We care deeply about global access to...

We care deeply about global access to high quality education. We collaborate closely with Oxford University Press to develop valuable resources which meet the needs of teachers and students all over the world, and are pleased to endorse Oxford resources for Cambridge IGCSE.

Ann Puntis, Chief ExecutiveUniversity of Cambridge International Examinations

.

Now even more comprehensive - and with a free student CD-ROM!

Endorsed by University of Cambridge International Examinations

This new second edition provides full coverage of the most recent Cambridge IGCSE Biology syllabus in a highly illustrative and accessible way. It also comes with a free CD to stretch your most able pupils and is now supported by a Teacher’s Resource Kit.

A free student CD contains even more material to stretch your students, including revision support, past exam questions, model answers, repeated questions from the Student Books and more

Full colour, student-friendly design caters to all learning types, with plenty of diagrams, charts and visuals to explain challenging concepts

A step-by-step approach simplifies difficult concepts, easing comprehension

Uses clear, straightforward English, ensuring clarity for your EAL students

Plenty of case studies on relatable, internationally-focused issues help students understand the importance of their learning

By Ron Pickering, an experienced author, written specifically for the international classroom

Companion Teacher’s Resource Kit and Revision Guide also available to provide additional support and optimally prepare students for exam success

Characteristics and classification of living organisms

1.1 Biology is the study of life and living organisms1.2 The variety of life1.3 Bacteria and viruses1.4 Fungi1.5 Plants1.6 Invertebrate animals1.7 Vertebrate animals: five classes

Organisation and maintenance of organisms

2.1 Organisms are made up of cells2.2 The organisation of living organisms2.3 Movement in and out of cells2.4 Enzymes control biochemical reactions in the living organisms in living organisms2.5 Humans use enzymes from micro-organisms2.6 Enzyme experiments & the scientific method2.7 All living things are made up of organic molecules2.8 Testing for bio chemicals2.9 Food and the ideal diet: carbohydrates, lipids and proteins2.10 Food and the ideal diet: vitamins, minerals, water and fibre2.11 Food from micro-organisms2.12 Using fungi to produce antibiotics2.13 Baking and brewing: the economic importance of yeast2.14 Food is the fuel that drives the processes of life2.15 Balancing energy intake and energy demand2.16 Malnutrition and famine2.22 Plants and minerals

2.17 Photosynthesis and plant nutrition2.18 The rate of photosynthesis2.19 The leaf and photosynthesis

2.20 The control of photosynthesis2.21 Photosynthesis and the environment2.27 Uptake of water and minerals by roots2.28 Transport systems in plants2.29 Transpiration: water movement in plants2.30 The leaf and water loss2.31 Transport systems in animals2.32 Combating infection2.33 Antibodies and the immune response2.34 The circulatory system2.35 Capillaries2.36 The heart is the pump for the circulatory system2.37 Control of blood pressure and exercise2.38 Coronary heart disease

2.39 Respiration provides the energy for life2.40 Contraction of muscles and respiration2.41 The measurement of respiration2.42 Gas exchange supplies oxygen for respiration2.43 Breathing ventilates the lungs

2.44 Smoking and disease2.45 Excretion2.46 Dialysis and the treatment of kidney failure2.47 Homeostasis: maintaining a steady state2.48 Control of body temperature

2.49 Coordination: the nervous system2.50 Neurones can work together in reflex arcs2.51 Muscles can work as effectors

2.52 The brain is the processor for the central nervous system2.53 Integration by the central nervous system2.54 Receptors and senses

2.55 The endocrine system2.56 Drugs and disorders of the nervous system2.57 Sensitivity and movement in plants: tropisms

Development of organisms and the continuity of life

3.1 Reproduction and living organisms3.2 Reproduction in flowering plants3.3 Pollination3.4 Fertilisation & the formation of seed and fruit3.5 Dispersal of seeds and fruits3.6 Germination of seeds3.7 Vegetative propagation3.8 Artificial propagation

3.9 Reproduction in humans3.10 The menstrual cycle3.11 Copulation and conception3.12 Contraception3.13 Pregnancy: the role of the placenta3.14 Pregnancy: development and antenatal care3.15 Birth and the newborn baby3.16 Sexually transmitted diseases3.17 Growth and development

