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Contents
lntroduction
1
Unit 1 Characteristics and classification
of living organisms
1.1 Characteristics of living organisms
1.2 Classification
1.3 Arthropods
1.4 Vertebrates
1.5 Microorganisms
1.6 Flowering plants
1.7 Use of keys
Summary and exam questions
Unit
2
Cells
3
2
4
6
8
10
12
14
16
24
Movement in and out of cells
26
26
3.1 Diffusion
3.2 Osmosis
3.3 Osmosis in plant and animal cells
3.4 Active transport
28
30
32
Summary and exam questions
34
Enzymes
36
Unit
4
4.1 Structure and action of enzymes
4.2 Factors affecting enzyme action
4.3 Enzymes in industry
Summary and exam questions
Unit 5 Nutrition
5.1 Nutrients
5.2 Chemical tests for nutrients
5.3 Sources of nutrients
5.4 Use of microorganisms in industry
5.5 Food additives
44
44
46
48
50
nutrition
Photosynthesis
56
56
6.2 What is needed for photosynthesis? 5g
6.3 Products of photosynthesis 60
6.4 Rate of photosynthesis
62
Summary and exam
questions
64
66
6g
70
Plant transport
8.5
Unit
88
90
92
environments
94
96
98
9 Transport in humans
100
100
102
104
(CHD)
Summary and exam questions
Unit 10 Respiration
10.1 Respiration
1 0.2 The gas exchange system
10.3 Gas exchange
10.4 Breathing
10.5 Rate and depth of breathing
10.6 Anaerobic respiration
Summary and exam questions
Unit 11 Homeostasis and excretion
11.1 Controlling conditions in the body
11.2 Controlling body temperature
11.3 Excretion
11,4 Kidney function
1.5
82
84
86
Translocation
Summary and exam questions
9.1 Circulation
9.2 The heart
9.3 Blood vessels
9.4 Coronary heart disease
9.5 Blood
9.6 Blood in defence
9.7 Lymph and tissue fluid
1
72
74
76
78
80
88
8.1 Transport systems
8.2 Water uptake
8.3 Transpiration
8.4 Adaptations of plants to different
52
54
6.5 Glasshouse production
6.6 Leaves
6.7 Mineral requirement5
8
Unit
36
38
40
42
Summary and exam questions
Unit 6 Plant
6.1
Summary and exam questions
18
20
22
Summary and exam questions
72
7.2 Balancing energy needs
7.3 Starvation
7.4 Digestion
7.5 Teeth
7.6 The stomach and small intestine
7.7 Absorption and assimilation
2
18
2.1 Structure of cells
2.2 Different types of cells
2.3 Levels of organisation
Unit
Unit 7 Animal nutrition
7 .1 A balanced diet
Kidney dialysis and kidney
transplants
Summary and exam questions
106
108
110
112
114
116
116
118
120
122
124
126
128
130
130
132
134
136
138
140
Contents
Unit 12 Coordination and response
12.1 Nervous control in humans
12.2 Neurones and reflex arcs
12.3 Reflexes and antagonistic muscles
12.4 Sense organs
12.5 The eYe
12.6 Hormones
'12.7 TroPic responses
SummarY and exam questions
Unit 13 Drugs
13.1 Drugs and how theY work
13.2 Heroin
13.3 Alcohol
13.4 Smoking and health
SummarY and exam questions
Unit 14 ReProduction in Plants
14.1 Asexual and sexual reproduction
14.2 Flower structure
14.3 Pollination
14.4 Fertilisation and seed formation
14.5 Fruits and seeds
14.6 Growth and develoPment
SummarY and exam questions
142
'142
'144
'146
'148
150
152
't54
156
158
158
160
162
164
166
15.3 Fertilisation and imPlantation
't5.4 Preg na ncY
15.5 Ante-natal care and birth
15.6 The menstrual cYcle
15.7 Sex hormones
15.8 Methods of birth control
15.9 Sexually transmitted diseases
Summary and exam questions
Unit 16 lnheritance
16.1 Chromosomes, genes and DNA
16.2 Mitosis and meiosis
16.3 Genes and chromosomes
6.4 MonohYbrid inheritance
16.5 Codominance
1
SummarY and exam questions
genetic engtneering
SummarY and exam questions
Unit 18 Energy and nutrient transfer
18.1 Food chains and food webs
18.2 Pyramids of number and biomass
18.3 Shortening the food chain
18.4 Nutrient cYcles
18.5 The nitrogen cYcle
SummarY and exam questions
Unit 19 Human influences on
the ecosYstem
214
214
216
218
220
222
224
224
226
228
230
232
234
SummarY and exam questions
236
236
238
240
242
244
246
248
250
252
254
Alternative to Practical PaPer
256
Revision checklist
262
192
GlossarY
270
194
196
lndex
279
Acknowledgements
284
168
168
170
172
174
176
178
180
Unit 15 Sexual reproduction in humans 182
182
15.1 The male reProductive sYstem
'15.2 The female reProductive system
Unit 17 Variation and selection
17.1 Variation
17.2 Mutations
17.3 Natural selection
17.4 Artificial selection and
184
186
188
190
198
200
202
202
204
206
208
210
212
19.1 PoPulattons
19.2 Human PoPulations
19.3 Resources
19.4 Pollution
'19.5 The greenhouse effect
19.6 Acid rain
'19.7 Water Pollution
'19.8 Conservation
19.9 Sewage treatment and recycling
lntrod I ction
Ttris book is designed specifically
for Biology
TGCSE
(Syllabus 0610) and is fully endórsed
by Uñíversity
of Cambridge tnternational Examinations (Clf). Cíf
IGCSE Principal Examiners have been involved
in all
aspects of the book, including detailed planning
to ensure that the content gives the best match
possible to their syllabus.
Using this book will ensure that you are well
prepared for the Biology IGCSE examination
and
for studies beyond IGCSE level in pure sciences, in
applied sciences or in science-dependent vocational
courses. The features of the book outlined below
are designed to make learning as interesting and
effective as possible:
. These are at the start of each
spread and willtell you what
you should be able to do at
the end of the spread
c
.9
c
a)
x
t¡.t
.
Some outcomes will only be
needed if you are taking paper
3 and these are clearly labelled,
as is any Supplementary
content in the spread
EXAMINER SAYs...
thLs.provLdes a chawce
To r th e. tqes E priwcL¡
aL
Ç. xawLwers
to ,tnare-i[,ei,
expe.ñ.ewoe
gf wawg
Aeafs warleíwq awd
tr*t^ø exawLiatLows
i:X"u::^yy"riJi,H""
,
i
-.
cowwow errors
or gLve
advLce ow how
\t.f!L
to
taclzLe
1uêstLows.
ÞID YOU KNOW?
These are not needed in the
examination but are found
throughout the book to
stimulate your interest in biology.
PRACTICAL
These show the opportunities for practical
work. The results are included to help you if
you do not actually tackle the experimánt
or are
studying at home.
These summarise the most
important things to learn from
the spread.
SUMMARY QUESTIONS
Ihese questions are at the end of each spread
and.allow you to test your understanding of the
work covered in the spread.
At the end of each unit there is a double page of
examination-style questions written by the véry
CIE
-aiology
Examiners that set the papers for the
06t 0
exams. ln most cases the questions are only set
on the
contents of the unit. ln the examination you will
find
questions that deal with the contents of iwo
or more
units. ln Papers 2 and 3 you may have to complete
graphs by adding labels and unrts for axes, plotting
points, adding bars to bar charts or joining points
or
giving lines of best fit. you will not have tõ
draw the
axes yourself. You can also expect to have photographs
which are not included in these questions.
At the end of the book you will also find: Alternative
to practical' section - this provides guidance if you
are taking Paper 6 instead of coursework or the
practicaltest.
A useful Revision checklist is also provided to help
you prepare for the examination in paper 1,2
and 3.
.
List the characteristics of
which are
Biology is the study of living things or,livìng organisms'
kingdoms:
ctass¡iãd into five major groups called
(bacteria)
animals, plants, fungi, protoctists and prokaryotes
.
living organisms
Describe the characteristics of
living organisms
These
There are seven characteristics of living organisms'
processes:
characteristics are often described as life
respiration, movement, growth, excretion' sensitivity'
L
ì ,-rt ìlrliiirliÍ r iíilili l{ i{r,ii/1,
),
nutrition,
reproduction.
Nutrition
and substances
Nutrition is the obtaining of food to provide energy
that may
compounds
are
Nutrients
..lJà¿ for growth and iepair.
or
complex (like carbohydrates, proteins and vitamins)
simple (like mineral ions).
in which the
Nutrition in green plants involves photosynthesis'
dioxide
carbon
turn
to
used
änd
.î"tgy ttotiunlight is absorbed
sugars
plants
simple
these
convert
then
ãnJ *.,., into siriple sugars.
need
They
proteins'
and
cellulose
into complex compounds", such as
proteins'
mineral ions from the soil to make
;i;;g. ;.i
Salmon provide nutrition for bears
EXAMINER SAYS...
ætspLratLow Ls the reLease
of ewergg front" food that
ha;p1ws Lw aLL the LLvLwg
oeLLs.Lwthebodg. ttLs
wot breathLwg, whLch
ha¡qews Lw orgaws, sttoh
'Ø# ØLtts or Lwwgs.
plants, so they have to eat
Animals cannot make their own food like
nutrients' The process of
and
pìu'nit ãt ã,Áei animals to gain energy
is digested, absorbed
food
The
i;kì.é in tooa is caileJ ingästion.
growth and repair'
for
cells
by
rt" af..'à blood and then aisimllated
in faeces'
egested
is
iooO *t"'l.f-, is not digested and absorbed
Respiration
energy' Respiration
All living organisms respire because they all,,need
down
iÀuotu.i.ftãtlcal reactíons that occur in cells to break
is
nrti¡.ntt, such as glucose, to release energy Oxygen usually
for
nã.i.0 for respiraion to happen' This is the word equation
respiration involving oxygen:
glucose
+ water + energy released
this energy for movement' growth' repair and
+ oxygen --->
Living things use
carbon dioxide
reproduction,
Movement
themselves into new
Organisms move themselves or move parts of
areas or to change Position.
move down into the
Plants move slowly when they grow' Their roots
the light' Leaves can
towards
soil and their leaves and stems move up
light as possible'
much
as
move to face the Sun so they can absorb
Most animals are abre move their whore bodies. They move
to obtain
their food or to avoid being caught by predators. some
animari
remain fixed to one prace throughouf their rives, but
they ur"lor. to
move parts. such as the tentacles on a sea anemone.
Growth
Growth
is a permanent increase in size and the dry
mass of an organism.
It can involve an increase in ceil number; ceil size
or both. rt arwãyiinvolves making more comprex chemicars, such
as proteins, *r,"'r-.,-i, *hy
the dry mass increases. prants carry on growing throughout
their rives.
Animals stop growing when they rea.h a certain size.
Sea anemone
Excretion
EXAMINER SAYS...
All living organisms produce toxic (poisonous) waste substances
as a
result of metabolism. Metaborism is ail the chemicar
reactions
occur in an organism. Respiration is a major part of
metabolism.
tÀat
Excretion is the removar of these waste substances
from the body.
Plants store waste substances in their reaves, so
the waste chemiäars
are removed when the reaves fall off. Animars breathe
out carboÀdioxide; other waste substances leave the body in the
urine.
