IGCSE Biology Topic 20: Human influences on ecosystems MCQs – 30 Practice Questions with Answers (Cambridge 0610)
Free practice for Cambridge IGCSE Biology 0610 on human influences on ecosystems, covering food supply, habitat destruction, pollution and conservation, with every question followed by a worked explanation.
Food Supply and Farming Methods
Q1. How has agricultural machinery helped humans increase food production?
- (A) It allows larger areas of land to be farmed more efficiently
- (B) It removes the need for soil altogether by growing crops in machines
- (C) It removes the need for water in crop growth
- (D) It stops insect pests from reaching crops
Show Answer
Answer: A – Machines let farmers work bigger areas faster and more efficiently, raising the amount of food that can be produced.
Q2. How do chemical fertilisers improve crop yields?
- (A) By killing all insect pests on the crop before they can damage the leaves in the field
- (B) By supplying mineral ions that plants need for healthy growth
- (C) By increasing rainfall over the fields
- (D) By replacing sunlight in photosynthesis
Show Answer
Answer: B – Fertilisers add ions such as nitrate, phosphate and potassium, which are often in short supply in soil and limit growth.
Q3. What is the purpose of applying an insecticide to a crop?
- (A) To fertilise the soil around the plants so that they grow taller and faster in the field
- (B) To kill weeds competing with the crop
- (C) To control insect pests and so improve the quality and yield of the crop
- (D) To pollinate the flowers of the crop
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Answer: C – Insecticides reduce damage by insect pests, so more of the crop survives in good condition to harvest.
Q4. How do herbicides help a crop plant?
- (A) By killing insects that eat its leaves
- (B) By adding mineral ions to the soil
- (C) By speeding up photosynthesis in its leaves so the crop grows faster
- (D) By reducing competition from weeds for light, water and ions
Show Answer
Answer: D – Weeds compete with crops for the same resources, so removing them leaves more light, water and mineral ions for the crop.
Q5. What does selective breeding involve in food production?
- (A) Choosing parents with wanted features and breeding from them over generations
- (B) Moving a single gene from one species into another species by genetic modification
- (C) Using machines to harvest a larger area
- (D) Applying fertiliser to raise the yield of a field
Show Answer
Answer: A – Selective breeding crosses individuals of the same species that show desired traits, unlike genetic modification, which transfers genes directly.
Q6. What is one advantage of a large-scale monoculture of a crop plant?
- (A) It increases the biodiversity of the farmland by supporting many wild species
- (B) It allows uniform, efficient management and harvesting of a large area
- (C) It steadily improves the fertility of the soil
- (D) It prevents disease from spreading between plants
Show Answer
Answer: B – Growing one crop over a wide area suits standard machinery and routines, which keeps large-scale production efficient.
Q7. What is one disadvantage of a large-scale monoculture of a crop plant?
- (A) It needs a wider variety of skilled labour and machinery than mixed cropping does
- (B) It creates many new wildlife habitats
- (C) A pest or disease can spread rapidly through a genetically similar crop
- (D) It always gives lower yields than mixed cropping
Show Answer
Answer: C – When plants across a large area are very similar, a pest or pathogen that attacks one plant can attack almost all of them.
Q8. What is one disadvantage of intensive livestock production?
- (A) Animals always grow more slowly than outdoors
- (B) It needs more land per animal than extensive farming and produces less meat overall
- (C) It greatly reduces the risk of disease
- (D) Crowded conditions let disease spread easily and produce large amounts of waste
Show Answer
Answer: D – Keeping many animals close together raises the chance of infection spreading and concentrates waste that must be managed.
Habitat Destruction and Deforestation
Q9. What does biodiversity mean?
- (A) The number of different species that live in an area
- (B) The number of individuals of a single species in an area
- (C) The total mass of all organisms in an area
- (D) The number of separate habitats in a country
Show Answer
Answer: A – Biodiversity counts how many different species are present, not how many individuals of one species there are.
Q10. Which is a major reason for habitat destruction?
- (A) Replanting cleared woodland with native trees to restore the habitat
- (B) Clearing land for housing and for crop and livestock production
- (C) Creating nature reserves on farmland
- (D) Reducing pollution from factories
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Answer: B – As demand for homes, food and grazing grows, natural habitats are cleared to make room for them.
