IGCSE (Complete Biology) Chapter 1

8/14/2019 IGCSE (Complete Biology) Chapter 1

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Characteristicsandclassification

oflivingorganisms

6

ObjectivesTo understand that living things differ from

non- living things

To be able to list the characteristics of living thingsTo understand that energy must be expended to

maintain lif e

You may see other similar lists of these characteristics

using slightly different words. You can remember

this particular list using the word RINGER. It givesRingers solution its name. This is a solution of ions

and molecules that physiologists use to keep living

tissues in it keeps the cells alive.

As well as the characteristics in the ringer list,

living things have a complex organisation that is

not found in the non-living world. A snowflake or a

crystal of quartz is an organised collection of

identical molecules, but even the simplest living cell

contains many different complex substances

arranged in very specific structures.

Living things also show variation the offspring

are often different from one another and from their

parents. This is important in adaptation to the

environment and in the process ofevolution.

How the characteristics of life dependon each otherEach of the characteristics of life is linked to the

others for example, organisms can only grow

if they are nourished. As they take nourishment

from their environment, they may also produce

waste materials which they must then excrete.To respond to the environment they must organise

their cells and tissues to carry out actions. Because

of the random nature of reproduction, they are

likely to show variation from generation to

generation.

Depending on energyThe organisation in living things and their ability to

carry out their life processes depends on a supply of

energy. Many biologists today define life as a set of

processes that result from the organisation of matterand which depend on the expenditure of energy.

In this book we shall see:

how energy is liberated from food molecules and

trapped in a usable form

how molecules are organised into the structures

of living organisms

how living organisms use energy to drive their

life processes.

The dawn of lifeScientists believe that the Earth was formed from an

enormous cloud of gases about 5 billion years ago.

Atmospheric conditions were harsh (there was no

molecular oxygen, for example), the environment

was very unstable, and conditions were unsuitable

for life as we know it.

Many scientists believe that the first and simplest

living organisms appeared on Earth about 2.8 billion

years ago. These organisms probably fed on molecules

in a sort of soup (called the primordial soup)

which made up some of the shallow seas on the

Earth at that time. A question that has always

intrigued scientists, philosophers and religious

leaders is:

What distinguishes these first living organisms

from the molecules in the primordial soup?

In other words, what is life?

Characteristics of living organismsYou know that a horse is alive, but a steel girder is

not. However, it is not always so obvious whether

something is alive or not is a dried-out seed or

a virus particle living or non-living? To try to

answer questions like this, biologists use a list

of characteristics that living organisms show.

Living organisms:

Respire

show Irritability (sensitivity to theirenvironment) and movement

Nourish themselves

Grow and develop

Excrete

Reproduce.

The opposite page gives more detail of the

characteristics of life.

Biology is the study of life and living organisms1 1


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Respirationis the process bywhich living cells release energy

from organic molecules. The

form of respiration that releases

the most energy uses oxygen.

Many organisms havegaseous

exchange systems that supply

their cells with oxygen from

their environment.

I rritability (or sensitivity) is theability to detect changes in the

environment either inside or

outside the organism, and to

respond to them. These responses

often involve movement.

Nutrition supplies an organism

with the food it needs for

respiration, growth, repair and

reproduction. Plants make their

foods using the process of

photosynthesis, whilst animals

obtain their foods ready-made

by eating them.

Growth and development arethe processes by which an

organism changes in size and in

form. For example, as a young

animal increases in size (as it

grows), the relative sizes of it s

body parts change (it develops).

Excretion removes the waste

products of processes such as

respiration and nutrition from

the organisms body.

Reproduction is the generation of

offspring new individuals. An

organism may simply split into

two, or reproduction may be a

more complex process involving

fertilisation. Reproduction makes

new organisms of t he same

species as the parents. This

depends on a set of chemical

plans (the genetic information).

contained within each living

organism.

Approximately how many years passed between

the formation of the Earth and the appearanceof the fi rst living organisms?

What sort of moleculesdo you think might havebeen present in the primordial soup?

RINGER isaword that helps people remember

the characteristics of living organisms. Think ofyour own word to help you remember these

characteristics.

Suggest twoways in which reproduction is

essent ial to living organisms.