Excre{øwktherew
,^*r^brf*;;;:;;";i:!:{
tsþodwhLchhasãsx;ea
i:f
th e g
o
ut
wíth
"Ø1.
oeun4
dþæted.Þo
o
ut
not
oowfuse the two
terA^.s.
Sensitivity
Living organisms are able to detect or sense changes
in their
environment. A change rike this is a stimurus (pru"rar:
stimuri)
sensitivity is the abirity to detect these stimuri and
respond to
them.
Plants respond to movement of the sun by moving
their reaves to face the
light. The flowers of some prants open ¡n ihe morÃing
and crose at niéHt
Animals have sensory ceils.and sense organs for deteáing
tigrìt, sãun¿í,
touch. pressure and chemicals in the air and in food.
Reproduction
organisms reproduce to make new individuars. Asexuar
reproduction
involves one parent giving rise to offspring that
are often idänticar to
each other and to the parent. sexuar reproduction
invorvesiwå pur.na
organisms producing gametes (sex ceils) which fuse
to give ,.iru to
next generation. The offspring show variation. They
areïot i¿enticario
each other or to their parents.
t"
lí.1 I
)i;'
lÌ'1r
))r
t')iirl,,
The mnemonic, 'Mrs Gren,
can help you remember the
seven characteristics of living
organisms:
Movement causes an organism
to change its position or place.
Respiration involves chemical
reactions that release energy
in cells.
SUMMARY QUESTIONS
Sensitivity is being able to detect
and respond to stimuli.
1 A visitor from outer space lands on Earth. The first
thing that
it sees is a motor car passing by.
Growth is a permanent
increase in size and mass.
a
b
2
two reasons why the visitor thinks that the car is arive
Give two reasons why you think that the visitor
is wrong.
Give
Plants and animals are
Reproduction results in the
formation of new individuals.
Excretion is the removal of
two groups of living organisms. Find
out and then describe how prants differ from animars in
the
waste chemicals made in the
cells during metabolism.
a feed, b
Nutrition involves the use of
food for energy and growth.
ways in which they:
move,
c grory d
use their senses.
I
ir l^)'lliìù1ll lÌÑl(i,l
.
j)ili.l r({'l())iùf
j
lÌ
L',;
Define the term binomial
system
.
Describe the external features
of three invertebrate PhYla:
nematodes, annelids and
molluscs
. Describe how the animals
in
these phYla are adaPted to
their environment
grouping is the
We classify organisms into groups The largest
is the species.
smallest
the
LingJor'treã previous spread) and
For
features'
similar
ïÀuîtgun¡its in a kingdom share some
carry
and
green
plants
are
all
.*utpí., within the plãnt kingdom,
known
groups
into
is
subdivrded
ári ptloiot¡lnthesis. Each kinglom
three
with
we
deal
spread
(slnsular: phvlum)' ln this
;;;;,ii"
within the animal
,rJr-rór-,vrà (nÉmato'deí annelids and molluscs)
are named'
organisms
how
But first we must explain
f.i.òi"t
The binomial sYstem
type of mongo-ose
Meerkat, suricate and Sun angel are names for a
confusion
tf,ui ¡u.i in the Kalahari Desert in southern Africa. To avoid
system
binomial
àrganisms are given scientiflc names using the
(binomial means'two names')'
They live in the
A species is a group of individuals that look alike
which are fertile
give
offspring
to
together
same habitat añd breed
and can also breed together'
f
two names: the first name is for the genus
applies to one species
and the second name is the trivial name that
be used on its own'
never
genus. The trivial name should
Each species is given
*iif.ù
the
but.do not
A genus is a group of species that are closely related'
(plural of genus) only
intÉrbreed wúh each other. Some genera
This may be
consist of one species, as is the case with meerkats
because other species in that genus are extinct'
the world as it is
The binomial system is used by biologists all over
The table has some
organisms
an internationál lungrug. for naming
examples.
A meerkat.
EXAMINER SAYS...
æcvwevwber that the
waywe of a speoles Ls
both
wînLes. tf a wavt*e has
beew vtsed owoethewLt
oaw be shovtewed LLÞe
thís: ..........Ft sa¡Lews.
L-"
common name
scientific name
meerkat
Suricata suricatta
human
Homo sapiens
baobab tree
Adansonia
cholera bacterium
Vibrio cholerae
malarial parasite
Plasmodium falciParum
oyster mushroom
Pleurotus ostreatus
lnvertebrates
column
lnvertebrates are animals that do nof have a vertebral
orbackbone.onthenextpageisinformationaboutthreephylaof
invertebrates: nematodes, annelids and molluscs'
Nematodes
Nematodes or roundworms are a group of worms
that have thread-rike
bodies that taper at mouth and ar,rs. ihey have no
obvious head and
no legs. Their bodies are not made up of segments. Most
are very tiny
and live in soils and water. There are many tlpes of nematoder,
species are parasites living inside another aïimal,
the host.
1\
t\,(
ár"
\
Annelids
Annelids are worms with soft bodies made up of segments.
Some
have paddle-like extensions for moving and they
harie chaetae or
bristles.for making contact with mud ór soir. Most species
of annerids
live in the sea, but some live in the soil and in fresh
water frtrurrr,
lakes and rivers).
\
Ascaris lumbricordes, a parasitic nematode.
DID YOU KNOW?
Ascaris lumbricoides is a parasitic
nematode that lives in the human
gut. lt absorbs digested food and
can grow to a length of 30cml
Earthworms burrow through soil. Io help them move
through the
soil, earthworms have a pointed front end to their
oooy unjtt àf
make mucus as a lubricant.
Molluscs
Molluscs have soft bodies that are not segmented.
They have a
muscular 'foot' that they use for burrowiñg or movement.
Many
species of molluscs have one or two sheils for protection.
the animar is
able to retreat inside the sheil if a predator is ciose
by, or if Ú,uv n"uJ to
avoid excessive water ross. some, rike the octopus, do
not havé a sheil.
Other animals in this phylum are snails. slugs, clams
and squids.
Bearded fireworm
-
an annelid
1 Copy and complete the sentences using the words
below:
fertile genus shared trivial
classification binomial breed
The system of putting organlsms into groups is
cared
The
system is used for naming organisms. Each organism
has
two names. The first is called the
name and the second
the
name. A species is a very similar group of individuals
-.
,1u,.:uL
rogether and prodlce
classify living things on the basis of their
2
3
a
b
a
b
-
_
-
_-
Banded snaii
lil r i'
2 A species
is a group of
individuals, living in the same
habitat that breed together
to produce fertile offspring.
3
lnvertebrates are animals
without a vertebral column
(backbone).
4
Three invertebrate phyla are
nematodes, annelids and
them alongside their common names.
4 ln the l Bth century,
Carl Linnaeus worked out the binomial
system of naming living things. Find out about
his life and
work and then write a brief biography in your own words.
"lrìr r¡iil:,,
the genus name and the
trivial name.
Explain the term binomialsystem.
Find the scientific names of two plant species
and two
animal species not mentioned in this spread and write
a mollusc.
1 The binomial system uses
two names for each species:
featurãs.
State three ways in which nematodes differ from
annerids.
State two features that are shown by both annelids
and
molluscs.
-
molluscs.
Arthropods
kingdom as it
Arthropods is the largest of the phyla rn the animal
in this phylum
contains the largest number of species' Each species
and
(exoskeleton)
ñãr u t.g*"nteá body, an external skeleton
LEARNING OUTCOMES
.
Describe the external features
jointed legs.
of arthroPods
.
dry land When
The hard exoskeleton allows arthropods to live on
and grow a new
moult
they
they grow too bi9 for their exoskeleton,
Describe the features
of nsects, crustaceans,
moult during the
ànã. Éotu mouliall through their lives, others only
early stages of their life
i
arachnids and mYriaPods that
are used to classifY them into
.
classes
Eachphylumisdividedintoclasses.Wewillnowconsiderfourofthe
Describe how the animals in
these classes are adaPted to
classes in the arthroPod PhYlum:
crustaceans, myriapods, insects and arachnids
their environment
Crustaceans
(head-thorax)
Crustaceans have a body divided into a cephalothorax
a very
provides
that
anJ aOdomen. Many have a chalky exoskeleton
have
Crustaceans
predators
hard and effective protection against
between
two pairs of antennae and compound eyes They have
gills'
using
five and 20 pairs of legs. They breathe
on land but return
Nearly all crustaceans live in water' Some crabs live
some land
to wáterto breed. Woodllce (also known as slaters) and
crabsareexceptionsastheydonotUseWaterforbreeding.Examples
of crustaceans include crabs, shrimps, crayfish and lobsters'
Woodlouse or slater. Notìce its antennae for
detectrng stimuli
Myriapods
centipedes and the millipedes They have long
bodies made uP of manY segments'
such as the thorax
Thelr bodies are not divided into separate regions
each segment
and abdomen. Centipedes have one pair of legs on
many segments
how
upon
depends
legs
of
so that the total number
have powerful
They
carnivores'
fast-"moving
are
th.r. ur". Centipedes
These are the
)'
D
rfÉ-%,t
jaws and can ParalYse therr
PreY'
TheV a19.
Millipedes have two pairs of legs on each body segment
in leaf litter
you
feeding
them
find
cãn often
slow-moving herbivores.
,
Sally lightfoot crab, Grapsus grapsus Notice
its large claws for feeding and defence
Millipede - with its manY legs for
moving efficientlY.
Centipede
-
a fast-moving carnivore
lnsects
lnsects have bodies that are divided into three parts:
head, thorax
and abdomen.
On the thorax there are three pairs of legs and many
species have
two pairs of wings. They have one pair of antennae on the
head and
compound eyes that are made of many tiny individuat
.orpoÀ.nir.
Th,ey breathe.through holes in the sides of ihe
thorax and abdomen
called spiracles.
lnsects have colonised most habitats in the worrd,
arthough there
are very few species that rive in the sea. Two reasons
whyihey are so
successful on rand is that they are covered by a
waterproof cuticre
that stops them losing too much watel and they can
Monarch butterfly, Danaus plexippus.
Notice its wings for its migration over
long distances.
fly!
This,is th.e largest group within the arthropods.
Examples include
beetles, flies, locusts, cockroaches, dragonfries, butteifries,
bees and wasps.
rotÀr,
Arachnids
These arthropods have bodies divided into
and abdomen.
two parts, the cepharothorax
Arachnids have four pairs of legs and no wings. They
have no
antennae but do have several pairs of simple. not compound,
eyes.
They paralyse their prey with poison fangs. spiders
are abre to weave
silken webs with their spinnerets. This ãrass of arthropod
arso
includes scorpions, ticks and mites.
1
a
b
c
Name four classes of arthropod.
List the key features
of insects.
State three ways in which arachnids look different
from
insects.
2 Distinguish between the foilowing on the
a
b
Tarantula - a large spider with venom to
paralyse its prey.
basis of visibre features
centipedes and millipedes
crustaceans and arachnids.
DID YOU KNOW?
There are over a million known
species of insects and it is
estimated that there may be 30
million species altogetheç but no
one knows.
3 Describe the features of insects that adapt them for living
successfully on land.
4 Copy and complete the table:
feature
number of
pairs of legs
body regions
number
of pairs of
antennae
type of eyes
wings
myriapods
crustaceans
insects
arachnids
lirl iir' i ilt'i tlr '
,
1 Arthropods are segmented
animals with jointed legs and
an exoskeleton.
