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Cambridge IGCSE0610

Food supply

Biology 0610 Chapter Notes

What this chapter covers

Food supplyHabitat destructionPollutionConservation
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Food supply notes

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In this chapter

  1. 1Machinery and chemical fertilisers
  2. 2Insecticides and herbicides
  3. 3Selective breeding
  4. 4Large-scale monocultures
  5. 5Intensive livestock production
  6. 6Biodiversity
  7. 7Reasons for habitat destruction
  8. 8Food webs and food chains
  9. 9Deforestation: habitats and species
  10. 10Deforestation: loss of soil and flooding
  11. 11Deforestation: carbon dioxide
  12. 12Untreated sewage and excess fertiliser
  13. 13Non-biodegradable plastics
  14. 14Sources of methane and carbon dioxide
  15. 15The enhanced greenhouse effect and climate change
  16. 16Eutrophication
  17. 17Sustainable resources
  18. 18Why species become endangered
  19. 19Conserving endangered species
  20. 20Conserving forests
  21. 21Conserving fish stocks
  22. 22Reasons for conservation
  23. 23AI and IVF in captive breeding
  24. 24Small populations and genetic variation

1. Machinery and chemical fertilisers

Agricultural machinery lets farmers use larger areas of land and improves efficiency.

Chemical fertilisers improve yields. Fertilisers contain nitrates, which plants use to make proteins.

As the mass of fertiliser increases, the yield increases and then decreases slightly or becomes constant.

percentage change = (change in yield)/(original yield) × 100

Examiner insight

“While most candidates chose an item of farm machinery, used to farm larger areas of land, some incorrectly put descriptions of how the land is cleared or farmed e.g. deforestation, monoculture.” “Candidates need to be aware that fertiliser is a collective term and that it is better to be more precise with terminology. For instance, magnesium ions are required to make chlorophyll and nitrate ions are required to make proteins.”

Worked example 13 marks

Scientists investigated the effect of the mass of fertiliser used on potato crop yield. Using the data in Table 3.1, calculate the percentage change in the potato crop yield when the mass of fertiliser used was increased from 60 kg per hectare to 285 kg per hectare. Give your answer to three significant figures.

mass of fertiliser used / kg per hectarepotato crop yield / tonnes per hectare
6032.5
11540.0
17043.5
23045.0
28544.5
34044.0
  1. 1

    change in yield = 44.5 - 32.5 = 12.0 tonnes per hectare [1]

  2. 2

    percentage change = 12.0/32.5 × 100 [1]

  3. 3

    = 36.9% [1]

2. Insecticides and herbicides

Insecticides improve the quality and yield of crops. They kill insects that would eat or damage the crops.

Herbicides kill weeds. This reduces competition between weeds and crop plants, so crop yields increase.

Examiner insight

“Most candidates knew that insecticides kill insects. This response is insufficient as an explanation and to complete the answer and gain both marks it was necessary for a candidate to say, for example, that if left untreated, insects will eat or damage the crops or that killing the insects will result in a higher crop yield.”

Worked example 11 mark

Why are herbicides used in crop production?

A to increase crop yields by reducing competition between weeds and crop plants B to increase crop yields by increasing competition between weeds and crop plants C to decrease crop yields by reducing competition between weeds and crop plants D to decrease crop yields by increasing competition between weeds and crop plants

  1. 1

    A: to increase crop yields by reducing competition between weeds and crop plants. [1]

3. Selective breeding

Selective breeding improves production by crop plants and livestock. It is also called artificial selection.

Humans select parents with the feature they want. In crops, pollen from them is put on the stigma of other plants.

The offspring are observed. The best are selected and bred together. This is repeated for many generations.

Examiner insight

“While many candidates appreciated that selective breeding involves parents that possess desirable features, some candidates incorrectly believed that it involves a struggle for survival.”

Worked example 14 marks

Crop plants have been bred to increase yield. Complete the sentences by writing words or phrases in the spaces to describe this process.

Humans select crop plants that have the largest yield. The pollen from these plants is taken and rubbed onto the ...... of other plants of the same species. The ...... of these plants are then observed and the ones with the highest yields are then selected and bred together. This is repeated for many ......, until all the plants produced have a high yield. This process is called ......

