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BiologyPreliminary CourseStage 6

Life on Earth

Part 4: Classification of life on Earth

Incorporating October 2002

AMENDMENTS

Part 4: Classification of life on Earth 1

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

2 Life on Earth

Introduction

The study of present-day organisms increases our understanding of pastorganisms 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 assistclassification

• describe the main features of the binomial system in namingorganisms 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 toconstruct and use simple dichotomous keys and show how they canbe used to identify a range of plants and animals using live andpreserved specimens, photographs or diagrams of plants andanimals.

Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originallyissued 1999. Revised October 2002. The most up-to-date version can befound on the Board’s website athttp://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.


Organising life: why classify?

Have you ever stopped to consider how the things around you arenamed? How do you locate items in the supermarket? Some largerstores provide a floor plan or map to enable the consumer to locate theitems they require. Other guides include signs that indicate the type ofproduct located in that area eg. children’s clothing.

How are things classified (grouped) in your local supermarket? How aredifferent stores classified or grouped in a shopping centre?

If you were presented with a previously unseen object, how would yougo about classifying it? In other words, how would you decide the groupto which it should belong?

Most things are grouped to make them easier to identify. This process iscalled classification. The practice of classification is called taxonomy.Every day you come across a diversity of objects that you mentallyclassify 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 suchas physiology (function), structure, reproductive means or methods ofobtaining nutrition. This makes it possible to identify unknownspecimens by a comparison with known examples. The criteria forclassification becomes more specific as the group to which the organismbelongs becomes smaller.

If you look at the contents of your house it is possible to classify all theobjects based on function.

4 Life on Earth

For example, the first level of grouping or classifying might be the roomin the house where you usually find the object. The object might befound in the kitchen, bathroom, lounge room or a bedroom. Once youhave 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 furtherclassified into a smaller group of specialised items, usually located inthe kitchen.

You can then use your mental classification of an object to locate theobject in the house. For example, the coffee plunger will probably be inthe kitchen with the toaster. While the bath, basin and electric toothbrushwould be together in the bathroom.

The need to classify

In order to classify, you need to carefully observe the things you want toclassify. Then you compare them. To compare things, you look forsimilarities and differences. Similar things are put in the same group.

Once you have established your groups and the reasons for placing thingsinto each group, you have built a classification system. When you applya classification system, you usually follow a systematic approach tonarrow down the specific identification of the specimen.

Scientists all around the world use the same naming system. This makesit possible to communicate information with the confidence that


everyone is talking about the same organism. The classification systembrings order into the millions of organisms that inhabit the Earth andreflects 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 inclassification is hierarchical. A hierarchy means that the groups becomesmaller as you work your way through the classification system.

When considering the classification of living things, the largest group iscalled the kingdom. Each kingdom has several smaller groups calledphyla or phylum (singular), these are sub–divided into groups calledclasses. Classes contain many orders, which are made up of families.A family is still further divided into two other smaller groups, the genusand 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 ownmethod of naming organisms? This occurs quite frequently within

6 Life on Earth

regions or even countries, where plants and animals are given commonnames. Some species could end up with a number of different namesdepending on the location. For example, the fish called a mulloway isalso known as a jewfish, a jewel fish and a butterfish. People in differentregions would all call this fish a different name but in all regions itsscientific name is Argyosomus hololepidotus. Confusion would occur ifyou were trying to communicate information about a particular organismwithout 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 basedon two words. The two words used to identify all organisms are thegeneric name (genus) and its specific name (species). The genus is speltwith a capital letter and the species with a lower case letter. Both wordsare italicised or underlined. This approach to naming organisms is calledthe binomial system.

These systematic (or scientific) names are usually written in Latin orGreek. This system of naming things is described in the InternationalRules of Nomenclature and its application is supervised by aninternational committee. The rules used to name plants and animals aredifferent. An international register of biological names is kept to ensurethat 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 similarlooking trees that are closely related. They share many of the samecharacteristics but differ in the shape of their leaves. They share thesame classification until you get down to the species level.

The final classification into genus and species is based on more thananatomical similarity. A species is defined as a group of organisms thatcan interbreed under ‘natural conditions’ producing fertile offspring.The species level is based primarily on reproductive and geneticsimilarities rather than structural or morphological features.


For example if a horse and donkey mate, the resulting offspring is amule, which is not fertile. The stipulation of natural conditions isimportant as some species have been crossbred in captivity, where theywould not have been able to in the wild, for example tigers and lions inzoos. However it is possible for flowers to be cross–pollinated to formfertile hybrids.

A genus contains closely related organisms that cannot interbreed butshare a recent common ancestor.

