Edexcel International GCSE Biology 4BI1: Ecology and the 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 4, Ecology and the environment (points 4.1–4.18), of the Pearson Edexcel International GCSE Biology (4BI1) specification, Issue 3, for the June and November series examined under Issue 3. The course is untiered and a calculator may be used on both papers. Questions 3, 8 and 12 test bold B statements and are labelled “Paper 2 only”.

Learn the content first in the study guide and the revision notes. The course hub is Edexcel IGCSE Biology and the printable checklist lists every point.

Questions

1. State what is meant by each term.

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

2. A student estimates the number of daisies on a lawn measuring 60 m × 45 m. She places eight 1 m² quadrats. Her counts are: 4, 7, 2, 5, 0, 6, 3, 5.

(a) Describe how she should place the quadrats at random. [2] (b) Calculate the estimated number of daisies on the lawn. Show your working. [3] (c) A second area of the lawn lies beside a footpath. Suggest two reasons why fewer daisies grow there. [2]

3. (Paper 2 only) A student records the number of plants of each species in ten random quadrats at two sites.

Species	Site 1	Site 2
Daisy	12	2
Clover	9	0
Plantain	4	17
Buttercup	6	0
Dandelion	3	1

(a) State what is meant by biodiversity. [1] (b) Which site has the higher biodiversity? Use the data to justify your answer. [3] (c) Describe how the student could investigate how the distribution of plantain changes between the two sites. [2]

4. Explain how each change could affect the size of a population.

(a) A long drought, on the population of grass in a field. [2] (b) An increase in the number of foxes, on the population of rabbits. [2]

5. In a pond, algae are eaten by water fleas and mayfly larvae. Dragonfly larvae eat mayfly larvae. Small fish eat water fleas and dragonfly larvae. Herons eat small fish.

(a) Name the producer. [1] (b) Name one primary consumer. [1] (c) Explain why the small fish is both a secondary and a tertiary consumer. [2]

6. In a grassland, grass receives 12 500 kJ per m² per year. Rabbits receive 1100 kJ per m² per year and foxes receive 99 kJ per m² per year.

(a) Calculate the percentage of energy transferred from grass to rabbits. [2] (b) Give three reasons why most of the energy in the rabbits is not passed to the foxes. [3] (c) A food chain is oak tree → caterpillars → blue tits. Explain why its pyramid of numbers is not pyramid-shaped but its pyramid of energy is. [2]

7. Describe how carbon in carbon dioxide in the air can become part of a fox, and how it returns to the air after the fox dies. [5]

8. (Paper 2 only) A farmer grows clover and then ploughs it into the soil.

(a) Explain how growing clover increases the nitrate in the soil. [3] (b) Explain why a waterlogged field contains less nitrate. [2]

9.

(a) Explain why breathing air with a high concentration of carbon monoxide can make a person tired. [2] (b) Explain how sulfur dioxide from a power station can cause fish to die in a distant lake. [2]

10. Explain how human activities lead to an enhanced greenhouse effect, and describe two possible biological consequences of global warming. [7]

11. Untreated sewage enters a river. The dissolved oxygen concentration is 9.2 mg per dm³ upstream of the outlet and 3.1 mg per dm³ 100 m downstream.

(a) Calculate the percentage decrease in dissolved oxygen. [2] (b) Explain why the oxygen concentration falls downstream of the outlet. [3] (c) A nearby lake develops an algal bloom after heavy rain on fertilised fields. Explain how this can lead to the death of fish. [4]

12. (Paper 2 only) A large area of rainforest is cleared and burned. Explain the effects on the soil, on local rainfall and on the balance of atmospheric gases. [6]

Answers

1. (a) All the organisms of one species living in an area [1] (b) All the populations of different species living in an area [1] (c) A community and its abiotic environment, interacting [1] Examiner insight: A community answer that does not make clear more than one species is involved scores zero, because it describes a population.

2. (a) Lay two tapes at right angles to make a grid [1]; use random numbers (from a generator or table) as coordinates for each quadrat [1] (b) Total = 32, so mean = 32 ÷ 8 = 4.0 per m² [1]; area = 60 × 45 = 2700 m² [1]; population = 4.0 × 2700 = 10 800 daisies [1] (c) Trampling damages or kills plants [1]; soil is compacted, so less water or air reaches the roots [1] Examiner insight: A correct final answer with no working usually earns full marks, but a wrong answer with a correct mean still earns the method marks, so write the mean and area on separate lines.

3. (a) The variety of different species (living organisms) in an area [1] (b) Site 1 [1]; it has 5 species compared with 3 at Site 2 [1]; its numbers are more evenly spread, while Site 2 is dominated by plantain (17 of 20 plants) [1] (c) Lay a tape (transect) from Site 1 to Site 2 [1]; place a quadrat at regular intervals and count plantain at each [1] Examiner insight: In (b), “use the data” means quoted figures are required; a bare statement that Site 1 has more species gets the choice mark but not the data mark.