  1. 1

    stigma [1]

  2. 2

    offspring [1]

  3. 3

    generations [1]

  4. 4

    artificial selection / selective breeding [1]

4. Large-scale monocultures

A monoculture is the growing of one type, or one species, of crop plant. It is not one plant.

An advantage: in a monoculture the yield is higher. Answers must be comparative.

Disadvantages: an increased risk of a disease spreading, heavy infestations of pests, depletion of nutrients from the soil, and reduced biodiversity as habitats are destroyed. A polyculture, with several crop species, supports more species of pollinator.

Examiner insight

“It is important that candidates clearly state that a monoculture involves the culture of one type, or one species of plant, and is not the culture of one plant.” “It is important that answers contain comparative descriptions – for example in a monoculture the yield is higher and there is an increased risk of a disease spreading.”

Worked example 13 marks

A polyculture is a farming system which involves planting several different types of crop plants in the same area. The numbers of different species of pollinator were counted in a polyculture and in a monoculture. Using the information in Table 5.1, suggest the advantages to the environment of polyculture farming compared to monoculture farming.

type of crop plant farming systemnumber of crop plant speciesnumber of different species of pollinator
polyculture390
monoculture157
  1. 1

    increased biodiversity / species diversity: 90 species of pollinator against 57 [1]

  2. 2

    increased chance of pollination / fertilisation [1]

  3. 3

    better maintenance of food chains / food webs [1]

5. Intensive livestock production

Describe intensive livestock production by comparing it with non-intensive production.

Advantages: less agricultural land is needed, livestock grow faster, and optimum conditions can be provided.

These are not advantages: livestock must have food provided for them, there is a greater chance of infections being transmitted between animals, and a greater chance of environmental damage.

Examiner insight

“Candidates often did not give responses that were specific to intensive farming. Thinking about how extensive farming compares with intensive farming might have helped them to find advantages.” “Some gave references to crop plant production rather than livestock production.”

Worked example 13 marks

Goats are often kept as livestock. Some types of livestock are farmed intensively. Underline three statements that describe advantages of intensive livestock production compared to non-intensive livestock production.

• Less agricultural land is needed. • Livestock grow faster. • Livestock must have food provided for them. • Optimum conditions can be provided. • There is a greater chance of infections being transmitted between animals. • There is a greater chance of environmental damage.

  1. 1

    Less agricultural land is needed. [1]

  2. 2

    Livestock grow faster. [1]

  3. 3

    Optimum conditions can be provided. [1]

Recap

  • Machinery: larger areas of land and improved efficiency.
  • Fertilisers improve yields. Plants use nitrates to make proteins.
  • Insecticides improve quality and yield: they kill insects that eat or damage the crop. Herbicides kill weeds and reduce competition.
  • Selective breeding: select parents, breed, select the best offspring, repeat for many generations.
  • Monoculture: one type of crop. Higher yield, but more risk of disease spreading and less biodiversity.
  • Intensive livestock: less land, faster growth, optimum conditions. Food must be provided, infections are transmitted more easily and the environment can be damaged.

6. Biodiversity

Biodiversity is the number of different species that live in an area.

It counts species, not individual organisms. An area with many species has high biodiversity.

Examiner insight

“A large number of candidates confused the description of biodiversity with ecosystem.” “Some candidates incorrectly thought that reducing biodiversity would conserve endangered species.”

Worked example 12 marks

State what is meant by the term biodiversity.

  1. 1

    the number of different species [1]

  2. 2

    that live in an area [1]

7. Reasons for habitat destruction

Humans destroy habitats to make increased area for housing, crop plant production and livestock production.

They also destroy them for the extraction of natural resources.

Freshwater and marine pollution destroy the habitats of the organisms that live there.

Examiner insight

“Some just stated deforestation without explaining the reason for it so did not gain a mark.” “Common answers that did not gain credit were bulleted lists of words without any context, and vague mentions of pollution or chemicals.”

Worked example 13 marks

Give three reasons for habitat destruction.

  1. 1

    increased area for housing, crop plant production or livestock production [1]

  2. 2

    extraction of natural resources [1]

  3. 3

    freshwater and marine pollution [1]

8. Food webs and food chains

Through altering food webs and food chains, humans can have a negative impact on habitats.

