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Biology
Preliminary Course
Stage 6
Life on Earth
Part 4: Classification of life on Earth
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Number: 43210
Title: Life on earth
This publication is copyright New South Wales Department of Education and Training (DET), however it may contain
material from other sources which is not owned by DET. We would like to acknowledge the following people and
organisations whose material has been used:
Photograph of foraminifera courtesy NASA
Part 2 p 17
Photographs of archaeobacteria © R.A. Binns, CSIRO, taken from JAMSTEC
submersible “Shinkai-6500”
Part 3 p 15
Graph showing relationship of plant formations to rainfall and temperature, from
Camm, E et al (1995) Interactions and change, Longman Australia, Melbourne.
Part 6 p 6
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Any further reproduction or communication of this material by you may be the
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Contents
Introduction ............................................................................... 2
Organising life: why classify? .................................................... 3
The need to classify .............................................................................4
Constructing dichotomous keys ................................................ 8
Plant classification..............................................................................10
Animal classification...........................................................................21
Additional resources................................................................ 25
Suggested answers................................................................. 27
Exercises – Part 4 ................................................................... 31
Part 4: Classification of life on Earth
1
Introduction
The study of present-day organisms increases our understanding of past
organisms and environments.
In this part you will be given opportunities to learn to:
•
explain the need for scientists to classify organisms
•
explain how levels of organisation in a hierarchical system assist
classification
•
describe the main features of the binomial system in naming
organisms and relate these to the concepts of genus and species
In this part you will be given opportunities to:
•
perform a first-hand investigation and gather information to
construct and use simple dichotomous keys and show how they can
be used to identify a range of plants and animals using live and
preserved specimens, photographs or diagrams of plants and
animals.
Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Revised October 2002. The most up-to-date version can be
found on the Board’s website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.
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Life on Earth
Organising life: why classify?
Have you ever stopped to consider how the things around you are
named? How do you locate items in the supermarket? Some larger
stores provide a floor plan or map to enable the consumer to locate the
items they require. Other guides include signs that indicate the type of
product located in that area eg. children’s clothing.
How are things classified (grouped) in your local supermarket? How are
different stores classified or grouped in a shopping centre?
If you were presented with a previously unseen object, how would you
go about classifying it? In other words, how would you decide the group
to which it should belong?
Most things are grouped to make them easier to identify. This process is
called classification. The practice of classification is called taxonomy.
Every day you come across a diversity of objects that you mentally
classify or group. This helps you understand the world around you.
Putting things into groups tells you something about objects.
This enables you to talk about them and pass on information easily.
Scientists use taxonomy to classify organisms based on similarities such
as physiology (function), structure, reproductive means or methods of
obtaining nutrition. This makes it possible to identify unknown
specimens by a comparison with known examples. The criteria for
classification becomes more specific as the group to which the organism
belongs becomes smaller.
If you look at the contents of your house it is possible to classify all the
objects based on function.
Part 4: Classification of life on Earth
3
For example, the first level of grouping or classifying might be the room
in the house where you usually find the object. The object might be
found in the kitchen, bathroom, lounge room or a bedroom. Once you
have decided on the room you might find it in, consider its function.
The cake tin, shown above, belongs to the kitchen, but it can be further
classified into a smaller group of specialised items, usually located in
the kitchen.
You can then use your mental classification of an object to locate the
object in the house. For example, the coffee plunger will probably be in
the kitchen with the toaster. While the bath, basin and electric toothbrush
would be together in the bathroom.
The need to classify
In order to classify, you need to carefully observe the things you want to
classify. Then you compare them. To compare things, you look for
similarities and differences. Similar things are put in the same group.
Once you have established your groups and the reasons for placing things
into each group, you have built a classification system. When you apply
a classification system, you usually follow a systematic approach to
narrow down the specific identification of the specimen.
Scientists all around the world use the same naming system. This makes
it possible to communicate information with the confidence that
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Life on Earth
everyone is talking about the same organism. The classification system
brings order into the millions of organisms that inhabit the Earth and
reflects the evolutionary relationships between organisms.
In summary scientists need to classify organism to:
•
bring order into the multitude of living organism
•
to show evolutionary relationships between organisms
•
to create a universal naming system to improve communication.
Levels of organisation
Within any classification system the groups are ordered. The structure in
classification is hierarchical. A hierarchy means that the groups become
smaller as you work your way through the classification system.
