
By the end of today’s exercise, you should be able to:
•
Separate the Plant Kingdom from all other kingdoms based on diagnostic characters.
•
Recognize and classify the nonvascular and vascular plants to the appropriate Phylum.
•
Name and describe the function of the terms in bold face in the exercise.
•
Relate details of sexual life cycles involving sporic meiosis to the plants viewed today.
B. Seedless Nonvascular Plants (Bryophytes):
Seedless nonvascular plants, like algae, have a comparatively simple “body-plan”. However, unlike the algae,
they (and all other plants): i) exhibit cell division in three planes, ii) possess multicellular gametangia
(antheridia and archegonia) and iii) have the embryo (sporophyte) develop within the archegonium. All are
relatively small, and lack true stems, roots and a specialized conduction system. Like all plants, they exhibit
heteromorphic alternation of generations. However, the gametophyte is the dominant generation in seedless
nonvascular plants.
The phyla Anthocerophyta (hornworts), Hepatophyta (liverworts) and Bryophyta (mosses) collectively make
up the seedless nonvascular plants. Of these, we will only examine the Phylum Bryophyta in detail.
Representatives from the other two groups will be available as demonstration material.
42
All mosses produce a thread-like structure called a
protonema (plural: protonemata) as the first stage
after spore germination. Examine prepared slides of
moss protonemata and sketch their appearance in the
space to the right.
Can you still distinguish the spore that divided by mitosis to produce the protonema?
Are protonemata haploid or diploid?
The buds present on the protonemata (some of which may have developing rhizoids) will eventually develop
into leafy gametophytes. However, you should realize that the protonema is also part of the gametophyte
generation.
Examine living moss gametophytes and diagram them.
Some of these gametophytes will produce female
reproductive structures (archegonia) at their tips, while
others will produce male reproductive structures
(antheridia). As these are not easily observed in fresh
material, please consult prepared slides of moss
antheridial and archegonial heads.
Under low power, locate the antheridia at the top of the
antheridial head. Make a sketch to the right. Then, move
to the 40X objective and focus on one antheridium.
Observe the sterile jacket surrounding the sperm and/or
sperm forming tissue. Note the sterile hairs interspersed
between the antheridia. Make a second sketch. Are the
sperm produced by mitosis or by meiosis? Are they
haploid or diploid?
Under low power, locate the archegonia at the top of
the archegonial head. Make a sketch showing what
you see. Find and focus on an archegonium using
the 40X objective (hint: look for a long blue
structure with a red cell in the centre). Locate the
archegonia and identify the egg cell. Draw another
sketch and label all structures observed. Is the egg
haploid or diploid?
43
How do the sperm cells produced in the antheridium reach the egg cells in the archegonial heads?
Examine fresh or dried demonstration material of a moss and distinguish between the sporophyte and the
gametophyte. The sporophyte results from mitotic divisions of the fertilized egg in the archegonium. It is
dependent upon the gametophyte for some of its nutrients. Examine sporophytes under the dissecting
microscope and look for all of the structures described below. Sometimes a calyptra, which represents the
remnants of the archegonium, may still be present. Beneath the calyptra the operculum should be visible. In
some of the sporophytes, the operculum has fallen off of the capsule (also called the sporangium). This allows
for examination of peristome teeth underneath. What is the function of the peristome?
Relate this material to prepared slides of Mnium or Polytrichum sporophyte sections and sketch a typical moss
capsule below. Indicate which structures are haploid and which are diploid.
Observe demonstration material available for the other two phyla of seedless nonvascular plants. Hornworts
(Phylum Anthocerophyta) are very small and have specialized pores called stomata similar to moss
sporophytes. A typical hornwort is available on demonstration. Refer to Fig. 29.9 in Campbell and Reece,
2005) to distinguish between the sporophyte and the gametophyte generation. Conversely, liverworts (Phylum
Hepatophyta) are much larger and more common. Use a hand lens to examine the surface of the living
Marchantia, a typical liverwort. Note the presence of pores on the surface. They differ from stomata found in
hornworts. What is their function? Make sketches of both organisms in the space below. Be sure to label the
gametophytes and sporophytes on each diagram, and indicate the ploidy of each structure.
Hornwort
Liverwort
44
Examine the liverwort again. Look for gemmae cups on the surface. Inside the cups are packets of cells called
gemmae. Gemmae function as asexual propagules. Are the gemmae formed by mitosis or by meiosis?
Describe some of the characteristics seen in the bryophytes you viewed which have enabled them to survive life
in a terrestrial habitat.
Based on the observations made in the lab, complete the life cycle below. Be sure to label the sporophyte and
gametophyte generation and indicate the ploidy of all parts.
Figure 1: Life Cycle of a Typical Bryophyte (from Campbell and Reece, 2005).
45
C. Seedless Vascular Plants (Pteridophytes):
Vascular plants first appear in the fossil record about 410 million years before present. Development of
vascular tissue allowed plants to successfully colonize habitats that until then were not available to them.
Xylem is the tissue responsible for water conduction in vascular plants, but also provides support due to its
lignified cell walls. The earliest vascular plants were seedless. Although they no longer dominate the presentday landscape, there are still two extant (living) phyla. All have an alternation of generations life cycle, as do
the bryophytes, but here, the sporophyte is the dominant generation and the gametophyte is reduced and either
free-living or contained within the spore. As you look at representatives of these phyla today, compare them to
the bryophytes and observe further adaptations they have made to survive life on land.
Most ferns and related plants (Phylum Pterophyta), and some lycopods (Phylum Lycophyta) are
homosporous, meaning that:
•
The plant produces only one size of spore in its sporangia.
•
The spores germinate and produce free-living gametophytes that in turn produce both antheridia and
archegonia.
We will examine the fern (Phylum Pterophyta) life cycle to demonstrate homospory. Begin by looking at the
living fern sporophytes on display. Are you looking at haploid or diploid organisms?
Ferns generally consist of an underground stem,
called a rhizome, from which the fronds (leaves)
arise. The frond consists of pinnae (singular: pinna)
attached to a rachis, or stalk. Sometimes, the pinnae
may be further subdivided into pinnules. Examine
the undersides of the pinnae or pinnules for clusters
of sporangia, termed sori (sing; sorus). Each sorus
may be covered with a separate, protective flap of
tissue called a true indusium. In other instances,
the leaf curls around the sori; this is called a false
indusium. Still other ferns lack indusia completely.
Identify these structures on living material and
herbarium sheets provided. Draw and label a sketch
which illustrates these structures.
Using a dissecting microscope, examine a piece of a
frond containing sori. Note the ring of thick-walled
cells (annulus) surrounding each sporangium. The
annulus functions to open the sporangium and
disperse the spores. Look at prepared slides of
Cyrtomium sori for further clarification of sporangial
detail. Label the diagram to the right.
46
View the living fern gametophytes, called prothalli (singular:
prothallus), available on demonstration. The prothalli are
bisexual, free-living and photosynthetic. At maturity, the
prothallus is flat and heart-shaped. Examine the lower
surface for rhizoids, antheridia and archegonia. What is
the function of each of these structures?
You may need to consult prepared slides to observe the
reproductive structures. On the slide there are two prothalli,
one with archegonia and one with antheridia. Both develop
on one prothallus, but not at the same time (prevents
inbreeding). Draw a fern gametophyte and label the
structures.
Sperm are released from the antheridia, swim to the neck of
the archegonium and then travel down to the egg. The
fertilized egg, termed the zygote, then develops into a
sporophyte. The sporophyte initially is attached to and
dependent upon the gametophyte for nutrients, but soon
becomes free-living, while the gametophyte shrivels and dies.
Examine prepared slides of young sporophytes to illustrate
this relationship and make a sketch in the space to the right.
Human embryos are retained in and protected by the female reproductive organ. How does a fern plant
approximate this condition?
What does this retention of the zygote and subsequent embryo development seem to be an adaptation to?
47
Label all parts of the fern life cycle below, indicating the ploidy levels of all stages.
Figure 2: Life Cycle of a Typical Fern (Phylum Pterophyta).
48
Some ferns and some members of the Lycophyta have evolved heterospory, meaning that they produce two
sizes of spores (microspores and megaspores) in two kinds of sporangia (microsporangia and
megasporangia, respectively). Heterosporous plants are thought to have evolved from homosporous plants.
They demonstrate life cycles intermediate between homosporous plants and seed plants, which we will examine
in detail in the next lab. In this part of the exercise, we will examine the features of a heterosporous plant life
cycle using Selaginella (Phylum Lycophyta).
Examine the living Selaginella (ground pine) plant on display. When the plants are ready to reproduce
sexually, they produce small cones called strobili on the tips of their branches. The strobili contain the
microsporangia and the megasporangia. You may need to use a hand lens to view these strobili as they are not
easily observed. Are any visible?
Consult prepared slides of Selaginella strobili to
gain further insight into these structures. Each
strobilus, or cone, is made up of many fertile leaves,
each of which bears a sporangium on its upper
surface. Note that some of these sporangia contain a
few large spores, while others contain many small
spores. Sketch a strobilus and label the micro- and
megasporangia and micro- and megaspores. Are the
spores haploid or diploid? Are the microspores and
megaspores produced by mitosis or by meiosis?
Heterosporous plants differ from homosporous plants in that the spores, although released from the sporangium,
do not germinate into free-living gametophytes. Instead, gametophytes develop inside each spore. Would you
predict that these gametophytes are bisexual or unisexual? What evidence do you have which would help you
answer this question?
Water is still required to complete the life cycle in these plants. Why?
49
Compare the life cycle of Selaginella with that of the fern, indicating the similarities and the differences.
Similarities
Differences
Examine and sketch various other members of the Lycophyta and the Pterophyta on display.
Describe some of the characteristics seen in the seedless vascular plants you viewed that enable them to survive
in terrestrial habitats.
50
A number of characteristics of plants and several plant Phyla are shown in the table below. Use the information you
have acquired in lecture and lab as well as your text to complete the table.
Characteristic
Phylum
Bryophyta
Dominant
Generation
Uni- or Bisexual
Gametophytes
Structure that aids
in Spore Dispersal
Water Required
for fertilization
Seeds
Produced
Hepatophyta
Pterophyta
Lycophyta
51
KINGDOM PLANTAE Part 2: PLANT ANATOMY
A. Introduction:
Land plants exhibit a variety of morphological and physiological modifications of their body organization that are
responses to selection pressures associated with the terrestrial environment. These include the development of distinct
above ground (shoot) and below ground (root) regions. Some of these adaptations are related to reproductive strategies
and will be examined in a subsequent lab. In this lab we will focus on the structural and cellular organization of
vascular plants (those plants that contain conducting tissues) and particularly, flowering plants (angiosperms), since
they show the most structural diversity. Prior to today's lab you should read the material on pp 712-724 in chapter 35 of
Campbell and Reece (2005).
Laboratory Objectives:
At the conclusion of today's lab, you should be able to:
•
Recognize the basic types of cells, tissues, and organs found in vascular plants.
•
Describe the basic characteristics, function and locations of the various types of plant cells and tissues.
•
Distinguish between the root and the shoot based on function, development, organization, and structure.