The organisms in a food web depend on one another. Removing or adding one organism changes the numbers of the others.

Examiner insight

“Weaker candidates stated that, as hawks did not eat snakes, nothing would happen to the number of hawks.” “It is important that candidates realise the interdependence of organisms within a food web.”

Worked example 12 marks

Hunters remove all the foxes from a woodland. Foxes eat rabbits, and rabbits eat grass. Explain how this affects other organisms in the food web.

  1. 1

    rabbits are no longer eaten by foxes, so the number of rabbits increases [1]

  2. 2

    rabbits eat more grass, so the amount of grass decreases [1]

9. Deforestation: habitats and species

Deforestation is the removal of forest. It is an example of habitat destruction.

It causes loss of habitats. With fewer habitats there are fewer species, so biodiversity is reduced. Species can be lost completely, which is extinction.

Examiner insight

“Some candidates were not able to gain full credit for their response as they did not use scientific language. An example of this is the use of the term home instead of habitat.” “Some responses described effects of secondary events such as soil erosion and climate change on the animals rather than the required direct effects.”

Worked example 11 mark

What is least likely to result from deforestation?

A increase in flooding · B increase in species · C loss of habitats · D loss of soil

  1. 1

    B: increase in species. Deforestation causes loss of habitats, so species are lost, not gained. [1]

10. Deforestation: loss of soil and flooding

Tree roots hold the soil. When trees are removed, the soil is lost by soil erosion.

More water runs off the land. This increases the risk of flooding.

Less fertile soil remains for the growth of crops.

Examiner insight

“The idea of soil erosion from disturbing the tree roots was often seen with this also leading to flooding or landslides.” “The best responses related deforestation to the effects on the soil such as soil erosion, increased runoff, and the leaching of minerals.”

Worked example 11 mark

Deforestation can have a negative impact on the environment. Which statement about the negative impact of deforestation is correct?

A It decreases the levels of carbon dioxide, which can lead to reduced rates of photosynthesis. B It decreases the amount of water flowing in local rivers, so there is less flooding. C It leads to soil loss, so there is less fertile soil for the growth of crops in the area. D It provides less land for the extraction of natural resources.

  1. 1

    C: it leads to soil loss, so there is less fertile soil for the growth of crops in the area. A and B are the wrong way round: carbon dioxide and flooding both increase. [1]

11. Deforestation: carbon dioxide

Trees take in carbon dioxide for photosynthesis.

When trees are removed there is a decrease in photosynthesis. Less carbon dioxide is removed from the atmosphere, so the carbon dioxide in the atmosphere increases.

Examiner insight

“One misconception was that reduced carbon dioxide in the atmosphere is an undesirable effect of deforestation.” “Many candidates only gave a partial answer, either stating that there would be more carbon dioxide in the atmosphere, instead of less carbon dioxide was removed from the atmosphere and did not say this was because of a decrease in photosynthesis.”

Worked example 13 marks

Explain how deforestation increases the carbon dioxide in the atmosphere.

  1. 1

    there are fewer trees, so there is a decrease in photosynthesis [1]

  2. 2

    less carbon dioxide is removed from the atmosphere [1]

  3. 3

    so the carbon dioxide in the atmosphere increases [1]

Recap

  • Biodiversity is the number of different species that live in an area.
  • Habitats are destroyed for housing, crop plant and livestock production, and extraction of natural resources.
  • Freshwater and marine pollution also destroy habitats.
  • By altering food webs and food chains, humans can have a negative impact on habitats.
  • Deforestation causes loss of habitats, reduced biodiversity and extinction.
  • Deforestation causes loss of soil and flooding.
  • Deforestation decreases photosynthesis, so carbon dioxide in the atmosphere increases.

12. Untreated sewage and excess fertiliser

Untreated sewage and excess fertiliser both pollute water. Each leads to increased growth of producers and a fall in the oxygen concentration of the water.

Decomposers break down the sewage. They use up dissolved oxygen and release mineral ions. Fertiliser that runs off fields adds nitrate ions to the water.

With less oxygen, aquatic organisms that need oxygen for respiration die.

Examiner insight

“Candidates were unsure about the consequences of untreated sewage pollution on aquatic ecosystems.” “A few incorrectly thought that the level of oxygen rises when sewage is released into a river.”