When considering the classification of living things, the largest group is
called the kingdom. Each kingdom has several smaller groups called
phyla or phylum (singular), these are sub–divided into groups called
classes. Classes contain many orders, which are made up of families.
A family is still further divided into two other smaller groups, the genus
and then species. This means that as you go from one level to the next,
the organisms become more alike.
phylum
class
order
family
genus
species
What’s in a name?
Naming organisms would be very difficult without some sort of system.
Can you imagine what it would be like if everyone used their own
method of naming organisms? This occurs quite frequently within
Part 4: Classification of life on Earth
5
regions or even countries, where plants and animals are given common
names. Some species could end up with a number of different names
depending on the location. For example, the fish called a mulloway is
also known as a jewfish, a jewel fish and a butterfish. People in different
regions would all call this fish a different name but in all regions its
scientific name is Argyosomus hololepidotus. Confusion would occur if
you were trying to communicate information about a particular organism
without having a common scientific name.
To overcome difficulties in naming living things a Swedish naturalist,
Carolus Linnaeus, published a naming system in 1753 which was based
on two words. The two words used to identify all organisms are the
generic name (genus) and its specific name (species). The genus is spelt
with a capital letter and the species with a lower case letter. Both words
are italicised or underlined. This approach to naming organisms is called
the binomial system.
These systematic (or scientific) names are usually written in Latin or
Greek. This system of naming things is described in the International
Rules of Nomenclature and its application is supervised by an
international committee. The rules used to name plants and animals are
different. An international register of biological names is kept to ensure
that no two species have the same scientific name.
Common name
Genus
Species
earthworm
Lumbricus
terrestris
human
Homo
sapiens
dog
Canis
familiaris
paperbark
Melaleuca
quinquinerva
lemon-scented gum
Eucalyptus
citriodora
woollybutt
Eucalyptus
longifolia
The two members of the Eucalyptus genus in the table above are similar
looking trees that are closely related. They share many of the same
characteristics but differ in the shape of their leaves. They share the
same classification until you get down to the species level.
The final classification into genus and species is based on more than
anatomical similarity. A species is defined as a group of organisms that
can interbreed under ‘natural conditions’ producing fertile offspring.
The species level is based primarily on reproductive and genetic
similarities rather than structural or morphological features.
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Life on Earth
For example if a horse and donkey mate, the resulting offspring is a
mule, which is not fertile. The stipulation of natural conditions is
important as some species have been crossbred in captivity, where they
would not have been able to in the wild, for example tigers and lions in
zoos. However it is possible for flowers to be cross–pollinated to form
fertile hybrids.
A genus contains closely related organisms that cannot interbreed but
share a recent common ancestor.
Complete Exercise 4.1: Naming organisms.
Part 4: Classification of life on Earth
7
Constructing dichotomous keys
In biology, keys are used to compare the specimens being identified.
Biological keys vary in form but a commonly used key is a
dichotomous key.
The term ‘dichotomous key’ is derived from the Greek word that means
cut into two parts. The key narrows down the name of a specimen by
taking each group and dividing it two smaller groups, based on similar
features. Look at the example that follows.
animals
vertebrate
aquatic
not a vertebrate (invertebrate)
not aquatic
(terrestrial)
Can you think of
another branch for
this group?
What features were used to classify the organisms in this example?
_________________________________________________________
_________________________________________________________
Check your answer.
Other forms of keys
Sometimes a dichotomous key can be written as a series of questions
with a yes/no response, that determines the path taken through the key
until the specimens group or unique identification is established.
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Life on Earth
Look at the following example used to identify classes of mammals.
1
Does the animal lay eggs?
a) Yes ………………………………………………..monotreme
b) No …………………………………………………go to 2
2
Does the animal have a pouch?
a) Yes …………………………………………………marsupial
b) No ………………………………………………….placental
Use the key above to identify each of the animals pictured here.
Animal A
Animal B
Animal C
A:__________________________ C:__________________________
B:__________________________
Check your answers.
Each of these groups could be further sub-divided into smaller groups,
until you get individual animal types. Such keys will be used in the
next part of this module for identification of different plant and
animal species.
When using a dichotomous key there are some points to remember:
Part 4: Classification of life on Earth
9
•
always read both choices
•
if you get lost go back to the last division that you are certain of and
then go through the steps again
•
if you are not sure, try both alternatives and see where it takes you
•
if you don't know the meaning of a word look it up
•
measurements should be measured not guessed
•
make sure the answer makes sense.