3.18 Variation and inheritance3.19 Cell division3.20 Inheritance3.21 Studying patterns of inheritance3.22 Inherited medical conditions and co- dominance3.23 Sex is determined by X and Y chromosomes

3.24 Variation3.25 Causes of variation3.26 Variation and natural selection3.27 Natural selection3.28 Artificial selection3.29 Genetic engineering3.30 Gene transfer in plants and animals

Organisms and their environment

4.1 Ecology and ecosystems4.2 Flow of energy: food chains and food webs4.3 Feeding relationships4.4 Decay is a natural process4.5 The carbon cycle4.6 The nitrogen cycle4.7 Water is recycled too!

4.8 Factors affecting population size4.9 Human population growth4.10 Humans and agriculture4.11 Land use for agriculture4.12 Pollution of water: eutrophication4.13 Human impacts on the environment4.14 Humans may have a positive effect on the environment: conservation of species4.15 Conservation efforts worldwide4.16 Conservation of resources4.17 Management of solid waste4.18 Saving fossil fuels: fuel from fermentation

Practical biology

5.1 Practical assessment5.2 Laboratory equipment5.3 Questions with practical contentIndex

4.1

O R G A N I S M S A N D T H E I R E N V I R O N M E N T

246

O

Climatic e.g.temperaturehumidity

A living organisminteracts with its

environment

Abiotic(‘non-living’)

factors

Biotic (‘living’)factors e.g.

predatorsfoodmates

Physical e.g.oxygen and carbondioxide concentrationlight intensitywater availability

Environmental survival kitAll living organisms depend upon their environment for three ‘survival essentials’. These are a supply of food, shelter from undesirable physical conditions and a breeding site. The living organism interacts with its environment – for example, a living plant:� removes carbon dioxide, water and light

energy from its habitat� may be eaten by an animal or a parasite� depends upon soil for support.

Factors in the environment affect the growth of the plant. Some of these factors are biotic – other

living organisms – and some are abiotic – the non-living components of the habitat. Ecology is the study of living organisms in relation to their environment. The interactions between the organism and its environment are summarised below.

Changing with the seasonsThe ability of the habitat to supply living organisms with their requirements may vary at different times of year. The ecosystem in the photograph opposite will only exist for a certain period of time – as food or water becomes exhausted some animals may leave. These will then be followed by the predators which feed on them. The great animal migrations seen in East Africa result from the changing conditions in the animals’ environment, for example:� poor rain means little growth of grass� herbivores leave for areas of fresh growth� carnivores follow herbivores� (then scavengers follow carnivores!).

Living togetherLiving organisms normally exist in groups. The names given to these groups, and the way they interact with the abiotic environment, are explained opposite.

OB J EC T I VESOB J EC T I VES

� To understand that living organisms require certain conditions for their survival

� To understand that living organisms interact with one another, and with their non-living environment

� To defi ne population, community and ecosystem� To realise that available resources change through

the year

Ecology and ecosystems

Carbon dioxide

‘Fertiliser’in faeces

Water and mineralions from soil

Food

A giraffe feeds on a thorn tree. The tree requires water,mineral ions, carbon dioxide and light to grow. The giraffemay provide carbon dioxide from respiration, and ionsfrom decomposition of its faeces.

913876_IGCSE_BIO_CH04.indd 246 09/10/2010 14:50:55


247

Q1 Defi ne the terms population, community and

ecosystem.2 Name two abiotic factors that might determine

whether or not a habitat is suitable for a living organism.

3 Suggest two ways in which a plant and an animal in the same habitat may interact.

4 What must a habitat provide?5 How are the following observations related? � Very few fl ying insects are found in Britain during

the winter.

� Swallows migrate to Africa when it is winter in the UK. � Hobbies (small bird-eating falcons) leave Britain in

late autumn.6 What is meant by the term ecology?7 a A group of pupils were studying a forest.They

noticed that the plants grew in two main layers. They called these the tree layer and the ground layer.

