Download Week 9

Biol 160: Lab 8
Name: __________________________
Exploring Plant Diversity
OBJECTIVES
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Become familiar with the diversity of plants.
Understand how each group of plants is defined by one or more evolved traits.
Observe the parts of the flower and their variations.
Observe fruits, how they are formed and how they are dispersed.
Observe conifer seed and pollen cones and pollen.
Become familiar with the alternation of generations.
Describe the life cycle of a typical fern and a typical angiosperm; distinguish between
the gametophyte and sporophyte generations.
Understand the changes in the alternation of generation that occurred over time,
moving from the bryophytes to the vascular plants.
General Procedures
This lab will be broken into three parts:
Part 1: Plant diversity scavenger hunt & comparison of plant diversity
Part 2: Flowers, fruits and cones lab
Part 3: Group activities reviewing alternation of generations and major plant traits
Part 1: The assignment - Plant diversity scavenger hunt at home or in-class.
In order to help you become more familiar with common members of the major plant groups
your instructor will ask you to collect plants either during class or at home. We will be collecting
specimens from each group. You will later use these specimens to help you visualize how the
alternation of generations have changed between the different plant groups. While collecting,
pay attention to the overall size of the plants you are collecting from, and in what environment
type you found them. Each lab group of 4-5 people should collect one specimen from each of
the following groups (you may decide how to divide and conquer):
• Bryophytes or non-vascular plants (mosses)
• Seedless vascular plants (ferns and horsetail)
• Gymnosperms (conifers or cone-bearing trees)
• Angiosperms (flowering plants)
Be prepared to explain which generation(s) you have collected!
Information to help you in your search:
A) Nonvascular plants “Bryophytes” (mosses)
The Bryophytes, or nonvascular plants, represent the earliest group of terrestrial
plants. The most familiar species in this group are the mosses. They do not have
vascular tissue (some mosses have simple tubular structures). Vascular tissues
serve two main purposes in plants: 1) as a transport system (tubes) for moving
water, sugars and minerals throughout the plant, and 2) it provides structural
support. Because Bryophytes do not have vascular tissue, they do not have true
leaves, stems and roots. The lack of vascular tissue limits the Bryophytes
morphologically and ecologically. Without vascular tissue to transport water, a
Bryophyte must be low lying or mat-like, so that all of its body can be in contact
Rev. 1/2009
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Biol 160: Lab 8
with the moist environment, and also be fairly thin in structure (only a few cells thick). Since
water is moving via osmosis through cells (a relatively slow process), the plant cannot be very
thick. Most Bryophytes need to live in moist environments, although they have many
adaptations for living in dryer environments. Additionally, the lack of vascular tissue means that
Bryophytes do not have the structural support to grow tall. Since the Bryophytes are all fairly
short plants, this leads to strong competition for sunlight and space.
B) Seedless vascular plants (ferns & horsetails)
Vascular tissue is composed of cells joined into tubes transporting water
and nutrients throughout the plant body. Xylem tissue is the watertransport tissue carrying water and minerals from the roots up the plant
body, and phloem tissue is the food-transport tissue carrying phloem
sap (food nutrients) from food sources (leaves or food storage organs)
to food sinks (growing non-photosynthetic structures or food storage
organs). The bodies of the vascular plants are divided into an aerial
shoot system (stems, leaves, and reproductive structures), and an
underground root system. True leaves, stems, and roots all contain true
vascular transport tissue.
The development of vascular tissue allowed the vascular plants to grow much taller than the
non-vascular plants for two reasons: 1) plants with vascular tissue no longer had to have most of
their body in contact with a moist environment, and 2) vascular tissue provided structural
strength within stems. Growing taller meant that they could intercept the light before lowgrowing plants could. This allowed the seedless vascular plants to become dominant during the
Carboniferous period. The most familiar seedless vascular plants are ferns. Both seedless
vascular plants and Bryophytes use spores to disperse (move the next generation further away
from the parent generation). Ferns have special spore producing structures, called sori, that are
typically visible underneath their leaves, which often look like rows of brown, green or whitish
dots.
C) Seed bearing vascular plants: Gymnosperms
Seed bearing vascular plants developed two structures that helped this group be successful in
dryer environments: 1) pollen, and 2) the seed. These structures are found in both gymnosperms
and angiosperms. Pollen is the male gametophyte (which will produce the sperm), wrapped in
a protective coating. Pollen allowed for the dispersal of the male gamete (sperm) over longer
distances and without the need for water. In Bryophytes and seedless vascular plants the sperm
must swim to the egg, so they require a moist environment. In seed bearing vascular plants, the
zygote develops into an embryo within the ovary. The embryo, its food supply and a seed coat
are packaged together by the plant as a seed. The seed can be released from the plant
to germinate in appropriate environmental conditions. Seeds provide several reproductive
advantages for these plants. First, they can increase dispersal of the next
diploid generation as the seed can be carried by the wind, water, or
another organism. Second, the food supply gives the developing embryo
an energy boost early in its life. With this energy boost, the embryo will
produce leaves that allow for photosynthesis and metabolic
independence. Third, the seed coat provides protection for the embryo
while it waits to germinate until conditions are suitable.