B. Organization of the Plant Thallus (Body):
The plant body can broadly be divided into two regions, the above ground portion (the shoot) which includes the
leaves and stem, and the below ground portion (the root). The differences between the two can be related to both
habitat and function. Although we will use an angiosperm (flowering plant) - the bean (Phaseolus vulgaris) to
demonstrate the general structure of vascular plants, the presence of roots, stems, branches and leaves is nearly
universal among vascular plants.
Working in pairs, gently remove a bean plant from the tray. Try not to tear the roots off. Gently rinse the roots
off in the container provided and take the plant to your bench. Examine your bean plant carefully. As you read
the description below, label the parts of the plant on the diagram. Figure 35.2 of the text maybe useful for
labeling your diagram.
A vascular plant consists of a shoot system and a root system. The shoot consists of the stem and leaves and
collectively these organs function in plant nutrition and reproduction.
The leaves are the primary sites of photosynthesis and are arranged and oriented on the stem. How many leaves
arise from each node? Is that true for in all plants?
52
The leaf consists of a
flattened blade and petiole
that attaches to the stem.
Why are leaves flat? Are
all the leaves similar in
appearance? Does the
lower surface of the leaf
look similar in appearance
to the upper surface?
Why?
The point at which the leaf
attaches to the stem is
termed the node. The
regions of stem spaced
between the nodes are the
internodes. Look in the
axils of leaves (where the
petiole attaches to the
stem) to locate the axillary
buds. These buds give rise
to branches. Will the
branch be located above or
below the leaf?
Flowers (which are actually just modified leaves) serve a reproductive function and may also be found on the
shoot.
The root system anchors the plant in the soil and facilitates the uptake of water and minerals from the surrounding
soil. Label the long primary root and the lateral roots extending away from the primary root. How do you
think the root grows through the soil, from the tip or from the base? Where are the lateral roots located, near the
tip or base of the root?
53
C. Plant Cell Types:
A living plant cell possesses a rigid cell wall, a structure not present in animal cells, which surrounds the
protoplast, the living contents found inside the cell wall. The protoplast, which is surrounded by a plasma
membrane (located inside the cell wall), contains the nucleus, cytoplasm, and other membrane-bound structures
such as endoplasmic reticulum, mitochondria and chloroplasts. Fig. 6.9 on p. 101 of your text provides a good
review of plant cell structures.
Living, metabolically active plant cells have a primary cell wall that is composed largely of cellulose and is
somewhat flexible to permit growth (Figure 1A). Some cells also have a secondary cell wall that is deposited
inside the primary cell wall after the cell has stopped expanding (Figure 1B). In addition to cellulose, the
secondary cell wall also contains lignin, a chemical that renders the cell wall inflexible.
Figure 1. Representations of a typical living (A) and nonliving plant (B) cell showing the relative position of the
plasma membrane, primary cell wall and secondary cell wall.
What do you think the major function of cells with a secondary cell wall is?
54
One of the trends observed across numerous kingdoms is toward differentiation and specialization of cells. When
you studied the unicellular green algae, you discovered that these single cells have to accomplish all of the basic
functions of life. Over the course of evolution, multicellular organisms demonstrate a greater specialization in
cells and subsequently an increased diversity of function. In contrast to unicellular green algae, plants evolved
numerous specialized cells, such as those for photosynthesis, those for transport of organic and inorganic
nutrients, and those for reproduction.
Plant cells may fall into one of three general cell types. Each cell type is based on both the type of cell wall it
possesses and the cell's function. The three cell types are described below.
1.
Parenchyma cells - are unspecialized cells (that is they are NOT differentiated) that are characteristically thin
walled and many sided. They make up the bulk of the plant body and perform virtually all the metabolic activities
(e.g.: photosynthesis, respiration) required by the plant. Would you predict that parenchyma cells have a secondary
cell wall?
2.
Collenchyma cells - are cells with unevenly thickened, nonlignified primary cell walls that allow the cells to stretch.
Typically these cells are thickened in the corners and provide support for the plant body. Collenchyma cells do not
have a secondary cell wall. Do you think these cells are alive at maturity? In which regions of the plant body would
you expect to find collenchyma cells?
3.
Sclerenchyma cells - have thick, lignified secondary walls and generally lack a protoplast at maturity. There are
different types of sclerenchyma cells that we will not investigate in this lab. Sclerenchyma cells provide strength
and support in regions of the plant that have ceased elongating. Although collenchyma and sclerenchyma cells
both serve a support function within the plant, it is only the sclerenchyma cells that have well-developed
secondary cell walls. Do you think these cells are alive at maturity?
Before lab, several stalks of celery have been placed in water containing a differential stain , Toluidine Blue. The
stain can be useful in enhancing plant tissues by producing different colours when in contact with cell wall made
up of different polymers, specifically lignin (in sclerenchyma). It is also useful in tracking water transport in the
vascular bundles of leaf and stem tissue.
Using a razor blade, cut a thin cross section from the celery (Apium) petiole provided. Remember to always cut
away from yourself! Mount the celery cross section in a drop of water on a microscope slide and add a coverslip.
View your wet mount using the low power objective (10X) and then the (40X) objective. DO NOT THROW
this preparation away yet, you will view it again later during this lab.
55
The cells with the thickened corners near the ribs
(outer surface of the stalk) represent the collenchyma
cells. The relatively thin walled cells that make up the
bulk of your cross section represent the parenchyma
cells. The vascular tissue (the xylem and phloem
conducting cells) is located more internally and will
appear to be stained blue. In your cross section, the
'cap' of heavily thickened cells found to one side of the
vascular bundles represents the sclerenchyma cells.
Locate the parenchyma, collenchyma, and
sclerenchyma cells. Make a labeled sketch to the right
to depict the orientation and spatial relationship of
these cells.
D. Tissues:
The cells of plants (or multicellular organisms in general) are organized into groups that perform similar functions
and are called tissues. Plant tissues may be described as being simple or complex. Simple tissues are those in
which only a single type of cell is found. The names of simple tissues reflect the type of plant cell of which they
are composed. For example, a tissue solely composed of collenchyma cells would be called collenchyma tissue.
Complex tissues as the name might suggest, are composed of more than one cell type. In general, they are
defined by their function and location. We will examine three types of complex tissues: xylem, phloem, and
epidermal.
Xylem tissue - is made up of a number of cell types, including parenchyma cells and a variety of sclerenchyma
cell types. Xylem is the principal water conducting tissue in vascular plants. The cells associated with the actual
transport of water and minerals throughout the plant have heavily lignified secondary cell walls at maturity. The
parenchyma cells do not participate directly in conduction. Are the functional transporting cells living or
nonliving? Why?
Phloem tissue - is an aggregation of parenchyma and sclerenchyma cell types. Unlike xylem tissue, phloem
functions principally as a conducting tissue for photosynthate (food) in vascular plants. However, the conducting
cells of phloem are derived from parenchyma, while the sclerenchyma cells provide support. How are xylem and
phloem functionally different from each other?
56
Re-examine your previously prepared celery petiole wet mount
preparation and locate the vascular bundles containing xylem and
phloem. The xylem will be the larger, thicker-walled cells facing
toward the inside of the celery rib (the concave side) and the
phloem will be the smaller cells in the vascular bundle facing the
outside of the rib (the convex side). Draw and label your
findings.
Epidermal tissue - is the outermost cell layer of the plant body. It covers leaves, floral parts, fruits, seeds, stems
and roots. The epidermis is generally one cell layer thick and composed mostly of unspecialized parenchyma
cells. Most plants have parenchyma cells that are highly modified to form secretory cells, trichome (hair) cells, or
gas-exchange regulating cells (guard cells). Would you predict that epidermal tissue would afford the plant lots or
a little support? Why?
Prepare an epidermal peel using from the upper or lower
surface of the leaves provided (your instructor will
demonstrate this for you). Sketch what you see in the
space below. Label epidermal cells, guard cells, and the
spaces between the guard cells (stomata). Would you
predict that the upper and lower surfaces of a leaf would be
identical in appearance? Test your prediction by preparing
a peel from the other surface. Why might there be
differences? (hint: think about the function of the
epidermis)
Aggregates of tissues may form tissue systems. There are three tissue systems that can be found in plant organs
(shoots, leaves and roots). There are not abrupt changes in the organization of the tissue systems from organ to
organ, but rather the tissue systems are continuous from organ to organ. Associated with each of the tissue
systems are distinctive cell types that have specialized functions. The dermal tissue system comprises the
outermost covering of the plant and includes the epidermis as well as other tissues. Xylem and phloem
collectively form the vascular tissue system. The ground tissue system consists of all of the 'packing' cells that
are neither dermal nor vascular. We will examine these tissue systems in more detail in the next section - plant
organs.
E. Organs
Roots, stems and leaves are plant organs composed of tissues. The tissues are composed of specialized cells that
develop from actively dividing regions of undifferentiated cells called meristems.
Following fertilization of the egg, the resulting zygote undergoes many mitotic divisions to form a multicellular
embryo. Once the embryo has developed, the formation of new cells, tissues and organs becomes restricted
almost entirely to undifferentiated regions of cells called meristems. Cells in these regions continue to divide
57
mitotically and give rise to new cells which can then subsequently become specialized for particular functions in
specific tissues. There are two types of meristems: apical meristems and lateral meristems.
Apical meristems occur at the tips of the roots and shoots (Figure 2). Their primary function is to provide cells
that permit growth and elongation of the plant body. Apical meristems give rise to the primary tissues of the
plant forming the primary plant body, the dermal, vascular and ground tissue systems.
Lateral meristems are responsible for lateral growth (increases in girth) and they produce the secondary tissues
(e.g.: wood and cork). Lateral meristems are not located at the tips of the root or shoot, but rather occur as a
cylinder inside of the elongated portion of stems or roots, just below the epidermis (Figure 2).
Figure 2: Spatial representation of the apical and lateral meristematic regions in a plant.
Shoot Tissues
The shoot is comprised of both the stem and leaves. The primary function of the stem is to serve as the axis that
supports the leaves. Stems may be relatively flexible (e.g. bean plant) or inflexible (e.g. tree trunk) and are
generally, but not always, photosynthetic. The major function of the leaf is to provide a broad surface area that
can be used to capture light required for photosynthesis. Gas exchange (CO2 and O2) is also mediated by the leaf.
58
Obtain a prepared slide of a longitudinal section of Coleus stem tip from the side bench. Use the low power
objective (10X) to examine the slide. Locate each of the following structures and then label them on the diagram
provided. (Reference: Figure 35.15)
Regions of the shoot:
a.
Find the domed region at the tip of the shoot. It is flanked on either side by appendages that jut away from the
stem. The apical meristem cells are the densely stained cells that are relatively small in size, and have a
prominent nucleus. They can be found in tightly packed clusters near the stem tip just beneath the domed region.
b.
Leaf primordia are rudimentary
leaves that flank the apical tip
(dome) of the shoot.
c.
Axillary buds are the rudimentary
branches that are located in the axil
of the leaf primordia and in young
expanding leaves.
d.
Strands of vascular tissue can be
seen running lengthwise along the
sides of the stem. Xylem can be
easily picked out because of the
twisting, helical nature of the
secondary wall.
e.
The outermost layer surrounding
the shoot apical region is the
epidermis.
f.
The thin-walled cells forming the
bulk of the stem below the shoot
apex are parenchyma cells
forming the ground tissue.