2 Arthropods
are classified into
four different
classes:
crustacea ns, myria pods,
insects and arachnids
Vertebrates
LEARNING OUTCOMES
. Define the term vertebrate
. Describe the five main classes
.
are called
Animals that have a veftebral column or backbone
made of erther
skeleton
internal
an
have
vertebrates
All
vertebrates.
chordata which includes
bone or cartilage. They all belong to the phylum
the vertebrates.
some invertebåtes that share common features with
of vertebrates using visible,
external characteristic featu res
Describe how these
vertebrates are adaPted to
here are frve maln cl¿sses of vertebrates:
fish, amphibians, reptìles, birds and mammals'
their environment
species' such
Most fish live in water permanently, but there are some
lengths
varyrng
for
water
as the mud skìpper, that can survive out of
of time.
swimmrng and for
Typically, fish are streamllned and have fins for
pressure
frufun.é. They have eyes and a lateral line for detecting
lÀrng.t ìn water. Thãy breathe dissolved oxygen from the waler
,rtg-tt.r"it gills. Their tt in it covered with scales Examples include
tuna, herring, shark, catfish and cod'
I
Fish
for detecting
Unlike fish, the other classes of vertebrates have ears
soundandfourlimbs,althoughsomehaveevolvedintoleglessforms
This dace has fins, tail and a streamlined
shape adaPlations for swimming'
like snakes and some llzards.
Amphibians
most
These vertebrates have smooth, moist skin Although
Fertilisation
uÅpÁiuiun, Iive on land, they return to water to breed.
is external because
inrii"
rp"rt uni eggs are released into the water (not
eggs
u female body). Development is external: the fertilrsed
breathing'
hatch into swimming tadpoles whìch have gìlls for
but when
On land, the adult amphibians breathe usrng lungs'
Examples of
tt.ì.y urà'in wateç they can breathe through iheir skin
,rþhìbiunt include frogs, toads and salamanders'
Reptiles
The bright red eyes of this tree frog are
thought to startle predators, givìng time
for the frog to escaPe
loss They can lrve in
Reptiles have dry, scaly skin to cut down water
to breed'
water
to
return
to
Ji¡l iléi".t as they dó not have
Howeveç
Fertrlisation takes place insìde the female's body
waterproof
development is external as they lay eggs with leathery'
to breathe
lungs
have
iÀells which stop them from diying óut Reptiles
reptiles'
all
are
air. Crocodiles, lizards, snakes, turtles and tortoises
Birds
as wings lVìost
Birds have feathers and their front limbs are modified
cannot
ostriches'
and
penguins
are able to fly but some, like
ãi
deal
to
adapted
beaks
have
Birds have no teeth but different rp..i"t
ifl.t
with different
American crocodile, Crocodylus acutus'
tYPes of food.
Fertilisation is internarand deveropment is externaras
the femares ray
eggs which are protected by hard shells.
Birds are homeothermic (warm-brooded). This
means that they are
able to regulate their body temperature. they can
keep
it .onrtant
even though the outside temperature changes.
Examples
include hawks, eagles, sparrows, parrots and starlings
of birds
Mammals
Mammals are the vertebrates that have hair or fur. Fertirisation
is
internal and so is development. The young develop
in a womb and
they are born already well developui. ru.ñulu mammals
suckle their
young on milk from mammary glands. All mammals,
even aquatil
ones like whales and dolphins, use lungs for breathing
Grey Heron, Ardea cinerea a bird with a
long beak for catching fish.
Like birds, mammals are arso homeothermic,
maintaining a constant
internal temperature. Leopards, bats, dolphins, bears,
leñrurs and
wolves are all mammals.
EXAMINER SAYS...
::.yr,^,
ã rw
Le
tabLe
to
heg gout
e
at
.th fe u r es
u
ytve cLasses. >o
this"¡itn
Lw
the sawc.wag
as showw
t
e
w nuestt ow
+ ow
>,u a nL,,a irirîi åir,,Ír"
,
*
nrî gou L¿qTwthLstopLc.
ÞtÐ Y'ou KNOW?
A chimpa nzee has hands and feet adapted to living
in trees
'l
Copy and complete these sentences using the
words below:
development five wings scaly moist land water
classes breed fly fish fur fãathers
are
There
different groups or
sharks belong to the class called
_
of vertebrate.
and spend ail their
time
Amphibians have
skin and return to
water
Reptiles have
skin and lay their eggs
on
Birds have front limbs that are modifiãd to foiri
They also have
and most are able to
Mammals
or hair and give birth to their young in
an advanced state of
in
to
-.
2
a
b
c
_
_-
have _
.-
-.
State the features that are shown by all vertebrates.
Name the five classes of vertebrates.
1 Vertebrates are animals that
have a vertebral column or
backbone.
Give an example of each of class.
3To which
class
of vertebrates does each of the following belong
turtle, bbat, cwhale, dsalamandel esnake,
Í hawk, g shark?
a
Many amphibian species are
threatened with extinction.
Some rare Panamanian golden
frogs were filmed for Sir David
Attenborough's BBC W series life
in Cold Blood. After the filming the
frogs were removed to a zoo to
protect them from disease, habitat
loss and pollution.
2
The vertebrates are divided
into five classes:
fish, amphibians, reptiles,
birds and mammals.
Microorganlsms
or
Bacteria, viruses and fungi are all microorganisms
(see page 2)' Viruses are
kingdoms
in-separate
are
fungr
Bacteria and
so they are
Ãåì-firi"g organiims like the others we have considered
microbes'
LEARNING OUTCOMES
.
State the main features of
bacteria, fungi and viruses
.
Describe the adaPtations
classified in a different waY.
dead and decaying
Many species of bacteria arrcì furrgi break down
(see
page 230) Some
matérial and these are called decòmposers
food' for
our
making
in
used
spà.ie, of bacteria and fungi are
use of
made
have
We
wine
.*rÀpf . yoghurt, bread, ch-eese and
cause
that
Microbes
(see
page
22'l)
iígãnetic engineerìng
of each grouP to their
environment
;i;;tJt
disease are called
Bacteria
EXAMINER SAYS...
:Èactewa
you can see in the diagram'
Bacterìa have a simple cell structure that
in
are spherical and some are rod-shaped Many exist
length
in
short chains of cells. Most bacteria are a few micrometres
(One
microscopes
electron
and
light
with
and can only be seen
mrcrometreis one-thousandth of a millimetre )
iåÀe Ou.t"ria
awd,fingL
reprodvtceto gLvehwge
o{ LwdLvLdwak.
Mawt¿ do wot swwLve as
theg do natf,wd a s,,útabLe
þ o d s ovwce. e,qro dwctLo w
wwvwb ers
to gLve tnrge wwvwbers
owe adaytaú,owtotheLr
waA of LLfe.
Bacterialcellsaresurroundedbycellwalls.Thecellsofsomebacterlal
species are surrounded by slime capsules'
the cytoplasm Bacteria
There is no nucleus, just a loop of DNA within
c.alled
often have addition;l loops of DNA inside their cytoplasm
Ls
pluifnia,
stored
cell wall
food
;t),.:-
re5efve
a
o
a
a
membrane
..:
o
es
loop of
p lasmid
DNA
Figure
(see page 221).Thestructure
of bacteria differs from animal
mitochondria. some
ãnJôf un* cells as ihey do not have chloroplasts or
(singular flagellum) for moving
bacteria have extensions called flagella
through water or other fluids'
-ÞEE"
flagellum
Pathogens'
1.5.1
A tYPical bacterium
water and in the soìl'
Bacteria are found everywhere- rn the atr' in
20 minutes' so it
every
divide
may
gooO conditions, bacteria
UnJ.r
of bacteria that you
does nõt take long to have a very large number
just one cell'
from
starts
colony
can see on agar as a colony. fach
food source The food
Bacteria feed by secreting enzymes onto their
are absorbed.
L broken down and simfile mtlecules such as sugars
such as heat' cold and
Bacteria which can survive harsh conditions'
have a protective
These
cells
their
drought, produce spores within
.ou"ñng so they can survive for a long time When suitable
.ánJ¡tiãnt retuin, the spores germinate and divide agarn'
Fungi
are also vrsible
Fungi are visrble under a light microscope.' Many
yeasts are
although
multicellular
are
fuÃ9i
Most
to tñe naked eye.
out
,i.öi...rr.J. Each cell has ã nucleus and cellwallwhich is made and
chlorophyll
of Ër,itin, not cellulose as rn plants. They do not have
cannot carry out PhotosYnthesis'
Staphylococcus, a type of bacterium'
The main fungus body is called the mycelium.
lt consists of a
a.
branching network of threads or hypñae which grow
over the surface
of its food source, releasing enzymes which digest the
food ortriiå
the fungus. The digesred food ilthen absorbed by
the hyphae.
Fungi reproduce by making spores that can be
carried by the wind.
Most fungi are saprotrophs, which means they feed
oÁ O.u¿ o,.
decaying matter, but some are parasites.
Viruses
Viruses are extremery smail; far smailer than
bacteria and fungi. For
example, the virus that causes infruenza is about
120 nanometres in
?.
Bread mould, Rhizopus nigricans. The black
structu res contain spores.
size. (one nanometre is one-thousandth of a micrometre.)
Viruses are
only visible under an electron microscope.
Viruses are not cells. They are parlicres made
up of genetic materiar (DNA
or RNA) surrounded by,a protein coat. The genetic
irateriar ¡t lãÀpàrø
of a few genes that code for the proteins thãt form
;;tl.
the coat ..d
other proteins that herp it reproduce. Viruses are parasites
that enter the
cells of ano-ther organism (the host) in order
to murtipry. Viruses take over
the host cell and direct it to make new viruses.
rial
protein
coat
ce
proteins
lf you breathe in the viruses that cause cords or infruenza,
they enter
the cells of your nose and throat. Here they reproduce
and make
lots of new viruses. These are abre
even more viruses.
to invade more ceils to make
Figure 1.5.2
Structure of a human vlrus
Viruses can be very harmfu.l because they can
reproduce so quickly
and do not respond to antibiotics. They ãre constantry
changing iÁto
new strains.
KEY POINTS
1 Copy and complete the sentences using the
words below:
nucleus decay inside parasites hyphae
protein antibiotics reproduce colony genes
Viruses are not cells but are made up of a few
surrounded
by a
coat. Viruses are
that can only reproduce
healthy cells. Bacteria are cells with no
very quickly to form a bacterial
_
are cells but have no
nucleus. Ihey can be seen
under a light microscope.
2
Bacteria inside the human body can be killed
by chemicals
called
Fungi are made up of a networkof threads
. Fungi act as saprotrophs when they cause dead
materials to
_.
3
a
e
cholera,
b
typhoid,
athlete's foot,
f
c
tuberculosis (TB),
candidiasis.
d
syphilis,
Viruses can only be seen under
an electron microscope. They
are not cells but a few genes
inside a protein coat.
4
Viruses are parasites
that invade healthy cells,
2 Each of the following diseases
is caused by a bacterium or
fungus. ln each case, state whether the páthogen (disease_
causing organism) is a bacterium or a fungus
and then find
out how the disease is spread:
ln favourable conditions.
bacterial cells can divide
quickly to form a colony.
_
-
_.
called.
1 Bacteria
reproducing to produce
many new virus particles.
5
Fungi are made up of threads
called hyphae. These grow
over the food supply, digest it
externally and then absorb it.
Flowering Plants
Features of flowering Plants
LEARNING OUTCOMES
.
