Cambridge IGCSE Biology 0610: Organisms and their environment – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover topic 19, Organisms and their environment, of the Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028, sections 19.1 to 19.4. Questions on Supplement content are labelled (Extended); Core candidates (Papers 1 and 3) can leave them out, while Extended candidates (Papers 2 and 4) should attempt everything. Calculators may be used throughout.

See also the IGCSE Biology hub and the 0610 checklist.

Questions

1. State the principal source of energy input to biological systems. [1]

2. In a coastal ecosystem, phytoplankton are eaten by zooplankton. Zooplankton are eaten by sand eels and by herring. Sand eels are eaten by mackerel and by puffins. Mackerel and herring are both eaten by seals. Fishing boats catch large numbers of herring.

(a) Name the producer in this food web. [1] (b) Write out one food chain from this web that contains five organisms. [1] (c) Seals occupy more than one trophic level. State the trophic level of seals in two different food chains. [2] (d) Suggest and explain how overharvesting herring could affect the sand eel population. [3]

3. Describe what is meant by each term.

(a) producer [1] (b) decomposer [1] (c) trophic level [1]

4. An apple tree supports 1 800 caterpillars. The caterpillars are eaten by 24 small birds.

(a) Describe the shape of the pyramid of numbers for this food chain. [2] (b) Discuss the advantages of using a pyramid of biomass rather than a pyramid of numbers to represent this food chain. [2]

5. (Extended) In a grassland, producers transfer 24 000 kJ m⁻² yr⁻¹ into new biomass. Primary consumers gain 2 160 kJ m⁻² yr⁻¹ and secondary consumers gain 180 kJ m⁻² yr⁻¹.

(a) Calculate the percentage efficiency of energy transfer from producers to primary consumers. [2] (b) Calculate the percentage efficiency of energy transfer from primary to secondary consumers. Give your answer to 2 significant figures. [2] (c) Explain why the transfer of energy from one trophic level to the next is not efficient. [3] (d) Explain, in terms of energy loss, why food chains usually have fewer than five trophic levels. [2]

6. (Extended) A field of wheat provides 3.0 × 10⁷ kJ of food energy per year. If the wheat is fed to cattle instead, 12% of this energy ends up in beef that humans eat. One person needs 10 000 kJ of food energy per day.

(a) Calculate the number of days of food energy for one person provided by the wheat, and by the beef. [3] (b) Explain why it is more energy efficient for humans to eat crop plants than to eat livestock that have been fed on crop plants. [3]

7. This question is about the carbon cycle.

(a) Describe how carbon in carbon dioxide in the air can become part of the body of a rabbit. [3] (b) Describe how carbon in the body of a dead rabbit can return to the atmosphere. [2] (c) State how fossil fuels are formed and name the process that returns their carbon to the atmosphere. [2]

8. (Extended) This question is about the nitrogen cycle.

(a) Describe how nitrogen in the protein of a dead leaf becomes nitrate ions in the soil. [3] (b) State two ways in which nitrogen gas can be fixed. [2] (c) Name the process in which bacteria convert nitrate ions into nitrogen gas. [1] (d) Describe what happens to excess amino acids in a human and how their nitrogen returns to the environment. [2]

9. Describe what is meant by:

(a) a population [1] (b) a community [1] (c) an ecosystem [1]

10. A student grew yeast in a flask of sugar solution and counted the cells every 2 hours.

Time / h	0	2	4	6	8	10	12	14	16
Population / millions per cm³	2	3	6	14	30	48	56	58	58

(a) Identify the phase of growth between 0 h and 2 h, and between 14 h and 16 h. [2] (b) Calculate the mean rate of population growth between 6 h and 10 h. Give the unit. [2] (c) (Extended) Explain why the population stops increasing after 14 h. Refer to limiting factors. [3] (d) Name the phase that would follow if the flask were left for several more days, and suggest one reason for it. [2]

11. In a lake, algae are eaten by water snails, water snails are eaten by a native fish, and the native fish are eaten by otters. A large predatory fish from another continent was released into the lake. It feeds on the native fish. Over five years the native fish population fell from 5 600 to 1 400.

(a) Calculate the percentage decrease in the native fish population. [2] (b) Suggest the effect on the water snails and on the algae. Explain your answers. [3] (c) Describe how decomposers return carbon from dead fish to the algae. [2] (d) State two factors, other than predation, that affect the rate of growth of the otter population. [2]

Answers

1. The Sun [1] [1] Examiner insight: “the Sun” or “sunlight” gains the mark; “photosynthesis” does not, because it is a process, not a source.

2. (a) Phytoplankton [1] (b) phytoplankton → zooplankton → sand eels → mackerel → seals, with arrows pointing towards the feeder [1] (c) Tertiary consumer, in phytoplankton → zooplankton → herring → seals [1]; quaternary consumer, in the chain through sand eels and mackerel [1] (d) Fewer herring eat zooplankton, so more zooplankton are available [1]; sand eels have more food, so their population increases [1]; seals may eat more mackerel instead of herring, so fewer mackerel feed on sand eels [1] Examiner insight: each mark needs a direction of change linked to its cause; a bare “sand eels increase” earns one mark at most.

3. (a) An organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis [1] (b) An organism that gets its energy from dead or waste organic material [1] (c) The position of an organism in a food chain, food web or ecological pyramid [1] Examiner insight: “a plant” for producer or “breaks things down” for decomposer is usually too vague for the mark.