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3

2

1


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oflivingorganisms

8

ObjectivesTo appreciate why classification is necessary

To understand the use of a key

To be able to name the five kingdoms, and describetheir distinguishing characteristics

To understand the hierarchy of classif icati on

To know why a binomial system of nomenclature

is valuable

put all living organisms into categories. The science

of placing organisms into categories on the basis

of their observable characteristics is calledclassification. There are so many different types of

living organism (i.e. an enormous variety

of life) that the study of these organisms

would be impossible without an ordered way

of describing them.

Classification keysTaxonomists (people who study classification) place

organisms into groups by asking questions about

their characteristics, such as Does the organism

photosynthesise? or Does the organism contain

many cells?. A series of questions like this is called

a classification key. Examples of such keys are

shown below.

The need to classify living thingsVariation and natural selection lead to evolution.

Evolution, and the isolation of populations, leads to

the development of new species (see page 220).

Each species has different characteristics, and some

of these characteristics can be inherited by

successive generations of this species. Observing

these inherited characteristics allows scientists to

The variety of life1 2

A key may be used to place an organism in one of the five kingdoms.

This kind of key, with only two answers to

each question (in this case, YES or NO), is

called a dichotomous key (dichotomous

means branching). It can be written as a

branching or spider key, using the same

questions:

Branching keys

are easy to use, but

take up a lot of spacewhen fully drawn out.

For this reason the

listed form of a

dichotomous key is

usually used for

identif ication of

organisms outside

the laboratory.It is a fungus

It is an animal

YES

NO

Go to question 4

It is a plant

YES

NO

Go to question 3

It is a protoctistan

YES

NO

Go to question 2

It is a bacterium

YES

NODoes the organism have cells with a definite nucleus?

Is the organism made up of many dif ferent cells?

Is the organism a heterotroph?

Does the organism have cell walls and does it feed by

external digestion?

1

3

4

2

It is a bacterium

It is a protoctistan

3 Is the organism a heterotroph?

It is a plant

4 Does the organism have cell walls and

does it feed by external digestion?

It is a fungus It is an animal

NOYES

NOYES

NOYES

NO YES

All living organisms

1 Does the organism have cells with a definite nucleus?

2 Is the organism made up of many different cells?

The five kingdomsBacteriaProtoctistansPlants

FungiAnimals


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On movingdown the

hierarchy of groups,

note that thereare ...

M ore similarities

and

fewer differences

between the members

All animalsare ingestive

heterotrophs.

All chordates havea

notochord (becomes the

backbone).

All mammals have fur and

mammary glands.

All carnivores have well

developed carnassial

(flesh-cutting) teeth.

All Felidae have

retractable claws.

All Panthera(big cats)

can roar but cannot purr.

All lions can mate and

produce fertile offspring

with other lions. TheEnglish scientist John Rayused this feature to definethe term species.

Kingdom (Animalia)

Other speciesSpecies

Panthera leo

Other generaGenus (Panthera)

Other familiesFamily (Felidae)

Other ordersOrder (Carnivora)

Other classesClass (Mammalia)

Other phylaPhylum (Chordata)

Five KingdomsUsing the key opposite, it is possible to place any

living organism into one of five very large groups.

These groups, distinguished from one another by

major and obvious characteristics, are called the

five Kingdoms. Each of these kingdoms contains an

enormous number of different species, and keys can

be used within a kingdom to place any individual

species into further groups. The diagram below

shows the names of these groups, and how the lion

is classified within the Animal Kingdom. The

sequence of kingdom, phylum, class, order, family,

genus and species is called a hierarchy of

classification.

Notice that each classification group is given a

name. Lions belong to the class Mammalia and the

order Carnivora, for example. The final two group

names are written in italics this is a worldwide

convention amongst scientists. The lion is called

simba in Swahili, len in Spanish and leu in

Romanian but is known as Panthera leo to

scientists in each of these countries. This

convention of giving organisms a two-part name

made up of their genus and species was introduced

by the Swedish biologist Carolus Linnaeus. He gave

every organism known to science a two-part name

based entirely on the body structure of theorganism. This binomial system of nomenclature

is still in use today (binomial = two name). New

species today may be given names based on

characteristics such as chromosome number or gene

sequence, which Linnaeus knew nothing about.

The pages that follow describe the characteristics

that distinguish living organisms in some of the

most important phyla and classes.

The scientific names for the weasel and mink areMustela nivalisandMustela vison, respectively. Both

of theseanimals belong to the order Carnivora, asdo

the fox (Vulpes vulpes) and otter (Lutra lutra). Theotter, mink and weasel all belong to the family

Mustelidae.

a Which feature must they have in common tobelong to the order Carnivora?

b Which two animalsare most closely related?

c Which animal is the most dif ferent from the otherthree?

d Suggest one feature that placesall of theseorganisms in the Animal Kingdom.