Describe the main features of
flowering Plants
.
State the differences
between dicotYledons and
Like all plants,
colour
flowering plants are multicellu.lar' They are green in
chloroplasts
many of their ãells contain chloroplasts. These
for
light
absorbs
which
.oÀiu,n the gieen pigment chlorophyll,
cellulose'
of
made
wall
cell
a
by
pÀoiotyntf'.r"tis. Each"cell is surrc'urrclecl
n.iurrå
They have transport
Flowerrng plants have stems, roots and leaves
;";tisting of tiny tubes These a.re called xylem vessels'
;Áì;h .rr.ty wateiand m¡neral salts, and phloem tubes' which
monocotYledons
;yti;;;
transport dissolved food.
which make seeds'
Flowering plants reproduce by means of flowers
flower'
the
within
ovary
the
rÁe seedi are produced inside
apical bud
Shoots and roots
ground The shoot is made
The shoot is the part of the plant above
rs
,p J u-rt". bearing leaves, buds and flowers The apical budthe
supports
stem
iÅ" purt where the stem grows new leaves The
leaf
de buds
stem
so that they can
root
main root
food
r00t
Figure 1.6.1
structures of the shoot, u-nd tpu..t out the leaves
;;..ir; adequare light and air (see page 66.) tr holds the flowers in a
position which enables pollination to take place'
soil up to the leaves and
The stem allows transport of water from the
the roots'
from the leaves to other parts of the plant' such as
Structure of a tYPical
dicotyledonous Plant
below ground'
The roots are the parts of flowering plants found
Roots
chlorophyll
contain
noãt, ur" usually white since they do not
being
from
it
prevent
uÃihot the plani firmly in the ground and
and mineral ions
blown ou"r by the wind. Roots also absorb water
from the soil (see Page 90)
Dicotyledonous and monocotyledonous plants
EXAMINER SAYS...
groups:
Flowering plants can be divided into two main
lwthe
exat4,L
dicotyledons and monocotYledons
etw
w.fLow
uou vway be
a sk ed ab o,,+t"dLfþ,e,í"
r,
erLwg ¡ La ra,ts
awd awL,rwaLs. Note awd
Learw the dLfferewces
t w ceLL structwre awd,
rqrodutotLowthat aye
b
ee
desorLbed here.
"
,gÈ-j.
Magnolia is a dicotYledon
lrlaize, Zea mays, is a monocotyledon
Dicotyledons look like the plant at the top of the opposite page.
Their leaves are often broad with a network of branching
veins. The
parts of the flowet for example the male parts known
aí stamens,
are in multiples of four or five in each frower. Dicotyredons
have two
cotyledons (seed leaves) in a seed.
Grasses and cereals, like
monocotyledons.
EXAMINER SAYS...
Both these grouLps
ju:ow a Lot of varLatLow,
¡or exan*pLe wot aLL
the maize plant opposite, are
wow,ocot!)Ledows
The leaves of most monocotyredons have parailer veins. Grasses
and
cereals have long, narrow leaves. other monocotyledons
have leaves
with a variety of shapes, such as those of parm trees. The parts
of the
flower are in multiples of three. Monocotyredons have one cotyredán
inside each seed.
p-ara,LLeL
veLws.
sqecLes used
have
,4wg
Lwthe
exawLwatLow
wLLL
have
,,- cne teatLtres gLvew here.
t
PRACTICAL
Comparing dicotyledons and monocotyledons
Obtain two plants, one a dicotyledon and the other
monocotyledon.
leaf of
dicotyledon
clusters of fl
a
leaf of monocotyledon
Compare the shape of their leaves and look carefully
at the
leaf
pattern of their veins.
How do they differ?
Figure
1.6.2
ln what other ways do the two plants differ?
Structure of a typical
monocotyledon plant
Make labelled drawings to illustrate your answers.
SUMMARY QUESTTONS
1 Copy and complete the sentences using the words below:
KËY POINTS
I
parallel two narrow flowering
broad network one
Monocotyledons
with
are
plants that often have
veins. They have
cotyledon tnside
_
the seed. Dicotyledons often have
leaves with a
of veins. They have
cotyledons inside each seed.
leaves
2 Find the names of five dicotyledonous plants and five monocotyledonous plants that grow where you live.
3Fi nd out and list the functions (jobs) of each of the followi ng
a leaves, b stems, c roots, d flowers.
Flowering plants are
multicellular - each cell is
surrounded by a cellulose
cell wall and those in leaves
and some stems contain
chloroplasts.
2
Monocotyledons have one
cotyledon in their seeds and
leaves
3
with parallel veins.
Dicotyledons have two
cotyledons and broad leaves
with a network of branching
veins.
Sorting things out
.
Toidentifythenameofaplantoranimalyoucouldlookthroughthe
Use simple dichotomous keYs
to identify
Plants and animals
pi.trr",
would
iÁ a book until you found the right one. However, that
take a lot of time and effort'
. ldentify
external features of
animals and Plants that are
useful for making a keY
start
n0
yes
ln this section, we have used
has it got
a shell?
external features to identifY and
classify organisms. Cladistics is
the method used bY scientists
to classify organisms using
other features to show how
they evolved. TheY use manY
techniques including comParing
earthworm
has it got
6 legs?
I
spr0er
I
2 pairs of
the DNA of different sPecies to
see how closelY related theY are.
housefly
Figure
1.7.1
A branching d ichotomous
keY.
dichotomous keys to identify living things'
Dichotomous means dividing into two'
Scientists use
key
A key has a number of steps - you can see them in the branched
branching
in
the
and the numbered key on this page At each step
and
fuy Vo, find a question or statemènt' Start at the beginning
un,*.,,yes,or,no,to the first question or Statement.
This takes you
to anothlr question or to an identifrcation. Use the branching
above to identify the animals to the left'
key
Usethenumberedkeybelowtoidentifythesameanimals.ltisset
way' Start
àut differently from the first key, but it works in the same
stage'
each
at
questions
the
at the beginning and answer
legs
Has no legs
2 Has 6 legs
Has 8 legs
1 Has
Go to 2
Go to 4
Go to 3
SPider
3 Has 1 pair of wings HouseflY
Has 2 pairs of wings WasP
4 Has a shell
1,,7,2
:
Five invertebrates'
Has no
shell
Snail
Earthworm
PRACTICAL
Making a leaf key
Now try making a key of your own.
EXAMINER SAYS...
different leaves and label them A to F.
Put the six leaves out in front of you.
Think of a question that will divide them into two groups.
Take six
Write down the question.
Now think up questions to divide each group into two.
Write these down.
ylt:waFzLq
a þnu.
::Lze'ßasyj ? sooa{iature
,
LLví.vtøthLi,As
::e
uoy so wqchL*sLzí.
Ll*
t
Carry on until you come to the last pair of leaves.
Write out your key as a branching key or a numbered
key.
EXAMINER SAYS...
Pond animals key
,::,:,^
wtLL :
ua wivwtLo w
owLA
Now try making a key of these pond animals below
!As,
haveb
damsel fly larva
I
**
water
Y4t
Lt
usuaLLg wuwbered
r<eUs yath er th
freshwater
shrrmp
Ao
vLse
,fo"wíLL
a
w b ra n¿h ed
wothaveb
aevLse owe
gourseLf.
beetle
water
1
scorpion
pond snail
sna il
Figure 1.7.3
Pond animals
Dichotomous keys are used
to identify organisms, such
plants and animals.
2 A dichotomous
key includes
a series of paired statements
or questions which lead to an
identification. Dichotomous
means dividing into two.
SUMMARY QUESTIONS
1 when a scientist visited an isrand she discovered
some insects.
She made some drawings and brought them back
to the
laboratory. Her drawings are shown on the right.
a
b
Give each insect a suitable name.
Make a dichotomous key to identify them. present your
key
either as a branching key or as a numbered key.
2 write down the features that wourd enabre you to crassify
a fish,
an amphibian. a reptile, a bird and a mammal. (you
can üse the
photos on pages B and 9 to help you.) Now make
a key that you
could use to identify each of these vertebrate groups.
as
lf
.r.Hz..
^aå
EXAM-STYLE QUESTIONS
SUMMARY QUESTIONS
1
Write definitions of the following terms:
excretion, growth, movement, nutrition,
reproduction, respiration, sensitivity'
2 The binomial system is used to give scientific
names to organisms. State what the two
words in a binomial, such as Homo saplens'
stand for.
3 Write out the full scientific names of the
following:
meerkat
malarial Parasite
American crocodile
maize
Monarch butterflY.
4 List the external features used to identify the
following PhYla of animals:
annelids, arthropods, molluscs, nematodes'
5 List the external features used to identify the
following classes of the arthropod phylum:
arachnids, crustaceans, insects, myriapods'
6 Vertebrates are divided into five classes'
Name these classes and state three external
features shown by the animals in each class'
7 State the differences between
monocotyledons and dicotyledons that
are used to classify these two groups of
flowering Plants.
8 State what is meant by dichotomous when
used in the term dichotomous keY'
9 List the main features used to classify the
following groups of microorganisms:
1 Which process is carried out by all the
orgattisttts tlrat live in a forcst?
A moulting
B photosYnthesis
C pollination
D respiration
(Paper 1)
tll
2 What are characteristics of all organisms?
A excretion and resPiration
B Ingestion and growth
C photosYnthesis and egestion
D respiration and PhotosYnthesis
(Paper 1)
tll
3 Which group of animals includes those with a
segmenled body, an exoskeleton and jointed
limbs?
A annelids
B arthroPods
C molluscs
D vertebrates
(Paper 1)
tll
class of vertebrate includes those with
dry scaly skin and four legs?
4 Which
A amphiblans
B fish
C mammals
D reptiles
(Paper 1)
tl
5 The drawings show five animals, A to E' They
are not drawn to scale'
viruses, bacteria. fungi'
10 Explain how viruses, bacteria and fungi are
adapted to s urvive in their environments.
c
D
E
l
(a) Name (i) the phylum, and (ii) the class
into which each of these animals, A to E,
is
classified.
(a)
rcl
(b) Give three reasons for the choice of
phylum, and one reason for each choice of
class that you made in part (a).
til
(Paper 2)
6
(i)
ldentify the group of flowering plants
to which each species belongs.
(ii)
State the features that you used to
make your
t5l
(b) List five features shown by the leaves
identifications.
that would be useful in devising
a
dichotomous key to identify species of
flowering
Draw and complete the table using ticks and
to indicate whether the four phyla
show the features or not.
crosses
feature
UI
o
ttt
p
a)
c
16
E
o
r!
o
o.
o
a)
c
r^
t^
J
=o
E
ro
til
9 The drawing shows a giant pangolin, Smutsia
gigantea. Pangolins are mammals with bodies
covered in plates made of the protein keratin,
which is also found in skin, hair. claws and
nails. The body covering makes pangolins look
t^
E
plants.
(Paper 2)
similar to reptiles.
E
segmented bod v
lointed limbs
exoskeleton
(a) Explain what the giant pangolin's scientific
name tells us about how this animal is
internal or
classified.
external shell
(Paper 2)
t4l
7 (a) Define the term vertebrate.
tl
l
There are five classes within the vertebrate
group.
(b) List three external features shared by the
following classes of vertebrates:
amphibians. reptiles, birds and mammals.
t3l
(c) State two external features of mammals
that are not seen in reptiles.
t2l
(d) State two external features shared by
amphibians and
fish.
t2l
(Paper 2)
covering.
