Pearson Edexcel GCSE Combined Science · B9

Ecosystems and material cycles

Revision questions with answers for B9 Ecosystems and material cycles in Pearson Edexcel GCSE Combined Science (spec 1SC0). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

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Question 1 · Spec B9.1
Distinguish an individual, population and community.
Answer:
An individual is one organism; a population is one species in an area; a community contains interacting populations of different species.
Question 2 · Spec B9.1
What is an ecosystem?
Answer:
A community of organisms interacting with one another and with non-living environmental components.
Question 3 · Spec B9.2
Give examples of abiotic factors affecting a community.
Answer:
Temperature, light, water availability and pollutants.
Question 4 · Spec B9.2
Give examples of biotic factors affecting a community.
Answer:
Competition, predation and interactions with other living organisms.
Question 5 · Spec B9.2
How can competition limit population growth?
Answer:
Individuals compete for limited resources, reducing survival or reproduction when supplies are insufficient.
Question 6 · Spec B9.2
Why can predator and prey numbers rise and fall in linked cycles?
Answer:
More prey supports more predators; greater predation then reduces prey, eventually reducing predator food supply.
Question 7 · Spec B9.3
What does interdependence mean?
Answer:
Species rely on one another for resources or services, so changes to one can affect others.
Question 8 · Spec B9.4
What is parasitism?
Answer:
An interaction in which a parasite benefits while its host is harmed.
Question 9 · Spec B9.4
What is mutualism?
Answer:
An interaction in which both species benefit.
Question 10 · Spec B9.4
Why can plant-pollinator interactions be mutualistic?
Answer:
The animal gains food and the plant gains pollen transfer that supports reproduction.
Question 11 · Spec B9.5 · Core practical
How can quadrats estimate abundance of plants?
Answer:
Count individuals in sampled quadrats, calculate a mean density and scale it to the habitat area.
Question 12 · Spec B9.5 · Core practical
Why select quadrat positions using random coordinates?
Answer:
It reduces selection bias and helps the sample represent the habitat.
Question 13 · Spec B9.5 · Core practical
How does a belt transect investigate a habitat gradient?
Answer:
Sample adjoining quadrats or a strip along a line, recording how organisms and conditions change with distance.
Question 14 · Spec B9.5 · Core practical
Which environmental measurements could accompany a transect?
Answer:
Light intensity, temperature, soil moisture or another factor relevant to the investigation.
Question 15 · Spec B9.5 · Core practical
Why use numerous quadrats or repeat transects?
Answer:
They capture habitat variation and reduce the influence of unusual individual samples.
Question 16 · Spec B9.6
A 0.25 m² quadrat contains a mean of 5 plants. Estimate the total in 80 m².
Answer:
Density = 5 / 0.25 = 20 plants/m²; total = 20 × 80 = 1,600 plants.
Question 17 · Spec B9.6
Why should an estimated population not be presented as an exact count?
Answer:
Sampling covers only part of the habitat, so natural variation and measurement uncertainty affect the estimate.
Question 18 · Spec B9.5 · Core practical
Does a correlation between light and plant abundance prove causation?
Answer:
No. Other variables may change along the same gradient and contribute to the pattern.
Question 19 · Spec B9.9
Give a possible benefit of fish farming.
Answer:
It supplies food and may reduce pressure on some wild fish stocks when managed sustainably.
Question 20 · Spec B9.9
How can fish-farm waste damage nearby ecosystems?
Answer:
Uneaten food and waste add nutrients and organic material, potentially causing eutrophication and oxygen depletion.
Question 21 · Spec B9.9
Why can dense fish populations increase disease problems?
Answer:
Pathogens and parasites can spread more readily between closely packed hosts.
Question 22 · Spec B9.9
What is a non-indigenous species?
Answer:
A species introduced to a location where it does not naturally occur.
Question 23 · Spec B9.9
How can an introduced species reduce native biodiversity?
Answer:
It may outcompete, prey on or introduce diseases to native species.
Question 24 · Spec B9.9
What can start eutrophication?
Answer:
Excess nutrients, often from fertiliser runoff or sewage, enter water.