The pupils measured the amount of sunlight reaching each layer at different times in the year.Their results are shown on the graph.

i During which month did most light reach the tree layer?

ii During which month did most light reach the ground layer?

iii Suggest why the amount of sunlight reaching the ground layer is lower in mid-summer than in the spring.

b The pupils found bluebells growing in the ground layer. Bluebells grow rapidly from bulbs. They fl ower in April and by June their leaves have died.

i Suggest why bluebells grow rapidly in April. ii Suggest why the bluebell leaves have died

by June.

5 Ho�

5

An ecosystem is all the living organisms andthe non-living factors interacting togetherin a particular part of the environment.

A community is all of thepopulations of living organismsin one area (e.g. acacia trees,zebra, wildebeest and grass).The community is the bioticenvironment.

A population is all of themembers of the same species(e.g. wildebeest) in aparticular area.

Air, water and soilmake up the abioticenvironment.

A habitat is a part of the environment thatcan provide food, shelter and a breeding sitefor a living organism (e.g. a patch of grassland).

� Organisms exist in groups within an ecosystem

tree layer

ground layer

Month

Ligh

t in

tens

ity

Light reachingground layer

Light reachingtree layer

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

913876_IGCSE_BIO_CH04.indd 247 09/10/2010 14:51:09

4.2


248

O

Food chainsThe most obvious interaction between different organisms in an ecosystem is feeding. During feeding, one organism is obtaining food – energy and raw materials – from another one. Usually one organism eats another, but then may itself be food for a third species. The fl ow of energy between different organisms in the ecosystem can be shown in a food chain, as in the diagram below.

Energy transfer is ineffi cientThe amount of energy that is passed on in a food chain is reduced at every step. Since energy can be neither created nor destroyed, it is not

lost but is converted into some other form. During respiration, some energy is transferred to the environment as heat. The fl ow of energy through a food chain, and the heat losses to the environment, are illustrated in the diagram opposite.

Food websSince so little energy is transferred from the base to the top of a food chain, a top carnivore must eat many herbivores. These herbivores are probably not all of the same species. In turn, each herbivore is likely to feed on many different plant species. All these interconnected food chains in one part of an ecosystem can be shown in a food web.The more complicated a food web, the more stable the community is. For example, in the forest food web shown opposite, if the number of squirrels fell, the owls could eat more worms, mice and rats. The mice and rats would have less competition for food from squirrels, and so might reproduce more successfully.


� To know that the feeding relationships in an ecosystem can be expressed as food chains

� To understand why energy transfer through an ecosystem is ineffi cient

� To understand why complex food webs are the most stable

Flow of energy: food chains and food webs

Secondary consumers may beeaten by tertiary consumers. These longer food chains are more common in aquatic habitats. The final consumer in the food chain is called the top carnivore.

Sunlight provides the energy to drive the food chain.

Decomposers, fungi and many bacteria,obtain their energy and raw materials from the wastes (e.g. faeces) and remains(e.g. dead bodies) of other organisms.

Producers, usually green plants, can convert light energy to chemical energy in food compounds.

Consumers are organisms that obtainfood energy from other organisms.

Arrows point in the direction of energy flow along the food chain.

Primary consumers are herbivores.They obtain their energy in food compounds obtained from producers(i.e. plants).

Secondary consumersare carnivores. They obtaintheir energy in food compounds obtained by eating other animals.

� Food chains show energy fl ow through an ecosystem. The position of each organism in the food chain represents a different trophic (feeding) level.

913876_IGCSE_BIO_CH04.indd 248 09/10/2010 14:51:12


249

Because of this, food chains rarely havemore than 4 or 5 trophic levels.

Note that energy flow is not cyclic!

As a result there must be acontinuous input of light energy to‘drive’ life in an ecosystem.

heatsunlightchemicalbondenergy

Less than 1% of theenergy released fromthe Sun falls onto leaves.

Energy ‘fixed’ by producersis only 5–8% of the energythat falls onto their leaves,because: some is transmitted (passes right through) some is reflected some is not the correct wavelength (only red or blue light is absorbed – see page 64).

R RR

R

Energy transfer to decomposers is veryvariable, but eventually the entire energy contentof the animal and plant remains will be releasedas heat from inefficient respiration.

It is more efficient for humans to eat plantsthan to feed plants to animals, and then toeat the animals. Every step in the chain loses80–90% of the available energy as heat, so THEFEWER ‘STEPS’ THE BETTER!