Bl
(c) Explain why pangolins are classified as
mammals and nof as reptiles.
t3l
(d) Ihe table shows the features shown by
some microorganisms. Copy and complete
the table using ticks and crosses.
feature
vrruses
bacteria
leaves from three species
of flowering plant, A to C. They are not drawn
can make
ca psu les
produce
have
hyphae
scale.
t4l
(e) Explain how:
(i)
a fungus, such as Rhizopus nigricans
shown on page 1 1, is adapted to feed
and disperse from one source of food to
another;
(ii¡
(iii)
A
fungi
have nuclei
spores
8 The drawings show
to
pl
(b) State two external features that pangolins
share with reptiles otherthan the body
B
c
ßl
bacteria survive adverse conditions; 12/
viruses increase in
t3l
(Paper 3)
number.
Cells
.
.
Describe the structures of
plant and animal cells as seen
under a light microscoPe
Describe the differences in
structure between Plant and
animal cells
.Re ate the structures seen
under the light microscoPe
in the plant cell and in the
animal cell to their functions
Cellsarethesmallbuildingblocksthatmakeupalllivingorganisms
trih ut bacteria are made of only one cell'
ù"rv iÀrf l living things
one knows
An insect such as a fly may contain millions of cells' No
for certain how many celli there are in a human being - estimates
vary between 10 x 1012 and 50 x 1012'
Plant cells
Animal cells
loroplasts
cell
cell wa
nucl
cytop lasm
cell
membrane
I
A cheek cell (stained
with a blue dye).
A palisade mesoPhYll
cell from a leaf.
Differences between plant and an¡mal cells
Liver cells magnified bY
x300
EXAMINER SAYS...
Whew Uonhaveto state
dLfþreloes betweew
pLawt awd awLn*ak
ceLk, nt"aÞe svLre uow
w r t te s o,rwethLwg ib o,,ct
looth tgpes of oeLL.
summarised in
The differences between plant and animal cells are
this table.
feature
plant cell
animal cell
cellulose cell
wall
present
absent
sha pe
permanent shaPe
determined bY the cell
wall; shapes can be nearlY
spherical, box-like or
shapes vary as there is
no cellwall
cylindrical
chloroplasts
present in some cells
absent
vacuole
large permanent vacuole
containing cell saP
small vacuoles, do not
contain cell saP
nucleus
present (often at the side
of the cell close to the cell
wall)
present (found
anywhere within the
cell)
Functions of cell structures
cell structure
functions
cell membrane
. forms a barrier between
.
.
.
.
EXAMINER SAYS...
cell, e.g. oxygen, carbon dioxide and water
controls movement of other substances into and
out of cell, e.g. glucose
often described as partially permeable
of
awd paú.sade
wesophgLL ceLLs,
LabeL
the struott{res awd,
uwd,erweath eaoh
,
LabeL
wntethefuwotiows.
þu
yovtr dLagrawb
:o-:
"r,
neup gonr revLsLow.
. controls all activities in the cell
. controls how cells deve lop
cytoplasm
.
chloroplast
. photosynthesis
. stores starch
. stops cells from bursting when they fill with water
. gives shape to cells
. allows water and dissolved substances to pass
cellwall
t
surrou ndings
keeps contents of cell inside
allows simple substances to enter and leave the
(see page 28)
nucleus
d.rawLwgs
I?-,"t
tver oeLLs
the cell and its
place where many chemical reactions take place,
e.g. respiration and makin g proteins for the cell
-=
through freely (often described as freely or fully
permeable)
sap vacuole
.
.
full of water to maintain shape and ,firmness, of
cell
stores salts and sugars
Cells of
onion epidermis magnified by x250
SUMMARY QUESTIONS
1 Copy and complete this table by using ticks and crosses to
indicate if the structures are present or not.
cell
cheek cell
structures
(animal)
onion cell
(plant)
leaf cell
(plant)
nucleus
cellwall
large vacuole
1 A cell membrane. cytoplasm
and a nucleus are found in
both plant and animal cells.
cytoplasm
2 All plant
chloroplasts
c
o
a)
x
t¡J
2 State the functions of the following parts:
a chloroplast, b cell membrane, c cell wall, d nucleus
cells have a
cellulose cell wall; some have
chloroplasts and a vacuole
containing cell sap. Animal
cells do not have these parts.
Different tYPes of cell
cells
To function efficiently, many-celled organisms have
LEARNING OUTCOMES
. ldentify different
.
tYPes
of
cell from diagrams and
photograPhs
Relate the features of these
cells to their functions
.
Calculate magnification and
actual size of biological
specimens using millrmetres
as units
ciliated
cells
cilia move
mucus alonq
these cells
make
Specialised cells
(trachea and
Ciliated cells are found in the air passages in the lungs
bronchi)andintheoviductsinthefemalereproductivesystem.These
to create
cells have cilia on their surfaces. cilia beat back and forth
current in the fluid next to the cell surfaces'
a
pathogens
ln the airways, cìlia move the mucus that traps dust and
egg from
the
move
cilia
oviducts,
,p to tt',. nóse and throat' ln the
the ovary to the uterus.
\-J
C
0 C
surface
Root hair cells have long extensions that give them a large
area to absorb water and ions from the soil'
xylem vessels
root hair cells
Figure 2.2.1
that are
that the functions
specialised to carry out certain functions. This means
cells'
of
groups
different
of the body are divided between
produced. These
ãrguÀiffi ievelops from a fertilìsed egg, new cells are
functions. ln
certain
for
specialised
i"í, gro* and change to become
cells'
specialised
of
examples
this ipread we look ãt tom"
Ciliated cells line the
airways.
c
o0
o
o
a l^t
EXAMINER SAYS..,
Whew expLaLwLwg how
a ceLLLs adaptedto Lts
fwwctLows ttralze sure
gow gLv e the stntctt LraL
featwres awd sat¿ how
each owe hel¡s the
caryr¿ ottt Lts
ceLL
fwwctLow.
Þ,-¿
o
co
Figure 2.2.2
Root haìr cells are long
and thìn to absorb
water from the soil.
Figure 2.2.3
Xylem vessels are small
tubes that carry water
up the stem.
Xylem vessels are cylindrical and empty' They are arranged into
.ãlrÀn, like pipes. T-he cell walls are thickened wrth bands or spirals
allow
of cellulose and a waterproof material called lì9nin. These cells
plant
They
the
of
rest
the
to
roots
water and ions to move from the
leaves'
also help to support the stem and
Some
Muscle cells make u p frbres that are able to shorlen or contract
contract they move
muscles are attached to the skeleton; when they
the heart
bones at joints. Muscle cells are also in the gut and in
Red blood cells contain
the protein haemoglobin
red blood cells
(_,
that carries oxygen. TheY are
shaped lrke flattened discs.
muscle cells
Figure 2.2.4
These muscle cells contract
to move bones.
This shape Provides a large
sudace area comPared with
their volume whlch makes for
efficient absorPtìon of oxYgen
Figure 2.2.4
Red blood cells have a substance
called haemoglobin that carries
oxygen.
Size
of cells and specimens
r!
a
0
Look at the photograph of some human cheek cells.
t
The cells are 1000 times larger than in real life.
l
This means that they have been magnified 1000 times.
a
1
I
To work
out the actual size of a cell measure the length of one
magnified cell in millimetres. Let,s say that it measures 13 mm.
t
i;
Now we can use this formula to work out actual size:
So the actual size
of our..¡¡
ì.Ë-'
Human cheek cells.
image size
actual size =
magnification
: --13 :
000
0.013 mm
1
There are 1000 micrometres (!m) in a millimetre. we can convert the
answer to micrometres by multiplying by .1000 to give 13gm.
we can use a similar technique when the image size has been reduced,
as in this photograph of a goldfish. This time ìhere has been a
reduction of actual size in the photograph. lf you calculate the fish,s
actualsize using the sameformula you willfind it is 90mm long.
To calculate the magnification of an image we reorganise the formula:
-
magnificat'on
The image of this goldfish is one third
(x0.33) actual size.
ilmage slze
actual size
EXAMINER SAYS...
Vlhew,vweasnrLwg
o r,o Lo
1 Draw a table matching the type of cell in the first column with
ciliated
cells
long banded threads
wea
Function
keep the air passages
free from dust
muscle cells
xylem vessels
long and thin
have cilia that move
contract (shorten) to
move muscles
transport oxygen
absorb water from the
soil
b¡rk
KEY PO¡NTS
1 During development,
cell, b nerve cell, c white blood cell,
human egg cell, e palisade mesophyll cell.
often their shape.
2
onpageslBandl9.
Specialised cells have a
structure that enables them
to carry out a particular
function, e.g. ciliated cells
have cilia
sperm
3 calculate the actual sizes of the liver cells and the onion cells
cells
change their structure and
2 Here are some other specialised cells. use this book to find out
the functions of these cells and how they are adapted to carry
out their functions.
a
d
sure Lw wLLLl,vuetres,
wever Lw cewtLvuetres.
transport water and
ions
root hair cells flat discs
L specLvwews
specLwews, aLways
its correct shape and function:
Type of cell Shape
red blood cells hollow tube
gL c a
orphotographs of
to move mucus
along the windpipe.
3
We can calculate both the
magnification and actual
sizes of images of biological
specimens.
isation
ll jr :t^ i ,ìr.!litiì1lii
.
.
i|)llll
i¡ i,
r
Tissues and organs
lrilr i '
A group of similar cells is called a tissue. All the cells in a tissue look
thã ,ur. and they work together to carry out a shared function.
Muscle tissue is made up of identical muscle cells. These cells work
together and so the muscle tissue contracts'
Define the terms tissue, organ
and organ sYstem
Describe examples of the
above that occur in Plants
and animals
cells:
the building blocks
organ:
similar cells working
together in the same waY
groups of tlssues working
together
a group of organs working
together
your heaft is made of muscle
and other tissues. lt Pumps
blood around your bodY
vour heart and blood vessels
'make
up your circulatorY sYstem
which carries blood around
your body
=
Æ
æ=
muscle cells contract and
relax
the human circulatory sYstem.
EXAMINER SAYS...
L¿a rw these def,wLtLon s
of
orøaw awd orgaw
sgstent". MaÞe a List of
Ë,LssrLe,
AanLpLes of awLwaL awd,
plar,r,t tíssø es, orgaws awd,
a w sgsten+s
fron,"
lûook.
-----tri<:
cardiac muscle tissue is made
of muscle cells that contract
and relax together
Levels of organìsation in
?rØ
system:
tissue:
th"s
An organ is made up of a group of different tissues that work
together to perform specific functions.
The heart is an example of an organ. lt is made up of different tissues
such as cardiac muscle, nervous tissue, fibrous tissue and blood that
work together to pump blood around the body'
The stomach, lungs, brain and kidneys are all organs'
Different organs work together as part of an organ system' Organ
systems .on"ritt of a group of organs with related functions, working
tågether to perform body functions F91 example, the heart and
blõod vessels work together as part of the circulatory system. Here
are some other organ systems:
. The digestive
.
.
.
system is made up of the gullet, stomach, pancreas.
liver and intestines.
The excretory system is made up of the kidneys, ureters and bladder'
The nervous system is made up of the brain, spinal cord and nerves
The reproductive system in females is the ovaries, oviducts, uterus
and vagina; in males it is the testes, sperm ducts, prostate gland
and penis.