Plant classification
Plants are divided into five major groups based on structural and
reproductive features.
The table following summarises the important points in plant
classification. You do not need to memorise all the information in the
table. Once it is completed you will use the information from the table
and a dichotomous key to identify some examples of plants.
Read through the table below describing the plant groups. Complete the
missing words as you go. The first letter of the missing word is provided as
a clue. Answers are given in the suggested answer section.
Group
Examples
Red algae
(Rhodophyta)
Diatoms and other singlecelled algae.
Brown algae
(Phaeophyta)
Characteristics (structural and
reproductive)
Simple plants without true
r__________, s____________ or
l_____________. No vascular tissue
for transporting food and water.
No v____________ tissue for
transporting food and water.
Most are aquatic (marine and some
freshwater)
Green algae
(Chlorophyta)
Single-celled forms can reproduce
asexually by binary fission or by
producing spores as well as sexually
by producing gametes.
Bryophytes
mosses and liverworts
Small plants without true r________.
Instead of roots they have simple
cellular filaments called
r____________.
Possess simple stems and leaves.
No v__________ tissue for
transporting food and water.
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Life on Earth
Most grow only in moist habitats.
Depend on water for sexual
reproduction. Mosses have alternation
of generations involving gametophyte
and sporophyte.
Pteridophyta
ferns eg. fish-bone, maiden
hair, tree fern, bracken fern
Have true roots, stems and leaves.
Have vascular tissue for food and
water transport.
Can live in dry as well as moist
habitats.
Reproduce by rhizomes, spores and
gametes. Have an alternation of
generations involving
s_____________ and g____________
plants. The gametes require
w_______ so that male and female
can be transferred.
Gymnosperms
conifers such as pines;
cycads such as Australian
burrawang palm.
Land plants some of which can grow
into large trees.
Vascular system well developed.
Reproduce by s____________ that
are u_________________. In most,
the uncovered seeds rest on woody
scales that are part of a c________.
(Seeds are reproductive structures
containing an e____________, stores
f__________ and a protective cover).
Angiosperm
(monocots
and dicots)
all f______________
plants, for example
eucalyptus, wattle, daisy,
daffodil, orchids, grass
Vascular system well developed.
The reproductive structures are the
f__________. Following pollination
and fertilisation, s__________ are
formed, usually enclosed within the
f_________, which is the ripened
ovary.
The pteridophytes, gymnosperms and angiosperms are commonly
grouped together as the tracheophytes or vascular plants.
1
Can you suggest a reason for the division into the different plant groups
listed in the table?
Hint: Look at the types of features that are described for each plant
group. Which features are always included?
_____________________________________________________
_____________________________________________________
_____________________________________________________
Part 4: Classification of life on Earth
11
2
Which of these features would be easy to observe? Which would be
more difficult.
______________________________________________________
______________________________________________________
______________________________________________________
Check your answers.
Using a plant key
Use the key to identify the plants pictured following. List the steps used to
name the plant pictured. The first one is done for you.
Dichotomous key for the plant kingdom
1
a) contains vascular tissue …………………………………go to 2
b) no vascular tissue ……………………………………….go to 4
2
a) possess flowers ……………………………………Angiosperm
b) no flowers ……………………………………………….go to 3
3
a) naked seeds ……………………………………….Gymnosperm
b) spores under leaves ………………………………Pteridophytes
4
a) small, spore producing land plants ………………….Bryophytes
b) aquatic spore producing plants …………………………. .Algae
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Life on Earth
Plant
Features
Produces spores in capsules
No vascular tissue
No flowers
Small land plant
Steps:
1 (b) no vascular tissue go to 4
4 (a) small spore producing land
Answer: Bryophyte
(Photo: Jane West)
vascular tissue
no flowers
naked seeds in cones
Steps:
(Photo: Julie Haeusler ©LMP)
Answer:
Part 4: Classification of life on Earth
13
vascular tissue
no flowers
spores under leaves
Steps:
Answer:
(Photo: Jane West)
no vascular tissue
no flowers
aquatic
Steps:
Answer:
(Photo: Jane West)
14
Life on Earth
vascular tissue
flowers
Steps:
Answer:
(Photo: Jane West)
Check your answers.
