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Work through the notes, try the practice questions, then take the quiz. The report tells you exactly what to revise next. (2026)
Question
A pond contains 240 frogs, plus newts, dragonflies, pondweed and bacteria. State (i) the population, (ii) the community, (iii) what extra would be needed to call this an ecosystem. (3 marks)
Solution
Population = all individuals of ONE species. The 240 frogs are the frog population.
Community = all species. Frogs, newts, dragonflies, pondweed and bacteria together are the community.
Ecosystem = community + abiotic factors (water, oxygen, light, temperature, dissolved minerals).
Answer
(i) The 240 frogs are the frog population (1). (ii) All the species — frogs, newts, dragonflies, pondweed, bacteria — make the community (1). (iii) Add the abiotic (non-living) factors such as water, temperature, light and minerals to make an ecosystem (1).
Question
A young birch sapling germinates beneath a mature oak in a UK woodland. Suggest why most such saplings fail to grow tall. (4 marks)
Solution
Competition for LIGHT — the oak canopy blocks most light, so the sapling cannot photosynthesise enough.
Competition for WATER — oak roots already drain the soil.
Competition for MINERAL IONS — oak roots remove most nitrate and other minerals.
Limited photosynthesis + limited water and minerals → slow growth → outcompeted and dies.
Answer
The sapling competes with the mature oak for light (canopy shade), water and mineral ions in the soil (1+1+1). With less light it cannot photosynthesise enough, so it grows slowly and is outcompeted and dies (1).
Question
A new tall hedge shades a garden flowerbed. Explain why daffodils in the bed produce fewer flowers the following spring. (3 marks)
Solution
Less light reaches the daffodils.
Less light → slower photosynthesis → less glucose produced.
With less stored glucose in their bulbs, daffodils produce fewer flowers.
Answer
The hedge blocks light reaching the bed (1). With less light the daffodils photosynthesise less and produce less glucose (1). Less stored energy in the bulb means fewer flowers can be produced (1).
Question
Brown trout disappear from a UK stream after sewage spills upstream. Explain why low dissolved oxygen is the likely cause. (4 marks)
Solution
Sewage adds organic matter to the water.
Bacteria decompose the sewage and respire aerobically, USING UP dissolved oxygen.
Dissolved O₂ falls below the level trout need for aerobic respiration.
Trout suffocate or move away — population drops to zero.
Answer
Sewage feeds bacteria that respire aerobically and use up dissolved oxygen (1+1). Trout need high dissolved O₂ for aerobic respiration through their gills (1); when O₂ drops too low they cannot survive and the population falls (1).
Question
American mink escaped from fur farms and spread along UK waterways. Water vole numbers fell by 90%. Explain how mink act as a biotic factor in vole populations. (4 marks)
Solution
Mink are a NEW PREDATOR — water voles did not evolve with them so have no effective escape behaviour.
Mink are small enough to follow voles into burrows, where voles previously escaped native predators.
High predation rate → vole numbers crash.
Below a critical population, voles cannot find mates → local extinction.
Answer
Mink are a new (introduced) predator, so water voles have no co-evolved defence (1). Mink are small enough to enter vole burrows, bypassing the voles' usual escape route (1). Heavy predation reduces vole numbers (1) until populations fall below the level needed to find mates and recover (1).
Question
Explain TWO biotic factors that have caused red squirrel populations in the UK to fall as grey squirrels have spread. (4 marks)
Solution
INTERSPECIFIC COMPETITION — greys are larger and eat a wider range of foods including unripe acorns, leaving less food for reds.
Greys also tolerate fragmented habitats better, taking more space.
NEW PATHOGEN — greys carry squirrelpox virus harmlessly but it is lethal to reds.
Reds have no immunity, so infection wipes out local populations.
Answer
Competition: greys outcompete reds for food and habitat, leaving reds with too little to survive (1+1). Pathogen: greys carry squirrelpox virus which is lethal to reds, who have no immunity (1+1).
Question
For each of the following camel features, state whether it is structural, behavioural or functional: (a) hump full of fat, (b) resting in shade in the day, (c) producing very concentrated urine. (3 marks)
Solution
(a) Hump of fat is a body PART → structural.
(b) Resting in shade is something the camel DOES → behavioural.
(c) Producing concentrated urine is a body PROCESS → functional.
Answer
(a) Structural (1). (b) Behavioural (1). (c) Functional (1).