All the different organ systems make up a living organism'
Plant tissues and organs
The diagrams show the tissues in a leaf. The tissue that carries out
photosynthesis in leaves is called mesophyll. The cells making up the
upper layer of the mesophyll are called palisade cells. These cells are
closely packed and full of chloroplasts so that they are well adapted
to absorb lots of light. The palisade cells make up the palisade
mesophyll tissue. All the cells making up this tissue look alike and
do the same function - they absorb light for photosynthesis.
DI.D YOU KNOW?
The word 'palisade' is used
because the cells are close
together líke the wooden stakes
used to make walls known as
palisades.
A leaf is an organ. other plant organs are roots and stems. other
structures, such as flowers and fruits, are modified leaves.
cells; the building blocks
organ: groups of tissues
leaf palisade
tissue: similar cells working
cells absorb light
together in the same way
\
working together
the leaf makes
food and allows
for gas exchange
/
palisade mesophyll cells
u
pper
\|
epidermis
photosynthesis takes place
in the mesophyll tlssue
cells
organism: the
milkweed plant
spongy mesophyll cells
is made up of
0rga n5
lower epidermis cells
Figure 2.3,2
Levels
of organisation in a flowering plant.
EXAMINER SAYS...
1 Copy and complete the sentences using the words below:
organ
system cells tissues
Mal"e suLre
function
wesophgLL
A tissue is made up of
that carry out the same
An organ is formed from a group
working together
An ----.-- is a group of organs working together to perform
several body functions.
-
-.
correct system from those listed on the right.
oaw
ceLL Ls
adapted to carrytt
out
p.hotosAwthesLibu
of
2 Copy out the organs listed on the left. Match
HouL
expLaLw how'a
paLLsade
Lt
st.Ln,g ttne
ft atuft.s a wd
%pLar.wLng how each
owe
ncLÞs.
each with the
:
I
Organs
System
lungs and trachea
heart and blood vessels
digestive
brain and spinal cord
ovaries, oviducts and uterus
gullet, stomach and intestínes
kidneys and bladder
gas exchange
.,-:{u
NETVOUS
I
function are grouped
together to form tissues.
excretory
reproductive
circulatory
3 Arrange the following words into the correct sequence,
starting with the smallest and ending with the largest:
organ
organ
system tissue
organism
Cells that have the same
cell
2
Different tíssues make up
organs which work together
to do a particular function.
3
Different organs work
together as organ systems.
SUMMARY QUESTIONS
EXAM-SWLE QUEST¡ONS
I
1 Which structure
State three structures that are present in both
plant and animal cells.
2 State three structures present in plant cells
that are never found in animal cells.
3 Match the cell types with their functions:
cell type
function
red blood cells
root hair cells
movement of mucus
contraction and movement
absorption of water and ions
muscle cells
xylem vessels
ciliated cells
transport of oxYgen
conduction of water and ions
4 Write definitions of the following
(a) tissue
(b) organ
(c) organ system.
5 (a) Name three animal tissues.
(b) Name three Plant tissues'
.9
o
x
t¡J
6 The following structures are present in both
plant and animal cells:
cell membrane, cytoplasm and nucleus.
State the functions of each of these
structures.
7 All plant cells have cell walls; some plant cells
have chloroplasts and large vacuoles. State
the function of each of these structures.
is
found only in plant
cells?
A cell membrane
B chloroplast
C cytoplasm
D nucleus
(Paper 1)
l
tl
2 Which of the following structures
is
nof found
ìn animal cells?
A cell membrane
B cell wall
C cytoplasm
D nucleus
(Paper 1)
tt
l
tt
l
is the correct sequence, starting with
the smallest and ending with the largest?
A tissue, organ system, organ, cell
3 Which
B cell, tissue, organ system, organ
C tissue, cell, organ, organ sYstem
D cell, tissue, organ, organ sYstem
(Paper 1)
made a drawing of a biological
specimen. The length of the specimen in the
drawing is 140 mm. The magnification rs
x40. What is the actual size of the specimen?
4 A student
A 5600mm
C 35mm
(Paper 1)
B
D
56mm
3.5mm
tl
l
5 The palisade mesophyll cell is a type of plant
cell. A liver cell is a type of animal cell. Copy
and complete the table to compare these two
cells. Copy the table and put a tick (/) if you
think the structure is present and a cross (X) if
you think it is absent.
cell structure
palisade
liver cell
mesophyllcell
cellwall
cell membrane
cytoplasm
nucleus
chloroplast
large vacuole
t6l
(Paper 2)
6 The diagram shows three animal cells.
8 (a) Name:
(¡) an animal cell which does not have a
nucleus;
tl l
(ii)
a plant cell that does not have
nucleus;
(iii) the organ
a
mammals;
A
(iv) the plant tissue that transports
c
B
sugars.
(a) ldentify the cells A, B and C.
t3l
(b) State the functions of the three cells.
t3l
(c) State where in the body these cells are
found.
t3l
(d) Ihe magnification of cell A is x 1000,
Calculate its actual size.
t2l
(Paper 2)
tl
l
system for transport in
tll
tl
l
(b) Distinguish between the following pairs of
terms.
(i)
tissues.
(íi) Cytoplasm and nucleus.
(iii) Cell membrane and cell wall.
(iv) Organ system and organism
Organs and
t2l
t2l
t2l
t2l
(Paper 2)
7 The diagram shows three plant
o
a
cells,
9 (a) Match each cell structure on the left with
its function on the right.
o
nucleus
.aj
oo
D
E
controls the entry and exit of
materials from the cell
cell
full of cell sap as a store of
membrane water and ions
cell
wall
contains chlorophyll and carries
out photosynthesis
large
vacuole
F
(a) ldentify the cells D. E and F.
t3l
(b) State the functions of the three cells. t3l
(c) For each cell, D, E and F, state a plant
organ where it is found. ln each case give
a different organ.
t3l
(d) The actual length of cell D is 0.05 mm.
Calculate the magnification of the
drawing.
t2l
(Paper 2)
place where most chemical
reactions in the cell take place
chloroplast contains the instructions for the
cell
cytoplasm made of cellulose to withstand
pressure of water inside the cell
t6l
(b) A student looked at a cell under a light
microscope. She made a drawing of
the cell and showed the diameter of
the nucleus in her drawing as 70 mm.
She calculated the magnification of her
drawing as x 1 0 000. What is the actual
size of the nucleus?
t2l
(Paper 3)
i
l; Trtllri
iii
ilti r¡ I Ír)1 Lllr
iì
Ìrr) ùrliì
Molecules in gases move about in a random way. They bump into one
another and spread out to fill up all the space available. Molecules in
a liquid do this as well, although it takes longer for them to fill the
space. Movement in a gas is faster as the molecules are more spread
out. The difference in speed between movement in gases and liquids is
rl' i
. Define the term diffusion
. Describe the importance of
.
diffusion of gases and solutes
Describe the importance of
water as a solvent
important for organisms.
This movement of molecules ìs called
diffusion.
water
molecules
ooo
oo
-Oo
^oo
o o
o o
oo
o
at^a
.i'
o
o
before
o
o
o
o o
oa
ôo
o
o
o
o
o
o
o
a
a
o
Õ
diffusion
o
o
o
o¡
o
Whew gor,twrLte
alOovtt ttt"oLeonLes
that are dLffusLwg
tronL owe¡Laoeb
awothev aLwags
swrethat uon
sagtheg,^ou,
fo**
the oowoewtratLow
gradLewt.
A
oowoewtrated
soLvttLow has a Large
@
%%.. @@
@@@
@
@
o@ o
.i@
o "o
@
substance soluble
in water
molecules of solute
dispersed through water
after diffusion
before diffusion
Diffusion in a liquid.
after diffusion
EXAMINER SAYS...
@ @
@
9oo
@
o
Diffusìon in a gas. Molecuìes
@
@
@o
Õ
of a coloured gas sPread out
through the container.
nLaþ,e
@
o -o
o au o
a
o
o
When molecules diffuse they spread out from where there are lots
of them in a given volume (a high concentration) to where there are
not as many of them (a low concentration). The difference between
the concentration of molecules in two places is a concentration
gradient. Molecules carry on diffusing until they are spread out
ãvenly. When this happens the molecules keep moving, but there is
no longer a difference in concentrations so diffusion has stopped'
Diffusion is the net movement of molecules from a region of
high concentration to a region of lower concentration down
a concentration gradient.
Cells gain some of the substances they need by diffusion from their
surroúndings. They also lose some of their waste substances to their
surroundings by diffusion. These substances have to cross cell membranes
they allow the movement of small
moleculés such as oxygen, carbon dioxide and water to pass through
easily, but not larger molecules. The movement of molecules by diffusion
across cell membranes is passive movement as cells do not need to use
that are partiaily permeable
as
wass of soLute
energy to move the molecules.
dLssoLved Lw a gLvew
voLnnt"e ùf the soLvewt.
Factors that affect diffusion
A
These factors influence the efficiency of diffusion.
dLLvtte soLv*Lowhas
a sntaLL nt"ass of soLv*e
,,dLssoLved L* a gLve*
YoLun+e of the soLvewt.
.
The distance molecules have to travel
-
note that cell membranes
are very thin.
.
The concentration gradient - cells use the substances that diffuse in
as quickly as possible, so they keep a low concentration inside the
cytoplasm. This means that molecules keep diffusing into the cell
because the cell is maintaining a steep concentration gradient'
.
The surface area
.
The temperature
- some cells have cell membranes that are folded to
give a large surface to allow many molecules to cross by diffusion.
-
molecules move faster and colìide more often as the
is faster at warmer temperatures.
temperature increases. Diffusion
.
The size of molecule
-
small molecules diffuse faster than large ones.
Gas versus liquid
Animals and plants exchange the gases oxygen and carbon dioxide
with their surroundings at gas exchange surfaces. ln mammals, the
gas exchange surface is formed of the alveoli in the lungs (see page
'l
21). Blood transports these two gases between the lungs and all
the cells in the body. ln the alveoli, oxygen diffuses across a very thin
layer of cells into the blood. Carbon dioxide diffuses in the opposite
direction. Breathing constantly refreshes the air in the alveoli and
blood constantly removes oxygen and brings carbon dioxide, so the
concentration gradients are always steep. There are many alveoli to
There is a short distance between the
red blood cells and the air in the alveoli
Magnification x 1500.
give a very large surface area for gas exchange.
ln plants, gas exchange occurs inside the leaves. The spongy mesophyll
cells provide a large surface area for exchange of gases. There are air
spaces between the cells in a plant and each cell exchanges gases with
this air (see page 66). Thìs is efficient because diffusion through the air is
EXAMINER SAYS...
300 000 times faster than through water.
ALwags reþrb
o o w c e wtr ate d
s o L utLo ws
awd dLLwte soLvctions,
weverto,stronq, awd
' weaÞ' soLutLows.
tw thLs
Water as a solvent
A solution is made up of two parts, the solute and the solvent.
The solute dissolves in the solvent. lf you dissolve sugar in wateryou
make a sugar solution. The sugar is the solute and the water is the
solvent. The solute is not always a solid like sugar. Liquids and gases
can be solutes as they can dissoìve in solvents too. Something which
dissolves in a solvent is described as being soluble.
Water is sometimes called the universal solvent. About 75o/o of
cytoplasm is water and it is the main component of transport fluids
like blood, and xylem sap and phloem sap in plants. Everything
transported in plants and animals has to dissolve in water and most
of the chemical reactions that occur in cells happen in water.