Question 25 · Spec B9.9
How can excess nutrients lead to loss of submerged plants?
Answer:
Rapid algal growth blocks light, reducing photosynthesis so submerged plants die.
Question 26 · Spec B9.9
Why does decomposition after an algal bloom reduce dissolved oxygen?
Answer:
Microorganisms respire aerobically while breaking down dead material, using oxygen.
Question 27 · Spec B9.9
Why may fish die during eutrophication?
Answer:
Oxygen concentration can fall too low to support their aerobic respiration.
Question 28 · Spec B9.10
What is biodiversity?
Answer:
The variety of species within an area or across the Earth.
Question 29 · Spec B9.10
Why is conserving biodiversity valuable?
Answer:
It supports ecosystem functions, preserves genetic resources and maintains species for ecological and human benefits.
Question 30 · Spec B9.10
How can protecting habitats help conserve animal species?
Answer:
It preserves food, shelter and breeding conditions needed for their survival.
Question 31 · Spec B9.10
How can reforestation improve biodiversity?
Answer:
It restores habitat and resources for many organisms, especially when suitable native species are planted.
Question 32 · Spec B9.10
Why evaluate a conservation proposal using both ecological and social evidence?
Answer:
Benefits to species must be weighed against costs and effects on people's livelihoods or land use.
Question 33 · Spec B9.12
Why must materials cycle between living and non-living components?
Answer:
Organisms need a continuing supply of limited elements and water, which are reused rather than newly created.
Question 34 · Spec B9.13
How does carbon enter plant biomass?
Answer:
Photosynthesis incorporates carbon from carbon dioxide into organic molecules.
Question 35 · Spec B9.13
How does carbon pass from plants to animals?
Answer:
Animals eat plants or organisms that previously obtained carbon from plants.
Question 36 · Spec B9.13
How does respiration return carbon to the environment?
Answer:
Carbon-containing molecules are broken down and carbon dioxide is released.
Question 37 · Spec B9.13
What is the role of decomposers in the carbon cycle?
Answer:
They break down dead organisms and waste, releasing carbon dioxide through respiration.
Question 38 · Spec B9.13
How does combustion affect the carbon cycle?
Answer:
It converts carbon in fuels or biomass into atmospheric carbon dioxide.
Question 39 · Spec B9.14
What drives evaporation in the water cycle?
Answer:
Energy from the Sun transfers energy to water, allowing it to enter the atmosphere as vapour.
Question 40 · Spec B9.14
What happens during condensation and precipitation?
Answer:
Vapour cools into droplets forming clouds; water then falls as rain, snow or other precipitation.
Question 41 · Spec B9.14
How do plants return water to the atmosphere?
Answer:
Through transpiration: evaporation from cells and diffusion of vapour out of leaves.
Question 42 · Spec B9.14
What is potable water?
Answer:
Water safe to drink, with sufficiently low levels of harmful microbes and chemicals.
Question 43 · Spec B9.14
Why may desalination be useful during drought?
Answer:
It removes dissolved salts from seawater, providing a water source where fresh water is scarce.
Question 44 · Spec B9.14
How does distillation remove salt from water?
Answer:
Water evaporates and its vapour condenses separately; dissolved salt remains behind.
Question 45 · Spec B9.15
Why do plants need nitrates?
Answer:
They supply nitrogen needed to make amino acids and proteins.
Question 46 · Spec B9.15
How do fertilisers increase nitrate availability?
Answer:
They add nitrogen-containing compounds to soil, increasing mineral nutrients available to roots.
Question 47 · Spec B9.15
What do nitrogen-fixing bacteria do?
Answer:
Convert atmospheric nitrogen into nitrogen compounds that can enter biological nutrient cycles.
Question 48 · Spec B9.15
What do nitrifying bacteria do?
Answer:
Convert ammonium compounds into nitrites and then nitrates in soil.
Question 49 · Spec B9.15
What do denitrifying bacteria do?
Answer:
Convert nitrates into nitrogen gas, returning nitrogen to the atmosphere, especially in low-oxygen conditions.
Question 50 · Spec B9.15
How can crop rotation with legumes improve soil nitrogen?
Answer:
Legume root nodules contain nitrogen-fixing bacteria; leaving suitable residues returns nitrogen compounds to soil.

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