Plant classification within a genus
Each level of classification shares similar features with the other
organisms at the same level. You will recall that as you move down the
classification hierarchy the similarities between the organisms at each
level increases. For example, similar groups of organisms within a
family would belong to the same genus, and these are divided again into
even more specifically similar organisms called species.
In this activity you will be identifying four species of the genus Banksia
from either live specimens or using the diagrams following.
If you have access to live specimens list the species below.
(You might like to send your teacher dried plant material eg. a leaf from
each plant.)
_________________________________________________________
_________________________________________________________
_________________________________________________________
Part 4: Classification of life on Earth
15
If you cannot gain access to any of the plants within this group, use the
diagrams and photographs provided.
If you have access, look at the Biology page on the LMP website where the
photographs and key are reproduced in colour.
http://www.lmpc.edu.au/science
A key to the most common species of the Sydney region is given below.
Banksia: a key to the most common species of the
Sydney region
This key has been modified from Beadle, Evans and Carolin (Eds) Flora
of the Sydney region.
1
a) Style permanently hooked at tip ……………………………….2
b) Style finally straight or gently curved upwards ………………..3
2
a) Leaves small, 10-15 mm long, narrow and crowded on branches,
margins curved under ………………………..Banksia ericifolia
b) Leaves 3-8 cm long, narrow, small teeth present near tip,
margins curved under………………………Banksia spinulosa
3
a) Leaves 2-10 cm long, white on undersurface ………………….4
b) Leaves 8-16 cm long, lighter but not white on undersurface.
Margins distinctly and evenly serrated ……...Banksia serrata
4
a) Leaves less than 1 cm wide. Spike flowers 4-9 cm long, yellow
………………………………………………Banksia marginata
b) Leaves generally 1-2 cm wide …………………………………5
5
a) Tree up to 16 m high. Adult leaves mostly with smooth
margins, juvenile leaves toothed. …………Banksia integrifolia
b) Shrubs, usually not more than 3 metres high. Leaves mostly
irregularly toothed. Young shoots with covering of rusty hairs
…………………………………………….Banksia oblongifolia
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Life on Earth
Unknown Banksia 1
(Photo: Jane West)
(Photo: Jane West)
Name of Banksia___________________________________________
Part 4: Classification of life on Earth
17
Unknown Banksia 2
(Photo: Jane West)
(Photo: Jane West)
Name of Banksia ___________________________________________
18
Life on Earth
Unknown Banksia 3
(Photo: Jane West)
(Photo: Jane West)
Name of Banksia___________________________________________
Part 4: Classification of life on Earth
19
Unknown Banksia 4
Underside of leaf is white
Leaf irregularly toothed
Shrubs, usually not more than 3
metres high.
(Photo: Jane West)
Styles straight
Name of Banksia ___________________________________________
20
Life on Earth
Complete Exercise 4.2: Plant classification.
Animal classification
The animal kingdom is also classified according to the similar structural
features possessed by the organisms within a division. The following
key summarises the major commonly used groupings for the kingdom.
The kingdom classification represents one division from the four
kingdom classification system, hence the protozoans are included as part
of the animal kingdom. You do not need to remember the names of the
groups in the key.
The division following shows only the classification of the chordata.
ANIMAL KINGDOM
Phylum
Chordata
Sub-phylum
Vertebrata
Classes:
Agnatha
Chondrichthyes
Osteichthyes
Amphibia
Reptilia
Aves
Mammalia
Part 4: Classification of life on Earth
Sub-phylum
Urochordata
For example:
sea squirts or
cunjevoi
21
Vertebrate groups
The table below provides more information about one of the groups from
this key – phylum chordata, sub-phylum vertebrata. You will use
information from the following table to construct a dichotomous key.
Class/example
Characteristics
Agnatha
(lamprays, hagfish)
gills, no bony jaws, cartilage skeleton, no paired fins,
two chambered heart, ectothermic
Chondrichthyes
(sharks, rays)
gills, cartilage skeleton, mouth on ventral side, paired
fins, two chambered heart, ectothermic
Osteichthyes
(snapper, bream)
gills, bony skeleton, paired fins, two chambered
heart, ectothermic
Amphibia
(frog, toad)
spend part of their life cycle in the water and part on
land adults breathe with lungs, thin moist skin, three
chambered heart, lay eggs in water, ectothermic
Reptila
(snakes, lizards, turtles)
breathe with lungs, three chambered heart, lay
leathery eggs on land, dry scaly skin, ectothermic
Aves
(kookaburra, cockatoo)
breathe with lungs, covered with feathers, fore legs
modified as wings, lay hard shelled eggs
(calcareous) on land, four chambered heart,
endothermic
Mammalia
(wombat, possum)
breathe with lungs, body covered with hair, females
nourish young with milk from mammary glands, four
chambered heart, endothermic
Use the information to design your own key for the vertebrate groups in the
space below. You may find it helpful to complete a branching key first,
such as the one for the animal kingdom on the preceding page.