59
STEMS
Work in pairs to prepare a bean (Phaseolus vulgaris) shoot and root cross section. A selection of other plant material
may be available to try as well. Examine the tissues found within your preparations. (Reference figures: 35.13 and
35.16 in Campbell and Reece 2005)
1.
Make a cross section of the bean plant near the growing tip of the shoot in the same manner as you did
with the celery leaf petiole. The disks will be very small, so it may be helpful to make your cuts over a
paper towel spread on the lab bench.
2.
Transfer the sections to a drop of dilute toluidine blue stain on a slide and apply a cover slip.
3.
View your cross sections using the 4X (scanning) and 10X objective lenses. Make drawings of the shoot
cross section and label the following structures: epidermis, vascular tissue (xylem and phloem), and
ground tissue (parenchyma cells).
4.
Compare your stem section with the prepared slides provided for you.
5.
Root cross-sections may be possible to obtain from your bean plant and are well-worth trying. If your
bean plant roots are too thin to handle easily or too fibrous, use the fresh carrot root provided to handsection and examine as above. Save the slide for your drawing of the root cross-section.
Bean stem cross section
Geranium / Coleus stem
cross section
How are the vascular bundles within the bean stem arranged?
What is the function of the epidermis? Do you see any little hairs on the epidermal surface? What might their
function be?
60
LEAVES
The morphology of leaves is highly variable among the vascular plants and is useful for identifying plant species.
In most plants (e.g.: poplar trees, bean plants), the blade of the leaf is attached to the stem by a petiole. Some
plants like corn have the blade of the leaf directly attached to the stem and thus lack a petiole. Most leaves serve
as the primary photosynthetic surface in the plant; however in a subsequent lab you will observe that leaves can be
modified for other purposes.
Obtain a microscope slide showing a cross-section of Syringa (lilac) from the side bench. Use the low power
objective (10X) to examine the prepared slide of the leaf and then switch to high power (40X) to examine some of
the cellular detail. Locate each of the following structures and then sketch and label a drawing representing the
leaf. (Reference: Figure 35.17)
a.
Note that there is an upper and lower surface
to the leaf. The epidermis is the outer most
layer on both surfaces of the leaf. Sometimes
there is a waxy covering on the epidermis.
What is the purpose of this waxy covering?
Look for gaps in the epidermis. Each gap is
enclosed by two cells called guard cells. The
gaps are called stomata. What is their
function?
b.
Sandwiched between the epidermal layers are
parenchyma cells that contain chloroplasts
and are actively involved in photosynthesis.
Are all of the parenchyma cells in the leaf
tightly packed together? What separates
them? Why?
c.
Vascular tissue consisting of xylem and
phloem appears as circular bundles in the
middle area of the leaf. The xylem is
generally closer to the upper epidermis and
the phloem is closer to the lower epidermal
surface. The xylem cells are stained red and
have much thicker walls than the blue stained,
thin-walled phloem cells.
61
ROOTS
Roots function to anchor the plant and to absorb water and nutrients. Some roots are also important storage
organs. Can you think of an example of a root whose major function is storage? The root is the first organ to
emerge from the germinating seed. The actively growing and dividing region in the root, the meristem, is located
near the root tip, just behind the root cap. As growth and development progress, the main (primary) root
elongates and lateral roots that originate endogenously (within the main root), are formed in the region well
behind the actively growing root tip.
Obtain a young radish seedling from the side bench. Place the seedling on a slide and carefully trim away the old
seed remnants and shoot tissue using a razor blade. Keep ALL of the tissue beneath the seed as this is the root
tissue. Observe the root using the dissecting microscope. Make a diagram of the root and label the root hairs.
What is their function?
Examine a prepared slide showing a longitudinal section through a corn (Zea) root tip. Look for the following
structures, and add them to your root sketch. (Reference: Figure 35.12)
Regions of the root:
a.
The root cap is located at the very tip of the root,
covering the root apical meristem. The cells are loosely
arranged and not in files or rows. What function does
the root cap play?
b.
The root apical meristem is located behind the root cap.
The cells appear to be closely packed and the region is
slightly darker in color.
c.
The epidermis is the outermost layer of cells
surrounding the root.
d.
The vascular tissue (xylem and phloem) forms a central
cylinder in the innermost region of the root. Can you
identify xylem and phloem cells?
e.
The ground tissue is the middle tissue layer sandwiched
between the vascular tissue and the epidermis. What
types of cells would you expect to find here?
f.
Lateral roots, when present, form away from the root
cap. Are any lateral roots present along the length of the
primary root? From what region would they originate?
62
Examine the cross sections of the root that you prepared. Make a drawing in the space below and label the
following structures: epidermis, vascular tissue (xylem and phloem), and ground tissue (parenchyma cells).
Compare your root preparation with that of the prepared root cross section of Ranunculus.
Hand-sectioned root
Ranunculus root cross section
What characteristics should an absorbing system have?
How does a root grow through the soil? Does it grow from the tip or from the base?
Where would you expect to see lateral roots, near the growing tip of the root or behind the growing tip? Why
would lateral roots not be found in both locations?
How are the vascular systems of roots and shoots similar? In what manner are they different? (Hint: think about
the organization of vascular tissues)
63
KINGDOM PLANTAE Part 3: SEED PLANTS
A. Introduction:
Since the evolution of the seed about 350 million years ago, seed plants have become the most dominant feature of
the terrestrial landscape. Seeds offer both protection and stored food reserves for developing embryos and it is
these two characteristics which are thought to have given seed plants their great selective advantage over their
free-sporing ancestors.
All seed plants are heterosporous, with a dominant sporophyte generation and a much reduced gametophyte
generation that develops on the sporophyte, rather than existing as a free-living stage on or in the soil.
Dispersal of male gametes via pollen grains eliminated the requirement for water as the fertilization medium.
As you complete this exercise, think about the modifications necessary to evolve seed plants, using the seedless
vascular plants examined last week as your starting point. Please read Chapter 30 of Campbell and Reece
(2005) prior to attending lab.
Laboratory Objectives:
Following completion of today’s exercise, you should be able to:
•
Recognize and classify the vascular plants to their appropriate Phylum.
•
Compare and contrast the non-seed plants (last week’s lab) with the seed plants.
•
Identify structures described in the laboratory exercise, and give their function.
•
Relate sexual life cycles with sporic meiosis to the plants you view today.
•
Appreciate and describe adaptations made by plants to survive terrestrial habitats, particularly with respect
to modification of plant organs.
B. The Gymnosperms:
The gymnosperms are all seed plants with their seeds borne naked (gymnosperm [Greek] = “naked seed”),
rather than in ovaries, as in the angiosperms, which will be discussed later in this exercise. Usually the seeds
are borne in cone-like structures called strobili. All gymnosperms are woody perennials. The gametophyte is
extremely reduced, but still distinctly present.
There are four extant gymnosperm phyla, three of which are relatively small. The Cycadophyta, although still
somewhat common in some parts of the world, is considerably less dominant than it was in the past. The
Ginkgophyta is a relictual group, with Ginkgo representing the only extant genus. Members of the
Gnetophyta are common in certain, mostly arid areas, but this Phylum consists of only three living genera that
do not appear to be closely related. Representatives from each of these three phyla are present as demonstration
material today. Make sketches of these.
64
Cycadophyta
Ginkgophyta
Gnetophyta
The Coniferophyta is by far the most abundant and successful of the gymnosperm phyla. This Phylum consists
of trees like pines, spruces, firs and larches. The objective of this part of the exercise is to become familiar with
a typical gymnosperm life cycle, using pine as our example. You should become familiar with the structure and
significance of pollen grains, ovules, and seeds.
Begin your examination of the life cycle of pine by viewing living sporophytes available on display. Can you
come to any conclusions about the type of terrestrial environment in which you would expect to see these
plants?
Examine frozen material of male cones. Note how small
they are. The cone is composed of a number of leaves that
bear microsporangia on their lower surfaces. You will
need to consult prepared slides of a longitudinal section
through a male cone to fully understand this relationship.
The microsporangia are the site of meiosis in the male
cone. What are the products of meiosis? Are they visible
on the slide?
Make sketches and label all components of a male pine
cone.
65
Microspores then develop into pollen grains, the
male gametophyte of conifers. Examine the
demonstration of slides of pollen grains from pine.
The pollen grain consists of a vegetative cell (also
referred to as a tube cell), which is responsible for
growth of the pollen tube, a generative cell, which
will divide to produce two sperm cells, and two
sterile prothallial cells, which represent the remains
of the vegetative body of the male gametophyte.
Note the presence of two bladder-like wings. What
is their function?
Draw a pollen grain and label all structures
described above.
Observe the slide of the young ovulate (female)
cone. Sketch it to the right. Female cones are more
complex than male cones. Megasporangia are
borne on the upper surface of a flat structure called
the scale, which in turn sits above another structure
termed a bract. They are difficult to recognize as
sporangia because some changes have occurred.
They are now referred to as ovules.
Continue with your examination of the female cone
by looking at preserved specimens. Remove the
bract/scale complex and look for ovules on top of
the scale. Examine various dried cones on display
and try to find the scale and bract. Make a diagram
and label the bract, scale and ovule. How many
ovules are present on each scale?
66
Now examine the prepared slide of a mature pine
ovule. It is drawn for you to the right. The
megasporangium is enclosed in an extra
covering called the integument. Together, these
structures form the ovule. At one end of the
integument is an opening termed the micropyle.
It opens into a small ‘pollen chamber’. Inside the
integument, the megasporangium wall is not as
clearly evident. It is now referred to as the
nucellus. The nucellus layer is most easily
observed at the micropyle end of the ovule. The
female gametophyte develops inside the nucellus
through multiple cell divisions. Archegonia are
eventually produced at the micropylar end. Label
the drawing and indicate whether each structure is
haploid or diploid.
After pollen grains reach the pollen chamber, they germinate and pollen tubes grow through the nucellus and
into the archegonium. Fertilization is accomplished when the two non-motile sperm nuclei are discharged from
the pollen tube into the egg cell. One fuses with the egg nucleus and one degenerates. The fertilized egg, or
zygote, develops by mitosis to form an embryo surrounded by female gametophyte tissue. This tissue serves as
a nutrient supply for the developing sporophyte. Meanwhile, the integument develops into a resistant seed coat.
The seed, then, is a package containing an embryo, food storage material, and a protective coat.
Examine pine seeds available as demonstration
material. Note the hard seed coat. From what tissue
is it derived? Look at and dissect one of the ‘pinenuts’ provided. In this case, the seed coat has been
removed. Make a labeled diagram of a pine seed
illustrating the seed coat, nucellus,
megagametophyte and embryo. Indicate the ploidy
of each structure observed. What parts of the seed
represent the sporophyte generation?
What parts of the seed represent the gametophyte
generation?
You have now examined various structures associated with the pine life cycle. Refer to the life cycle in Figure
30.6 of your text. Think about what stages in the life cycle are similar to the homosporous and heterosporous
life cycles viewed for the seedless plants. How is this life cycle different from those viewed for seedless plants?
67
C. The Angiosperms:
The flowering plants are the most diverse and widespread group of plants in existence today. There are
presently about 235,000 species, all of which are placed into one Phylum, the Anthophyta (from the Greek
“antho” meaning flower). The Phylum is further subdivided into two classes: the Monocotyledones, which
includes the grasses, lilies, palms, and grain crops; and the Dicotyledones, which includes roses, legumes,
sunflowers, and trees like poplars and oaks.