Worked example 11 mark

What is an effect of untreated sewage on aquatic ecosystems?

effect
Adecreased decomposition
Bdecreased nitrate ion concentration
Cincreased biodiversity
Dincreased growth of producers
  1. 1

    Decomposers break down sewage, so decomposition increases and A is wrong.

  2. 2

    Decomposition releases mineral ions, so nitrate ion concentration increases and B is wrong.

  3. 3

    Less oxygen means organisms die, so biodiversity does not increase and C is wrong.

  4. 4

    D: increased growth of producers [1]

13. Non-biodegradable plastics

Non-biodegradable plastic is not broken down, so it stays in the environment.

On land and in water, animals eat the plastic or get tangled in it. Sharp pieces cause injuries. In water, plastic can block light, so producers photosynthesise less and less food enters the food web.

Small pieces of plastic, microplastics, pass along the food chain because they are not broken down.

Examiner insight

“Some described damage to the ecosystem, or toxin release rather than damage to the individual animal.” “Other candidates tended to say that the oceans would become polluted and that the water would become dirty and unhygienic.”

Worked example 12 marks

Scientists investigated the nests of five different species of bird on an island.

Suggest two disadvantages to birds of having nests containing non-biodegradable plastic.

  1. 1

    any two from:

  2. 2

    chicks / birds get tangled in the plastic [1]

  3. 3

    chicks / birds eat the plastic [1]

14. Sources of methane and carbon dioxide

Humans add methane and carbon dioxide to the air.

Methane comes from livestock such as cattle and sheep, from rice farming (flooded rice fields) and from landfill sites (rubbish tips). Carbon dioxide comes from the combustion of fossil fuels. Deforestation leaves fewer trees to take in carbon dioxide.

Examiner insight

“Many candidates gave combustion or burning which was not accepted.” “Some candidates gave natural sources of the chemical substances stated rather than sources of pollution caused by humans which was not accepted.”

Worked example 14 marks

Scientists have observed increasing levels of methane in the atmosphere.

Describe the sources of methane and the effects of methane pollution on ecosystems.

  1. 1

    any four from sources and effects:

  2. 2

    source: cattle / sheep / livestock [1]

  3. 3

    source: rice farming [1]

  4. 4

    effect: enhanced greenhouse effect [1]

  5. 5

    effect: climate change / global warming [1]

  6. 6

    also credited: loss of habitats; organisms may become extinct or endangered

15. The enhanced greenhouse effect and climate change

Methane and carbon dioxide are both greenhouse gases. More of them in the air gives the enhanced greenhouse effect.

The effects are climate change and global warming. Ice melts and sea levels rise. Habitats are lost and species may become extinct.

Human activity does not cause the greenhouse effect. It enhances it.

Examiner insight

“Another common error was to state that the greenhouse effect was caused by the factors discussed rather than being enhanced by them.” “Many weaker candidates thought that an increase in atmospheric carbon dioxide concentrations would result in acid rain or holes in the ozone layer.”

Worked example 11 mark

Which row correctly shows if each gas is responsible for the enhanced greenhouse effect?

carbon dioxidemethane
Anono
Bnoyes
Cyesno
Dyesyes
  1. 1

    Carbon dioxide is a greenhouse gas, so its answer is yes.

  2. 2

    Methane is a greenhouse gas, so its answer is yes.

  3. 3

    D [1]

16. Eutrophication

Eutrophication happens in this order. Nitrate ions and other ions become more available in the water. Producers such as algae grow faster.

The producers die. Decomposers increase and decompose the dead producers. They respire aerobically at a higher rate.

The dissolved oxygen concentration falls. Organisms that need dissolved oxygen die.

Examiner insight

“Common misconceptions included attributing the lack of oxygen in water bodies to the lack of photosynthesis of producers and manure covering the surface blocking light for producers.” “A minority mistook algae for decomposers and stated that algae were responsible for the reduction in the oxygen concentration in the water.”

Worked example 11 mark

The graph shows the relative concentrations of three substances in the water of a river.

The three substances are oxygen, algae and mineral ions.

The graph also shows where fertiliser is released into the river.

Which substances do lines X, Y and Z represent?