The scientific name for the human isHomo sapiens.

Try to find out the meaning of this name.

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1

The hierarchical classification of the lion


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oflivingorganisms

10

ObjectivesTo know the structure of a typical bacterial cell

and a typical virus

To know the requirements for bacterial growthTo know how bacteria reproduce

To understand some of the ways in which bacteria

and viruses affect human activities

To understand why viruses do not fit into the five

kingdoms of living organisms

Bacterial structureBacteria (singular: bacterium) are single-celled

organisms that have no true nucleus. Bacterial cells

do not contain organelles like those found in typicalanimal and plant cells (see page 23), but are able to

carry out all of their life processes without them. A

few can photosynthesise, but most feed off other

organisms. They may be parasites, feeding off

living organisms, or saprotrophs, feeding off dead

organisms.

Bacteria are very small, usually about 12 m in

length, and so are only visible using a high-

powered microscope. The structure of a typical

bacterium is shown in the diagram below.

Bacteria exist in a number of different shapes, some

of which are shown below. Shape can be used to

classify bacteria.

Bacteria and viruses1 3

Bacteria have a cell wall but do not have a nucleus or organelles.

Cytoplasm contains enzymesand

foodmolecules but no organelles.

Glycogengrains

may bea food store

Cell membrane

Plasmidsare small

rings of DNA,

carrying only a

few genes.

0.1m

Cell walldoesnot

contain cellulose.

Slime coat is present

in some species.

Main DNA strand

isnot contained

insideanucleus.

Flagella may be

one (flagellum)

or several, which

beat to move

bacterium

Requirements of bacteriaBacteria have certain requirements that their

environment must provide. An understanding of

these requirements (see page 272) has been

important in biotechnology and in the control of

disease. If the environment supplies these needs, the

bacteria can multiply rapidly by binary fission

(see page 164). In this process each bacterium

divides into two, then each of the two divides again

and so on, until very large populations are built up.

A bacterial colony can quickly dominate its

environment, making great demands on food andoxygen and perhaps producing large quantities of

waste materials.

Thegeneration time (time taken for each cell to divide into two)

can beas litt leas 20 minutesunder ideal conditions. One E. coli

cell in the human gut couldtheoretically become 2 cells in

24 hours this number of cells weighsabout 8000 kg!

72

Bacterial shapes.

Vibrio

(cholera)

Treponema

(syphilis)

Pneumococcus

(pneumonia)

Staphylococcus

(causes boils)

Spirilli (singular

spirillum) are

spiral bacteria

Salmonella t yphi

(typhoid)

Lactobacillus

(sours milk)

Bacilli (singular

bacillus) are rod-

shaped bacteria

Cocci (singular

coccus) arespherical

bacteria


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The importance of bacteriaBacteria are important to humans in many ways.

Some are pathogenic they cause disease (see

page 258). All pathogenic bacteria are parasites.

Some are involved in nutrient cycles (see

pages 2403).

Some are exploited by humans in food

production and in biotechnology (see page 48).

Bacteria are probably the organisms that carry out

the largest number of different activities, and are the

most numerous organisms on Earth. There may be as

many as 5000 undiscovered bacterial species in 1 m3

of woodland soil, and more bacteria live on or in

your body than all of the humans that ever existed!

VirusesWhen the five-kingdom system of classification was

devised, no one was able to find a place for the

group of organisms called the viruses. This is

because viruses do not show the typical features ofliving things respiration, nutrition and

reproduction, for example unless they are inside

the cells of another living organism. In other words,

all viruses are parasites and therefore cause harm to

their host. Some taxonomists have suggested that

viruses belong in a sixth kingdom. There is great

variation in the structure of viruses, but they all

have certain common features. The structure of a

typical virus is shown below.

Most viruses cause disease they may infect

humans, domestic animals or plants.

A typical virus has genetic material and a prot ein coat, butcannot carry out its life processes. It has no cytoplasm.

Spikes may contact and

recognise the cell to be

infected.

Protein coat protects thesingle strand of nucleicacid.

Made of many subunits.

Genetic material may be

DNA or RNA, but alwaysa

single strand.

Look at the diagram of bacterial shapes. Makea

dichotomous key that would enablea biologistto distinguish the different bacterial types on the

basis of their structure.