Flowering plants exhibit a wide range of reproduction strategies including vegetative (asexual) and sexual
reproduction. Because most angiosperms are hermaphroditic, sexual reproduction can occur either through
self-fertilization or through cross-pollination (outcrossing). The evolutionary consequences of these different
breeding systems are quite different.
For sedentary organisms like plants, dispersal can often only be accomplished through processes related to
reproduction. Pollen, seeds and fruits are all adapted for dispersal. In general, dispersal is aided by both abiotic
(wind, water, gravity) and biotic (insects, birds, other animals) agents. Specifically, pollen dispersal is
accomplished through attraction of biotic agents (pollinators) by the flower. Colour, shape, smell and rewards
(nectar and pollen) all serve as attractants to pollinators. Seed dispersers are similarly attracted by floral
characters but in this case it is the mature ovary (fruit) which is specialized for attraction. Colour, shape, smell
and rewards (edibility) are again the attractants.
Adaptations for abiotic dispersal (wind pollination and seed dispersal) are also common and evident. Flowers
with reduced sepals and petals allow pollen to be released into the air more easily while small, winged fruits are
more easily dispersed by wind. What should be clear from the above discussion is that the flower plays an
important role in the dispersal of genes within a population. When you examine and learn the parts of the
flower today try to keep in mind the various functions of the parts you are looking at. You will need to know
not only what the various structures are but also what they will develop into.
D. The Flower:
A flower is a highly modified and specialized shoot whose function is reproduction. Use a dissecting
microscope to examine one of the fresh or frozen flowers provided. Note that the flower is composed of four
whorls of parts; each whorl is derived from leaves. Starting from the outside, identify the small, leaflike sepals.
Petals, generally coloured for attraction of pollinators, comprise the second whorl. Stamens comprise the third
whorl. Each stamen is composed of a slender stalk, termed the filament, and a pollen-bearing anther, derived
from a microsporangium. Carpels constitute the fourth (innermost) whorl. Each carpel is composed of (i) a
swollen ovary, containing one or more ovules, (ii) a style, that connects the ovary to the stigma, and (iii) a
stigma, the pollen receiving site. There may be more than one carpel present in the flower depending on the
species. In some cases the carpels remain separate, in others the carpels fuse together to form a single
reproductive structure (the gynoecium). Are the ovaries in this flower superior (above the base of the petals)
or inferior (below the base of the petals)?
68
Make a cross section through the ovary. The small, whitish structures are ovules. These will develop into seeds
as the ovary matures into fruit.
Draw a complete flower and label all the parts. Refer to Figure 30.7 in your text, if necessary. Is this flower
radially symmetrical or bilaterally symmetrical?
E. The Pollen Grain:
Next, examine prepared slides of Lilium anther cross-sections (drawn below). The anther is derived from a
microsporangium. Microspores produced inside the anther develop into pollen grains. Are the microspores
produced by mitosis or meiosis?
Observe pollen grains with the 40X objective lens. Two cells are visible. What are their names and functions?
69
F. The Female Gametophyte
Examine a cross-section of a Lilium (lily) ovary and identify the ovules. Each ovule is attached to the ovary by
a stalk called the funiculus, which may be visible. Label the ovule below to indicate the funiculus,
integuments, nucellus (modified megasporangium wall), micropyle and the megaspore mother cell.
In typical angiosperms, the megaspore mother cell inside the nucellus divides meiotically to produce four
haploid nuclei. Three degenerate, and one undergoes mitosis three times to result in eight haploid nuclei (cell
membranes develop around them later). These nuclei comprise the female gametophyte, or embryo sac.
Examine the prepared slide of a Lilium embryo sac at the eight nucleate stage on demonstration. Although it is
unlikely that all eight nuclei will be visible, you should look for the some of the following: three antipodal cells
at the end of the embryo sac (opposite the micropyle); two nuclei in the central region of the embryo sac,
termed the polar nuclei; and three nuclei at the micropylar end of the embryo sac, consisting of two synergids
surrounding an egg. During the process of double fertilization, one sperm nucleus fuses with the egg to form a
zygote (2n), which eventually divides by mitosis to become the embryo. The second sperm nucleus does not
degenerate (unlike fertilization in conifers), but instead fuses with the two polar nuclei to form the endosperm
nucleus (3n). The endosperm nucleus then divides to form endosperm tissue, which provides nutrition for the
developing embryo. The fertilized ovule is termed a seed. Seeds remain inside the ovary, which develops into
the fruit (see Section H).
Draw an embryo sac and label all of the nuclei visible.
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G. The Seed:
Obtain bean seeds that have been soaked in water
overnight. On the bean, two scars, the micropyle
(the smaller scar) and the hilum (the larger scar)
should be visible on the seed coat. The latter is
where the ovule was attached to the funiculus.
Relate the structures to those you found on the ovule
in the previous section. Sketch what you see in the
space to the right.
Carefully remove the seed coat and locate the two
large cotyledons. Cotyledons are fleshy and leaflike, and function as a food storage tissue until the
growing seedling becomes photosynthetic. The
embryo is located between the two cotyledons. The
plumule, located near the top of the embryo,
represents the first set of true leaves produced by the
embryonic shoot apical meristem. The radicle is an
embryonic root that emerges from the bean seed as it
splits the seed coat.
Sketch and label a drawing that illustrates these
structures. Can you relate the seed structures to
structures in the ovule?
H. The Fruit:
A fruit develops from ovary wall material following fertilization of the ovules within. As the seeds develop, the
ovary wall simultaneously thickens to become the pericarp (the wall of the fruit). For example, the bean in the
preceding section is a seed, while the pod containing the bean seeds is a fruit. The function of a fruit is to
protect the seeds and to aid in their dispersal.
Examine the demonstration material provided as you read through the following section.
Fruits may consist of one or more ovaries (true fruits), or they may incorporate other floral parts in addition to
the ovary (accessory fruits).
Fruits may be dry or fleshy. Dry fruits may remain intact at maturity, or may split apart. Nuts and samaras
are fruits that remain intact at maturity. Note the wing on the samara; this is an adaptation for dispersal in ash,
elm and maple trees. Conversely, a legume is a fruit type that splits apart when the fruit is mature. Peas and
beans are good examples of this type of fruit. Sketch some dry fruits.
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Fleshy fruits like grapes and cherries often have distinct layers within the pericarp. The endocarp is the
innermost portion around the seed(s). The skin of the fruit is the exocarp, and the fleshy region between the
endocarp and exocarp is called the mesocarp. Can you observe these layers on the fleshy fruits provided?
Berries (grapes and tomatoes) and drupes (peaches, plums, cherries and olives) are fleshy fruits composed of
only ovary tissue (are they true or accessory fruits?). The mesocarp and endocarp of berries are both soft, and
enclose many seeds. Drupes have a distinctive stony endocarp surrounding a single seed.
The fleshy portion
of pomes (apples and pears) is derived from receptacle tissue; only the core comes from the ovary. Are pomes
true fruits or accessory fruits? Sketch representative fleshy fruits.
I. Environmental Adaptations:
As described earlier, Angiosperms are by far the most diverse and widespread of all vascular plants, meaning
that they are able to survive and reproduce in many different types of habitats. In part, this is due to the
development of flowers, but be aware also that various vegetative modifications may be necessary to survive
these seemingly extreme conditions. Examine the demonstration material available and for each specimen,
describe what structure (i.e. leaf, stem or root) has been modified and for what purpose.
Modified Leaf Examples
Modified Stem Examples
Modified Root Examples
72
A number of characteristics of plants and the two seed plant phyla are shown in the table below. Use the
information you have acquired in lecture and lab as well as your text to complete the table.
Characteristic
Phylum
Coniferophyta
Dominant
Generation
Uni- or Bisexual
Gametophytes
Seed and pollen
dispersal mechanisms
Water Required in
fertilization
Seeds
Produced
Anthophyta
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Use information from lab and your textbook to fill in the blanks in the figure below, depicting the phylogenetic
relationship among the phyla covered in last week’s and today's lab. For each of the major branches in the plant
phylogeny, indicate the diagnostic characteristic(s) that link the taxa that fall after each starred point on the tree.
74
KINGDOM FUNGI
A. Introduction:
The fungi are a unique group of organisms that possess cell walls made of chitin and a distinctive form of cell
division. All fungi exhibit a sexual life cycle with zygotic meiosis. Fungi are primarily non-motile and obtain
their nutrients by absorption, rather than ingestion. Within the kingdom the major phyla are defined partly
based on reproductive structures. The name of each phylum is based on its reproductive structure - the suffix
“mycota” means fungus-like, and the prefix (asco, basidio or zygo) reflects the reproductive structures
associated with that group. As you examine the specimens take special note of these and relate them to
vegetative structures.
Fungi are one of the groups of organisms responsible for decomposition in the biosphere. Their activities are as
useful to the world as those of the food producers because decomposition releases carbon dioxide back into the
atmosphere and returns nitrogenous compounds and other nutrients to the soil, thereby making these
constituents available for plants, and eventually, animals. Fungi participating in this activity are termed
saprobic fungi.
Fungi also play an important role in symbiotic relationships with other organisms. Symbiotic associations of
fungi with termites enable both organisms to utilize cellulose as a food supply; their association with plant roots
provides plants with increased surface area for absorption of water and minerals, while supplying the fungi with
a steady supply of carbohydrates. Such interactions are termed mutualistic because both members benefit from
the association. Parasitic fungi absorb nutrients from living host cells. In some cases, they may be pathogenic.
Examples of pathogenic fungi include the organisms responsible for athlete’s foot and Dutch elm disease.
All fungi, other than unicellular species like the yeasts, exist as a diffusely organized mass of filaments called a
mycelium. Each filament in the mycelium is termed a hypha (plural; hyphae). Fungal hyphae can be aseptate
and coenocytic, meaning that they do not have cross-walls and instead consist of a continuous mass of
cytoplasm containing many nuclei. Other hyphae are septate; cross walls of some form are present. Most of
the body of the fungus is generally hidden underground or buried within its food source. The only exposed
structures are the reproductive structures. It is important to remember this as you view the material available
today.
You should read Chapter 31 in Campbell and Reece (2005) prior to attending lab. For a review of fungal life
cycles, consult Activities 31A and 31B on the CD ROM that came with your text.
Laboratory Objectives:
By the conclusion of today’s exercise you should be able to:
•
Separate the fungi from other kingdoms based on their unique characteristics
•
Recognize and classify fungal specimens to Phylum and Class (where applicable)
•
Define and use terminology pertaining to fungi
•
Compare and contrast the reproductive strategies employed by the three fungal phyla.
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B. Phylum Zygomycota:
Rhizopus stolonifer (black bread mould) is an organism you are all familiar with, although perhaps
unknowingly! Members of this phylum live in soil or on decaying plant or animal material. All members have
aseptate hyphae and undergo zygotic meiosis. Is the dominant stage in the life cycle haploid or diploid?
Observe and draw vegetative stages under the light microscope
using the prepared slides provided. Label the mycelium
(composed of hyphae), sporangia (sacks containing spores)
and spores. These spores are produced asexually by mitosis.
Asexual reproduction is very common in this phylum.
