What you'll be able to do by the end
- Define an adaptation and explain what it means for an organism to be adapted to its environment
- Classify adaptations as structural, behavioural or functional, and justify your classification
- Explain how a named adaptation increases an organism's chance of survival
- Describe what extremophiles are and give examples
- Distinguish abiotic from biotic factors and explain how each affects populations
- Explain what organisms compete for, and why
- Define interdependence and explain the consequences when one species is removed
- Interpret data on populations, distributions and environmental factors
Part 1 — What is an adaptation?
The definition that gets the mark
An adaptation is a feature of an organism that increases its chance of survival and reproduction in its environment.
Three things in that sentence matter, and students lose marks on all three.
"Feature." It can be a body part, a behaviour, or something happening inside the body. Not just body parts.
"Increases its chance." Not guarantees. A well-adapted animal still dies.
"In its environment." Most often missed. Nothing is adapted in general — it's adapted to somewhere. A polar bear is superbly adapted, and would die in a desert.
Students write: "The hedgehog grew spines to protect itself."
No individual organism grows an adaptation because it needs one. Adaptations arise through natural selection across generations. An individual hedgehog does not develop spines in response to danger — hedgehogs with better spines survived to breed, over very long timescales.
Write "hedgehogs have evolved spines, which protect them from predators", never "grew spines to protect itself." Examiners mark this down every single year.
The three types of adaptation
Every adaptation you meet at GCSE is one of three types. Questions frequently say "name the type of adaptation" for one mark.
Structural — physical features you could see, photograph or measure
| Animal | Structural adaptation | How it helps survival |
|---|---|---|
| African pygmy hedgehog | ~5,000 keratin spines | Predators cannot easily bite or grip; rolls into a ball presenting only spines |
| Bearded dragon | Flattened body, spiny "beard" | Flattens against warm rock to absorb heat; beard darkens and inflates to appear larger |
| Panther chameleon | Zygodactyl feet & prehensile tail | Grips branches securely in an arboreal habitat |
| Sugar glider | Patagium — wrist-to-ankle membrane | Glides between trees, escaping ground predators and saving energy |
| Aldabra giant tortoise | Heavy domed shell | Protection; the dome sheds heat and rain |
Behavioural — things the organism does (actions, not features)
| Animal | Behavioural adaptation | How it helps survival |
|---|---|---|
| Bearded dragon | Basks in the morning, shade at midday | Regulates body temperature — it cannot generate its own heat |
| Hedgehog | Nocturnal activity | Avoids daytime predators and heat; insect prey is active at night |
| Hamster | Caching food in cheek pouches | Survives periods when food is scarce |
| Wild rabbit | Living in groups in a warren | More eyes watching for predators; safety in numbers |
| Chameleon | Slow, rocking movement | Mimics a leaf in wind, avoiding detection |
Functional — processes inside the body (biochemistry & physiology)
| Animal | Functional adaptation | How it helps survival |
|---|---|---|
| Bearded dragon | Concentrated uric acid, not urea | Loses very little water — essential in an arid habitat |
| Hedgehog | Can enter torpor | Survives cold periods when food is unavailable |
| Reptiles generally | Ectothermic metabolism | Requires far less food than a mammal of the same size |
| Camel | Fat stored in the hump | Insulation would be fatal in heat; fat is also a water source when metabolised |
Yes, in one still image → structural. Yes, but I'd need video → behavioural. No, I'd need a lab → functional. "Thick fur" is a photo. "Huddling together" needs video. "Antifreeze proteins in the blood" needs a lab.
✅ Check yourself — Part 1
Classify each as structural, behavioural or functional. (Answers are in the mark scheme.)
- A tortoise withdrawing its head into its shell
- A hedgehog's spines
- A desert lizard producing very concentrated urine
- A sugar glider's gliding membrane
- A hamster storing food in its burrow
- A snake's venom composition
- A chameleon changing colour (deliberately tricky — think about what's actually happening)
- A gecko's toe pads
Part 2 — Extremophiles
Some organisms live in conditions that would kill almost everything else. These are extremophiles: organisms adapted to environments with extreme conditions — very high or low temperature, high pressure, high salt concentration, or extreme pH. Most extremophiles are bacteria, and this is the detail exam questions test.
| Extreme condition | Where | Example |
|---|---|---|
| High temperature | Deep-sea hydrothermal vents (>100°C) | Thermophilic bacteria |
| High salt concentration | Salt lakes, the Dead Sea | Halophilic bacteria |
| High pressure | Deep ocean trenches | Barophilic bacteria |
| Extreme pH | Acidic hot springs, alkaline soda lakes | Acidophiles and alkaliphiles |
Thermophilic bacteria gave us Taq polymerase, the heat-stable enzyme that makes PCR possible. Every COVID test, DNA fingerprint and genetic screening test relies on an enzyme from a bacterium living in a hot spring. Exam boards like this example because it links adaptation to a real application.