Makea table to show which of the followingstructuresare present in:a an animal cell b a plant cell c a bacterial cell.Write if the structure is present and if it is

absent.Cell wall, slime capsule, cell membrane, nucleus,

chloroplast, mitochondrion, DNA, cytoplasm

Why is it difficult to classify viruses into one of

the five kingdoms of living organisms?

If ten bacteria landed on a bowl of soup,andreproduced every 30 minutes, how many wouldbe present after 5 hours?

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3

2

1

Coat of

spiral protein

TMV (tobacco mosaic virus) infects

the leaves of tobacco plants.

Protein

outer coat

RNA

RNA

cut-away view

Influenza virus,

cut-away view

Virus Bacteria

Covered by Protein coat Cell wall

Cell membrane No Yes

Cytoplasm No Yes

Genetic material DNA or RNA DNA enough for

only a few genes several hundredgenes

Living or Non-livingunless Living

non-living? in host

Virusesand bacteriaalso differ in the method of nutrition: all

virusesare parasitic, but some bacteria feedas parasites, someas

photosynthesisers and some feed likeanimals (as heterotrophs).

Virus and bacteria compared


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oflivingorganisms

12

ObjectivesTo know the structure of a fungus

To understand the methods of nutrition used

by fungi

To appreciate the impact of fungi on the lives

of humans

Fungal cells have a common structureThe fungi are a very large group of organisms. They

range in size from single-celled yeasts to enormous

fungi whose underground parts may occupy an area

greater than a football or hockey field.

Fungal cells have a cell wall made of a mixture of

substances including chitin. The cytoplasm contains

many organelles, since the fungus manufactures

digestive enzymes. It feeds by saprotrophic (dead-

feeding) nutrition, as illustrated below.

Reproduction in fungiSingle-celled yeasts reproduce asexually by binary

fission (see page 164), but all other fungi reproduce

by the production ofspores, as shown above right.

Fungi1 4

Saprotrophic nutrition involves external digestion by enzymes.

Themycelium is madeup of

branchinghyphae, and

penetrates throughout the food

source. The foodmay be the

remains of an animal or plant.

One section of the

hyphamay contain

several nuclei

Cell wall

Cytoplasm mayreleasedigestive

enzymes

Cross wall

Vacuole

DigestiveInsoluble

compounds

in food

source

Soluble

products of

digestion

absorbed by

fungus by

diffusion or

active transport

Hypha

enzymes

Spore formation in a pin mould fungus

Spores

Sporangium

Vertical hypha

Hyphae

of the

mycelium

Sporesare

dispersed

when

sporangium

bursts open.

Spore lands on food source it can

germinate andanew mycelium can develop.


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Requirements of fungiFungi have very similar requirements to those of

bacteria, that is:

a moist environment, so that they can absorb the

soluble products of digestion of their food source

in solution

a warm environment, so that enzymes can work

at their optimum temperature

a nutrient source to provide the raw materialsand energy required for growth

Fungi do not require light since they do not rely

on photosynthesis for the production of food

compounds. This means that fungi are rarely

found in light environments, since such

environments are usually too warm and dry for

fungal growth.

Parasitic fungiFungi may also feed by parasitic methods. These

fungi produce digestive enzymes, but only oncethey have killed the host and can no longer obtain

soluble foods directly from its tissues. An example

of a parasitic fungus is shown right.

The importance of fungiFungi have a number of effects on the lives of

humans, for example:

They are decomposers, and play a vital role in

nutrient cycles (see page 240).

Their decomposing action may destroy materials.

Wooden buildings, in particular, are at risk fromwet and dry rot.

Mould fungi consume food which might

otherwise be eaten by humans.

Fungi may be agents of disease, as in athletes

foot for example.

They may themselves be a source of food, for

example mushrooms.

Fungi are used in biotechnology the brewing

and baking industries (see page 50) are entirely

dependent on the activities of yeast, for example.

Cell wall containing

chitin.

Cell membrane

Cytoplasm, containing

organelles and manyvacuoles with digestive

enzymes

Nucleus

Single cell of a fungus such as yeast

Parasitic fungus

The best of both worlds!

A bracket fungus

eventually weakens and

kills its host. It then feeds

as a saprotroph on the

dead remains of the tree.

Feeding mycelium

penetrates to vascular

bundles of the host tree.

Only the reproductive

hyphae are visible on

the outside of the tree

clumped together to

form a bracket.

Suggest why toadstoolsare likely to be found in dark areas of woodland where green plantsare very limited.

