"Structural adaptations", "behavioural adaptations", "physiological adaptations": the three-way split is in the Australian Year 5 science curriculum, the US grade 3 to 8 standards, England's Year 6 evolution unit and CBSE Class 10, and the exam always does the same two things: gives an example and asks which type, then asks how adaptations come about. This page gives the definition, the three types with the one-question test that separates them, thirty examples sorted by type and organism, the natural-selection explanation in the form the mark scheme wants, and the difference from acclimatisation that catches students out. The printable has the chart and practice on two pages.
Download the adaptations chart (PDF) (the three types with the test question, 30 examples sorted by type, how adaptations arise in four steps, adaptation against acclimatisation, and twelve practice questions with answers; two pages, free).
The definition
An adaptation is an inherited feature (a structure, a behaviour or a process) that helps an organism survive and reproduce in its environment. Three parts of the definition carry marks: it is inherited (passed on in the genes, not learned or acquired), it is a feature of the organism (not of the place), and it helps with survival and reproduction in a particular environment (a polar bear's blubber is an adaptation to the Arctic and a liability in a zoo in Delhi).
The three types, and the test
| Type | What it is | The test | Examples |
|---|---|---|---|
| Structural (physical, morphological, anatomical) | a part of the body: its shape, size, covering, colour | Can you see it or touch it on the body? | fur, blubber, spines, webbed feet, beak shape, camouflage, a long neck, a hump, thorns, a thick waxy leaf |
| Behavioural | something the organism does | Could you film it as an action? | migration, hibernation (entering the den), nocturnal hunting, huddling, playing dead, courtship dances, burrowing, pack hunting, a plant's leaves turning to the sun |
| Physiological (functional) | a process inside the body: chemistry, metabolism, organs at work | Does it happen inside, where you cannot see it? | venom, concentrated urine, antifreeze proteins, slowed heartbeat, body-temperature control, bioluminescence, CAM photosynthesis, extra red blood cells at altitude |
Some adaptations are two types at once, and the exam likes those: hibernation is behavioural (the bear enters a den in autumn) and physiological (its heart rate and body temperature fall); camouflage is structural (the colouring) and sometimes behavioural (the animal keeps still against the matching background); a chameleon's colour change is physiological (the skin cells shift pigment) in the service of behaviour.
Thirty examples, sorted
| Organism | Adaptation | Type | What it does |
|---|---|---|---|
| Camel | wide padded feet, long eyelashes, closable nostrils, a fat-storing hump | structural | walks on sand, keeps sand out, stores energy for weeks without food |
| Camel | body temperature allowed to rise 6 °C before sweating; concentrated urine | physiological | saves water in the desert |
| Polar bear | thick fur, black skin under it, a layer of blubber, large paws | structural | insulation, absorbing heat, floating and gripping ice |
| Polar bear | mothers den through the winter and give birth there | behavioural | the cubs are born in shelter |
| Arctic fox | a white winter coat and a brown summer coat | structural | camouflage in both seasons |
| Cactus | spines instead of leaves, a thick waxy stem, a wide shallow root net | structural | cuts water loss, stores water, catches rain fast |
| Cactus and other desert plants | opening the stomata only at night (CAM photosynthesis) | physiological | takes in carbon dioxide without losing water in the day heat |
| Giraffe | a neck up to 2 metres long, a 45 cm tongue | structural | reaches leaves no other browser can |
| Giraffe | a very high blood pressure and valves in the neck veins | physiological | pumps blood to a head 2 metres above the heart without fainting when it bends down |
| Duck | webbed feet, oily waterproof feathers | structural | swimming and staying dry |
| Eagle | hooked beak, talons, eyes that see a rabbit from 3 km | structural | catching and tearing prey |
| Hummingbird | a long thin beak and a hovering wingbeat | structural | feeding from deep flowers |
| Stick insect, leaf insect | a body shaped and coloured like a twig or leaf | structural | camouflage from predators |
| Peppered moth | dark and pale forms | structural | camouflage on soot-darkened or clean bark; the classic natural-selection case |
| Arctic tern | migrates from the Arctic to the Antarctic and back every year, about 70,000 km | behavioural | summer feeding at both ends of the Earth |