Part 3 — Abiotic and biotic factors
Abiotic factors — the non-living ones
| Factor | Effect on organisms |
|---|---|
| Light intensity | Plants need light for photosynthesis; low light limits growth and the whole food chain |
| Temperature | Affects enzyme activity and reaction rate; determines which species survive |
| Moisture / water | All organisms need water; scarcity limits distribution |
| Soil pH & minerals | Determines which plants grow, and so which animals live there |
| Wind | Increases water loss from plants; affects seed dispersal |
| CO₂ level | Limits photosynthesis rate |
| Oxygen (aquatic) | Low oxygen kills fish and invertebrates |
Biotic factors — the living ones
| Factor | Effect on organisms |
|---|---|
| Availability of food | Fewer resources means smaller populations |
| New predators | Prey populations can collapse if they have no defence |
| New pathogens | A population with no resistance can be devastated |
| Competition | One species may outcompete another to local extinction |
"Predators" is a biotic factor — students often write it as abiotic. The test is simple: is it alive, or made by something alive? If yes, biotic.
Worked example — reading a distribution question
A student records the number of a plant species at increasing distance from a large oak tree.
| Distance from oak (m) | Plants per m² |
|---|---|
| 0 | 2 |
| 2 | 5 |
| 4 | 14 |
| 6 | 21 |
| 8 | 23 |
Suggest one abiotic factor that explains this pattern. (2 marks)
Step 1 — describe the data. As distance from the oak increases, plant numbers increase.
Step 2 — identify the factor. Light intensity.
Step 3 — link causally. Near the oak the canopy blocks light; further away, more light reaches the ground.
Two marks: one for naming the factor, one for the explanation linking it to the data. Name the factor → say what it does → link it to the numbers. Name it and stop, and you get one mark out of two, every time.
Part 4 — Competition
Organisms compete when they need the same limited resource.
What animals compete for: food · water · territory (space & its resources) · mates.
What plants compete for: light · space · water · mineral ions from the soil.
The lists are different. Plants don't compete for mates the way animals do; animals don't compete for light. Exam questions test whether you know which list applies.
A worked example using real husbandry
Two African pygmy hedgehogs are housed in one enclosure. Within a week, one has lost weight and has bite marks; the other has gained weight. Why?
Hedgehogs are solitary in the wild. Two adults compete for food (the dominant eats first and more), territory (neither can establish a separate area), and the nest site (one warm hide, both want it). The dominant wins each contest; the subordinate eats less, is stressed, and loses weight.
Every reputable hedgehog care guide says house adults separately — that's competition theory applied to a cage. The same principle explains why rabbits should be kept in pairs: rabbits are social and live in warrens, so isolation causes stress. Two species, opposite housing rules, both explained by the same biology.
Intraspecific and interspecific competition
Intraspecific — within a species (two hedgehogs for the same food). Usually the more intense form, because members of one species need exactly the same resources.
Interspecific — between species (a grey and a red squirrel for the same nuts).
Grey squirrels outcompeted red squirrels in most of the UK because greys are larger, digest acorns more efficiently, and carry squirrelpox — to which they're immune and reds aren't. Interspecific competition plus a pathogen — a favourite exam context.
Part 5 — Interdependence
Within a community, each species depends on other species for food, shelter, pollination, seed dispersal and so on. If one species is removed, it affects the whole community. A food web is not a list — it's a network. Remove one strand and the others move.
Worked scenario. In a garden ecosystem: hedgehogs eat slugs and beetles. Slugs eat plants. Beetles eat aphids. Aphids eat plants.
All hedgehogs are removed. Predict the effect on the plant population. (3 marks)
Hedgehogs removed → slugs increase (predator gone) → slugs eat more plants → plants decrease.
But also: hedgehogs removed → beetles increase → beetles eat more aphids → aphids decrease → fewer aphids eating plants → plants increase. Two opposing effects. A three-mark answer must recognise both and reach a judgement.
What examiners reward here is the word "however." Questions worth 3+ marks in ecology almost always have a competing effect. Spot only one direction and you've answered a 1-mark question.
Exam-style questions
Answer all questions. Marks are shown in brackets. Total: 35 marks.
Question 1
The bearded dragon (Pogona vitticeps) is a lizard native to the arid woodlands of central Australia.
(Total 8 marks)
Question 2
| African pygmy hedgehog | European rabbit | |
|---|---|---|
| Social structure | Solitary | Groups (warrens) |
| Activity period | Nocturnal | Crepuscular |
| Defence | Rolls into a ball, spines | Runs to burrow |
(Total 7 marks)
Question 3
A student investigated the distribution of daisies along a transect from a shaded hedge into open ground, using a quadrat at 5 m intervals.
| Distance from hedge (m) | Daisies per quadrat |
|---|---|
| 0 | 0 |
| 5 | 3 |
| 10 | 11 |
| 15 | 18 |
| 20 | 19 |
| 25 | 20 |
(Total 8 marks)
Question 4
Grey squirrels were introduced to the UK from North America in the 1870s. Red squirrels are now absent from most of England.
(Total 6 marks)
Question 5 — extended response
A conservation group is planning to reintroduce hedgehogs to parkland where they became locally extinct. Using your knowledge of adaptation, competition and interdependence, evaluate the factors the group should consider before the reintroduction. (6)
In your answer refer to abiotic factors, biotic factors, and interdependence.