Some fungi are saprotrophs,and secrete enzymes onto their food source. Suggest three such enzymesand nametheir substratesand products.

List, with examples, four ways in which fungi affect the lives of humans.3

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1

Yeast is a single-celled fungus.


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oflivingorganisms

14

ObjectivesTo recall that all plants are autotrophs, and are

able to absorb light energy to drive photosynthesis

To understand some of the steps in the adaptationof plants to life on dry land

To recall the characteristics of the four main

plant groups

to absorb water from cold soil). They do not rely on

insects for pollination (flying insects are uncommon

in cold areas) conifers reproduce using structurescalled cones.

AngiospermsThe angiosperms or flowering plants are the most

successful of plants they have evolved into many

species and have colonised almost every available

habitat. More than 80% of all plants are

angiosperms (plants with enclosed seeds). Many

features of the lives of flowering plants are covered

elsewhere in this book (see pages 6073, 8693, 160

and 186199, for example). The diagram at the top

of the opposite page summarises these features, and

emphasises the adaptations of flowering plants to a

successful life on land, including warmer habitats.

Two groups of angiospermsThere are two major subgroups within the

angiosperms. In one group there is a single

cotyledon in the seed (see page 195) these are the

monocotyledons. In the other group there are two

cotyledons these are the dicotyledons. There are

other differences between monocotyledons and

dicotyledons, as shown in the diagram on the

next page.

Plants are autotrophsAs autotrophs, plants manufacture food molecules

from simple, inorganic sources by the process of

photosynthesis using light as a source of energy.

Plants all contain the light- absorbing pigment

chlorophyll (or similar molecules which perform the

same function) inside cells which have a definitecellulose cell wall.

Adaptations to life on landThe first plants lived in water, but as living

organisms evolved, plant forms developed that

could live on land. The classification of plants into

groups follows this sequence of evolution.

The Plant Kingdom may be divided into four main

groups (phyla): algae, mosses, ferns and seed

plants.

Seed plantsAlgae, mosses and ferns all depend to some extent

on a moist environment, especially for the transfer

of gametes. The seed plants have proper roots, stems,

leaves, vascular tissues and waterproof coverings,

and their gametes can be transferred without a

film of moisture. As a result the seed plants are able

to live and reproduce in dry environments.

The two groups of plants that dominate our fields,

woods and gardens are the conifers (cone bearers)

and the angiosperms (flowering plants).

ConifersThe conifers dominate the landscape in colder

climates where flowering plants cannot compete.

Conifers have needle-like leaves with a very thick

cuticle which prevents water loss (it is very difficult

1 5 Plants

Fungus Plant

Nucleus in cell Yes Yes

Cell wall Yes, but not made Yes, made

of cellulose of cellulose

Movement No No

Chlorophyll present No Yes

Method of nutrition As saprotroph By photosynthesis

or parasite

Fungus or plant?


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Flowers the colour, pattern, shape, scent

or nectar of the flower may attract insects,

birds or mammals. These animals transfer

pollen from male to female flower parts

much more efficiently than wind or water.

Large leaf surface allows high

rate of photosynthesis to supply

energy for growth and fruit

production. However, water losses

by evaporation and diffusion

through stomata are high.

Xylem vessels have

no end walls and

conduct water efficiently.

Roots form beneficial associations with other

organisms. For example, legumes such as peas

and beans form root nodules with nitrogen-

fixing Rhizobiumbacteria. See page 242.

rowt , part cuar y o repro uct ve structures, can e very rap .

For example, pollination, pollen tube formation and fertilisation

may take only one hour (compared with one year in some conifers),

and some bamboos can grow 1m per day.

Theovary protects the ovules and developing

embryo, part icularly f rom drying out.

(Angiosperm means enclosed seed)

Endosperm is a store of nutrients for the developing

plant embryo. It does not develop until after fertilisationso that f ood stores are not wasted, as they might be in conife

Fruitsare formed from ripened ovaries.

Their specialised shapes, colours, smells and textures aid

dispersal by wind, water and animals.

Stomata with guard cells regulate loss of water vapour and

exchange of oxygen and carbon dioxide between plant and

atmosphere

Specialised supporting tissues (air has a low density and doe

not offer support as water does)

Waterproof cuticle reduces water loss to atmosphere

Vascular system transports water, ions and organic solutes

Extensive root systems anchor the shoot systems and

absorb water and ions

One

cotyledon

Two

cotyledons

Seed

One seed

leaf

Two seed

leaves

Mature leaf

Parallel

veins

Branched

veins

M onocotyledone.g. maize

Dicotyledone.g. pea

Seedling

M onocotyledons and dicotyledons two groups of angiosperms (flowering plants)

Angiosperm adaptations

Name the four different plant groups. Why arealgaeconfined to water, whilst fernsare well adapted to

life on land?

