IGCSE Biology Topic 19: Organisms and their environment MCQs – 30 Practice Questions with Answers (Cambridge 0610)
Free practice for Cambridge IGCSE Biology 0610 on organisms and their environment, covering energy flow, food chains and food webs, pyramids, nutrient cycles and populations, with every question followed by a worked explanation.
Energy Flow, Food Chains and Food Webs
Q1. Which is the principal source of energy input to most biological systems?
- (A) Light reflected from the Moon
- (B) Light energy from the Sun
- (C) Heat from deep underground rocks
- (D) Chemical energy stored in soil minerals
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Answer: B – The Sun supplies the light energy that producers capture in photosynthesis, and this energy then passes through food chains.
Q2. In a food chain, in which direction do the arrows point?
- (A) From the feeder towards its food
- (B) From the decomposer back towards the producer at the start of the chain
- (C) From the top consumer downwards
- (D) From the food organism towards the feeder
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Answer: D – Arrows show the direction of energy transfer, so each arrow points from the organism being eaten to the organism doing the eating.
Q3. Which description best fits a producer?
- (A) An organism that makes its own organic nutrients, usually using energy from sunlight
- (B) An animal that gains energy by eating plants
- (C) A fungus that gains energy from dead material
- (D) An animal that gains energy by hunting and eating other animals in its habitat throughout the year
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Answer: A – Producers, usually green plants, build their own organic nutrients by photosynthesis rather than feeding on other organisms.
Q4. In the food chain grass → rabbit → fox, which organism is the primary consumer?
- (A) The grass
- (B) The fox
- (C) The rabbit
- (D) A bacterium in the soil
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Answer: C – The rabbit feeds directly on the producer, so it is the primary consumer, while the fox is the secondary consumer.
Q5. Which animal is a herbivore?
- (A) An animal that gets its energy by eating plants
- (B) An animal that gets its energy by eating other animals
- (C) An animal that gets its energy from dead or waste material
- (D) An animal that gets its energy by eating both plants and animals
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Answer: A – Herbivores feed on plants, whereas carnivores feed on animals and omnivores feed on both.
Q6. Which feeding relationship describes a carnivore?
- (A) A cow grazing on grass in a meadow
- (B) A rabbit feeding on clover leaves
- (C) A deer browsing on young tree shoots
- (D) An owl catching and eating a mouse
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Answer: D – The owl gains its energy by eating another animal, which is the definition of a carnivore.
Q7. What is the role of a decomposer in a food web?
- (A) To make organic nutrients using sunlight and store them for other organisms
- (B) To get energy from dead or waste organic material
- (C) To feed on living green plants
- (D) To hunt living animals for food
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Answer: B – Decomposers, such as many bacteria and fungi, break down dead organisms and waste, returning nutrients to the ecosystem.
Q8. How does a food web differ from a single food chain?
- (A) A food web shows only one feeding route through a single producer
- (B) A food web shows producers only
- (C) A food web is a network of interconnected food chains
- (D) A food web shows decomposers only
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Answer: C – Most organisms feed on, or are eaten by, more than one species, so their feeding relationships form a linked network.
Q9. In a food chain, what is a quaternary consumer?
- (A) An animal that feeds on tertiary consumers
- (B) A plant that makes its own food by photosynthesis
- (C) An animal that feeds only on producers
- (D) A fungus that feeds on dead leaves
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Answer: A – Consumers are named by position: primary consumers eat producers, secondary eat primary consumers, tertiary eat secondary consumers, and quaternary consumers eat tertiary consumers.
Q10. A lake food web loses most of its large fish because of heavy harvesting. What is a likely wider result?
- (A) Every other population in the lake increases because more food becomes available
- (B) Only the producers are affected
- (C) No other level of the food web changes
- (D) Populations at other levels change as feeding relationships are disrupted
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Answer: D – Removing a heavily harvested species alters what its predators eat and what its prey experiences, so effects spread through the web.
Q11. Why can a foreign species introduced to a new habitat damage the existing community?