The most familiar gymnosperms are members of the conifer, or
“cone-bearing”, group which includes pine, fir, cedar and spruce trees.
Gymnosperm means “naked seed”. The seeds of gymnosperms are not
enclosed. In conifers they develop on the scales of the cone.
Gymnosperms can be quite tall and can be found both in moist and dry
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Biol 160: Lab 8
environments. Almost all the conifers are “evergreen”, holding their needle-like or scale-like
leaves year round. This allows for growth year round, although this growth is reduced in the
seasons of least sunlight. The reduced leaves are adapted to colder, drier climates with a thick
cuticle (waxy layer that prevents water loss). Commercially, most of our lumber and paper pulp
comes from the wood of conifers.
D) Seed bearing vascular plants: Angiosperms
The angiosperms are recognized as the
“flowering plants.” In addition to pollen and
seeds, the angiosperms developed two other
distinctive traits: 1) flowers, and 2) fruits. Flowers
are made up of four main parts: 1) sepals, 2)
petals, 3) stamen, and 4) carpels. Many flowers
have
been modified to attract insect, bird or
mammal pollinators. Modifications include
bright colors, scents or nectar rewards.
Angiosperm means “container seed”,
and the seeds are found within fruit. Fruit is a
development of the
ovary tissue that surrounds the seed. Fruit
evolved to aid in dispersal of the seeds. We will be looking at types of fruits and dispersal
mechanisms in Part II of this lab.
Part 2 Flower Dissection
Flower Structure
Flowers consist of 4 whorls (or layers) of modified leaves: sepals, petals, stamens and carpels.
Sepals are the outer whorl. They cover the flower before it is open, helping to protect it. They are often
green, but may also be brightly colored, similar to the petals.
Petals are the next whorl. They are often brightly colored. The coloration of both the petals and sepals
functions to attract pollinators.
Pollinators are organisms (typically insects, but some mammals) that move pollen from one flower to
another flower. Flowers that are wind pollinated, like grasses, typically are not brightly colored.
Stamens are the third whorl in, and are the male reproductive structures. They produce the pollen, which
contains the sperm. The pollen is formed in the anthers, and the filament attaches the anthers to the
flower.
The carpel is the female reproductive structure, found at the center of the flower, or the innermost whorl.
There may be one or many carpels. (This structure is also referred to as the pistol.). The top of the carpel
is the stigma. This is the structure that receives the pollen. The style connects the stigma to the ovary.
The ovary contains structures called ovules, which contain the eggs. An ovary may have one or many
ovules (so one or many eggs).
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Biol 160: Lab 8
When pollen lands on the stigma, the process is called pollination. Once the pollen lands, the sperm
matures and burrows down the style, into the ovary and ovule to reach the egg. When the sperm and egg
fuse, the process is called fertilization.
Once the egg has been fertilized, the egg will go through several rounds of mitosis, forming the
multicellular embryo, which is the developing plant.
The seed will then begin to develop. A seed is the embryo and a food supply wrapped in a protective
covering called a seed coat. The seed protects the embryo from drying out and provides food until the
embryo is able to grow its first true leaves and start photosynthesizing to produce its own food.
In angiosperms, the seed is enclosed in a fruit. A fruit is the ripened ovary of a flower. It functions to
protect the seed and to aid in dispersal of the seed. Remember that gymnosperms also form seeds, but
they are found naked on cones, not in a fruit.
Flower Observations
In order to understand the structure of a flower it helps to take it apart and examine each of its structures
individually. In this lab you will be dissecting both monocot and eudicot flowers. The differences
between monocots and eudicots are illustrated above.
You will use a dissecting needle and razor blade to dissect the flowers. Use a petri dish to hold your
specimen and examine it using the dissecting microscope. You will begin by removing the outermost
segments and work your way inward. Make sure you examine each part of the flower under the
dissecting scope.
Name of plant flower is from ________________________________________
 Remove the sepals. What color are they? _________ How many are there? ____Is each sepal separate
or fused together?______ Do they have any markings?____ Hairs? ____What is the function of
sepals? _________________________________________________________________________
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Remove the petals. What color are they? _______How many are there? _______Is each petal
separate or fused together? _____ Do they have any markings? _______ Hairs? ________What is the
function of petals?____________ How is their structure/ appearance related to their function?
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Examine the stamens. How many are there?____ What is the shape of the anther? ___________
Where is the filament attached (to base of flower, to petals, etc.)? _______ Is there pollen visible on
the anthers? _____ If yes, what color is the pollen? _______ Where are the anthers located in relation
to the stigma? _________ Remove the stamens and observe under the microscope. What is the
function of stamens?____________________ How is their structure related to their function?
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Examine the carpel. Does the flower have a single carpel or multiple carpels? _________ How many
are there? ________ Examine the stigma. Describe the stigma (shape, is it branched, how many
branches, etc.) _________________________________________________________________
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What is the function of carpels? _______________ What is the function of a stigma? ____________
How is their structure related to their function?
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Make a cross-section of the ovary at its widest point and exam it under the dissecting scope. How
many chambers are present? _________ Are there ovules present? __________How many? _____
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