Complete Exercise 4.1: Naming organisms.

8 Life on Earth

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 adichotomous key.

The term ‘dichotomous key’ is derived from the Greek word that meanscut into two parts. The key narrows down the name of a specimen bytaking each group and dividing it two smaller groups, based on similarfeatures. Look at the example that follows.

animals

vertebrate not a vertebrate (invertebrate)

aquatic not aquatic(terrestrial)

Can you think ofanother branch forthis 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 questionswith a yes/no response, that determines the path taken through the keyuntil the specimens group or unique identification is established.


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 thenext part of this module for identification of different plant andanimal species.

When using a dichotomous key there are some points to remember:

10 Life on Earth

• always read both choices

• if you get lost go back to the last division that you are certain of andthen 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 andreproductive features.

The table following summarises the important points in plantclassification. You do not need to memorise all the information in thetable. Once it is completed you will use the information from the tableand a dichotomous key to identify some examples of plants.

Read through the table below describing the plant groups. Complete themissing words as you go. The first letter of the missing word is provided asa clue. Answers are given in the suggested answer section.

Group Examples Characteristics (structural andreproductive)

Red algae(Rhodophyta)

Brown algae(Phaeophyta)

Green algae(Chlorophyta)

Diatoms and other single-celled algae.

Simple plants without truer__________, s____________ orl_____________. No vascular tissuefor transporting food and water.

No v____________ tissue fortransporting food and water.

Most are aquatic (marine and somefreshwater)

Single-celled forms can reproduceasexually by binary fission or byproducing spores as well as sexuallyby producing gametes.

Bryophytes mosses and liverworts Small plants without true r________.Instead of roots they have simplecellular filaments calledr____________.

Possess simple stems and leaves.

No v__________ tissue fortransporting food and water.


Most grow only in moist habitats.

Depend on water for sexualreproduction. Mosses have alternationof generations involving gametophyteand sporophyte.

Pteridophyta ferns eg. fish-bone, maidenhair, tree fern, bracken fern

Have true roots, stems and leaves.

Have vascular tissue for food andwater transport.

Can live in dry as well as moisthabitats.

Reproduce by rhizomes, spores andgametes. Have an alternation ofgenerations involvings_____________ and g____________plants. The gametes requirew_______ so that male and femalecan be transferred.

Gymnosperms conifers such as pines;cycads such as Australianburrawang palm.

Land plants some of which can growinto large trees.

Vascular system well developed.

Reproduce by s____________ thatare u_________________. In most,the uncovered seeds rest on woodyscales that are part of a c________.(Seeds are reproductive structurescontaining an e____________, storesf__________ and a protective cover).

Angiosperm(monocotsand dicots)

all f______________plants, for exampleeucalyptus, wattle, daisy,daffodil, orchids, grass


The reproductive structures are thef__________. Following pollinationand fertilisation, s__________ areformed, usually enclosed within thef_________, which is the ripenedovary.

The pteridophytes, gymnosperms and angiosperms are commonlygrouped together as the tracheophytes or vascular plants.

1 Can you suggest a reason for the division into the different plant groupslisted in the table?

Hint: Look at the types of features that are described for each plantgroup. Which features are always included?

_____________________________________________________

_____________________________________________________

_____________________________________________________

12 Life on Earth

2 Which of these features would be easy to observe? Which would bemore difficult.

______________________________________________________

______________________________________________________

______________________________________________________

Check your answers.

Using a plant key

Use the key to identify the plants pictured following. List the steps used toname 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


Plant Features

(Photo: Jane West)

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: Julie Haeusler ©LMP)

vascular tissue

no flowers

naked seeds in cones

Steps:

Answer:

14 Life on Earth

(Photo: Jane West)

vascular tissue

no flowers

spores under leaves

Steps:

Answer:

(Photo: Jane West)

no vascular tissue

no flowers

aquatic

Steps:

Answer:


(Photo: Jane West)

vascular tissue

flowers

Steps:

Answer:

Check your answers.

Plant classification within a genus

Each level of classification shares similar features with the otherorganisms at the same level. You will recall that as you move down theclassification hierarchy the similarities between the organisms at eachlevel increases. For example, similar groups of organisms within afamily would belong to the same genus, and these are divided again intoeven more specifically similar organisms called species.

In this activity you will be identifying four species of the genus Banksiafrom 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 fromeach plant.)

_________________________________________________________

_________________________________________________________

_________________________________________________________

16 Life on Earth

If you cannot gain access to any of the plants within this group, use thediagrams and photographs provided.