- (A) It always increases the number of species present and improves the habitat
- (B) It may outcompete native species or escape its natural predators
- (C) It never interacts with local food webs
- (D) It only ever feeds on producers
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Answer: B – An introduced species may compete with natives for food or space, or grow unchecked without its usual predators, pushing native populations down.
Pyramids and the Transfer of Energy
Q12. What does the term trophic level mean?
- (A) The number of organisms at one stage of a food chain
- (B) The total dry mass of all the organisms found at one stage of a food chain or ecological pyramid
- (C) The position of an organism in a food chain, food web or ecological pyramid
- (D) The amount of energy lost between two stages of a food chain
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Answer: C – Trophic level is a position, for example producer, primary consumer or secondary consumer, not a count or a mass.
Q13. Why can a pyramid of numbers have an inverted shape?
- (A) A single large producer, such as one tree, can support many small consumers
- (B) Energy always increases towards the top of a food chain as larger consumers feed
- (C) Biomass is always measured in kilojoules
- (D) Decomposers are always placed at the top
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Answer: A – Pyramids of numbers count individuals, so one tree with hundreds of feeding insects gives a narrow base and a wider level above.
Q14. What is an advantage of a pyramid of biomass over a pyramid of numbers?
- (A) It is always upright in every food chain, even when one producer is very large indeed
- (B) It includes the energy content of each level
- (C) It counts producers only
- (D) It takes account of the mass of organisms at each level, not just their number
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Answer: D – Biomass reflects the size as well as the number of organisms, so one large tree is no longer treated as equal to one tiny insect.
Q15. Why does a pyramid of energy always narrow towards the top?
- (A) Energy increases at each transfer between levels as organisms feed and grow
- (B) Energy is lost at each transfer, so less is available at the next level
- (C) Each level stays the same width by definition
- (D) Pyramids of energy are inverted in woodland food chains
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Answer: B – Only part of the energy at one level reaches the next, so a pyramid of energy is always narrower above than below.
Q16. Why is the transfer of energy from one trophic level to the next often inefficient?
- (A) Producers capture far too little light energy to support any consumers at all
- (B) Consumers eat their food too quickly
- (C) Energy is lost through respiration, excretion, egestion and movement
- (D) Sunlight is too weak to support consumers
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Answer: C – Much of the energy an organism takes in is used for its own life processes or lost as waste and heat, so only a part passes on.
Q17. Why do food chains usually have fewer than five trophic levels?
- (A) Too little energy remains after successive transfers to support another level
- (B) Top predators grow too large to be eaten by any other animal in the same habitat
- (C) Producers die out before a fifth level can form
- (D) Decomposers remove the top level of every chain
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Answer: A – With energy lost at every step, there is eventually not enough energy left to sustain a further population of consumers.
Q18. In terms of energy, why is it more efficient for humans to eat crop plants than to eat livestock fed on those crops?
- (A) Crop plants contain more protein than meat
- (B) Livestock waste less of the energy they take in than crop plants do when they grow in the same field
- (C) Crop plants grow faster than livestock
- (D) Eating the crop directly avoids the energy lost through an extra trophic level
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Answer: D – Feeding crops to livestock adds a transfer at which much energy is lost, so less of the original energy reaches a human eating the livestock.
Q19. What eventually happens to energy as it passes through living organisms?
- (A) It is stored permanently inside top consumers and never leaves their bodies
- (B) It is returned directly to the Sun
- (C) It is transferred to the environment, largely as heat
- (D) It is converted back into light energy
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Answer: C – Energy flows through organisms and is eventually lost to the surroundings, mainly as heat released during respiration and other processes.
Q20. What is an advantage of a pyramid of energy over pyramids of numbers or biomass?
- (A) It is the easiest pyramid to draw accurately from field data collected in a habitat
- (B) It shows the energy at each level, undistorted by organism size or numbers
- (C) It places decomposers at the top of the pyramid
- (D) It never narrows towards the top
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Answer: B – Because it is based on energy flow rather than counts or masses, a pyramid of energy gives a fair comparison between levels.