XYZ
Aalgaeoxygenmineral ions
Bmineral ionsalgaeoxygen
Coxygenalgaemineral ions
Doxygenmineral ionsalgae
  1. 1

    Fertiliser adds mineral ions, so the line that jumps at the outflow is Z.

  2. 2

    Producers such as algae then grow, so the line that rises is X.

  3. 3

    Decomposers use up dissolved oxygen, so the line that falls is Y.

  4. 4

    A: X algae, Y oxygen, Z mineral ions [1]

Recap

  • Untreated sewage and excess fertiliser increase the growth of producers and lower the oxygen concentration of the water.
  • Non-biodegradable plastic is not broken down. Animals eat it or get tangled in it, on land and in water.
  • Methane sources: livestock, rice farming, landfill. Carbon dioxide sources: combustion of fossil fuels and deforestation.
  • Both gases cause the enhanced greenhouse effect, leading to climate change and global warming.
  • Extended: eutrophication runs nitrate ions up, producers grow, producers die, decomposers respire aerobically, dissolved oxygen falls, organisms die.
  • Extended: the oxygen is used up by the aerobic respiration of decomposers, not by the death of the plants.

17. Sustainable resources

A sustainable resource is one which is produced as rapidly as it is removed from the environment so that it does not run out.

Forests and fish stocks can be conserved and managed sustainably.

Examiner insight

“Often candidates understood that a sustainable resource is produced as rapidly as it is used but fewer went on to say that it does not run out.”

Worked example 12 marks

Describe what is meant by a sustainable resource.

  1. 1

    a resource that is produced as rapidly as it is used [1]

  2. 2

    so it does not run out [1]

18. Why species become endangered

A species becomes endangered or extinct because of climate change, habitat destruction, hunting, overharvesting, pollution or introduced species.

Habitat destruction and pollution cause a lack of, or more competition for, resources. An introduced species brings a new predator or more competition. Each cause decreases the population size.

Examiner insight

“When predation was mentioned, few specified that it was the introduction of new predators that would result in extinction. Several candidates listed habitat destruction and deforestation which were the same point.”

Worked example 14 marks

Describe reasons why animals such as the Arabian oryx become extinct in the wild.

  1. 1

    hunted by humans / poaching [1]

  2. 2

    (named) destruction of their habitat [1]

  3. 3

    pollution (of their habitat) [1]

  4. 4

    introduced / foreign species, or competition from other organisms [1]

19. Conserving endangered species

An endangered species can be conserved by monitoring and protecting species and habitats, by education, by captive breeding programmes and by seed banks.

Animals kept alive in zoos can be bred and then reintroduced into the wild. Seed banks suit plants: many seeds are dormant and most need little space for storage.

Examiner insight

“However, there was a tendency to state the same point with slightly different terminology. For example, protecting the habitat and creating a nature reserve would be the same marking point.” “A few candidates describe selective breeding rather than captive breeding.”

Worked example 11 mark

Some Arabian oryxes were still alive in zoos in 1972. They were successfully reintroduced back into the wild in 1978. State the name of the process that zoos use to increase the number of individuals of an endangered species.

  1. 1

    captive breeding [1]

20. Conserving forests

Forests can be conserved using education, protected areas, quotas and replanting.

A quota limits the number of trees that may be cut. Replanting puts new trees in place of those that are cut down, so the forest is a sustainable resource.

Examiner insight

“Some candidates did not understand that cutting down only selected trees is part of ensuring the forest is used sustainably.”

Worked example 14 marks

A forest company may cut down no more than 500 trees a year and must plant new trees. Name the two methods of conservation and explain how each helps to conserve the forest.

  1. 1

    quotas [1]

  2. 2

    limit the number of trees that are cut down [1]

  3. 3

    replanting [1]

  4. 4

    new trees replace those cut down, so trees are produced as rapidly as they are removed [1]

21. Conserving fish stocks

Fish stocks can be conserved using education, closed seasons, protected areas, controlled net types and mesh size, quotas and monitoring.

The aim is to let young fish grow to adults and reproduce, so that the population is maintained. Large holes in a net let small, young fish escape, so only large, old fish are caught.

Examiner insight

“Fewer were able to provide more detail on how their stated method was able to conserve fish stocks. The best responses often related to allowing young fish to survive in order to breed to replenish the population.”