Once you have completed this you should transfer the information on to the
scaffold provided here. Look back to the key on plants as a model.
1
a) …………………………………………………………….….
b) ………………. ………………………………………………
2
a) ……………………….……………………………………….
b) ……………………….…………………………...…………..
3
22
a) …………………………………..……………………………
Life on Earth
b) ………………………………………………………………..
4
a) ………………………….…………………………………….
b) ………………………………………………………………...
5
a) …………………………………………………………………
b) …………………………….………………………...…………
6
a) ………………………………..……………………………….
b) …………………………………………………………………
Check a possible answer.
The number of questions asked will vary, based on the features you
decide to separate the groups with. Remember to put a “go to” statement
at the end of each question to direct the reader of the key to the correct
path to follow.
Complete Exercise 4.3: Invertebrate classification.
Part 4: Classification of life on Earth
23
24
Life on Earth
Additional resources
Invertebrate groups
The protozoans are usually microscopic
organisms that move by cilia, flagella or
pseudopodia (these are external projections
that enable mobility.)
Amoeba
The Porifera are commonly called the
‘sponges’. These animals have lots of tiny
pores and are aquatic. Water is circulated
through these pores, transporting food, oxygen
and wastes. The animals are sessile, this
means that they are permanently attached to
Sponge
the surfaces on which they are found.
The Cnidarians include animals such as the
corals, hydra, sea anemones. These animals
are aquatic with one opening to the gut through
which water is circulated, transporting food,
oxygen and waste. These animals possess
tentacles that contain nematocyst cells or
stinging cells. The body parts are arranged
Sea anemone
around one central point (radially
symmetrical). This means that if it were cut in
half the two halves would be mirror images of
each other regardless of where you cut through
the middle.
The Platyhelminthes have flattened bodies.
They are commonly called the ‘flat worms’.
The body is bilaterally symmetrical (can only
be cut in half one way for the two halves to be
identical). They are parasitic usually, or can be
Part 4: Classification of life on Earth
25
found free living. They posses a mouth but no
‘gut’ as such. Organisms that belong to this
group include tapeworms, liver fluke and
planarian worms.
Liver fluke
The Nematodes are commonly called the
‘round worms’ because they posses long,
unsegmented bodies. The gut has two
openings, a mouth and anus. They are
bilaterally symmetrical. Examples of this
group are the hookworm, ascaris or
threadworm.
The Annelids are animals with long segmented
bodies. Common examples include the
earthworms, leeches and polychaete worms.
The gut has two openings. They have
well-developed digestive, circulatory and
nervous systems.
The Mollusca include animals such as the
snail, chiton, oyster, squid and octopus.
They have soft body parts with a mantle.
A protective shell may be secreted to protect
this soft tissue. Many molluscs such as snails
have a muscular ‘foot’ that is used for
locomotion. The animals in this group possess
well-developed digestive, circulatory and
nervous systems.
Sea stars, sea urchins and sea cucumbers
belong to a group of organisms called the
Echinoderms. These are all marine and have
spiny, hard skin on their bodies. They are
radially symmetrical and have well-developed
digestive and circulatory systems.
The Arthropods are a very diverse group and
include animals such as the spiders, insects,
crustacea, beetles and millipedes. They all
possess segmented bodies with jointed
appendages such as legs. They have a hard
exoskeleton and are bilaterally symmetrical.
They possess a ventral nerve cord.
26
Thread worm
Leech
Chiton
Sea star
Prawn
Life on Earth
Suggested answers
Constructing dichotomous keys
The first division was based on whether the organisms had a backbone.
The second division was based on where the organism lived.
Other forms of key
A: marsupials B: monotreme C: placental
Constructing dichotomous key
Features in this key include: the presence of a backbone (or absence) and
environment (aquatic or terrestrial).