4. (a) Less water for photosynthesis, or plants wilt [1]; fewer grass plants survive, so the population falls [1] (b) More rabbits are eaten, so the death rate rises [1]; the rabbit population falls [1] Examiner insight: Each two-mark part needs a linked cause and an effect on numbers; “the population changes” is not credited.

5. (a) Algae [1] (b) Water flea (or mayfly larva) [1] (c) When it eats water fleas (primary consumers) it is a secondary consumer [1]; when it eats dragonfly larvae (secondary consumers) it is a tertiary consumer [1] Examiner insight: Naming the prey is not enough in (c); you must state the trophic level of each prey organism.

6. (a) (1100 ÷ 12 500) × 100 [1] = 8.8% [1] (b) Energy released as heat in respiration [1]; parts of rabbits not eaten, such as bones and fur [1]; energy lost in faeces or urine [1] (c) One large oak tree supports many caterpillars, so the bottom bar is narrow [1]; energy is lost at each level, so each energy bar is smaller than the one below [1] Examiner insight: “Energy is used for respiration” is weaker than “released as heat”; “energy is lost” alone repeats the question and scores nothing.

7. Plants take in carbon dioxide in photosynthesis and make glucose or other carbon compounds [1]; rabbits eat the plants and the carbon compounds become part of their bodies [1]; the fox eats rabbits [1]; decomposers (bacteria and fungi) feed on the dead fox [1]; they release carbon dioxide by respiration [1] Examiner insight: Each process must be named; “the fox rots and carbon goes into the air” misses both the decomposer and the respiration marks.

8. (a) Nitrogen-fixing bacteria live in the root nodules of clover [1]; they convert nitrogen gas into nitrogen compounds [1]; when the clover is ploughed in, decomposers produce ammonium, which nitrifying bacteria convert to nitrate [1] (b) Waterlogged soil has little oxygen [1]; denitrifying bacteria convert nitrate to nitrogen gas [1] Examiner insight: Names of bacteria are not required, but the type of bacterium must be correct; swapping nitrifying and denitrifying loses the mark.

9. (a) Carbon monoxide binds to haemoglobin [1]; less oxygen is carried to respiring cells, so less energy is released [1] (b) Sulfur dioxide dissolves in rain to form acid rain [1]; this lowers the pH of the lake, killing fish [1] Examiner insight: Giving the effect of the wrong gas (carbon monoxide causing acid rain) is a contradiction and cancels the mark.

10. Burning fossil fuels releases carbon dioxide [1]; cattle or rice fields release methane (or fertiliser breakdown releases nitrous oxide) [1]; greenhouse gases absorb infrared radiation emitted from the Earth’s surface [1]; they re-radiate heat back towards the Earth [1]; higher concentrations trap more heat, so mean temperature rises [1]; melting ice raises sea level and floods coastal habitats [1]; species’ distributions change or some become extinct (or crop yields fall) [1] Examiner insight: Each human activity must be linked to its named gas; a list of gases with no sources earns fewer marks than two matched pairs.

11. (a) (9.2 − 3.1) ÷ 9.2 × 100 [1] = 66.3% [1] (b) Bacteria feed on the organic matter in sewage [1]; the bacteria multiply [1]; their aerobic respiration uses up dissolved oxygen [1] (c) Nitrates or phosphates are leached into the lake, causing rapid algal growth [1]; algae block light, so plants below die [1]; decomposing bacteria feed on dead plants and algae and multiply [1]; their aerobic respiration uses up oxygen, so fish die [1] Examiner insight: In (a) dividing by the downstream value (3.1) is a method error; percentage change always divides by the original value.

12. Without roots, soil is washed or blown away (erosion) [1]; rain leaches mineral ions from the unprotected soil, making it infertile [1]; less evapotranspiration from trees [1]; so less water vapour, fewer clouds and less local rainfall [1]; burning (and decay) releases carbon dioxide [1]; fewer trees photosynthesise, so less carbon dioxide is absorbed and less oxygen released [1] Examiner insight: This is marked point by point across three areas; covering only soil in detail caps the mark, so give two points for each area named in the question.

Where marks are usually lost

• Describing a population when asked for a community.
• Scaling quadrat data without calculating a mean first, or dividing by the wrong number of quadrats.
• Writing “use the data” answers without quoting any numbers.
• Leaving out the trophic level of prey when explaining a food-web position.
• Saying “energy is lost” without a route (heat from respiration, faeces, parts not eaten).
• Blaming algae, not bacteria, for oxygen loss in eutrophication.
• Swapping nitrifying and denitrifying bacteria.
• Listing greenhouse gases without matching each to a human source.
• Dividing by the final value in a percentage change.

Next steps

• Recap with the revision notes.
• Reread any weak section in the study guide.
• Browse other topics on the Edexcel IGCSE Biology hub.
• Track coverage with the printable checklist.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Pearson Edexcel International GCSE in Biology (4BI1) specification, Issue 3, first examination June 2019, Pearson Education Limited – Topic 4, Ecology and the environment.