Seed plantsare well adapted to live and to reproducein dry environments. What major adaptation allows

reproduction on dry land?

21


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oflivingorganisms

16

ObjectivesTo know the difference between a vertebrate

animal and an invertebrate animal

To be able to describe the main characteristics offour invertebrate groups annelids, nematodes,

molluscs and arthropods

To be able to distinguish between different classes

of arthropods

To understand the importance of metamorphosis

in insects

Vertebrates and invertebratesAll animals share one characteristic they feed on

organic molecules (see page 76). Members of the

Animal Kingdom can be divided into two large

groups based on whether they have a backbone as

part of a bony skeleton. Animals with a backbone

are called vertebrates and those without a backbone

are called invertebrates.

Four groups of invertebrates are described here:

1 6 Invertebrate animals

AnnelidsAnnelids such as the earthworm have a long

segmented body and chaetae.

Chaetae (bristles) are found on each

segment used during movement.

Clitellum used to bind two worms

together during sexual reproduction.

Cross-section ofworm, showing

chaetae

Single segment

Mouth can bite

off pieces of

fallen leaves

Anus

Long, cylindrical body

covered with a mucus layer

helps to stop drying out

MolluscsMolluscs have a hard shell protecting a soft body

with no limbs.

Snailshave a

single, coiled shell.

Shell - hardened by calcium

carbonate. Protects the soft body

of the snail from predators and

from drying out. The whole body

can be withdrawn into the shell.

Foot muscle with a slimy covering so that

snail can move by creeping over the surf ace.

Mouthparts to

scrape at vegetation

Eye on tentacle

Mouth with sucking mouthparts

for drinking blood

Has long muscles for wriggling

movements

Long, thin body so not washed

out of hosts intestine

Body covered with mucus to resist

attack by host's digestive juices

Large sex organs to produce many

sperm and eggs

Anus

NematodesHookworms are nematodes with bodies that are

specialised for feeding and reproducing; often they

are parasites inside the gut of another animal.

Annelid Nematode Mollusc

Body Hard, slightly Soft , not Soft shell helpscovering waterproof waterproof to save water

Segments Yes No No

visible

Movement Uses chaetae Wriggles but Creeps on foot

(bristles) to lives in from place

move from one place to place

place to place

Feeding Herbivores Mainly Mainly herbivores

method parasites some carnivores

Annelid, nematode or mollusc?

Arachnids are arthropods with four pairs of legs and no wings.


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ArthropodsThe arthropods are the most numerous of all

animals, both in terms of the number of different

species and the number of individuals in any one

species. The insects are arthropods that show an

interesting adaptation in their life cycle called

metamorphosis that allows them to use the

resources of their habitat to the maximum.

Apart from insects, the arthropod phylum includesthree other classes:

CrustaceaCrabs are slightly unusual because many of their

segments are tucked under their body.

Myriapods

Antennae: these are important

sense organs in t he

millipedes' dark, damp

environment . They can

'sense' chemicals and the

level of moisture in the

environment

Mouthparts: these are

modified legs! Have hard

edges for biting vegetation

(millipedes) or other animals

(centipedes)

Hard exoskeleton: protection

against predators

Walking legs: have manyjoints and internal muscles,

and allow movement over

rough surfaces

Body covering: waterproof,

helping animal to live on land

M any body segments:

body is flexible for

movement and

wriggling around

and under leaves

and stones

Jointed limbs: flexible

to help with feeding

Hardened, serrated edge to claw:

can hold onto slippery food, and

break open shells of molluscs

Carapace:a thick,hardened shell for

protection against

predators

Gills under shell:

allow uptake of

oxygen from water

Eyes:important sensors

in aquatic environment

Copy and complete the following paragraph.

All animals have one common characteristic . The invertebratesareanimals that do not have .Examples of important invertebrate groupsare , which are very clearly segmented with bristles called

to aid in movement; , which havea soft body inside one or two hard shells; and , which are the most

numerous of all.