If you have access, look at the Biology page on the LMP website where thephotographs 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 theSydney region

This key has been modified from Beadle, Evans and Carolin (Eds) Floraof 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 smoothmargins, juvenile leaves toothed. …………Banksia integrifolia

b) Shrubs, usually not more than 3 metres high. Leaves mostlyirregularly toothed. Young shoots with covering of rusty hairs…………………………………………….Banksia oblongifolia


Unknown Banksia 1

(Photo: Jane West)

(Photo: Jane West)

Name of Banksia___________________________________________

18 Life on Earth

Unknown Banksia 2

(Photo: Jane West)

(Photo: Jane West)

Name of Banksia ___________________________________________


Unknown Banksia 3

(Photo: Jane West)

(Photo: Jane West)

Name of Banksia___________________________________________

20 Life on Earth

Unknown Banksia 4

Underside of leaf is white Leaf irregularly toothed

Styles straight

Shrubs, usually not more than 3metres high.(Photo: Jane West)

Name of Banksia ___________________________________________


Complete Exercise 4.2: Plant classification.

Animal classification

The animal kingdom is also classified according to the similar structuralfeatures possessed by the organisms within a division. The followingkey summarises the major commonly used groupings for the kingdom.The kingdom classification represents one division from the fourkingdom classification system, hence the protozoans are included as partof the animal kingdom. You do not need to remember the names of thegroups in the key.

The division following shows only the classification of the chordata.

ANIMAL KINGDOM

PhylumChordata

Sub-phylumVertebrata

Classes:AgnathaChondrichthyesOsteichthyesAmphibiaReptiliaAvesMammalia

Sub-phylumUrochordataFor example:sea squirts orcunjevoi

22 Life on Earth

Vertebrate groups

The table below provides more information about one of the groups fromthis key – phylum chordata, sub-phylum vertebrata. You will useinformation 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, pairedfins, two chambered heart, ectothermic

Osteichthyes(snapper, bream)

gills, bony skeleton, paired fins, two chamberedheart, ectothermic

Amphibia(frog, toad)

spend part of their life cycle in the water and part onland adults breathe with lungs, thin moist skin, threechambered heart, lay eggs in water, ectothermic

Reptila(snakes, lizards, turtles)

breathe with lungs, three chambered heart, layleathery eggs on land, dry scaly skin, ectothermic

Aves(kookaburra, cockatoo)

breathe with lungs, covered with feathers, fore legsmodified as wings, lay hard shelled eggs(calcareous) on land, four chambered heart,endothermic

Mammalia(wombat, possum)

breathe with lungs, body covered with hair, femalesnourish young with milk from mammary glands, fourchambered heart, endothermic

Use the information to design your own key for the vertebrate groups in thespace 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 thescaffold provided here. Look back to the key on plants as a model.

1 a) …………………………………………………………….….

b) ………………. ………………………………………………

2 a) ……………………….……………………………………….

b) ……………………….…………………………...…………..

3 a) …………………………………..……………………………


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 youdecide to separate the groups with. Remember to put a “go to” statementat the end of each question to direct the reader of the key to the correctpath to follow.

Complete Exercise 4.3: Invertebrate classification.

24 Life on Earth


Additional resources

Invertebrate groups

The protozoans are usually microscopicorganisms that move by cilia, flagella orpseudopodia (these are external projectionsthat enable mobility.)

Amoeba

The Porifera are commonly called the‘sponges’. These animals have lots of tinypores and are aquatic. Water is circulatedthrough these pores, transporting food, oxygenand wastes. The animals are sessile, thismeans that they are permanently attached tothe surfaces on which they are found. Sponge

The Cnidarians include animals such as thecorals, hydra, sea anemones. These animalsare aquatic with one opening to the gut throughwhich water is circulated, transporting food,oxygen and waste. These animals possesstentacles that contain nematocyst cells orstinging cells. The body parts are arrangedaround one central point (radiallysymmetrical). This means that if it were cut inhalf the two halves would be mirror images ofeach other regardless of where you cut throughthe middle.

Sea anemone

The Platyhelminthes have flattened bodies.They are commonly called the ‘flat worms’.The body is bilaterally symmetrical (can onlybe cut in half one way for the two halves to beidentical). They are parasitic usually, or can be

26 Life on Earth

found free living. They posses a mouth but no‘gut’ as such. Organisms that belong to thisgroup include tapeworms, liver fluke andplanarian worms.

Liver fluke

The Nematodes are commonly called the‘round worms’ because they posses long,unsegmented bodies. The gut has twoopenings, a mouth and anus. They arebilaterally symmetrical. Examples of thisgroup are the hookworm, ascaris orthreadworm.