Sexual reproduction only occurs if conditions become
unfavourable for growth. Two separate mating strains must
also be present for sexual reproduction to occur. Examine
prepared slides of Rhizopus to observe structures associated
with sexual reproduction. Locate gametangia (sacs
containing gametes), which are located on the ends of hyphal
extensions. Gametangia from two different mating strains fuse
to form a zygosporangium. The zygosporangium holds the
zygotes, which result from the fusion of nuclei contained
within the gametangia. Zygosporangia are thick walled and
resistant, and are very noticeable on your slides.
Can you relate these structures to stages in the life cycle?
(refer to Fig. 31.12 in your text)
C. Phylum Ascomycota:
This phylum is very large, and ranges from small unicellular organisms like yeasts to very large, complex
organisms like cup fungi and truffles. Members of this phylum have septate hyphae, but the septa are
perforated, so the cytoplasm and nuclei are still able to move freely through the hyphae. Asexual reproduction
(via production of naked spores called conidia) does occur, but as with all of the fungal phyla, the sexual
structures are the defining feature of the Ascomycota.
Begin your examination of Ascomycota by
viewing yeast (Saccharomyces cerevisiae)/water
suspensions under the microscope. Locate the
cells using the 40X objective and sketch your
observations. What shape are they? Are they
budding? Is this an example of sexual or asexual
reproduction?
76
Penicillium is an asexual ascomycete that reproduces by conidia (spores that bud off of hyphal-like
conidiophores). Some species of Penicillium play a major role as the source of important drugs, including
antibiotics and anti-rejection drugs, while others are used in the production of some of our tastiest cheeses.
Examine a prepared slide of Penicillium. Sketch your
observations in the space to the right. Can you distinguish
between hyphae and conidia?
Examine the "blue" area of the blue cheese provided for you
under the dissecting microscope. You will not be able to see
conidia because they are too small and fragile, but the
organism you see is Penicillium. Can you think of any other
ways that humans have been able to utilize this organism?
Sexual reproduction in the Ascomycota involves the formation of a saclike structure called an ascus (plural; asci),
within which haploid ascospores are produced following meiosis. Asci are themselves formed in a complex
structure called an ascocarp. You will look at three types of ascocarps in this part of the exercise: a cleistothecium
(closed and spherical) a perithecium (vase-shaped with a small pore at one end) or open and an apothecium (cupshaped). The asci usually develop as a layer inside the ascocarp.
Examine prepared slides of Erysiphe (powdery
mildew, a plant parasite). When you look at this slide,
remember that most of the body of any fungus is
located inside something; in this case, the plant stem,
which occupies most of the slide. The ascocarps are
located on the outer edge of the plant stem so that
spores can be dispersed by air currents. Locate the
ascocarps containing asci and ascospores. This
ascocarp is a cleistothecium. Why?
Sketch a typical cleistothecium and its contents in the
space to the right.
77
Sordaria is an example of a fungus that has a type of
ascocarp called a perithecium. Remove some
perithecia from the fresh culture provided and place
them on a microscope slide. Add a drop of water and a
coverslip and gently press down with your thumb to
release asci from the ascocarps. Sketch your
observations.
Examine prepared slides and locate the perithecia using
the 40X objective lens. Look for the ostiole (pore).
Sketch and label a diagram. What shape are the asci?
How many ascospores per ascus can you see? How
many do you expect?
The cup fungus Peziza provides an obvious example of
an apothecium. Examine prepared slides of the
apothecium in longitudinal section (use the 40X
objective lens) and make drawings illustrating what you
see. Locate the layer of asci and the sterile
paraphyses. Examine the demonstration of the whole
organism under the dissecting microscope.
D. Phylum Basidiomycota:
This phylum includes the fungi you are probably most familiar with: the puffballs, mushrooms, bracket fungi,
and rusts and smuts. Members have septate hyphae, but the septa are perforated and surrounded by bracketlike structures. Unlike other fungi, most reproduction is sexual. Meiosis produces basidiospores, which are
borne on a club-shaped structure called a basidium (plural; basidia). Basidia are located on or in a complex
structure called a basidiocarp. What type of life cycle is exhibited by these organisms?
The two classes in this Phylum that we will examine today are defined based on the relationship between
basidia and basidiocarp. Note that class names within the fungi end in “mycetes”.
D-1. Class Hymenomycetes:
This class contains the gill fungi (mushrooms) and the pore fungi (bracket fungi). Agaricus bisporus, the
commercial mushroom, is an example of a gill fungus. In Class Hymenomycetes, the basidia and basidiospores
are borne on a basidiocarp.
78
Make a longitudinal section of a mushroom (basidiocarp)
and locate the stipe (stalk), cap, and lamellae (gills). The
gills of an immature mushroom are covered for some time by
a membranous tissue. This tissue breaks as the basidiocarp
increases in size and may remain on the stipe in the form of a
distinct scar, or annulus.
Sketch your observations in the space to the right.
Consult a prepared slide of Coprinus, showing a crosssection through the cap. The cross section is
somewhat reminiscent of a spoked wheel. Locate the
central region that represents the stipe. Radiating
away from the stipe are the gills. Locate the gills and
basidia protruding into air spaces between the gills.
Golden basidiospores are located above the basidia.
Sketch and label a drawing showing the gills, basidia
and basidiospores. How many spores are normally
attached to each basidium?
Examine members of the pore fungi on display. This
group includes shelf and bracket fungi. Note how the
fertile lower region is organized into pores rather than
on gills. Basidia line the insides of the pores. Sketch
a representative from this group to the right.
Can you think of an external morphological feature
that would separate the mushrooms and bracket fungi?
D-2. Class Gasteromycetes:
In this class, basidia and basidiospores are borne in a basidiocarp, rather than on a basidiocarp, as in the Class
Hymenomycetes. Representatives include puffballs, earthstars, stinkhorns and birdsnest fungi. Examine
demonstration material of various gasteromycetes and sketch some typical members in the space below.
79
E. Lichens:
As noted at the beginning of this exercise, fungi play an important role as symbionts with other organisms. The
symbiosis of a fungus with an alga forms an organism known as a lichen. Generally, the fungal component of a
lichen is usually a member of the Ascomycota (sometimes Basidiomycota) and the photosynthetic component is
either Nostoc, a blue-green bacteria, or one of about six species of green algae.
Lichens are widespread in nature, and able to inhabit areas where neither symbiont could survive as a separate
entity. They can be found in the Arctic, in deserts, on alpine peaks. Lichens are economically important as
pollution indicators, source of natural dyes, and food for animals.
There are three common growth forms:
a)
crustose – forms a thin flat crust that is glued to the substrate.
b) foliose – flat and leafy or round in outline; distinct upper and lower surface
c)
fruticose – basally attached strands with hair-like, or shrub-like growth form
Identify the following lichens using the dichotomous key provided. Write your identification in the space
below. Some of the terms you will encounter are illustrated on the cards above the specimens.
•
Before you begin, examine the specimens and read through the key.
•
At each couplet, you will be required to make a choice. Choose the lead that best describes the
specimen. Some species are quite variable, so be sure you examine all available.
•
Be prepared to go back in the key when you run up against a ‘dead end’.
Lichen A
Lichen D
Lichen B
Lichen E
Lichen C
Lichen F
F. Mycorrhizae:
About 95% of all plants have a mycorrhizal association with members of the Zygomycota, Ascomycota or
Basidiomycota. One of the most economically important functions of this symbiosis is put to work in the
forestry industry where mycorrhizae inoculants are commonly used to promote faster growth in pine seedlings.
Examine the plants on demonstration. One has been treated with a fungicide to kill the soil fungi, while the
control has been allowed to grow in untreated soil. From this, can you infer which plant is associated with
mycorrhizae? Do you think the association is beneficial to green plants?
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Test your knowledge of the three fungal Phyla by completing the table below.
Phylum
Characteristic
Zygomycota
The structure where
meiosis occurs:
Products of
meiosis are:
Asexual Reproduction
occurs via:
Hyphae are:
(septate/aseptate)
Diagnostic
Character(s):
Ascomycota
Basidiomycota
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KINGDOM ANIMALIA Part 2: “Armoured” Invertebrates
A. Introduction:
You will survey the remaining protostomic Lophotrochozoan phylum (the Mollusca), survey the Ecdysozoa,
and dissect the grasshopper, Romalea microptera in today’s exercise. All of the invertebrates seen in today’s
lab possess some type of tough body covering or “armour”. To prepare for this lab, you should read Chapter
33, pp. 656-665 of Campbell and Reece (2005).
Laboratory Objectives:
Following the completion of this exercise, you should be able to:
•
Describe the features of protostomes
•
Recognize and classify (into phyla, subphyla, and classes, where appropriate) the organisms viewed based
on diagnostic and other characters.
•
Identify the external and internal features of the grasshopper, and indicate their functions.
B. Survey of the Protostomia:
LOPHOTROCHOZOA: (Continued - Phylum Platyhelminthes, Phylum Rotifera, and Phylum Annelida
were examined in Part 1 of Kingdom Animalia).
Phylum Mollusca Molluscs are bilateral, eucoelomate protostomes which lack segmentation, and
have bodies composed of a muscular foot (used for locomotion or food capture), visceral mass
(which contains the organ systems), mantle ( a soft tissue that secretes the shell) mantle cavity (where
gills and excretory organs are located), and calcareous shell. Most species are marine and possess a
radula (a rasping organ in the mouth used to scrape up food).
Class
Polyplacophora
(chitons)
Gastropoda
(snails and slugs)
Diagnostic Characteristics
• 8 overlapping shell plates
along dorsal midline
• Foot used as suction cup
to adhere to rock
• Radula used to scrape
algae from rocks
• Gills found in mantle
cavity (groove between
foot and mantle edge)
• Single spiral shell if
present
• Bodies show torsion
(twisting)
• Secrete mucus to aid in
locomotion
• Radula used for feeding
Notes / drawing
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Bivalvia
(clams, oysters, scallops,
mussels)
•
•
•
•
Cephalopoda
(nautiluses, squids,
octopuses)
•
•
•
•
•
Paired lateral shells
(valves) hinged dorsally
Radula absent, head
reduced
Gills enlarged for
suspension/filter feeding
Foot used for anchorage
and locomotion
Head and foot fused
Carnivorous
Shell multi-chambered
and external, internal and
calcareous, internal and
proteinaceous or absent
Head modified into
tentacles for prey capture
and manipulation
Foot forms a siphon for
jet-propelled locomotion
ECDYSOZOA: These animals, like the Lophotrochozoa (seen earlier in the semester), are grouped on the
basis of molecular evidence. However, both phyla in this group display ecdysis, or molting of the
outermost layer.
Phylum Nematoda (round worms) Nematodes are
pseudocoelomate, unsegmented, round in cross section,
tapered at both ends, covered by a resistant, secreted cuticle,
and lacking in appendages. Nematodes are widespread and
common; they can be either free-living or parasitic. On display
are Enterobius (pinworm) and Ascaris. In both species, the
male is smaller and has a hooked posterior end.
Phylum Arthropoda
Members of this phylum are bilaterally symmetrical, segmented, eucoelomate protostomes that have a chitinous
exoskeleton, open circulatory system, complete (with anus) digestive tract, dorsal brain with ventral nerve cord,
and paired jointed appendages. Typically, the body is divided into three regions: the head, thorax, and
abdomen, although some regions may be fused. Arthropods are the most numerous and diverse of all the
animal phyla. The phylum is further subdivided into 4 Subphyla.