Plant classification
The algae are placed with the plants in this classification system but in
other systems they are placed in the Protista.
Group
Examples
Red algae
(Rhodophyta)
Diatoms and other single
celled algae.
Brown algae
(Phaeophyta)
Green algae
(Chlorophyta)
Part 4: Classification of life on Earth
Characteristics (structural and
reproductive)
Simple plants without true roots, stems
or leaves. No vascular tissue for
transporting food and water.
No vascular tissue for transporting food
and water.
Most are aquatic (marine and some
freshwater)
Single-celled forms can reproduce
asexually by binary fission or by
producing spores as well as sexually by
producing gametes.
27
Bryophytes
mosses and liverworts
Small plants without true roots. Instead
of roots they have simple cellular
filaments called rhizoids.
Possess simple stems and leaves.
No vascular tissue for transporting food
and water.
Most grow only in moist habitats.
Depend on water for sexual
reproduction. Mosses have alternation
of generations involving gametophyte
and sporophyte.
Pteridophyta
ferns eg. fish-bone,
maiden hair, tree fern,
bracken fern
Have true roots, stems and leaves.
Have vascular tissue for food and water
transport.
Can live in dry as well as moist habitats.
Reproduce by rhizomes, spores and
gametes. Have an alternation of
generations involving sporophyte and
gametophyte plants. The gametes
require water so that male and female
can be transferred.
Gymnosperms
conifers such as pines;
cycads such as Australian
burrawang palm.
Land plants some of which can grow
into large trees.
Vascular system well developed.
Reproduce by seeds that are
uncovered. In most, the uncovered
seeds rest on woody scales that are
part of a cone. (Seeds are reproductive
structures containing an embryo, stores
food and a protective cover).
Angiosperm
(monocots
and dicots)
28
all flowering plants, for
example eucalyptus,
wattle, daisy, daffodil,
orchids, grass
Vascular system well developed.
The reproductive structures are the
flowers. Following pollination and
fertilisation, seeds are formed, usually
enclosed within the fruit which is the
ripened ovary.
1
The plant groups have been divided into groups on the basis of their
physical structure and method of reproduction.
2
The structure is usually easily seen with the naked eye, such as the
presence of roots, stems and leaves, but the reproductive methods
may be more difficult to see.
Life on Earth
Using a plant key
A. Bryophyte
B. Gymnosperm
C. Pterydophyte
D. Algae
E. Angiosperm
Animal classification
1
a) ectothermic…………………………………………….…go to 2
b) endothermic. ……………………………………………..go to 3
2
a) breathe using gills……………………………………….go to 4
b) breathe with lungs……………………………...……….go to 6
3
a) lay eggs……………………………………………………..Aves
b) feed young milk………………………………………Mammalia
4
a) cartilage skeleton…………………………………………go to 5
b) bony skeleton…...…………………………………Osteichthyes
5
a) paired fins……………………………………….Chondrichthyes
c)
6
no paired fins…………………………………...……….Agnatha
a) lay eggs in water………………………………………Amphibia
c)
lay eggs on land……………...………………………….Reptilia
Part 4: Classification of life on Earth
29
30
Life on Earth
Exercises – Part 4
Exercise 4.1 to 4.3
Name: _________________________________
Exercise 4.1: Naming organisms
a)
Explain the need for a classification system.
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b) Define the term hierarchy and explain the system used in biology to
assist classification of organisms.
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c)
i)
Describe the main features of the binomial system in naming
organisms.
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Part 4: Classification of life on Earth
31
ii) Using the binomial names of two similar plants or two similar
animals, explain how the names identify the two different
organisms. In your answer, include information to show that
you understand what genus and species mean.
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Exercise 4.2: Plant classification
a)
From your identification of Banksia species what criteria were used
in this key to distinguish between the species of Banksia?
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b) What are the advantages of this key?
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c)
What are some disadvantages of this key?
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32
Life on Earth
Exercise 4.3: Invertebrate classification
The invertebrate group of animals is characterised by the absence of a
backbone. The group is organised into phyla based on structural
features.
a) Read the descriptions of the invertebrate groups located in the
Additional resources. Summarise the distinguishing feature of each
group in a table.
Part 4: Classification of life on Earth
33
b) Now design a dichotomous key that can be used to identify members
of the respective classes.
c)
What are the advantages of using the binomial classification system?
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34
Life on Earth