Thearthropods include four classes insects,arachnids, crustaceansand myriapods.

a List three features that all of these classes possess.

b List three features that only insects possess.

c Compare insectsand spidersunder the headings Number of legs, Number of body sections, Number of wingsand Type of eyes.

Insectsare the most abundant of all animals on land. Many of them show an adaptation called complete

metamorphosis. What does this term mean,and how does it help to explain why there are so many insect species?

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The body issegmented, with thesegments grouped intohead thorax and abdomen.

Compound eyesdetect foodand avoidpredators

Antennae:

sensechemicalsin theenvironment

Mouthparts:very specialisedfor feedinge.g. piercing bymosquitoes

Three pairs of legs,attached to the thorax.Allow walkingmovements, overfood or to avoidpredators.

Two pairs ofwings for flying(rear set maybe absent

or not usedfor f lying).

The adultblowfly ishighlyadapted forlocomotion(aids dispersal)and reproduction.

M etamorphosis (means changeof body form) allows differentstages which:

do not compete for the samefood sourcescan be highly specialised fordifferent functions. The larva

is adapted for feeding andgrowth, and the adult forlocomotion and reproduction.

Insectse.g. housefly, mosquito (page 274)

Powerful, piercing jaws all spiders are predators

Head and thorax are combined intoone body part, the cephalothorax.

Simple eyes (but more than onepair) help to detect prey

Four pairs of legs attached towardsthe rear of the cephalothorax. Allowchasing prey or holding onto web

Abdomen

Spinneret which produceslong, thin strands of silk.(The word arachnid comesfrom the Greek goddessArachne who was skilledat spinning.)

Spider silk is so strong and thin that ithas been used to make the cross hairs inthe telescopic sights of ri fles.

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oflivingorganisms

18

ObjectivesTo know the characteristics of the vertebrates

To understand how different classes of vertebrates

show increasing adaptation to dry landTo know the five classes of vertebrate, and to

provide examples of each

If asked to name an animal, most people would

probably name a mammal because these are the

most familiar animals to us. Mammals are just one

class of the phylum Chordata. The chordates are

often called the vertebrates, although strictly

speaking there are a few chordates that arent

vertebrates. Vertebrates have a hard, usually bony,

internal skeleton with a backbone. The backbone is

made up of separate bones called vertebrae which

allow these animals to move with great ease.

There are five classes of vertebrates, which, like the

members of the Plant Kingdom, show gradual

adaptations to life on land. The classes are fish,

amphibians, reptiles, birds and mammals.

1 7 Vertebrate animals: five classes

Vertebrates

All have a backbone

Do they have smooth skin?

YES NO

YES NO

YES NOYES NO

Amphibians

Fish, Repti les, Birds, Mammals

Fish, Reptiles

Are scales dry?

Birds, M ammals

Feathers on skin?

Scales on skin?

Reptile Fish Birds M amma

Vertebrates can

be separated into

classes based on

their skin!

Scales

covered in mucus helpstreamlining f orswimming

Lateral line contains sense

organs to detect vibration

Operculum covering gills: gills

have a large surface area for gasexchange

Fins for movement and

stability

Nostrils leadingto lungs whichare used forgas exchange

M oist skin(also usedforgas exchange)

Wide mouth as adultamphibians are allcarnivorous

Four limbs,with hindlimbs webbed:walking andswimming

Fish

Amphibians


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Dry, scaly skin -

limit s water lossTail can be used

for swimming,

as in crocodiles

Limbs efficient

for crawling

and climbing

Mouth has teeth orbony ridges

to aid feeding

Reptiles

Nostril , leading to lungs which

are the organs of gas exchange

Forelimbs are

modified aswings.

Beak:very l ight

since no bone or

teethFeathers, vital for f light

and for endothermy

(they give excellentinsulation against

heat loss)Scales on legs: feet ideal

for perching

Whiskers aresensitive to touchand vibration.

Mouth: contains teeth whichallow mammals to use a widevariety of foods (page 42)

Pinna on ear can be movedfor maximum efficiency insound detection.

Fur bodycovering whichallows

endothermy as ameans ofkeeping aconstant bodytemperature.

Penis an organ of the male thatenables efficient internal fertilisation.

The crocodile has the typical dry scaly skin of reptiles, and the eyeson the top of its head and its sharp, pointed teeth adapt it forcatching prey in water.

Mammals are endothermic vertebrates that have

the characteristics shown in the diagram below.

A wide range of adaptations has allowed mammals

to colonise many habitats as diverse as the polar

wastes and the Arabian desert.