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Subphylum 1: Cheliceriformes Chelicerates have 4 pairs of legs plus 2 pairs of head appendages: one pair of
chelicerae and one pair of pedipalps; they lack antennae. Chelicerae are pincerlike and used for feeding;
pedipalps are mainly sensory but can be used in feeding, locomotion, or reproduction.
Class Arachnida (spiders, mites and ticks, scorpions) Terrestrial, with characteristics of subphylum;
spiders with bulbous and legless abdomen (hindbody), mites and ticks with abdomen fused with legbearing region, scorpions with elongate abdomen bearing poisonous sting. On which body region (head,
thorax or abdomen) do you find legs?
Make sketches below of representatives of the main arachnid groups: spiders, ticks and mites, and
scorpions.
Subphylum 2: Crustacea
Class Crustacea: Arthropods with mandibles (mouthparts used to crush and grind food), 2 pairs of
antennae and conspicuous thoracic and abdominal appendages, biramous (branched) appendages.
Appendages may be highly modified to perform tasks like feeding, swimming and reproduction.
Lower crustaceans (water "fleas", brine shrimp, copepods, barnacles, etc.) have many, relatively
unspecialized appendages. Higher crustaceans (shrimp, lobsters, crabs, hermit crabs) exhibit fewer, but
more specialized limbs, shortening of the body, and development of a carapace (a fold of the exoskeleton
behind the head which protects the more important anterior region of the body and facilitates the setting up
of a water current for purposes of respiration and feeding) relative to lower crustaceans. Make sketches of
both higher and lower crustaceans in the space below.
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Subphylum 3: Myriapoda Mandibulate arthropods with uniramous (unbranched) appendages.
Class Chilopoda: (centipedes) Elongate, terrestrial carnivorous uniramians with conspicuous mandibles;
flattened in cross section; one pair of legs per segment. Can you distinguish the head, thorax and
abdomen?
Class Diplopoda: (millipedes) Elongate, terrestrial herbivorous uniramians with inconspicuous mandibles;
rounded in cross section; two pairs of legs per segment.
Subphylum 4: Hexapoda - Class Insecta: (insects) Uniramians with 3 pairs of legs (one pair on each of the
thoracic segments); 0, 1 or 2 pairs of wings (also on the thorax); one pair of antennae.
Some of the major orders are: Isoptera (termites), Lepidoptera (butterflies and moths), Odonata
(dragonflies), Orthoptera (crickets and grasshoppers), Siphonaptera (fleas), Anoplura (lice), Coleoptera
(beetles), Diptera (flies and mosquitoes), Hemiptera (true bugs), Hymenoptera (ants/bees/wasps), and
Trichoptera (caddisflies). Make sketches below of the examples shown in lab. It isn’t necessary that you
learn all the names of these orders, but you should be able to recognize any one of them as being in the
Class Insecta.
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C. Dissection of the Grasshopper:
External anatomy: Note the outer body covering; this chitinous exoskeleton is divided into a series of armor-like
plates. The thinner, flexible areas of exoskeleton between the plates form articular membranes (flex the abdomen
to observe these). The body is divided into three main regions, a head, a thorax, and a posterior abdomen.
Proceed with your examination as follows:
1.
Head:
Antennae: paired sensory appendages
Compound eyes: complex eyes, on either side of the head. Using a razor blade, remove a thin piece of the
surface of the compound eye, mount it in water beneath a cover slip on a slide, and examine it under the
compound microscope. Note the facets of the eye, each representing the lens of a single visual unit, an
ommatidium. Sketch them in the margin.
Ocelli (sing.; ocellus): three small, simple eyes; one located in the midline groove between the antennae,
two near the top-front corner of each compound eye
2. Mouthparts: The grasshopper mouthparts are relatively unspecialized compared to those of most other kinds of
insects, and are designed for manipulating and chewing food. Carefully grasp each mouthpart near its base with
forceps, loosen it by working it back and forth, and then remove it with a steady, even pull. Arrange the
mouthparts on a piece of paper as you remove them.
Labrum: the anterior mouthpart, like the upper lip.
Labium: the unpaired lower lip, which is provided with lateral feelers, the labial palps.
Maxillae (sing., maxilla): paired structures for food manipulation; each with a small, lateral maxillary
palp. The palps are segmented and are used to manipulate food and gather sensory information.
Mandibles: two massive jaws,
Hypopharynx: central, tongue-like structure.
Examine a prepared slide of grasshopper mouthparts mounted in an "exploded" view, and compare them with
the intact mouthparts of your specimen. Label the diagram below.
Figure 1. Grasshopper mouthparts (Class Insecta).
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3.
Thorax: consists of three segments each bearing a pair of jointed legs:
Prothorax: anterior segment of thorax (covered dorsally and laterally by the saddle-like pronotum),
bearing a pair of walking legs, called the prothoracic legs
Mesothorax: middle thoracic segment, bearing a second pair of walking legs, the mesothoracic legs
Metathorax: posterior thoracic segment, bearing the large metathoracic legs specialized for junping
2 pairs of wings: the outermost mesothoracic wings are leathery; beneath them are the membranous
metathoracic wings.
4.
Abdomen: relatively unspecialized, consists of 11 segments.
Tympanum: distinct rounded section of thin membrane on first abdominal segment, often partially
obscured by the metathoracic leg. What function does the tympanum have?
Spiracles: minute respiratory openings, at the anteroventral corners of segments 2-9.
5.
External genitalia: the terminal segments of the abdomen show some fusion, modifications to form genitalia.
Cerci: small, dark, triangular dorsolateral spurs; in males and females; have a tactile sensory function.
Ovipositor: conspicuous structure of 4 large conical prongs; only in females. What is the function of the
ovipositor?
Using the information above label the following diagram, depicting a female grasshopper.
Figure 2. Grasshopper external features (Class Insecta).
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Internal anatomy: Using scissors, snip off all the legs and wings. Beginning at the posterior tip of the abdomen,
make a longitudinal dorsal cut in the body wall with fine scissors. Cut carefully with just the tip of the
scissors, keeping the blade that is beneath the exoskeleton shallow. Extend your cut all the way to the front
of the head. Carefully pin out the body wall in a dissecting pan (locate the grasshopper slightly to one side
of the dissecting pan so that you can observe its anatomy under low magnification).
1. Locomotion and Respiration:
Muscles: found throughout the body; those in the thorax are especially well developed to move the legs and
wings.
Tracheae: transparent, delicate respiratory tubes. Pull the exoskeleton away from the thoracic tissue, and
carefully remove some of the transparent threads from the exoskeleton using your fine forceps. Place the
tissue in a drop of water on a slide, add a cover slip and view under the 40X objective of the compound
microscope. Notice the ring-like structures that keep the tracheae from collapsing. The tracheal tubes
branch and re-branch, extending through the muscles and other internal tissues of the grasshopper. What is
the function of tracheae? What is the function of blood in grasshoppers?
2.
Digestive and excretory systems: (The gonads (sex organs) overlie part of the digestive system, especially the
intestine, so they will have to be gently loosened and pushed to the side.)
Mouth: the anterior opening of the digestive system
Esophagus: short narrow tube leading extending from mouth into digestive tract.
Crop: thin-walled sac for storage.
Digestive ceca: finger-like projections posterior to crop (extending anteriorly and posteriorly), which
function to enlarge the digestive and absorptive area of the stomach below.
Intestine: extends posteriorly from the stomach and terminates in an anus.
Malpighian tubules: long, threadlike tubules surrounding lower intestine; these tubules are the excretory
and osmoregulatory organs of the grasshopper. Coelomic fluid containing metabolic wastes enters the
tubules and is eventually discharged via the anus.
3. Reproductive system: (examine that of your specimen and that of the other sex in another student's specimen;
ask your instructor if you are unsure of the sex of your grasshopper).
In females:
Ovaries: conspicuous paired structures, which overlay the intestine.
Oviduct: strap-like tube leaving each ovary posteriorly and turning under the intestine.
Vagina: point at which oviducts join to form a median tube.
Spermathecae: coiled tubular storage sacs for sperm received during mating. To observe these, cut
through the esophagus, grasp the crop and bend the entire gut posteriorly.
In males:
Testes (sing. = testis): paired organs located above the digestive tract in the abdomen.
Vas deferens (pl. vasa deferentia): thin tube extending posteriorly from each testis.
Ejaculatory duct: point of union of the vasa deferentia under the intestine.
Accessory glands: a number of small tubules lying anterior to the ejaculatory duct and joining with it. As
above, you must reflex the gut back to see these.
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5.
Nervous system: (Remove the reproductive tract and the remainder of the digestive tract.)
Ventral nerve cord: yellowish cord running under a thin overlying connective tissue in ventral floor of
coelom. (Remove the connective tissue to see it well).
Ganglia (sing. ganglion): swollen regions of the nerve cord; 3 in thorax and 5 smaller ones in abdomen.
Lateral nerves: lead away from the nerve cord in each segment.
The nerve cord cannot easily be traced in the head region, but the ganglion below the esophagus is connected to
the brain by nerves passing around the esophagus on each side.
Use the information in the internal anatomy section above to fill in the diagram depicting the digestive,
excretory, nervous, and reproductive systems.
Left diagram: nervous system
Right Diagram: Digestive and Excretory
and male reproductive organs
systems and female reproductive organs
Figure 3. Grasshopper internal anatomy (Class Insect).
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Based on observations made in the lab and reference to Campbell and Reece (2005), complete the table below:
Phylum
Habitat
Class
Mollusca
Polyplacophora
Gastropoda
Bivalvia
Cephalopoda
Nematoda
Arthropoda
Arachnida
Crustacea
Chilopoda
Diplopoda
Insecta
Feeding method
Mechanisms for
protection of body
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Use information from lab and your textbook to fill in the blanks in the figure below, depicting the phylogenetic
relationship among the phyla covered in today's lab. For each of the major branches in the animal phylogeny,
indicate the diagnostic characteristic(s) that link the taxa that fall after each starred point on the tree. (Note: You
will look at the deuterostomes next week but you should be able to indicate the diagnostic character that separates
them from the rest of the taxa.)
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KINGDOM ANIMALIA Part 3: Deuterostomes
A. Introduction:
In this exercise, you will examine representatives of the deuterostome phyla (and classes of the phyla
Echinodermata and Chordata), learn their important characteristics and dissect a sea star. Chapters 33 (pp. 665668) and 34 (pp. 671-700) of Campbell and Reece (2005) serve as reference for today’s lab.
Laboratory Objectives:
After completing today’s exercise, you should be able to:
•
Distinguish between protostomes and deuterostomes.
•
Recognize and classify the organisms viewed today to phylum, subphylum, and class, where appropriate,
based on diagnostic and other features.
•
Identify the external and internal structures of the sea star and indicate their functions.
B. Survey of the Deuterostome Phyla:
DEUTEROSTOMIA These animals show characteristic embryology: radial, indeterminate cleavage,
mesoderm and coelom formation by means of enterocoelic pouches, and the blastopore forming the anus (the
mouth is a new second opening).
Phylum Echinodermata: Members of this phylum are secondarily radially symmetrical eucoelomate
deuterostomes which develop from bilateral larvae. The echinoderms are all marine, have calcareous
endoskeletons, and display respiratory/locomotory/feeding appendages called tube feet (podia). We will
examine four echinoderm classes.