Energy transfer toprimary consumeris only 5–10%: much of plant body is indigestible consumer rarely eats whole plant – roots or stems may be left behind.

Energy transfer tosecondary consumeris between 10% and 20%: animal material has a higher energy value animal material is more digestible.

Respiration losses occur from each trophiclevel. Respiration is not 100% efficient andeventually all of this energy is lost as heat.

R respiration

Key

Producers

Primaryconsumers

Secondaryconsumers

Tertiaryconsumer

Trophic level

Hawk

Owl

Fallen leaves Living leaves Grasses Seeds

Rats Mice Squirrels Worms Woodlice Snails

Starling

Energy transfer

A simple forest food web

Q1 Defi ne the terms producer,

consumer and decomposer. Which of these could be omitted from an ecosystem? Explain your answer.

2 Write out a food chain from a named ecosystem which you have studied.

Why are food chains usually restricted to three or four trophic levels?

Whres

3

913876_IGCSE_BIO_CH04.indd 249 09/10/2010 14:51:19

250

Algae on rocks(seaweed) Limpets

Crabs Gull

4.2 Flow of energy: food chains and food webs

Algae (small green plants)

Water fl eas

Guppy (small fi sh)

Bass (large fi sh)

Green heron

More examples of feeding relationshipsFood chains and food webs in aquatic (watery) environments can be longer than those on the land. This is because this type of environment has space and ideal growth conditions for many producers. Even with energy losses at every stage there is enough ‘trapped’ energy for more steps in the chain. Many of these food chains begin with phytoplankton (tiny green plants) or algae.

A freshwater food chain

The seashore is an excellent environment for animals, at least as far as food is concerned, because fresh supplies are delivered with every tide!

Some of the top predators on seashores need so much food that they need to travel between different parts of the habitat. A gull, for example, might have to fl y to several different parts of the same shore.

A seashore food chain

Q1 Look at the three aquatic feeding relationships shown on this page and the next. Make a table like this one:

Producers Herbivores Carnivores Top carnivores

Shark fi shing is a popular sport. Explain what might happen if all of the sharks living around a section of reef were captured by fi shermen.Shcap

2

913876_IGCSE_BIO_CH04.indd 250 09/10/2010 14:51:26


251

Coral reef food webThe most complex food webs are found in the ocean.

Shark

Sea Turtle

Parrotfi sh

Phytoplankton

Zooplankton

Anemone

Crab

Butterfl yfi sh

Jellyfi sh

Octopus

Coral

Q Use words from the following list to complete the paragraph about ecosystems. You may use each word once, more

than once or not at all.

decomposition, producer, chemical, carnivore, consumer, photosynthesis, energy, light, elements, decomposers, herbivore.

In each ecosystem there are many feeding relationships. A food chain represents a fl ow of through an ecosystem, and always begins with an organism called a which is able to trap energy and convert it to

energy. An organism of this type is eaten by a , which is a kind of that feeds only on plant material. This type of organism is, in turn, eaten by a (an organism that consumes other animals).

Ustha

3

913876_IGCSE_BIO_CH04.indd 251 09/10/2010 14:51:27

4.3


252

O

Pyramids of numbersLook at the food chain on page 248. Two things should be clear:� The organisms tend to get bigger moving along

the food chain. Predators, such as the cat, need to be large enough to overcome their prey, such as the mouse.

� Energy is ‘lost’ as heat on moving from one trophic level to the next, so an animal to the right of a food chain needs to eat several organisms ‘below’ it in order to obtain enough energy. For example, a rabbit eats many blades of grass.

Food chains and food webs provide qualitative information about an ecosystem – they show which organism feeds on which other organism. How do we show quantitative information, for example how many predators can be supported by a certain number of plants at the start of the chain? We can use a pyramid of numbers or a pyramid of biomass, as shown in the diagram below.