Worked example 14 marks

One way of conserving wild fish stocks is to regulate the size of the holes in the nets that are used to catch the fish. Explain how this helps to conserve fish stocks.

  1. 1

    holes should be large [1]

  2. 2

    small / young fish escape, so only large / old fish are caught [1]

  3. 3

    the escaped fish grow to adults / reach breeding age [1]

  4. 4

    they can reproduce, which maintains the population of the fish [1]

22. Reasons for conservation

Biodiversity is the number of different species that live in an area.

Conservation programmes aim at maintaining or increasing biodiversity, reducing extinction and protecting vulnerable ecosystems. They also maintain ecosystem functions, limited to nutrient cycling and resource provision. The resources are food, drugs, fuel and genes.

Examiner insight

“Most candidates gave the importance of conservation projects in preventing extinction, maintaining biodiversity, and protecting ecosystems, but very few gave any further description.” “Those who expanded their answers included ideas of providing the sources of new drugs, genes, and crop plants, and for future research.”

Worked example 14 marks

Describe two reasons for a conservation programme in a rainforest.

  1. 1

    maintaining biodiversity [1]

  2. 2

    keeps up the number of different species that live in the area [1]

  3. 3

    resource provision, for example food, drugs, fuel or genes [1]

  4. 4

    so the rainforest still supplies, for example, a source of new drugs [1]

23. AI and IVF in captive breeding

Both are used in captive breeding programmes.

In artificial insemination (AI), sperm is collected and inserted into the female's vagina, uterus or oviduct, at the time of ovulation.

In in vitro fertilisation (IVF), eggs and sperm are collected and fertilisation occurs outside the body, in a dish. The embryo is then inserted into the uterus.

Examiner insight

“A common misconception was that the resultant zygote is inserted into the uterus rather than insertion of an embryo.” “Many candidates stated that sperm is collected, but then went on to describe in vitro fertilisation (IVF) rather than artificial insemination.”

Worked example 15 marks

Describe the processes of artificial insemination (AI) and in vitro fertilisation (IVF).

  1. 1

    AI: semen / sperm collected [1]

  2. 2

    AI: sperm inserted into the vagina / uterus / oviduct [1]

  3. 3

    IVF: eggs and sperm collected [1]

  4. 4

    IVF: fertilisation occurs outside the body, in a dish [1]

  5. 5

    IVF: embryo inserted into the uterus [1]

24. Small populations and genetic variation

If a population size decreases, there is less genetic variation within the species.

The species is then less able to adapt to a changed environment, such as climate change. A disease can kill most of the population. It is also harder to find a mate, so there is reduced reproduction.

Knowledge of genetic drift is not required.

Examiner insight

“The best responses went on to explain the risks to having such low population numbers in terms of lack of genetic diversity, inbreeding and risk of genetic disease.” “Many candidates described the effects on the rest of the food web, but the question specifically asked for the risks to a population rather than the environment.”

Worked example 14 marks

The population of a rare frog has fallen from 5000 to 40 individuals. Explain the risks to the species of the smaller population size.

  1. 1

    less genetic variation in the species [1]

  2. 2

    so it is less able to adapt if the environment changes [1]

  3. 3

    a disease could kill most of the population [1]

  4. 4

    harder to find a mate, so reduced reproduction [1]