Class Asteroidea (sea stars, sea star) Generally
flattened echinoderms with central disk not sharply
delineated from arms; arms having open ambulacral
grooves; carnivores or scavengers. Can you see
suction disks on the tube feet? Do any of the
specimens show regeneration of arms?
Class Ophiuroidea (brittle stars) Generally
flattened echinoderms with central disk sharply
delineated from arms; arms with closed ambulacral
grooves; scavengers or filter feeders. How do these
organisms differ from members of the Class
Asteroidea?
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Class Echinoidea (sand dollars and heart or biscuit
urchins). Armless echinoderms with well developed
endoskeletons which may be either (1) globose with
enlarged spines [sea urchins], or (2) flattened with
numerous short spines [sand dollars], or (3) slightly
inflated with numerous short spines [heart or biscuit
urchins]. Echinoids are grazers, scraping the
substrate with specialized teeth.
Class Holothuroidea (sea cucumbers) Worm-like
armless echinoderms with vestigial skeletons
lacking spines and bodies strongly elongated along
the oral-aboral axis. Note the 5 rows of tube feet.
Most are suspension feeders.
Phylum Chordata: Bilateral deuterostomes having (at some stage in the life cycle) a dorsal hollow nerve
cord, a notochord, and paired pharyngeal (gill) slits. Most chordates also have a postanal tail. There are 3
main subphyla.
Subphylum Urochordata: (tunicates or sea squirts). These are a diverse group of marine chordates with
planktonic tadpole-larvae showing all four phylum characteristics, and highly modified sessile filter feeding
adults with body walls composed of cellulose-like tunicin, and incurrent and excurrent siphons serving an
enlarged filtering pharynx. They may be found living alone or in colonies. What chordate features are shared
by the larvae and adults?
What function does the pharynx serve?
Sketch a larva and an adult in the space below; indicate the chordate characters present on your diagrams.
Subphylum Cephalochordata (lancelets) Marine fish-like chordates showing an anterior oral hood overlying
oral tentacles or cirri, chevron shaped (V-shaped) myotomes (muscle segments), but lacking any vertebral or
cranial skeleton. Amphioxis is an example of a Cephalochordate; it is discussed below.
Amphioxis is a primitive chordate that shows the four diagnostic features well, and also shows other structures
that appear to be the forerunners of some typical vertebrate structures. Unlike other chordates, the notochord in
Cephalochordates extends into the anterior most portion of the animal.
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Examine a whole mount of Amphioxis using transmitted light on a dissecting microscope, and/or using the
scanning objective on your compound microscope. Note that the animal tapers at both ends, but that the
posterior end is more pointed. Label the diagram below as you read through the following description.
Figure 1. Amphioxis whole mount, lateral view (Subphylum Cephalochordata)
The mouth, which is located at the anterior end of the body, is surrounded by tentacles. The mouth opens into
the cavity of the pharynx, which is enclosed by numerous gill bars; the openings between the gill bars are the
pharyngeal gill slits.
Dorsal to the pharynx and darkly stained intestine is a rodlike structure that extends from one end of the body to
the other. This is the supporting notochord. Immediately dorsal to the notochord is the hollow, dorsal nerve
cord.
Examine a cross section of Amphioxis made in the region of the pharynx, and correlate it with the anatomy you
observed in the whole mount. Water enters the mouth, moves into the pharynx, and exits through the gill slits. As
it moves across the gill slits, food is trapped and gases are exchanged. The food particles then enter the intestine
and water exits through the atriopore (not visible in cross section). Ventro-lateral gonads may or may not be
visible in your section. Label the diagram. Which chordate character is missing?
Figure 2. Amphioxis cross section (Subphylum Cephalochordata).
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Subphylum Craniata: Chordates having a head consisting of a brain, eyes, and other paired sensory organs,
enclosed in a cranium (skull). Below is a list of craniate classes.
Myxini (hagfishes)
Cephalaspidomorphi (lampreys)
Chondrichthyes (sharks and rays)
Osteichthyes (bony fish)
Amphibia (frogs, toads, salamanders)
Reptilia (snakes, lizards, turtles)
Aves (traditional class for birds)
Mammalia (mammals)
Use your observations, the information below and your text (Figure 34.2) or lecture notes to fill in the Table on the
next page:
• Vertebral column may be present or not.
• Jaws may be present or not.
• Skeleton may be cartilaginous or bony.
• Breathing may be via skin, gills, or lungs (or combinations thereof).
• The integument (body covering) may be smooth and glandular skin, scales, feathers, or fur. Note that skin per
se is present in all cases.
• Limbs may be fins (paired pectoral and pelvic), poorly- or well-developed walking legs, or wings, and may be
positioned under the animal or to the side.
• Teeth may be homodont (all of the same type) or heterodont (different types such as canines, incisors, etc.), or
lacking altogether.
• Eggs may be amniotic (shelled and water-retaining) or non-amniotic (shell lacking).
Class:
Myxini
Cephalaspidomorphi
Chondrichthyes
Osteichthyes
Amphibia
Reptilia
Aves (traditional class)
Mammalia
Vertebral
Column
Jaws
Skeleton
Breathing
Apparatus
Integument
Limbs
Teeth
Eggs
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C. Dissection of the Sea star:
The members of the phylum Echinodermata are entirely marine; they have bilateral larvae but show secondary
radiality as adults, have a spiny calcareous endoskeleton, and possess a well-developed coelom that includes a
unique manifestation, the water vascular system. The water vascular system functions as a network of
hydraulic canals that are involved with locomotion, feeding, and gas exchange in echinoderms. Echinoderms
are triploblastic organisms with a complete digestive tract (though the anus is vestigial in some). Although the
number of arms is quite variable, pentamerous symmetry is the most common arrangement; a typical sea star
will have 5 arms or rays, which arise from a central disk. Rays normally are the same size; if smaller ones are
present, they are being regenerated following injury to the sea star. As you follow dissection instructions
below, label the diagram provided.
External Features:
1. Oral surface: the under side (which normally faces the substratum to which the sea star is attached) of the sea
star. On the oral surface you can view the following:
Mouth: located in the center of the oral surface.
Ambulacral grooves: extending into the oral surfaces of the five rays from the region of the mouth.
Tube feet (podia): contained within the ambulacral grooves. Examine the podia under a dissecting
microscope, and note the sucker-like distal tip of each podium.
2. Aboral surface: the surface of the sea star that is typically exposed. Note the following features on the aboral
surface:
Epidermis: body covering, broken by calcareous spines, which project outwards from internal dermal
ossicles, which make up the endoskeleton of the sea star.
Madreporite: distinct circular structure just off center from the aboral axis, the opening in to the water
vascular system. The madreporite is at the opposite end of the water vascular system to the tube feet. Sea
water can enter the system through the madreporite.
Dermal branchiae: thin bladder like structures, extending up from the epidermis (often retracted in
preserved sea star, but look for them on the living specimen if available). These respiratory exchange
surfaces are filled with coelomic fluid, and can be retracted if anything disturbs the surface of the sea
star. To a lesser extent, respiratory gases can be exchanged via the tube feet.
Eyespots: tiny red spots at the tip of each arm (may be difficult to observe).
Pedicellariae: Scrape the epidermis (from the aboral surface) with your scalpel or scissors and place the
material on a slide. Add a drop of water and view under a compound microscope. Look for opaque pincerlike structures in the scraping. Some pedicellariae are 2-piece pincers, whereas others are 3-piece ones with
a basal part on which the two pincers articulate. Compare a pedicellaria from your sea star with those on
the prepared slides available in lab and sketch them in the margin. What is their function?
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Internal Features:
Using scissors, cut through the body wall along the sides of any two arms. The body wall is particularly thick
where two arms adjoin the central disk. Extend your cut along the entire aboral surface of the central disk. Lift
up the aboral body wall, leaving internal organs in place, and severing the madreporite connection with care.
Coelom: spacious body cavity, lined by a coelomic epithelium called the peritoneum.
Rectal cecum: antler-shaped structure that may be observable near the centre of the aboral axis; it is
about 0.5 cm long, branched, somewhat glossy, and reddish-brown in color; its function is unknown.
It attaches at the junction of the rudimentary intestine (which cannot be observed readily) and the
aboral portion of the stomach
Pyloric stomach: thin-walled, star-shaped sac
Pyloric ducts: connections of pyloric stomach to pyloric ducts
Pyloric ceca: paired digestive glands, located aborally in the arms.
Cardiac stomach: 5-lobed, muscular stomach, oral to the pyloric stomach; everted during feeding.
Cardiac retractor muscles: delicate muscles that insert in the lobes of the cardiac stomach. Observe
them by gently lifting a lobe of the cardiac stomach, which lifts the muscles away from the roof of the
ambulacral ridge, thus making them apparent. Can you guess at the function of these muscles?
Ambulacral ridge: the roof of each ambulacral groove as observed from the coelomic side in each
arm originates
Gonads: paired reproductive structures occupying the floor of the body cavity in the proximal region
of each arm; the members of each pair of gonads extend into adjacent arms. It is not possible to
distinguish the sexes of sea stares macroscopically, but they are dioecious.
Water vascular system:
Stone canal: a whitish, slender tube extending orally down from the madreporite
Ring canal: embedded in the bony ossicles surrounding the mouth. Remove the cardiac and pyloric
stomachs to trace these parts.
Radial canal: extends down each arm from the ring canal.
Lateral canals: extend from radial canals to connect with the tube feet.
Ampullae and podia (tube feet): The podia were viewed externally in the ambulacral groove and the
rounded ampullae can be seen internally on the ambulacral ridge. Try making the ampullae swell by
pressing on their associated podia, and vice versa. In living animals, contraction of the ampullae
extends the tube feet, whereas relaxation retracts them, providing a means of slow locomotion, and a
means of adhering to substrates.
Label the diagrams on the following page, using the above information.
97
Figure 3. Aboral view of sea star internal anatomy (Phylum Echinodermata).
Figure 4. Water vascular system in the sea star (Phylum Echinodermata).
98
Cross section of Arm:
With a safety razor blade provided, make a clean cut through one of the intact rays half way along its length.
Compare the structures observed here with those seen in prepared microscope slides of a cross section of sea
star arm. You should locate the following structures:
•
the thick body wall, the bony ossicles and spines (are dermal branchiae observable?)
•
the peritoneum lining the coelom
•
the ambulacral groove and ambulacral ridge
•
the radial canal (in the oral midline of the ambulacral groove).
•
the ampullae and podia
•
the gonads, pyloric ceca and coelom
Label the cross-section of the sea star arm below, including all the parts discussed above.
Figure 5. Cross-section through sea star arm (Phylum Echinodermata).
99
Use information from lab and your textbook to fill in the blanks in the figure below, depicting the phylogenetic
relationship among the phyla covered in today's lab. For each of the major branches in the deuterostome phylogeny,
indicate the diagnostic characteristic(s) that link the taxa that fall after each starred point on the tree.
100
APPENDIX I: MICROSCOPY & SCIENTIFIC DRAWINGS
A. Use of the compound light microscope:
Figure 1: The Compound Light Microscope
Uncover and plug in your microscope. The cord should have been wound carefully around the base and the
illuminator casing; unwind it taking care that you do not damage the condenser and diaphragm controls beneath
the stage.
