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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
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Characteristicsandclassification
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.
2
1
The hierarchical classification of the lion
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Characteristicsandclassification
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?
4
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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Characteristicsandclassification
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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
2
1
Yeast is a single-celled fungus.
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Characteristicsandclassification
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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Characteristicsandclassification
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.
Arachnids
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Characteristicsandclassification
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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Characteristicsandclassification
oflivingorganisms
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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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7
6
8
5
10
11
9
14
13
12
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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