(Total 6 marks)
TOTAL FOR PAPER: 35 MARKS
Mark scheme
Check yourself — Part 1
1. Behavioural (action) · 2. Structural · 3. Functional (internal process) · 4. Structural · 5. Behavioural · 6. Functional (biochemistry) · 7. Functional — the colour change is caused by internal cellular processes (chromatophores). Accept structural if the answer refers to the chromatophore cells themselves, with justification. · 8. Structural
Question 1
(a) 1 — Behavioural.
| (b) 3. Ectothermic / cannot generate own body heat | 1 |
| Basking absorbs heat from the sun, raising body temperature | 1 |
| Moving to shade prevents overheating / lethal temperature | 1 |
Additional credit: maintaining optimum temperature keeps enzymes at their optimum rate.
| (c) 2. Its habitat is arid / water is scarce | 1 |
| Uric acid conserves water, so it survives with little available water | 1 |
| (d) 2. Individuals do not develop adaptations because they need them | 1 |
| Adaptations arise through natural selection over many generations — favourable variations survived and reproduced | 1 |
Do not credit "evolution did it" without the mechanism.
Question 2
(a) 1 — Any of: avoids daytime predators; avoids daytime heat / reduces water loss; prey active at night; less competition with diurnal species.
(b) 2 — Any two: more eyes watching for predators; predator confusion; shared warmth; easier to find a mate; cooperative digging/maintenance.
| (c) 4. Hedgehogs are solitary in the wild, so two adults together is unnatural | 1 |
| Compete for food — the dominant eats more | 1 |
| Compete for territory / the nest site | 1 |
| The subordinate eats less and is stressed, so loses weight | 1 |
Credit intraspecific competition if named; credit stress raising energy demand.
Question 3
| (a) 2. Daisies increase as distance from the hedge increases | 1 |
| The increase levels off / plateaus after ~15 m | 1 |
The second mark is for reading the shape of the data — most candidates miss it.
| (b) 3. Names light intensity | 1 |
| The hedge shades the ground, so light is lower near it | 1 |
| Less light → less photosynthesis → fewer daisies | 1 |
Accept soil moisture or mineral ions if the explanation is equally complete.
(c) 2 — Any two: daisies were found at 5 m; only one transect (may not be representative); only one hedge/field; other variables uncontrolled.
(d) 1 — Any of: repeat in several places and mean; more quadrats per distance; measure light with a light meter.
Question 4
(a) 1 — Interspecific competition.
| (b) 3. Acorns are a food resource both need / food is limited | 1 |
| Greys get energy from acorns, reds cannot digest them efficiently | 1 |
| Greys survive better in oak woodland, outcompete reds, red numbers fall | 1 |
| (c) 2. Biotic | 1 |
| A virus is a living thing / from living organisms, affecting the population through a living interaction | 1 |
Question 5 — extended response (6 marks, levels-marked)
Level 3 (5–6): detailed evaluation of abiotic, biotic and interdependence, with clear links and a supported judgement. Level 2 (3–4): at least two areas with some explanation. Level 1 (1–2): relevant points, largely a list.
Indicative content — abiotic: suitable shelter (hedgerows, log piles, leaf litter); frost-free hibernation site; water; barriers to movement (roads, walls). Biotic: enough food (slugs, beetles, worms); predators (badgers); competition from other insectivores; disease; human hazards (slug pellets, strimmers, netting, ponds without escape). Interdependence: adding hedgehogs reduces slug/beetle numbers → knock-on to plants and other species; the niche may no longer be vacant after the local extinction. Judgement: likely to succeed only if food and hibernation sites are adequate and human hazards reduced first.
Common mistakes in this topic
"It adapted to the environment." Individuals don't adapt; populations evolve. Write "the population has adapted" or "hedgehogs have evolved."
Confusing adaptation with acclimatisation. Getting a tan is not an adaptation — it's a response within one lifetime. Adaptations are heritable.
Naming a factor and stopping. Almost every 3-mark ecology question wants: name it, say what it does, link it to the data.
Missing the "however." Extended interdependence questions nearly always have opposing effects — look for the second one.
Calling predators or disease abiotic. If it's alive, it's biotic.
Describing a graph without reading its shape. "It goes up" is one mark; "it goes up and then levels off after 15 m" is two.
Teaching notes
Sequence. Parts 1–2 in one session. Part 3 works well alongside a fieldwork or quadrat practical. Parts 4–5 need a session of their own — interdependence is the hardest idea and students routinely underestimate it.
The hedgehog housing example in Part 4 is the strongest hook in the unit. Students who keep pets have been told "house them separately" or "keep rabbits in pairs" without being told why. Explaining that both rules come from the same ecology lands well — it's where the topic stops being abstract.
Question 3(a) second mark — reading the plateau, not just the direction — is the single most common lost mark in data questions across the whole specification. Teach it explicitly.
Question 5 is levels-marked and should be practised as one. Students used to point-marked questions write a list and expect a mark per point; show them the level descriptors.
Real animals matter here. Showing a bearded dragon basking under a heat lamp does more for understanding ectothermy than any diagram — the behaviour is visible in real time.