Recap

  • Sustainable resource: produced as rapidly as it is removed, so it does not run out.
  • Forests and fish stocks can be conserved and managed sustainably.
  • Species become endangered or extinct through climate change, habitat destruction, hunting, overharvesting, pollution and introduced species.
  • Endangered species are conserved by monitoring and protecting, education, captive breeding and seed banks.
  • Extended: forests use education, protected areas, quotas and replanting.
  • Extended: fish stocks use education, closed seasons, protected areas, net types and mesh size, quotas and monitoring.
  • Extended: conservation maintains biodiversity, reduces extinction, protects ecosystems and keeps nutrient cycling and resource provision.
  • Extended: AI inserts sperm; IVF fertilises eggs outside the body and inserts the embryo.
  • Extended: a small population has less genetic variation, so it adapts less well and is at risk of extinction.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. State one way in which agricultural machinery has increased food production.1 mark
  2. Chemical fertilisers are added to a field of wheat. Name the mineral ion in the fertiliser that plants use to make proteins. State the effect of fertilisers on yield.2 marks
  3. A farmer sprays a field of maize with a herbicide. Explain why the maize yield increases.2 marks
  4. A farmer sprays an insecticide on a field of cabbages. Explain how this improves the yield.2 marks
  5. With 100 kg of fertiliser per hectare, a wheat yield is 8.0 tonnes per hectare. With 150 kg per hectare, it is 9.2 tonnes per hectare. Calculate the percentage increase in yield.3 marks
  6. Describe how selective breeding could be used to increase the mass of wool produced by a flock of sheep.4 marks
  7. State what is meant by the term monoculture.1 mark
  8. Describe two effects of large-scale monocultures on the wider ecosystem.2 marks
  9. A farmer rears chickens for meat in an intensive indoor shed and in a non-intensive outdoor field. Chicks of the same age and breed are put into each system. The table shows the results after six weeks. (a) Calculate the percentage increase in mean mass when chickens are reared in the shed instead of the field. (b) Use the table to state two advantages of the intensive system compared with the non-intensive system. (c) Use the table to state one disadvantage of the intensive system. | system | land used for 1000 chickens / m² | mean mass of a chicken / kg | chickens with an infection per 1000 | | --- | --- | --- | --- | | intensive | 60 | 2.4 | 45 | | non-intensive | 4000 | 1.6 | 18 |5 marks
  10. Two farms each have 200 hectares of land. Farm X is a monoculture of rice. Farm Y is a polyculture of rice, beans and squash grown together. The table shows data for one year. (a) Calculate how many more tonnes of rice farm X produces in the year than farm Y. (b) Farm X uses more insecticide than farm Y. Suggest why, and explain how the insecticide helps the farmer. (c) Use the table to describe the effect of the monoculture on the wider ecosystem. | farm | rice yield / tonnes per hectare | insecticide used / kg per hectare | number of different species of pollinator | | --- | --- | --- | --- | | X | 6.0 | 2.5 | 20 | | Y | 4.5 | 1.0 | 36 |6 marks
  11. State what is meant by biodiversity.1 mark
  12. Area P has 400 animals belonging to 3 species. Area Q has 60 animals belonging to 12 species. State which area has the greater biodiversity and give a reason.2 marks
  13. Give three human activities that lead to habitat destruction.3 marks
  14. A company mines ore from a hillside. Waste from the mine washes into a river. Identify two causes of habitat destruction in this situation.2 marks
  15. State how humans can have a negative impact on habitats through the organisms that live in them.1 mark
  16. In a sea, sardines eat plankton and tuna eat sardines. Overfishing removes most of the sardines. Explain two effects on the food web.2 marks
  17. Name two direct effects of deforestation on the organisms that live in a forest.2 marks
  18. Trees on a hillside are cut down. Explain how this can lead to flooding in the valley below.3 marks
  19. A forest on a hillside above a village is cleared so that cattle can graze. The table gives the results of surveys of the hillside before the clearance and five years after it. (a) State the reason for habitat destruction in this example. (b) A villager says: ‘There are more birds now, so clearing the forest has increased biodiversity.’ Explain why the villager is wrong. (c) Explain the change in the depth of soil, and state one undesirable effect of this change on the village. | | before | after | | --- | --- | --- | | number of bird species | 48 | 9 | | total number of birds | 620 | 1150 | | depth of soil / cm | 35 | 12 |6 marks
  20. A forest is cut down so that gravel can be dug out of the ground. Deer in the forest eat only the leaves of the trees, and wolves eat only deer. A student writes two statements. Statement 1: ‘With the trees gone there is less oxygen, so the carbon dioxide in the atmosphere goes up.’ Statement 2: ‘Wolves do not eat trees, so nothing happens to the number of wolves.’ (a) Rewrite statement 1 so that it gives the correct reason. (b) Explain why statement 2 is wrong. (c) One species of beetle lives only in this forest. Explain the effect of the clearance on this species and on the biodiversity of the area.7 marks