Note which objective lens is in position, and how close it is to the stage. The lens that should be in position is
the smallest one: the 4X scanning lens. Make sure you have this lens in place when you finish using the
microscope.
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Turn the microscope on, and adjust the interpupillary distance between the two ocular lenses so that you see a
single illuminated field, even if you move your head very slightly from side to side. If side-to-side movements
of your head cause one field to black out, the interpupillary distance is set incorrectly. You must set this
distance for your own eyes each time you use a microscope. The iris diaphragm in the substage condenser
serves primarily to vary the contrast of the specimen being viewed. Generally, this iris diaphragm should be
closed as far as possible consistent with good brightness (obtained by adjustment of the rheostat at the side of
the microscope). If the image is muddy, lacks contrast after such adjustment, or is overlaid by blotches that do
not move when the slide is moved back and forth with the mechanical stage, then some cleaning is indicated
(see below). Make sure the ocular focusing rings located on one or both of the ocular tubes are set at middle
positions on their numerical scales.
Examine the field of view through the scanning lens and then through each of the other objectives, noting
whether the field is clear and clean or blotchy. If the field is blotchy, turn each ocular, one at a time, to see if
the blotches are on the oculars. Clean the oculars with soft tissue or lens paper if necessary. How could you
determine if the blotches are on the objective lens or the uppermost surface of the condenser? If you are not able
to obtain a clean, evenly illuminated field using the 10X and 40X objectives, notify your instructor. He or she
will help you to clean your microscope.
The magnification you observe in the microscope is the product of the magnification of the ocular times that of
the objective that is in place at the moment. For example, a 10X ocular in combination with a 4X (scanning)
objective gives 40X magnification, whereas the same ocular in combination with a 10X objective gives 100X
magnification. Use of the 10X ocular with the most powerful objective lens (the 100X objective) gives a
maximum magnification of 1000X.
When you finish using your microscope, ensure that the light is switched off, the 4X objective lens is in place,
the stage is lowered, the cord is tightly wrapped around the base of the microscope, and the dust cover is
replaced. If immersion oil was used, it must be removed from the 100X objective lens and the slide using
cleaning solution.
B. Use of the dissecting microscope:
Several kinds of dissecting microscopes are available for use, so you may need to become familiar with more
than one "species". Generally, these microscopes give low magnification stereo images of larger fields of view.
They can be very useful for studying invertebrates.
Most living specimens of suitable size will be viewed by reflected rather than transmitted light, with the
illumination coming from the side or above the object being viewed. The disk in the stage is removable, and
can be positioned so that a black or a white surface faces upwards. If the disk cannot be easily removed, check
with the instructor. Develop the habit of changing the disk back and forth to determine which background gives
you better contrast for a particular observation.
Sometimes thick or tall specimens require the microscope head to be raised. This can be done by loosening the
clamping screw, but the microscope head must be carefully suspended to keep it from dropping unexpectedly
102
when the clamping screw is loosened. On some microscopes there is a failsafe ring, which can be tightened
just below the position of the head on its vertical shaft.
On some dissecting microscopes, you must take care that the objective lenses are in proper position, or fit
exactly in their click stops. If you see a double image when the magnification setting is in its proper position,
the microscope is out of adjustment. Call the instructor for help.
To view a specimen using a dissecting microscope, first place it on the plate, and adjust the light source so that
the beam of light falls directly upon the specimen. Starting with the lowest magnification, focus on the
specimen using the focus adjustment knob toward the back of the microscope. Then, increase the magnification
as necessary and make your observations. As with the compound light microscope, please ensure that you store
the dissecting microscope properly. The head of the microscope should be raised well above the base upon
which the light control box has been placed. The cord must be tightly wrapped around the microscope, and the
dust cover replaced.
C. Wet Mounts:
Preparation of wet mount slides allows you to view living microscopic organisms. To prepare a wet mount
slide you simply place your specimen with a drop or two of water on the center of the slide. You then place a
cover slip on the slide, touching the edge of the cover slip to the slide first away from the water drop then
dragging it up to the drop at a 45-degree angle. When the cover slip is touching the water, begin to carefully
lower it into place over the specimen. Placing the slip this way reduces the chance of air bubbles getting
trapped between the specimen and the cover slip.
While some specimens are large enough to be manipulated with your fingers or forceps, unicellular microscopic
organisms need to be retrieved from culture and transferred to your slide using a Pasteur pipette. If you hold
your rubber bulb-tipped pipette so that the sides of your thumb and index finger press through the sides of the
rubber bulb against the upper end of the glass tube of the pipette, you can control pressure on the bulb very
closely by means of slightly rolling your index finger and thumb over the top of the pipette tube. The narrow
end of the pipette can be held steady by allowing the barrel to pass between your little finger and the next one.
With practice, this will allow you to pick up and deliver single unicellular organisms to a slide. Remember to
use the iris diaphragm to adjust for the optimal contrast when looking at specimens under the compound scope.
Vaseline mounting is a preparation method that allows you to work with a slide for a longer period of time (up
to a week) than with traditional wet mounts. To prepare a Vaseline mount make an open spiral of Vaseline
about 1 cm in diameter on a slide using a “Vaseline gun” (a syringe loaded with Vaseline). This requires a fair
bit of pressure and a steady hand. The spiral should be in contact with the slide and not looped up into the air in
places. If your first attempt is not successful, practice one or two additional spirals on different spots on the
same slide. When you have achieved a neat open spiral, place a small drop of culture liquid inside the spiral
away from the open end. Do not fill the whole spiral with liquid, as you want the culture to fill and just flow
into the narrow channel between the open arms of the spiral when you lower the cover slip in place. Before you
add the cover slip you can use the dissecting microscope to check that you do have some organisms on your
slide. Then hold the cover slip to the slide at the closed edge of the spiral and from a 45-degree angle lower it
slowly and gently into place. Do not press the cover slip down into the Vaseline. Diagrams on display in the
lab will help you prepare your slide appropriately.
103
D. Scientific drawings:
A scientific drawing is a graphical means of presenting results or observations; it is an effective means of
communicating results. Over the course of the semester, and in subsequent biology courses, you will be required to
complete proper scientific drawings. The following section indicates the guidelines that must be adhered to for
scientific drawings in order to complete and receive full credit for a scientific drawing.
Scientific Drawing Guidelines:
1. Although the cells are microscopic, your drawing should be large in size. Make complete use of the space
allotted to complete a drawing. For example, if you have a full blank sheet of paper use the whole page, leaving
only enough room at the bottom for your figure caption.
2.
Use a sharpened pencil, never ink or colored pencil crayons.
3.
Place the drawing slightly to the left side of the space, leaving room for labels to the right of the drawing. If there
are many labels, position the drawing in the center.
4.
Draw more than one cell in your drawing. This indicates the cellular association to an observer (e.g. found
singly or as part of a tissue). The cellular detail of only one of the cells needs to be complete for labeling. If you
are drawing a complete multicellular organism you do not need to draw more than one.
5.
Make all lines clear; erase any overlaps or fuzzy or multiple lines. Draw with one continuous line and do NOT
retrace your lines.
6.
Generally it is not necessary to depict differences in texture. If necessary, texture can be indicated by careful
stippling. Do NOT shade in your drawing. Do NOT color your drawing.
7.
Place label lines horizontally (use a ruler to make them straight), with no crossed lines.
8.
Structure or organelle labels should be singular unless the label line branches to multiple structures.
9.
Only draw and label structures that are visible. Do NOT include structures that you know are present but are not
visible or detectable with the light microscope.
10. Every scientific drawing requires a figure caption. This should go below the figure, is written in sentence
format, and should include the following information:
• A figure number (e.g. Figure 1.)
• Name of the organism (with genus-species name underlined)
• Some indication of its classification (Phylum name at minimum)
• How it was viewed (e.g. in cross section, under a light microscope, etc.)
• The lens magnification if viewed under a microscope (Lens magnification = ocular lens power x objective
lens power).
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APPENDIX II: COMMON ROOT WORD MEANINGS
As you learn about the diversity of life, you will encounter many new terms and names of organisms that may
initially seem complex and confusing. However, if you know a little bit about the language used to name
organisms and structures the terminology does make sense. When you break the terms down into their root
words and have an understanding of where the words come from, remembering the new names is often easier.
This glossary gives the meanings for most of the roots found in the terminology you are required to know in the
Biology 1020 lab.
A, an – without
Coleo – sheathed, together
Alveo – referring to small sacs
Coll – glue
Amoebo – change (from amoibe)
Coni – cone
Amphi – both
Crusta – shell
Angio – container
Cteno – comb
Annula – rings
Cyto, cyte – cell
Anther – pollen (from Latin anthera) or flower
Derm – skin
(from Greek anthos)
Deutero – second
Antho – flower
Di, diplo – two
Anthocero – horn
Echino – spiny
Apo – away from
Ecto – outside
Arach – spider (from Greek arakhn)
Enchyma – infill
Arche – ancient
Endo – inside
Arthro – joint
Epi – upon
Asco – sac
Eu – true
Aster – star
Fera, fero – to carry
Bacillario – resembling bacilli or bacteria
Gameto – gamete
Basi – base, lower portion
Gastero, gastro – belly
Bi – two
Gonium – offspring (from gonos)
Bryo – moss
Gymno – naked
Carp – structure, body
Helminth – worm
Cephalo – head
Hemi – half
Chaeta – long hair (from chaite)
Hepato – referring to liver
Chara – a pointed stake
Hetero – different
Cheliceri – from kheilos for lips and cheir for
Hexa – six
arm
Holo – whole, entire
Chilo – lip (from Greek kheilos) (for centipede
Homo – same
chilo + -poda = “lipfoot”, so called because the
Hydro – water
first pair of legs are jawlike appendages)
Hymeno – membrane (from Greek humenion)
Chloro – green
Ichthyes - fish
Chondri – cartilage
Idium – suffix making word diminutive
Cleisto – closed
Iso – same
Cnido – nettle, referring to sting (from cnide)
Karyon, karya – kernal, refers to nucleus
Coelom – hollow (from koilos)
Lepido – scaly
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Lophos – crest
Pila – hair, (from pilos)
Lyco – wolf (from Greek lukos)
Placo – plates
Mega – large
Plasm – from plasma, material forming cells
Meso – middle
Platy – flat
Meta – behind
Poda, podium – foot
Micro – small
Poly – many
Mollusc – soft
Pori – pore
Myco – fungal
Pro, proto – first
Myria – ten thousand (from Greek murias)
Pseudo – false
Myxo – mucus or slime
Ptera, ptero – wing or feather
Nema, nemato – thread
Rhizae – roots
Oda – like, or similar to (from -oid)
Rhodo – red
Oligo – few
Roti – wheel
Ophiuro – from Greek ophis, snake + Greek
Scler – hard
oura, tail
Scypho – cup (from Greek skuphos)
Ortho – straight, correct, right
Sperm – seed
Ostei – bony
Stoma – mouth
Ovi – referring to egg
Stramen – straw (refers to flagellum)
Ovule – little egg
Thallus – body (from thallos for sprout)
Para – false, or beside
Thecium – small case
Peri – all around, encompassing
Uro – tail (from Greek ouro)
Phaeo – brown (from phaios)
Valvia – valves, shells
Phora, phore – to bear or carry
Zoa, zoo – animal
Phycea, phyta – plant (from phyton)
Zygo – yoke (from Greek zugo)