4. (a) Narrow base, as there is only one tree [1]; a much wider caterpillar bar with a narrow bird bar on top, so not a normal pyramid [1] (b) A pyramid of biomass takes the size of each organism into account, so the single large tree is shown correctly [1]; it gives a normal pyramid shape and a truer picture of the amount of living material at each level [1] Examiner insight: two distinct points are needed for the two marks; saying “more accurate” twice in different words earns one.

5. (a) (2 160 ÷ 24 000) × 100 [1] = 9.0% [1] (b) (180 ÷ 2 160) × 100 = 8.333… [1] = 8.3% [1] (c) Any three: energy released as heat in respiration [1]; some parts are not eaten, such as roots or bones [1]; some food is not digested and is lost in faeces [1]; energy lost in urea; energy used in movement (d) Energy is lost at every transfer, so the energy available falls at each level [1]; by the fourth or fifth level too little energy remains to support a population [1] Examiner insight: the method mark is for the correct ratio; an unrounded 8.333% loses the accuracy mark when 2 significant figures are asked for.

6. (a) Energy in beef = 0.12 × 3.0 × 10⁷ = 3.6 × 10⁶ kJ [1]; wheat: 3.0 × 10⁷ ÷ 10 000 = 3 000 days [1]; beef: 3.6 × 10⁶ ÷ 10 000 = 360 days [1] (b) Eating crops directly involves only one energy transfer [1]; feeding crops to livestock adds a trophic level, and energy is lost at that extra transfer [1]; the cattle lose energy as heat from respiration, in movement and in faeces, so less reaches humans [1] Examiner insight: error carried forward is normally allowed, so a wrong beef energy correctly divided by 10 000 can still earn the last mark.

7. (a) Plants take in carbon dioxide in photosynthesis [1]; the carbon becomes part of carbohydrates and other organic compounds in the plant [1]; the rabbit eats the plant (feeding) and builds the carbon into its own body [1] (b) Decomposers break down the dead rabbit (decomposition) [1]; the decomposers respire, releasing carbon dioxide into the air [1] (c) Dead organisms that do not fully decompose are converted into coal, oil or gas over millions of years [1]; combustion [1] Examiner insight: when a process is asked for, name it; “using fossil fuels” in place of combustion, or feeding with no link to carbon compounds, can cost marks.

8. (a) Decomposers break down the protein in the leaf [1] to form ammonium ions [1]; nitrifying bacteria convert ammonium ions to nitrate ions, which is nitrification [1] (b) Lightning [1]; nitrogen-fixing bacteria, in the soil or in root nodules [1] (c) Denitrification [1] (d) Excess amino acids are deaminated in the liver, forming urea [1]; urea is excreted in urine, returning nitrogen to the environment [1] Examiner insight: the type of bacterium must match the process; writing “bacteria” without “nitrifying” or “decomposers” in part (a) usually loses the mark for that step.

9. (a) A group of organisms of one species, living in the same area, at the same time [1] (b) All of the populations of different species in an ecosystem [1] (c) A unit containing the community of organisms and their environment, interacting together [1] Examiner insight: a population needs all three elements (one species, same area, same time); omit one and the mark is lost.

10. (a) 0 h to 2 h: lag phase [1]; 14 h to 16 h: stationary phase [1] (b) (48 − 14) ÷ (10 − 6) = 34 ÷ 4 [1] = 8.5 million cells per cm³ per hour [1] (c) Sugar (food) becomes a limiting factor as it is used up [1]; competition between yeast cells increases, and waste such as ethanol builds up [1]; the birth rate falls until it equals the death rate [1] (d) Death phase [1]; the sugar runs out, or toxic waste builds up, so deaths exceed births [1] Examiner insight: the accuracy mark in (b) needs the unit; “8.5” on its own usually earns only the method mark.

11. (a) (5 600 − 1 400) ÷ 5 600 × 100 [1] = 75% [1] (b) Water snails increase [1] because fewer native fish eat them [1]; algae decrease because the larger snail population eats more algae [1] (c) Decomposers break down the dead fish and respire, releasing carbon dioxide [1]; the algae take in the carbon dioxide in photosynthesis [1] (d) Any two from: food supply [1]; competition [1]; disease Examiner insight: a percentage change must be calculated from the original value, 5 600; dividing by 1 400 gives 300%, which earns no credit.

Where marks are usually lost

• Food-chain arrows drawn from predator to prey instead of towards the feeder.
• Writing “energy is used up” instead of “energy is lost to the environment as heat”.
• Giving the efficiency ratio upside down, so the answer comes out above 100%.
• Stating “bacteria” in the nitrogen cycle without naming which type.
• Leaving units off a rate of population growth.
• Describing the stationary phase without saying births equal deaths or naming a limiting factor.

Next steps

• Recap with the Organisms and their environment revision notes.
• Reread weak sections in the study guide.
• Browse the Cambridge IGCSE Biology hub and tick off the 0610 checklist.
• Take the Core diagnostic or Extended diagnostic, or try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Cambridge IGCSE Biology 0610 syllabus for examination in 2026, 2027 and 2028 (Version 3), Cambridge University Press & Assessment (Cambridge International Education). Topic 19, sections 19.1 to 19.4.