Q11. How does extraction of natural resources damage habitats?
- (A) It builds new habitats for native species in the quarries left behind
- (B) It increases the number of species in the area
- (C) Mining and quarrying remove vegetation and break up the habitat
- (D) It purifies nearby rivers and lakes
Show Answer
Answer: C – Digging for minerals, stone or other resources strips away the living surface and fragments what remains.
Q12. When humans remove a species from a habitat, what is a likely wider effect?
- (A) Only that one species is ever affected, and the rest of the habitat stays unchanged
- (B) Biodiversity always increases as a result
- (C) The habitat always becomes more stable
- (D) Food chains and food webs are altered, harming the habitat as a whole
Show Answer
Answer: D – Every species is linked to others through feeding, so removing one can change predator and prey populations across the habitat.
Q13. What is one undesirable effect of deforestation on wildlife?
- (A) It reduces biodiversity and can push species towards extinction
- (B) It increases the number of species in the forest by opening up new clearings
- (C) It has no effect beyond the trees that are cut
- (D) It only affects the trees themselves
Show Answer
Answer: A – Clearing forest removes the habitats and food sources that many species depend on, so some may die out locally or entirely.
Q14. How does deforestation lead to loss of soil?
- (A) The soil becomes richer once trees are gone and their leaves rot into it
- (B) Without tree roots to hold it, soil is washed away by rain
- (C) The soil gains nutrients from fallen leaves
- (D) Flooding becomes less likely in the area
Show Answer
Answer: B – Roots bind the soil and the canopy softens rainfall, so cleared ground erodes far more easily.
Q15. How does deforestation affect flooding and the atmosphere?
- (A) It decreases carbon dioxide in the atmosphere because fewer trees respire at night
- (B) It prevents flooding in lowland areas
- (C) It increases atmospheric carbon dioxide and flood risk as uptake falls
- (D) It increases the amount of rain absorbed by the soil
Show Answer
Answer: C – Fewer trees mean less photosynthesis to absorb carbon dioxide and less water uptake, while burning cleared trees releases more carbon dioxide.
Q16. A forest bird species is found nowhere else and its woodland is cleared for farming. Why is it at high risk of extinction?
- (A) All displaced animals always find an equally good habitat nearby to live and breed in successfully
- (B) New habitats form as soon as trees are removed
- (C) Every species adapts instantly to open farmland
- (D) It loses the habitat and food sources it depends on, with nowhere else to live
Show Answer
Answer: D – A species confined to one habitat cannot survive if that habitat is destroyed and no equivalent habitat remains.
Pollution of Water and Air
Q17. How does untreated sewage harm an aquatic ecosystem?
- (A) It adds nutrients feeding algal growth, causing oxygen loss when algae decay
- (B) It cleans the water by diluting pollutants and washing them safely downstream
- (C) It increases the dissolved oxygen in the water
- (D) It removes fertiliser from the water
Show Answer
Answer: A – Sewage is rich in nutrients, so it encourages producer growth whose later decay uses up dissolved oxygen.
Q18. What is the first step when excess fertiliser washes from fields into a lake?
- (A) Algae are killed directly by the fertiliser before they can grow in the lake
- (B) Nitrate and other ions become more available, so producers grow rapidly
- (C) Dissolved oxygen in the water immediately rises
- (D) Decomposition in the lake stops
Show Answer
Answer: B – Extra nitrate and other ions remove the nutrient limit on producers, starting the eutrophication sequence.
Q19. In eutrophication, what happens after the mass of producers dies?
- (A) Producers photosynthesise even faster because more nutrients remain available in the water
- (B) Dissolved oxygen in the water increases
- (C) Decomposers respire aerobically on the dead material, using dissolved oxygen
- (D) Fish populations rise sharply
Show Answer
Answer: C – Aerobic respiration by decomposers consumes oxygen from the water, which is the step that makes eutrophication lethal to aquatic animals.
Q20. What is the final harmful result of eutrophication for aquatic animals?
- (A) Algae thrive permanently at the surface
- (B) Decomposers die first from a lack of food
- (C) Fish grow faster in the nutrient-rich water because more food is available
- (D) Organisms that need dissolved oxygen in the water die
Show Answer
Answer: D – Once decomposers have used up the dissolved oxygen, fish and other oxygen-dependent animals suffocate.