  21. Untreated sewage enters a river. State the change in the oxygen concentration of the water.1 mark
  22. Rain washes excess fertiliser from a field into a pond. Describe two effects on the pond.2 marks
  23. A bird's nest contains non-biodegradable plastic. State two ways it can harm the chicks.2 marks
  24. Microplastics are eaten by small animals in the sea. Explain why microplastics are still present in animals at the end of the food chain.2 marks
  25. Give two sources of methane pollution caused by humans and state one effect of increased methane in the air.3 marks
  26. A farm has 40 cows. Each cow produces 50 kg of methane per year. A feed additive reduces the methane from each cow by 20%. Calculate the total reduction in methane for the whole herd in one year.2 marks
  27. Describe how human activities increase the concentration of carbon dioxide in the air, and state the effect of this increase.3 marks
  28. The statements describe eutrophication in a lake. Put them in the correct order. A dissolved oxygen concentration falls; B producers die; C nitrate ion concentration rises; D fish die; E decomposers respire aerobically at a higher rate; F producers grow faster.3 marks
  29. Untreated sewage enters a river. A student tested the water at site P, upstream of the sewage, and at site R, 3 km downstream. The results are in the table. (a) Calculate the percentage decrease in dissolved oxygen concentration from P to R. (b) Explain why the dissolved oxygen concentration falls between P and R. (c) Explain why the nitrate ion concentration rises between P and R. | site | dissolved oxygen / mg per dm³ | nitrate ions / mg per dm³ | | --- | --- | --- | | P | 9.5 | 1.0 | | R | 1.9 | 6.5 |5 marks
  30. A student tested why dissolved oxygen falls during eutrophication. She kept three tanks of lake water in the dark for five days. The table gives the contents of each tank and its dissolved oxygen concentration, in mg per dm³, on day 0 and day 5. (a) Calculate the percentage decrease in dissolved oxygen concentration in tank 1. (b) Use all three tanks to explain why the dissolved oxygen concentration fell most in tank 1. (c) Another student says the oxygen falls in a polluted lake because the dead algae can no longer photosynthesise. Explain how tank 2 tells you this is not the cause. | tank | dead algae | decomposers | day 0 | day 5 | | --- | --- | --- | --- | --- | | 1 | added | present | 9.0 | 2.7 | | 2 | added | all killed | 9.0 | 8.8 | | 3 | none | present | 9.0 | 8.1 |6 marks
  31. A farm cuts down 200 trees a year and plants 200 new trees each year. Explain why the wood from the farm is a sustainable resource.2 marks
  32. State two resources that can be conserved and managed sustainably.2 marks
  33. A rare orchid is threatened by clearing forest for farmland, cutting down forest for timber, and collectors digging up plants to sell. State how many different reasons for becoming endangered these give, and name them.3 marks
  34. A zoo breeds a rare frog and releases the young into a protected wetland. Name two methods of conserving an endangered species that the zoo and the wetland use.2 marks
  35. A seed bank stores the seeds of an endangered plant for many years. Give two reasons why seeds are suitable for conserving plants in this way.2 marks
  36. A paper company cuts down 300 trees a year in a forest. State one thing it should do so that the forest is a sustainable resource, and explain why.2 marks
  37. A government pays for a programme to conserve a wetland. Describe three reasons for the programme.3 marks
  38. A zoo uses in vitro fertilisation (IVF), not artificial insemination (AI), for a rare monkey. State three ways IVF differs from AI.3 marks
  39. A lake holds a stock of 30 000 fish. Each year 4000 fish are removed by fishing. With nets of 40 mm mesh, 2500 fish are added to the stock each year. With nets of 80 mm mesh, 4000 fish are added each year. Assume these numbers stay the same every year. (a) State which mesh size makes the fish a sustainable resource. Give a reason from the data. (b) Calculate how many years the stock lasts when the other mesh size is used. (c) Explain why more fish are added to the stock each year when the larger mesh is used.6 marks
  40. The table gives the number of breeding birds of a rare species on an island. (a) Calculate the percentage decrease in the number of breeding birds from 2000 to 2020. (b) Explain two risks to the species if the population stays this small. (c) The 15 birds are taken into a captive breeding programme. Sperm frozen in 1990, from males that have since died, is used for artificial insemination (AI). Explain why using this sperm reduces a risk you gave in (b). | Year | Number of breeding birds | | --- | --- | | 1990 | 320 | | 2000 | 250 | | 2020 | 15 |8 marks

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