Pyramids of energyA pyramid of biomass describes how much biomass is present in a habitat at the time the sample is taken. This can be misleading, because different feeding levels may contain organisms that reproduce, and so replace themselves, at different rates. For example, grass in a fi eld would replace itself more quickly than cattle feeding on the grass, so when the pyramid of biomass is constructed there would be more ‘cattle biomass’ than ‘grass


� To be able to describe pyramids of numbers, biomass and energy

� To understand how data can be gathered to make ecological pyramids

Feeding relationships: pyramids of numbers, biomass and energy

Pyramid of numbers – a diagrammatic representationof the number of different organisms at each trophic levelin an ecosystem at any one time

Note1 The number of organisms at any trophic level is

represented by the length (or the area) of a rectangle.2 Moving up the pyramid, the number of organisms

generally decreases, but the size of each individualincreases.

Producers

Top carnivore

Small carnivore

Herbivore

Butwait!

Problemsa The range of numbers may be enormous – 500 000

grass plants may only support a single top carnivore –so that drawing the pyramid to scale may be verydifficult.

b Pyramids may be inverted, particularly if theproducer is very large (e.g. an oak tree) or parasitesfeed on the consumers (e.g. bird lice on an owl).

So …

Pyramid of biomass – which represents the biomass(number of individuals × mass of each individual) ateach trophic level at any one time. This should solvethe scale and inversion problems of the pyramid ofnumbers.

Biomass expressed asunits of mass per unitarea (e.g. kg per m2)

Bird lice

Tawny owl

Blue tits

Insect larvae

Oak tree

Bird lice

Tawny owl

Blue tits

Insect larvae

Oak tree

� Ecological pyramids represent numerical relationships between successive trophic levels.The pyramid of biomass is useful because the biomass gives a good idea of how much energy is passed on to the next trophic level.

913876_IGCSE_BIO_CH04.indd 252 09/10/2010 14:51:39


253

biomass’ and the pyramid would be inverted. To overcome this diffi culty a pyramid of energy can be constructed. This measures the amount of energy fl owing through an ecosystem over a period of time. The time period is usually a year, since this takes into account the changing rates of growth and reproduction in different seasons. It is even possible to add an extra base layer to the pyramid of energy representing the solar energy entering that particular ecosystem.

� Pyramid of energy: energy values are expressed as units of energy per unit area per unit time (e.g. kJ per m2 per year)

GATHERING DATA FOR ECOLOGICAL PYRAMIDSGATHERING DATA FOR ECOLOGICAL PYRAMIDS

To construct a pyramid of numbers or of biomass, organisms must be captured, counted and (perhaps) weighed. This is done on a sample (a small number) of the organisms in an ecosystem. Counting every individual organism in a habitat would be extremely time-consuming and could considerably damage the environment.

The sample should give an accurate estimate of the total population size. To do this:

� The sampling must be random to avoid any bias. For

example, it is tempting to collect a large number of

organisms, by looking for the areas where they are

most common. To avoid this, the possible sampling

sites can each be given a number and then chosen

using random number generators on a computer.

� The sample must be the right size so that any

‘rogue’ results can be eliminated. For example, a

single sample might be taken from a bare patch of

earth, whereas all other sites are covered with

vegetation. The single sample from the bare patch

should not be ignored, but its effects on the results

will be lessened if another nine samples are taken.

A mean value can then be used.

Sampling plants and sessile animalsOnce the organisms in a sample have been identifi ed and counted, the population size can be estimated. For example, if 10 quadrats gave a mean of 8 plants per quadrat, and each quadrat is one-hundredth of the area of the total site, then the total plant population in that

area is 8 � 100 � 800.

Wire1 m

1 m

20 cm 20 cm

Wing nut

Metal or wooden frame

� A quadrat is a square frame made of wood or metal. It is simply laid on the ground and the number of organisms inside it is counted.

A quadrat is used most commonly for estimating the size of plant populations, but may also be valuable for the study of populations of sessile or slow-moving animals (e.g. limpets).

913876_IGCSE_BIO_CH04.indd 253 09/10/2010 14:51:41

4.4


254

O

Recycling nutrientsHumans have an unusual skill – they can modify their environment to suit themselves. For example, we cut down forests and plant crops, and we build houses. Many building materials are natural, such as wood and straw, and the environment treats these materials as the dead remains of once-living organisms – the environment reclaims the nutrients and returns them to the ecosystem.