SUMMARY QUESTIONS
1 Copy and complete the sentences using the words below
liquid random diffusion low gas
:
gradient, e temperature.
3 What do the terms so/ufion and concentration gradient mean?
4
aussoLved Lw a l¿woww
of soLvewt.
voLnvwe
tr.l
\Í
1
Diffusion is the net
movement of molecules
from a region of high
concentration to a region of
low concentration down a
concentration g radient.
2
Factors that affect
diffusion are: size of
a
- diffusion into cells:
factors affect
2 State how the following
a distance, b size of molecule, c surface area,
concentration
?o::
to
the oowoewtratLo*lf
the soLute - the wass
high
or a
is the net movement of molecules of a
concentration as
from an area of
to an area of
result of the
movement of molecules. -
d
Aon are yeferyLwg
Explain why water is an important solvent for animals and plants.
i'{o)lllill
L!,r
molecule, distance,
surface area, temperature
and the steepness of the
concentration grad ient.
I
f
f
. Define the term osrnosr
. Describe the effect of osmosis
on plant and animal tissues
.
c
o
c(¡,,
x
trl
Each cell is surrounded by a cell membrane. lt separates the contents
of the cell from the outside. The cell membrane has tiny holes in it
which allows small molecules to pass through but not large ones. The
cell membrane is described as being partially permeable.
Explain the movement
is a special kind of diffusion involving water molecules. lt
occurs when two solutions are separated by a partially permeable
of water into and out of
membrane.
cells using the term water
Osmosis is the diffusion of water from a dilute solution into a more
concentrated solution through a partially permeable membrane.
potential
Osmosis
The tiny holes in the
membrane allow small
water molecules to pass
through, but the large
solute molecules are
solute
molecu
tf
asked to defi,we
oswosLs orwrLte about
tt, yuake sure
tt:at
l4otL
Lt Ls the
o¡ water vwoLecuLes.
i
*n-
sau
aiffusLi,
a
is
many
diffusing from a place
where there is a dilute
solution with a high
EXAMINER SAYS...
o
water.
I
I
I
a ar
a
o
a
a
o
tl. o.o
i> oo
ala
a
o
a
-i>
a
+o
o
water
molecules
a
I
dilute solution
is a
concentrated solution with
a low concentration of
a
+
o
o
molecu les
concentration of water
to a place where there
o
rO
+
o
o
a
a
aa
Oa
a
too big to pass through
the partially permeable
membrane. Water
a
Water molecules
diffuse from a high
water concentration
to a lower water
concentration
concentrated solution
partially permeable
membrane
Figure 3.2"1
'
osmosis.
Water potential
ìs a way of thinking about the ability of water
by osmosis. This is influenced by how much water is
avail¿ble, but also by other factors such as the pressure exerted on
water in plant cells by the cell wall. lt is more accurate to say that
a dilute solution (containing a lot of water molecules) has a high
to move
water potential. A concentrated solution (containing fewer water
molecules) has a low water potential.
ln the diagram above, there is a water potential gradient between
the two sides of the membrane. The water molecules diffuse dor¡zn
this water potential gradient, from a region of high water potential
to a region of lower water potential.
A model cell
Dialysis tubing (Visking tubing) is partially permeable. We can use
to represent the cell membrane and the sugar solution
dialysis tubing
to represent the cytoplasm.
m
x
+
o
9.
o
:t
PRACTICAL
Cut two pieces of dialysis
tubing, each 12cm long.
Tie one end of each with
water diffuses
into 'cell'
sugêr
solution
cotton.
Fill one model
cellwith
a
dilute sugar solution (cell
A). Fill the other model
cell with water (cell B).
Tie the other end of both
model cells and weigh
them on a balance. Put
dialysis tubing
(partially
permeable
membrane)
'cell A
water diffuses
out of'cell'
EXAMINER SAYS...
'cell A into a beaker of
water and put 'cell B' into
a beaker containing a
concentrated solution of
sugar. After 30 minutes
take out the model cells
and weigh them again.
'Cell
A
yt( tA,LaAbe gLvewthe
r¿sa[ts of apraotLcaL
ewo t t stratío w tf o sw
o sis
a,wd t^e expectedto
uptaLw
the resvù3. Mal¿e stLre
uov
d,
dialysis tubing
(partially
sugaf
solution
permeable
membrane)
rew¿wb er
efi,vwtíoi
awd appLg Lt
to.the resuLts goi Lo^,ee.
'cell B'
tt
increases in mass because
water has diffused rnto the 'cell' by
osmosis. 'Cell B'decreases in mass
because water has diffused out of
capillary
tube
level of
tVte d
oswosLs
ALwaAs Q<?laLwthatthe
results are dwetowater
sugar
solution
wol¿cuLcs wovL^î¿b¡
the cell by osmosis.
OSt'uOsî.5.
An osmometer
You can see the effects of osmosis
if you set up this apparatus.
Fill
diaìysis tubing
conta in i ng
wateÍ
concentrated
sugar solution
l
*Þ
the partially permeable
membrane with a very concentrated solution of sugar.
Tie it to a capillary tube and stand it in water.
Very quickly you will see the liquid moving up the tube. You can
measure how fast it is moving using a ruler and a stopwatch. Use
your ideas about osmosis to explain why the liquid rises in the tube
1
SUMMARY QUESTIONS
1 Define the following terms:
diffusion osmosis partially permeable membrane
2 Describe how you can find out how fast water diffuses by
osmosis into a sugar solution. Remember to include all
practical details.
c
o
c
u
x
t¡J
3 Explain in terms of water potential, how water passes into
plant cells placed in distilled water.
Osmosis is the diffusion
of water molecules from
a region of their higher
concentration (dilute solution)
to a region of their lower
concentration (concentrated
solution) through a partially
permeable membrane.
2 A partially
permeable
membrane allows small
molecules such as water to
pass through but not large
solute molecules.
Osmosis in plant and
animal cells
LEARNING OUTCOMES
PRACTICAL
.
Osmosis in potato cells
Describe how water can
enter and leave plant cells by
osmosis
.
Describe how osmosis can
affect animalcells
Cut nine cores from a potato so that they are exactly the same
length. Record this length.
Feel the cores
to see how firm and 'bendy' they are.
Set up the following test-tubes
- distilled water
B - dilute sugar
A
test-tube A
EXAMINER SAYS..,
Whew descrLbLwa the
wevubrawe ai
ceLL
:: g;!
t' i ii,l:?å
::, wot ^sevwt
pervuealoLe,
"
I membrane
(partia lly
permeable)
cytoplasm
measure their lengths.
Calculate the average length
of the cores in each test-tube.
sol ution
A
-
lwall
(freely
permeable)
the solution outside the
cell is less concentraled
than in the vacuole
Figure
3.3.1
Osmosis in a plant cell
EXAMINER SAYS
c
.9
6
o
#
x
t¡J
lwPaper
s
Aor{ wa?t
be expectedío u-setñe
teynL, w ater potewtLalJ
w
n"tr.nq
ab
o
ut
Lw
ostn*osLs
awdplawt or anívuaL ceL.s
awdtLssues.
þu caw a"so
reter
'water potewtLaL
.yo
Øra dLev*s' to Upt_aLw water
tn*ovewe,wtLwto
awd out of
oeLk awdtíssx¿s.
Cores will be longer and
feel firmer than at the start.
C
-
up
no change
c
suga r
B
0sm0srs
tissue swells
Remove the cores and
passes
into the
vacuole by
suga r
test-tube C - concentrated
sugar solution.
of potato
into each test-tube and leave
them for 60 minutes.
\1æe
dilute
water
sol ution
Place three cores
_
perweabLe.
water
test-tube
solution
B
|TrrrfrT-rrrrrfrrrrrfrr
10r234s6789r0
tissue shrunken and flaccid
Cores will be about the same length and firmness as at the starl.
Cores
will be shorter and feel much softer and 'bendier' than
at the start.
These results are explained in the text.
Turgidity
The cell membrane of the plant cell is partially permeable and the cell
sap inside the vacuole is a solution of salts and sugars. When plant
cells are placed in water, the water enters the cells. This is because
there is a water concentration gradient so that water molecules
diffuse into the cells by osmosis.
As water enters it makes the cell swell up. The water pushes against
the cell wall. Eventually the cell contains as much water as it can
hold. lt's like a blown-up balloon. The strong cell wall stops the cell
bursting. We say that the cell is turgid. This is what has happened to
the cells in the potato cores in tube A. The cells have absorbed water,
swollen and caused the core to get slightly longer.
Turgid cells give the plant support. They keep the stems of many plants
upright. However, when these cells lose water, they are no longer firm
and turgid. Plant stems and leaves that have lost water wilt.
Plasmolysis
When plant cells are placed into a concentrated sugar or salt
solution water passes out of the cells by osmosis. As water passes
out, the sap vacuole starts to shrink. These cells are no longer firm,
and become limp. We say that they are flaccid. As more water
leaves the cells the cytoplasm starts to move away from the cell wall.
These cells are now plasmolysed. This is what has happened to the
cells in the potato cores in C. The cells have decreased in volume so
the whole core is shorter than at the start.
The cores in B did not change in length very much because the
water concentration of the sugar solution was about the same as
the water concentration of the cell sap in the potato cells. There has
been no overall diffusion of water into or out of the cells so they
the solution outside the
cell is more concentrated
than in the vacuole
water passes
oul of the cell
by osmosis
pulled
cell
the va
wall, the cell becomes
shrinks
Figure
3.3.2
plasmolysed
Water passes out of a plant
cell by osmosis.
have stayed about the same length.
Osmosis in animal cells
This diagram shows what happens to red blood cells when they are
placed in different concentrations of a salt solutlon. Remember that
the cell membrane is partially permeable.
The red blood cells in the picture have been placed into different liquids.
Their cytoplasm is a concentrated solution of proteins, salts and sugars.
The cells in D were in distilled water. Water passes rnto the
cells by osmosis. However, animal cells have no cell wall to stop
them swelling so they burst, When red blood cells are put into a
concentrated salt solution (F), they shrink as water passes out of the
cells by osmosis. The ceils in E have not changed in size as they are in
a solution which has the same water concentration as the cells. This
is how they are in the blood when surrounded by blood plasma.
öQ€ftP
Figure 3.3.3
tø
This shows what happens when red blood cells are put into distilled
water (D) and a concentrated solution of salt (F). E shows red blood cells
as they appear when suspended in blood plasma,
These epidermal cells from a red onion are
(a) turgid and (b) plasmolysed.
1 Water
passes into plant cells
by osmosis. A plant cell that
SUMMARY QUESTTONS
1 Explain what is meant by each of the follow terms:
turgid flaccid plasmolysis
is
2
.9
c
a)
x
t¿¡
3
Explain, using the Íerm water potential, what happens to cores of
potato when they are placed into distilled water for 60 minutes.
su ga
r
a
solution,
water passes out by osmosis.
These cell are no longer firm,
they are flaccid. As the vacuole
The mass of the potato cores had stayed unchanged.
a What does this tell you about the concentration of the
sugar solution?
Explain your answer to part a in terms of osmosis.
is turgid.
lf plant cells are placed into
concentrated
2 Some potato cores were weighed and then placed into a
dilute sugar solution. After 2 hours, they were taken out of
the solution, dried on a paper towel and weighed again.
b
full of water
Turgid cells provide support
for leaves and young stems.
shrinla, the cell membrane
moves away from the cell wall
- the cell is now plasmolysed.