Nutrient Cycles and Populations
Q21. Which process in the carbon cycle removes carbon dioxide from the atmosphere?
- (A) Photosynthesis by green plants
- (B) Combustion of fossil fuels
- (C) Respiration by animals
- (D) Decomposition of dead material
Show Answer
Answer: A – Photosynthesis takes carbon dioxide from the air and locks its carbon into organic nutrients in the plant.
Q22. Which process returns carbon from fossil fuels to the atmosphere as carbon dioxide?
- (A) Photosynthesis
- (B) Feeding by herbivores
- (C) Formation of fossil fuels underground
- (D) Combustion of coal, oil or gas
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Answer: D – Burning fossil fuels releases the carbon stored in them long ago back into the air as carbon dioxide.
Q23. How are fossil fuels formed?
- (A) From fresh leaves falling on the soil surface and rotting there within a few weeks
- (B) From carbon dioxide dissolving in rainwater
- (C) From dead organic material buried and compressed over a very long time
- (D) From volcanic rock cooling after an eruption
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Answer: C – Plant and animal remains buried without full decay are transformed over millions of years into coal, oil or gas.
Q24. In what form do plants take up most of the nitrogen they use from the soil?
- (A) As nitrogen gas from the air
- (B) As nitrate ions dissolved in soil water
- (C) As ammonia gas released by animals
- (D) As whole protein molecules from dead organisms
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Answer: B – Plants absorb nitrate ions through their roots and use them to build amino acids and proteins.
Q25. What is nitrogen fixation?
- (A) The conversion of nitrogen gas into usable compounds by lightning and bacteria
- (B) The uptake of nitrate ions by plant roots from the surrounding soil water for growth
- (C) The breakdown of proteins by animals during digestion
- (D) The release of nitrogen gas by denitrifying bacteria
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Answer: A – Lightning and nitrogen-fixing bacteria convert unreactive nitrogen gas into forms that can enter the cycle.
Q26. What happens during nitrification in the nitrogen cycle?
- (A) Nitrogen gas is fixed by lightning
- (B) Nitrate ions are converted back to nitrogen gas by denitrifying bacteria in soil
- (C) Ammonium ions are converted to nitrate ions by bacteria
- (D) Amino acids lose their nitrogen-containing group
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Answer: C – Nitrifying bacteria convert ammonium ions, formed during decomposition, into nitrate ions that plants can absorb.
Q27. What is the role of denitrification in the nitrogen cycle?
- (A) It converts nitrogen gas into ammonium compounds that plants can then absorb and use for growth
- (B) It builds plant proteins from nitrate ions
- (C) It breaks down dead plant and animal protein
- (D) It converts nitrate ions back into nitrogen gas, which returns to the atmosphere
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Answer: D – Denitrifying bacteria return nitrogen to the air as gas, completing the cycle.
Q28. Which best defines a population?
- (A) All the species living together in one habitat at the same time, plus their surroundings
- (B) A group of organisms of one species, living in the same area at the same time
- (C) A community together with its physical environment
- (D) A single organism and its offspring
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Answer: B – A population is one species only, in one place, at one time; all the populations together make a community.
Q29. Which combination of changes would be expected to slow the growth of a wild rabbit population?
- (A) Abundant food, very few predators and plenty of space for the population to expand
- (B) A spreading disease and an increase in predators
- (C) A mild winter and plentiful shelter
- (D) A fall in competition from other herbivores
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Answer: B – Food supply, competition, predation and disease are the factors that affect population growth rate, and disease plus predation both raise deaths.
Q30. In the sigmoid curve of population growth, what explains the stationary phase?
- (A) The birth rate far exceeds the death rate
- (B) Resources are unlimited, so growth stays rapid and the population keeps expanding
- (C) Limiting factors bring births and deaths into balance
- (D) The population is still in the early lag phase
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Answer: C – When food, space or other resources become limiting, the population levels off because births roughly equal deaths.
Revisit any questions you missed, especially energy losses and the steps of the carbon and nitrogen cycles, then test yourself again without looking at the answers.