Starting with scavengersWhen an organism dies, the nutrients in its body are returned to the environment to be reused. The nutrients are recycled by a series of processes carried out by other living organisms. The fi rst ones to appear are usually the scavengers which break up the dead bodies into more manageable pieces. Scavengers eat some of the dead body, but leave behind blood or small pieces of tissue.

Decomposition by microorganismsThe remains that are left are decomposed by the feeding activities of microorganisms. These fungi and bacteria feed by secreting enzymes onto the remains and absorbing the digested products. This form of nutrition is called saprotrophic feeding (see page 12).

The diagram on the opposite page illustrates some of the features of the decomposition process. The decay process provides energy and raw materials for the decomposers. It also releases nutrients from the bodies of dead animals and plants, which can then be reused by other organisms, for example:

In this way substances pass through nutrient cycles as microbes convert them from large, complex molecules in animal and plant remains to simpler compounds in the soil and the atmosphere. The next sections describe the recycling of the elements carbon and nitrogen.


� To understand that nutrients in dead organisms are recycled

� To know that the process of decay often begins with the activities of scavengers

� To know how saprotrophic nutrition is responsible for decomposition

Decay is a natural process

sugar in dead rabbit respiration by microorganisms

carbon dioxide photosynthesis in plant

sugar in plant

� Scavengers such as the vulture feed on dead bodies

Importance of decomposition processes to humans� Organic waste in sewage is decomposed and made

‘safe’ in water treatment plants (see page 284).� Organic pollutants such as spilled oil may be removed

from the environment by decomposing bacteria (see page 11).

� Food is spoiled due to decomposition by fungi and bacteria. Many food treatments alter physical conditions to inhibit enzyme activity.

� Wounds may become infected by saprotrophs, leading to tissue loss or even to death. Many medical treatments inhibit the multiplication or metabolism of saprotrophs.

i

913876_IGCSE_BIO_CH04.indd 254 09/10/2010 14:52:39


255

Antiseptics and disinfectantskill the living organisms thatcarry out the decay process.Good news! in hospitals andfor food preservation butBad news! in compost heapsand in sewage works.

Cell wall

Cytoplasm

Lipasesfats fatty acids + glycerol

Amylasestarch maltose

glucose

Proteasesprotein amino acids

Simple compoundsinclude fatty acids,

glucose, amino acidsand mineral salts.

Absorption bydiffusion and/orby active transport.

Absorbedsimple compounds

Environmentalfactors mayaffectdecomposition*

Metabolism inside the bacterialor fungal cells uses the absorbedproducts for respiration or for cellgrowth and division.

Cells of saprotrophs (bacteriaand fungi) nourish themselvesby secreting enzymes onto ‘food’and absorbing the products.

Complex organic compoundsinclude fats, proteins and starches.

*Oxygen is required for aerobicrespiration, which releases energyin bacteria and fungi to drive theirmetabolism. In the absence ofoxygen decomposition is slow andvery smelly, as methane andhydrogen sulfide may be produced.

*Heat – for rapid decomposition,need to maintain an optimumtemperature for the activity ofenzymes. Heat is generated bythe respiration that occurs duringthe decomposition process.

*Water – many decompositionreactions are hydrolysis reactions,i.e. they use water to split chemicalbonds. Water is also necessary todissolve the breakdown productsbefore they can be absorbed by thesaprotrophs or other organisms.

Saprotrophs cause decay.

Q1 Copy and complete the following paragraph. During the process of decay, and convert

complex chemicals into ones. For example, proteins are converted to , and to fatty acids and glycerol. These decay processes involve the biological catalysts called , and so the processes are affected by changes in and . Humans exploit decay, for example in the treatment of to provide drinking water, and may deliberately limit decay, for example in the preservation of .

Gardeners often place vegetable waste on a compost heap. Over the course of time the waste will be decomposed.

a What do gardeners gain from the decomposed waste?

b Why do gardeners sometimes spray water over the heap in warm summer weather?

c Why do gardeners often build compost heaps on a pile of loose-fi tting sticks or bricks?

Gahe

2

913876_IGCSE_BIO_CH04.indd 255 09/10/2010 14:52:43


1 The graph below shows changes in the population of bacteria that take place in a river when untreated sewage is added to it.

a Describe the changes in the population of bacteria that take place in this river.

b Suggest an explanation for these changes in the population of bacteria.