3
Animal cells burst if they are
placed into water as they
have no cell wall to resist the
increase in size.
Active transport
.
Define the term active
transporf
.
Explain the importance of
active transport as an energy-
Cells
take up molecules and ions and keep them in high concentrations.
Look at the concentration of magnesium ions in the root hair cell and
the concentration of magnesium ions in the soil solution:
consuming process
.
Describe the active transport
.
of ions in plant roots
Describe the active uptake
of glucose by epithelial cells
in villi
vacuole of root hair cell
W.
a
soil
solution
a
Key:
a:
t0ns
Root hair cells absorb ions by active transport.
The concentration of magnesium ions is far greater inside the vacuole
of the root hair cell than it is in the water in the soil. We might expect
magnesium ions to diffuse out of the root hair cell into the soil water
down a diffusion gradient. The magnesium ions are maintained at a
high concentration inside the root hair cell by a process called active
EXAMINER SAYS...
NotLoethe use of the
terw
,cowoewtratLow
gradLewt,Lwthe
deft wLtLow
of
Active transport is the movement of ions or molecules in or out of
a cell through the cell membrane against a concentration gradient,
using energy released during respiration.
aotLve
trawsport,. AgaLwst a
oo woewtr atL o w g
r a dLewt,
vweÌws
a
Low
fron*
oowoewtratLowto a hLgh
,.
'igoowoewtrûtLow.
ç
transport.
4000
o
P
@
o
o
3000
I
inside cell
l--l
in water outside
E
c
o
'F
2000
g
C
a
c
1
000
o
0
Nat
sodium
K+
N/g2+
potassium magnesium
ca2+
cl-
calcium
chloride
The bar chart shows the concentrations of some ions inside the cells
of a freshwater plant and in the water in which it lives. These ions
cannot have been taken into the plant by diffusion. They are taken in
against a concentration gradient by active transport.
Active transport needs energy
The cell membrane contains carrier proteins. These carrier proteins span
the cell membrane and provide means by which ions and molecules can
enter or leave a cell by active transport. First the molecule or ion combines
wìth a carrier protein. Energyfrom respiration enables the carrier protein
to change its shape to carry the ion or molecule to the inside of the
membrane. The molecule or ion is released to the inside of the membrane
and the carrier protein reverts to its original shape.
t0ns
o
outside cell
outside cell
cell membrane
cell membrane
energy
carrier protein
Figure
3.4.3
inside cell
O
oo
o
O
inside cell
o
Carrier proteins ìn membranes carry out active transport.
Epithelial cells lining the villi in the small intestine absorb glucose
by active transport (see page 84). These cells have high rates of
respiration to provìde energy for this active transport.
Active transport relies upon respiration to take up ions or molecules
against a concentration gradient. Any factor that affects the rate of
respiration will also affect the rate of active transport. So a lack of
oxygen would reduce respiration rate and active transport.
An ìncrease in temperature would increase the rate of respiration, up
to a point, so would also have the same effect on active transport.
The presence of poisons such as cyanide can stop respiration, so
active transport would stop altogether.
EXAMINER SAYS...
æoothaLr
ceL]'s
awd
qLtheLLaL ceLLs of vLLLL
are adapted
aotLve
for
trawnort bg haví.ng
wawA cawLerproteLwsLw
theLr ceLL,*e^bra*es
a wd
a hLgh rate ùf respLratLow
, toTrovLde e^ergy,.
*.
SUMMARY QUESTIONS
1
a
b
Explain what is meant by active transport.
Describe the role of carrier proteins and respiration in
active transport.
c
Give
two examples of active transport taking place.
2 Make a table to compare diffusion with active transport.
Make sure that you have three columns headed 'features',
'diffusion' and 'active transport'. For features you can include
'needs energy from the cell', 'concentration gradient'. You may
be able to think of some other features to use in your table.
3 State what effect each of the following would have on active
transport, in each case give reasons for your answer:
a a lack of oxygen
b
c
an increase in temperature
the presence of a poison, such as cyanide.
KEY POINTS
1 Actíve transport
the
movement of ions or
molecules across the cell
membrane. against a
concentration gradient, using
is
energy from respiration.
2 Active transport
enables root
hair cells to take up ions, and
epithelial cells of the villi to
take up glucose.
SUMMARY QUESTIONS
EXAM-STYLE QUESTTONS
1 Define the terms solvent, so/ufe and soluble.
1 Which of the following
2 Explain why diffusion occurs faster in a gas
than in a liquid.
A
B
C
D
3 Name the process by which each of the
following occur:
(a) molecules of oxygen move from the air
spaces in the alveoli in the lungs into the
blood
(b) molecules of carbon dioxide move from
respiring cells into the blood
(c) water molecules move into root hair cells.
1)
l
tl
is the besf definition
of
diffusion?
movement of molecules down
concentration g rad ient
4 Define the following terms:
B
(a) concentration grad ient
(b) diffusion
movement of molecules up
concentration g radient
C
movement of solvent molecules through
a partially permeable membrane down a
concentration
D
g
a
a
radient
random movement of molecules in a gas
or a liquid
(Paper
1)
3 Which of the following
l
tl
is the besf definition
of
osmosis?
6 Describe what happens to animal and plant
A
diffusion of molecules through a partially
permeable membrane from a dilute
solution to a concentrated solution
B
diffusion of molecules through a partially
permeable membrane from a high
concentration to a low concentration
Use the Term water potentialto explain why
plant cells increase in size when placed in
water and decrease in size when placed in
very concentrated solutions of salt or sugar.
C
diffusion of water molecules from a region
with a dilute solution to a region with a
concentrated solution through a partially
9 Some resources required by cells, such
as molecules and ions, are often in very
low concentrations in their surroundlngs.
Describe how root hair cells and epithelial
cells from the gut obtain resources from their
D
cells when they are placed in (a) water, and
(b) concentrated solutions of salt.
7 Explain your answers to question 6 (a) and
(b) using the terms partially permeable
membrane and osrnosls.
x
dialysis tubing
A
5 Water forms about 75% of the cytoplasm of
cells and a higher proportion of body fluids
such as blood. Explain the importance of
water as a solvent in the body.
a)
cellwall
2 Which of the following
(d) osmosis.
ul
noi partially
cell membrane of palisade mesophyll cell
cell membrane of red blood cell
(Paper
(c) partially permeable membrane
.9
is
permeable?
8
surroundings under these circumstances.
10 Explain why root hair
cells have
to provide
energy for the absorption of ions from the soil.
11
Explain what is meant by the term
concentration gradient and explain how the
term is used when describing the movement of
molecules across cell membranes.
permeable membrane
diffusion of water molecules through
partially permeable membrane
(Paper
4
a
1)
l
tl
Some fresh plant tissue was put into a
concentrated salt solution for 60 minutes. Which
best explains why the tissue became softer?
A
B
C
D
The cells became turgid.
to their surroundings.
Water diffused from a dilute solution in
the cells to a more concentrated solution
The cells lost water
outside the cells.
Water diffused by osmosis from the
cell sap in the vacuoles into the more
concentrated solution outside the cells.
(Paper
1)
tl
l
5 (a)
State three factors that increase the rate of
diffusion.
t3l
ln the lungs, oxygen and carbon dioxide are
exchanged between the blood and the air in
the alveoli by diffusion.
move up the
(b) State three ways in which the alveoli in
the lungs are adapted for efficient gas
exchange.
(Paper 2)
as shown in
the diagram below.
tube with
scale marked in
mm
15
tube.
t4l
(Paper 2)
t3l
6 A student set up some apparatus
(c) Calculate the rate of movement in
millimetres per minute of the meniscus
over the B minutes.
t2l
(d) Explain what caused the sugar solution to
meniscus of the
sugar solutìon in
tube
7 An experiment was set up to investigate
the factors influencing the uptake of ions
by plant roots. Some roots were cut from a
plant, washed and placed in three solutions,
A, B and C, containing potassium ions. A
mixture of gases was bubbled through each
of the solutions. A gas mixture rich in oxygen
was bubbled through solution A; solution
B received a gas mixture with a very low
concentration of oxygen; solution C received
no oxygen in the gas mixture. The roots were
left for 24hours and then the rate of uptake
of potassium ions was determined.
The rate of uptake of potassium ions was
highest in solution A and lowest in solution C.
dialysìs
concentrated
sugar solution
tu bi ng
The student measured the level of the
meniscus in the glass tube every minute and
the results are shown in the table.
time
(minutes)
0
position of the meniscus
in the tube (mm)
(a) Explain how the supply of oxygen to roots
influences their uptake of potassium ions.
The experiment was repeated with
solutions containing roots kept at different
temperatures. They were all provided with the
gas mixture that had been given to solution A.
The results are shown in the table.
temperature
fc)
U
1
24
2
52
3
73
4
102
5
127
6
138
7
180
B
190
(a) Draw a graph of the results.
t6l
(b) Describe the results shown by your graph.
t2l
13/
rate of uptake of potassium
ions (arbitrary units)
5
3
'10
5
20
10
30
20
40
15
(b) Draw a graph of the results.
t6l
(c) Describe the results shown in your graph.
t4l
(d) Explain the effect of temperature on the
uptake of potassium ions by the roots. t3l
(Paper 3)
ct¡on of
.
Define the term catalyst as a
substance that speeds up a
chemical reaction and is not
changed by the reaction
.
Define enzymes as proteins
that act as biological catalysts
to speed up the rate of
chemical reactions
a
.9
c
o
P
x
uJ
ain how an enzyme works
using the 'lock and key' model
A catalyst speeds up a chemical reaction and remains unchanged at the
end of the reaction. Enzymes are proteìns, produced by organisms, that
speed up chemical reactions. They are known as biological catalysts.
How enzymes work
Many chemical reactions take place in organisms. These reactions
happen too slowly to keep organisms alive unless they are speeded
up by enzymes. There are many different types of enzyme as each
one catalyses a different reaction. Most enzymes work inside cells,
but many of those that we will discuss here work outslde cells, for
example in the gut (see pages 7B and B2).
The reactions that enzymes catalyse can be divided into three types.
'l Breaking large molecules into small ones
This is important in nutrition when large food molecules are broken
down into small ones so that they can be absorbed and then used.
Bacteria and fungi release enzymes to break down their food and we
release enzymes into the gut for the same reason.
2 Building up large molecules from small ones
Small molecules, such as glucose, are joined together to make Iarge
molecules. These enzymes work inside cells to speed up the formation
of storage molecules, such as starch, and structural molecules such as
cellulose for cell walls of plants.
3 Converting one small molecule into another
This computer-generated image of an
enzyme (on the right) shows its 3D shape.
Many of the chemìcal reactions that occur inside cells involve small
to molecules, such as adding or removing atoms or groups
of atoms. For example, there are enzymes that remove hydrogen
from compounds during respiration.
changes
Figure 4.1.1 shows the way ìn which an enzyme catalyses the
breakdown of a molecule.
EXAMINER SAYS...
WhewwrLtLwg abowt
ewzAwes aLwaus sag
s at a s e
^= a
l.l!!.:
u
reActL)ws. ^e
i
i
hr¡Þ
enzyme
substrate
L
subslrate in
active sile
enzyme
products
released
Figure 4.1.1
Figure 4.'1.2 shows how an enzyme is involved in building a molecule
from two smaller molecules.