Humans are mammalsHumans show the typical mammalian

characteristics of hair, mammary glands and a

diaphragm, for example. Humans, though, are

unique amongst all animals in that the adaptations

they show allow them to modify their environment

so that it is suitable for human occupation. As a

result humans have been able to live and work in

many habitats no animal has a wider range.

Human adaptation has allowed advanced

development of the brain, and of all the complexactivities that the brain can coordinate. The human

brain is extremely sensitive to changes in

temperature. Human adaptations include many that

are concerned with the fine regulation of blood

temperature (see page 130). Other features that

make humans very special mammals include an

upright posture, freeing the hands for complex

movements including the use of tools.

The heron has typical bird features of feathers and a beak. It is welladapted to capture fish and frogs as it has large eyes to spot itsprey, a long pointed beak to grab its prey and large feet for walkingover soft , muddy ground.

Mammals

Birds


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oflivingorganisms

20

Questions on characteristics and classification

South Uist isa small island which provides one of the few remaining summer

habitats for a bird called the Corncrake (Crex crex). It lives in grass fields,

which are cut in the late summer for hay, where it feeds on insects, wormsandseeds. South Uist providesagood habitat because thereare plenty of grassfields where the Corncrake can nest and there are few predators.

However, a small mammal called the Hedgehog(Erinaceus europaeus) was

released onto the island. The Hedgehogalso has few natural predatorsand willfeed on the eggs of Corncrakes, as well as on insectsand worms. The number

of Hedgehogs on South Uist has risen rapidly to 10 000 while Corncrakesarebecoming endangeredas their numbers worldwide are falling.

a State two features which birdsand mammals have in common.b State two features which distinguish birds from mammals.

(IGCSE2004 [part])

Use the key to identify the five fish shown in the drawings. Write down theletter of each fish and its name.

(SEG June 1992)

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LIVINGORGA

NISMS

Ke

ysandclassification

*theFIVEKINGDOM

S

Akeyenablesidentificationofanorganismb

y

observationofitscharacteristics.Closeobservation

allowsaseriesofquestions(thebranchpointsin

thiskey)tobeanswered,eventuallyleadingto

theorganismbeingstudied.

PROTOCTISTA

NS*

e.g.P

lasmod

ium

BACTERIA*

e.g.Salmonella

Cellshavean

obviouscellwall

Cellshave

nocellwall

ANIM

ALS*

Cellshave

anobvious

nucleus

Cellshave

noobvious

nucleus

Madeupof

manycells

Madeupof

singlecells

Organ

ismhas

internalskeleton,

non-segm

entedbody

VERTE

BRATES

Softbodywith

nolimbscovered

byshell

Segmentedbody

withcha

etae

(bristles)

SPIDERS

e.g.tarantula

CRUSTACEAN

S

e.g.crab

INSECTS

e.g.mosquito

Fur/hair

Mam

maryglands

M

AMMAL

e.g.human

Feathers

Beak

Wings

BIRD

e.g.thrush

Moist

(mucus-coveredskin)

GillsFins

FISH

e.g.stickleback

Spores

produced

FERNS

Dryskin

REPTILE

e.g.lizard

Noscalesonskin

Scalesonskin

Seeds

produ

ced

SEEDPLANTS

e.g.oaktree

Skincovering

Nocovering

on

skin(smooth,

moistskin)

AMPHIBIAN

S

e.g.frog

Twobody

segments(head

thorax,abdomen).

Fourpairsoflegs.

Nowings

Twopairsof

antennae

Threebody

segments(head,

thorax,abdomen).

Threepairsoflegs.

Twopairsofwings.

Antennae

Organismhas

hardexoskeleton,

jointedlimbs,

segmentedbody

ARTHROPODS

Cellscontainchlorophyllin

chloro

plasts(soorganism

feeds

byphotosynthesis)

PLANTS*

Cellsdonotcontain

chlorophyll(

soorganism

feedsbyabsorption)

FUNG

I*e.g.

breadmould

Stem,leaves

androots

Stem,leaves

butnoroots

MOSSES

Noseparate

root,stem

andleaves

ALGAE

ANNELIDS

e.g.earth

worm

MOLLUSCS

e.g.snail

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5

10

11

9

14

13

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a What are you? Follow the branch pointsat 1, 3, 4, 8, 9and 11 to identifyyourself asamammal.

b Name two additional characteristics of mammals.

c In what way are humansspecial mammals?

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IGCSE (Complete Biology) Chapter 1

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