Question
Explain how spines (instead of broad leaves) help a cactus survive in a hot, dry desert. (4 marks)
Solution
Spines have a much smaller surface area than leaves.
Smaller surface area → less water lost by transpiration / evaporation from stomata.
Spines also deter herbivores from eating the water-rich stem.
The stem (not leaves) becomes the main photosynthetic organ — green, swollen, water-storing.
Answer
Spines have far less surface area than broad leaves (1), so transpiration / water loss is reduced (1). Spines also stop herbivores eating the water-rich stem (1). Photosynthesis happens in the green stem instead, which also stores water (1).
A single living thing.
All the individuals of the same species living in the same place at the same time.
All the populations of all the different species living in the same place at the same time.
A community of organisms together with the abiotic (non-living) parts of their environment.
All the ecosystems on Earth combined.
The way species in a community rely on each other for food, shelter, pollination, seed dispersal and other essentials.
A community in which biotic and abiotic factors are in balance so population sizes remain roughly constant.
A non-living physical or chemical feature of an environment that affects organisms.
The amount of light energy reaching a surface per unit area — affects photosynthesis.
The amount of water available to organisms — in soil, air or water bodies.
How acidic or alkaline soil is — controls which mineral ions are available and which plants grow.
Oxygen gas dissolved in water — required for aerobic respiration by aquatic animals.
A living factor — the effect of other organisms on a species in a community.
One organism (predator) catches, kills and eats another (prey).
A microorganism that causes disease — virus, bacterium, fungus or protist.
Competition between individuals of DIFFERENT species for the same resource.
Competition between individuals of the SAME species for the same resource.
A feature of an organism that helps it survive and reproduce in its environment.
A physical body feature, such as shape, size, colour or material.
Something the organism does — its actions or routines.
An adaptation in the organism's internal body processes or chemistry.
An organism (usually a bacterium) that lives and thrives in extreme conditions of temperature, pressure, salinity or pH.
Mistake
Mixing up 'population' and 'community'.
Why it happens
The words feel similar.
How to avoid it
Population = ONE species. Community = ALL species. If the question describes more than one species, it's a community.
Mistake
Saying 'plants compete for food'.
Why it happens
Forgetting that plants make their own food.
How to avoid it
Plants compete for the INPUTS they need for photosynthesis: light, water, CO₂ and mineral ions — plus space.
Mistake
Thinking a 'stable' community means nothing changes.
Why it happens
Everyday meaning of stable.
How to avoid it
Stable means population sizes stay ROUGHLY constant — small fluctuations are normal. The system is in balance, not frozen.
Mistake
Just naming the abiotic factor without explaining the effect.
Why it happens
Stopping after the keyword.
How to avoid it
Always say WHAT the factor does — link to photosynthesis, enzymes or another biological process for the marks.
Mistake
Saying CO₂ is the abiotic factor for aquatic animals.
Why it happens
Mixing up the two gases.
How to avoid it
AQA splits them: CO₂ matters for plants (photosynthesis). Dissolved O₂ matters for aquatic animals (respiration).
Mistake
Treating 'soil' as one factor.
Why it happens
Lazy answer.
How to avoid it
Soil has TWO separate AQA factors: pH and mineral content. Address them separately for full marks.
Mistake
Calling competition 'predation' or vice versa.
Why it happens
Both sound like 'fighting'.
How to avoid it
Predation = one EATS the other. Competition = both want the SAME RESOURCE. They are different mechanisms.
Mistake
Listing only one or two biotic factors when asked for the AQA list.
Why it happens
Forgetting the full set.
How to avoid it
Memorise the four: food availability, new predators, new pathogens, interspecific competition.
Mistake
Saying 'grey squirrels eat red squirrels'.
Why it happens
Confusing competition with predation.
How to avoid it
They COMPETE for food and space; greys also carry squirrelpox. Predation isn't part of the story.
Mistake
Naming an adaptation without saying what it does.
Why it happens
Stopping too soon.
How to avoid it
Use 'so that' — 'thick fur SO THAT it traps air and insulates the body'.
Mistake
Calling 'hibernates' a structural adaptation.
Why it happens
Confusing the three types.
How to avoid it
Action verb = behavioural. Body part = structural. Body process = functional.
Mistake
Saying a cactus has a behavioural adaptation.
Why it happens
Forcing all three types onto plants.
How to avoid it
Plants have very limited behaviour. Stick to structural and functional for plants, except for things like night-flowering or stomata opening at night (which AQA accepts).