Thread worm

The Annelids are animals with long segmentedbodies. Common examples include theearthworms, leeches and polychaete worms.The gut has two openings. They havewell-developed digestive, circulatory andnervous systems. Leech

The Mollusca include animals such as thesnail, chiton, oyster, squid and octopus.They have soft body parts with a mantle.A protective shell may be secreted to protectthis soft tissue. Many molluscs such as snailshave a muscular ‘foot’ that is used forlocomotion. The animals in this group possesswell-developed digestive, circulatory andnervous systems.

Chiton

Sea stars, sea urchins and sea cucumbersbelong to a group of organisms called theEchinoderms. These are all marine and havespiny, hard skin on their bodies. They areradially symmetrical and have well-developeddigestive and circulatory systems.

Sea star

The Arthropods are a very diverse group andinclude animals such as the spiders, insects,crustacea, beetles and millipedes. They allpossess segmented bodies with jointedappendages such as legs. They have a hardexoskeleton and are bilaterally symmetrical.They possess a ventral nerve cord.

Prawn


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) andenvironment (aquatic or terrestrial).

Plant classification

The algae are placed with the plants in this classification system but inother systems they are placed in the Protista.

Group Examples Characteristics (structural andreproductive)

Red algae(Rhodophyta)

Brown algae(Phaeophyta)

Green algae(Chlorophyta)

Diatoms and other singlecelled algae.

Simple plants without true roots, stemsor leaves. No vascular tissue fortransporting food and water.

No vascular tissue for transporting foodand water.

Most are aquatic (marine and somefreshwater)

Single-celled forms can reproduceasexually by binary fission or byproducing spores as well as sexually byproducing gametes.

28 Life on Earth

Bryophytes mosses and liverworts Small plants without true roots. Insteadof roots they have simple cellularfilaments called rhizoids.

Possess simple stems and leaves.

No vascular tissue for transporting foodand water.

Most grow only in moist habitats.

Depend on water for sexualreproduction. Mosses have alternationof generations involving gametophyteand sporophyte.

Pteridophyta ferns eg. fish-bone,maiden hair, tree fern,bracken fern

Have true roots, stems and leaves.

Have vascular tissue for food and watertransport.

Can live in dry as well as moist habitats.

Reproduce by rhizomes, spores andgametes. Have an alternation ofgenerations involving sporophyte andgametophyte plants. The gametesrequire water so that male and femalecan be transferred.

Gymnosperms conifers such as pines;cycads such as Australianburrawang palm.

Land plants some of which can growinto large trees.


Reproduce by seeds that areuncovered. In most, the uncoveredseeds rest on woody scales that arepart of a cone. (Seeds are reproductivestructures containing an embryo, storesfood and a protective cover).

Angiosperm(monocotsand dicots)

all flowering plants, forexample eucalyptus,wattle, daisy, daffodil,orchids, grass


The reproductive structures are theflowers. Following pollination andfertilisation, seeds are formed, usuallyenclosed within the fruit which is theripened ovary.

1 The plant groups have been divided into groups on the basis of theirphysical structure and method of reproduction.

2 The structure is usually easily seen with the naked eye, such as thepresence of roots, stems and leaves, but the reproductive methodsmay be more difficult to see.


Using a plant keyA. Bryophyte

B. Gymnosperm

C. Pterydophyte

D. Algae

E. Angiosperm

Animal classification1 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) no paired fins…………………………………...……….Agnatha

6 a) lay eggs in water………………………………………Amphibia

c) lay eggs on land……………...………………………….Reptilia

30 Life on Earth


Exercises – Part 4

Exercise 4.1 to 4.3 Name: _________________________________

Exercise 4.1: Naming organismsa) Explain the need for a classification system.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

b) Define the term hierarchy and explain the system used in biology toassist classification of organisms.

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

c) i) Describe the main features of the binomial system in namingorganisms.

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

_________________________________________________

32 Life on Earth

ii) Using the binomial names of two similar plants or two similaranimals, explain how the names identify the two differentorganisms. In your answer, include information to show thatyou understand what genus and species mean.

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

__________________________________________________

Exercise 4.2: Plant classificationa) From your identification of Banksia species what criteria were used

in this key to distinguish between the species of Banksia?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

b) What are the advantages of this key?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

c) What are some disadvantages of this key?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________


Exercise 4.3: Invertebrate classification

The invertebrate group of animals is characterised by the absence of abackbone. The group is organised into phyla based on structuralfeatures.

a) Read the descriptions of the invertebrate groups located in theAdditional resources. Summarise the distinguishing feature of eachgroup in a table.

34 Life on Earth

b) Now design a dichotomous key that can be used to identify membersof the respective classes.

c) What are the advantages of using the binomial classification system?

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

______________________________________________________

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