Q21. Why are non-biodegradable plastics a problem in aquatic ecosystems?
- (A) They persist for a very long time and can entangle wildlife or be eaten by animals
- (B) They break down quickly into harmless substances that wildlife can safely eat without harm
- (C) They add nutrients that feed aquatic plants
- (D) They increase the dissolved oxygen in the water
Show Answer
Answer: A – Because microbes cannot break them down, plastics accumulate and injure animals that swallow them or become tangled in them.
Q22. Why are non-biodegradable plastics a problem on land?
- (A) They decompose rapidly into fertiliser that improves the soil for plants to grow
- (B) They remain for long periods in habitats, harming animals that eat them
- (C) They improve the structure of the soil
- (D) They are safely eaten by soil animals
Show Answer
Answer: B – Plastics do not rot away, so they build up in terrestrial habitats where animals may eat them or be harmed by them.
Q23. What is the main effect of air pollution by methane and carbon dioxide?
- (A) It damages only the ozone layer high above the poles and nowhere else
- (B) It causes acid rain and nothing else
- (C) It strengthens the greenhouse effect, leading to climate change
- (D) It lowers global temperatures
Show Answer
Answer: C – Both gases trap outgoing heat, enhancing the greenhouse effect and warming the climate.
Conservation and Sustainable Resources
Q24. What is a sustainable resource?
- (A) A resource that is never used by humans
- (B) A resource that is replaced only after many centuries of slow natural processes
- (C) A resource found only inside protected reserves
- (D) A resource produced as rapidly as it is removed, so that it does not run out
Show Answer
Answer: D – If removal is matched by replacement, the resource can keep being used without running out.
Q25. Which list includes reasons why organisms become endangered or extinct?
- (A) Climate change, habitat destruction, hunting, overharvesting and pollution
- (B) Captive breeding programmes in zoos that raise young animals for release into the wild
- (C) Seed banks storing plant seeds
- (D) Protected areas set up as reserves
Show Answer
Answer: A – Endangerment is usually driven by a combination of habitat loss, exploitation, pollution, climate change and introduced species.
Q26. How can a captive breeding programme help an endangered species?
- (A) By increasing the hunting quota for that species to control its numbers in the wild
- (B) By breeding individuals in captivity and releasing them to rebuild numbers
- (C) By draining the wetland where it lives
- (D) By introducing a foreign predator to control it
Show Answer
Answer: B – Captive breeding raises young in safety, and releases can restore a population that is too small to recover alone.
Q27. What is the purpose of a seed bank in conservation?
- (A) To store timber for building houses and furniture for future generations
- (B) To breed animals in captivity
- (C) To preserve seeds so that plant species can be regrown in future
- (D) To monitor the size of fish stocks
Show Answer
Answer: C – Stored seeds safeguard the genetic material of plant species, allowing them to be re-established if wild populations are lost.
Q28. Which combination of measures can conserve forests?
- (A) Education, protected areas, quotas on felling and replanting
- (B) Clear-felling all mature trees at once to maximise the timber harvest
- (C) Converting forest to farmland as quickly as possible
- (D) Removing all predators from the forest
Show Answer
Answer: A – Teaching people the value of forests, protecting areas, limiting how much is cut and planting replacements together keep forest cover sustainable.
Q29. Which measures help to conserve fish stocks?
- (A) Fishing throughout the whole year without limits, quotas, closed seasons or monitoring
- (B) Using nets with a smaller mesh size
- (C) Closed seasons, protected areas, controlled mesh size, quotas and monitoring
- (D) Removing all quotas on catches
Show Answer
Answer: C – Each measure limits when, where or how much is caught, giving stocks time and space to recover.
Q30. Why is a species at risk if its population size falls sharply?
- (A) Its genetic variation increases because new alleles appear more quickly
- (B) It adapts to change more quickly
- (C) It becomes immune to disease
- (D) Its genetic variation falls, leaving it less able to adapt to change
Show Answer
Answer: D – A small population holds fewer different alleles, so it is less likely to contain variants suited to new conditions or to resist disease.
Revisit any questions you missed, especially the steps of eutrophication and the conservation measures for forests and fish stocks, then test yourself again without looking at the answers.