Cambridge IGCSE Biology 0610

Paper 2 Q8 May 2008

The wild dog is one of the smaller African carnivorous mammals. It has disappeared from 25 of the 39 countries where it used to live. Wild dogs hunt in packs, feeding on antelopes, which are grass-eating mammals.

A conservation programme has been started to increase the wild dog population in South Africa. Farmers are worried about numbers getting out of control because wild dogs breed at a very fast rate. However, conservationists are not concerned because the lion is a natural predator of the dogs.

a Wild dogs are carnivorous mammals. i Defi ne the term carnivore. ii State one external feature which

distinguishes mammals from other vertebrates.

b i Suggest two reasons why numbers of African wild dogs are decreasing.

ii Suggest what could happen to the species if numbers continue to decrease.

c Using the information in the passage above, construct a food chain for a wild dog, including its predator. Label each organism with its trophic level.

Thca

2

Questions on human impacts on ecosystems

d It is important that the wild dog species is conserved.

i Explain the meaning of the term conservation.

ii Outline the measures that could be taken to conserve a mammal, such as the wild dog.

e When wild dogs die, nitrogen compounds in their bodies may become available for plants. Outline the processes that occur to make these nitrogen compounds in the bodies of dead animals available for plants to absorb.


Paper 3 Variant 1 Q2 May 2008

The freshwater mussel, Margaritifera margaritifera, is a mollusc which lives in rivers and streams. When the mussel reproduces, gametes are released into the water and fertilisation takes place. The embryos, in the form of larvae, attach themselves to the gills of fi sh and develop there for a few months. The larvae then release themselves and grow in sand in the river, feeding by fi ltering food from the water. The number of mussels is falling due to human predation and the species is threatened with extinction.

a The mussel belongs to the group known as the molluscs. State two features you would expect the mussel to have.

b Explain how the species name of the freshwater mussel can be distinguished from its genus.

c State the type of reproduction shown by the mussel. Explain your answer.

d i Fish gills have the same function as lungs. Suggest one advantage to a mussel larva of attaching itself to fi sh gills.

ii The mussel develops on the fi sh gills. Defi ne the term development.

e The mussel is threatened with extinction. Name another organism which is also threatened with extinction and outline how it could be conserved.


Paper 3 Variant 1 Q1 November 2008

This

3

distance downstream(abitrary units)

populationof bacteria

(abitrary units)

raw sewagedischargedinto river

289

913876_IGCSE_BIO_CH04.indd 289 09/10/2010 14:54:15


290

Explain why it is more effi cient for humans to eat maize rather than meat from cows that have been fed on maize.

f i Complete the equation for photosynthesis.

ii Describe how leaves are adapted to trap light.

iii With reference to water potential, explain how water is absorbed by roots.

iv Explain how photosynthesising cells obtain carbon dioxide.


Paper 3 Variant 1 Q2 November 2008

5 The fi gure below shows population pyramids for a developing country and a developed country.

6CO2 � 6H2O C6H12O6 �light energy

65

45

15

0

age

percentage of total population

males females

developing country

2024 46 68 810 10

65

45

15

0

age

males females

developed country

percentage of total population

2024 46 68 810 10

The bar graph on the right shows crop productivity for a range of plants but it is incomplete.

a Complete the bar graph using the data below it.

Thpr

4

crop productivity per day of growing season / g per m2

world average highest yield

potatoes 2.6 5.6

b State which crop has i the highest average productivity, ii the greatest difference between the

average yield and the highest yield. c Outline how modern technology could be

used to increase the productivity of a crop from the average yield to a high yield.

d When the yield is measured, dry mass is always used rather than fresh mass.

Suggest why dry mass is a more reliable measurement than fresh mass.

e Maize is often used to feed cows, which are grown to provide meat for humans.

9.0

7.0

6.0

5.0

4.0

2.0

1.0

0

3.0

8.0

Key

highest yieldworld average

wheat oats maize rice

type of crop

sugarbeet

prod

uctiv

ity p

er d

ay o

f gr

owin

g se

ason

/ g

per

m2

913876_IGCSE_BIO_CH04.indd 290 09/10/2010 14:54:17

We care deeply about global access to...

Documents

Transcript of We care deeply about global access to...