| Monarch butterfly | migration of up to 4,000 km to Mexican forests | behavioural | escapes winter |
| Bear, hedgehog, dormouse | hibernation | behavioural (entering the den) and physiological (metabolism, heart rate and temperature fall) | survives winter without food |
| Emperor penguin | huddling in groups of thousands, taking turns on the outside | behavioural | shares warmth at −40 °C |
| Opossum | playing dead, with a foul smell | behavioural | predators that eat live prey lose interest |
| Meerkat | sentries that watch for predators while the group feeds | behavioural | early warning |
| Owl, bat, hedgehog | nocturnal activity | behavioural | avoids daytime heat and predators; bats hunt insects that fly at night |
| Peacock, bird of paradise | courtship displays | behavioural | attracts mates |
| Wolf, lion, orca | hunting in packs | behavioural | brings down prey larger than one hunter could |
| Rattlesnake, cobra, scorpion | venom made in glands | physiological | kills or paralyses prey, defends |
| Kangaroo rat | kidneys that make extremely concentrated urine; it never drinks | physiological | lives on the water in its seeds |
| Antarctic icefish and notothenioids | antifreeze proteins in the blood | physiological | blood does not freeze at −2 °C |
| Seals, whales, dolphins | the diving reflex: heart rate drops, blood goes to the brain and heart | physiological | long dives on one breath |
| Llama, Tibetan and Andean people | blood that carries more oxygen (more red cells, or haemoglobin that binds oxygen better) | physiological | life at 4,000 metres |
| Firefly, anglerfish | bioluminescence from a chemical reaction | physiological | attracting mates or prey in the dark |
| Mangrove | roots that breathe above the mud and leaves that excrete salt | structural and physiological | lives in salt water and airless mud |
How adaptations arise
The exam answer, in four steps, in the words of natural selection:
- Variation: individuals in a population differ, because of mutation and sexual reproduction (some rabbits have slightly thicker fur).
- Selection: the environment favours some variants (in a cold winter, thick-furred rabbits survive better and breed more).
- Inheritance: the favoured feature is passed to offspring (thick fur is in the genes).
- Change over generations: the feature becomes more common; over many generations the population is adapted.
What this rules out is the older idea (Lamarck's) that organisms adapt by trying: the giraffe did not stretch its neck and pass the stretch on. An individual cannot acquire an adaptation; a population acquires it over generations because the individuals that already had it bred more.
Adaptation against acclimatisation
| Adaptation | Acclimatisation (acclimation) | |
|---|---|---|
| Who changes | the population, over generations | one individual, within its lifetime |
| Inherited? | yes | no |
| Example | the Tibetan people's altitude genes; the polar bear's fur | a climber making more red blood cells at base camp; a dog's thicker winter coat; a suntan; fitness from training |
| Reversible? | no (in the individual) | yes, when the conditions change |
A student who writes "the polar bear adapted to the cold by growing thick fur" has described acclimatisation and will lose the mark; the population became adapted because thick-furred bears out-bred thin-furred ones.
Where it sits in school
The three-type split is the wording of the Australian Curriculum for Year 5 (structural, behavioural and physiological adaptations) and Year 10; in the United States, adaptations appear in grade 3 (NGSS 3-LS4-3) and grade 4 (4-LS1-1, "structures that function to support survival"), with natural selection as the mechanism in middle school (MS-LS4-4) and high school; in England, Year 6 (Evolution and Inheritance: "animals and plants are adapted to suit their environment") and GCSE Biology (structural, behavioural and functional adaptations, extremophiles); in CBSE, Class 7 (Weather, Climate and Adaptations of Animals), Class 9 and Class 10 (Heredity and Evolution). The errors on every board: calling an action structural, calling an internal process behavioural, and explaining the origin as effort rather than selection.
Practice: twelve questions
Name the type (structural, behavioural or physiological).
- A hare's white winter coat.
- Geese flying south in autumn.
- A snake producing venom.
- A frog burrowing into mud before the dry season.
- A whale's blubber.
- A dormouse's heart rate dropping to a few beats a minute in winter.
- A cactus opening its stomata only at night.
- A tortoise's shell.
- Penguins huddling.
- A camel's long eyelashes.
- A human's extra red blood cells after a month at altitude: adaptation or acclimatisation?
- In four steps, explain how a population of moths became dark-coloured in a sooty city.
Answers: 1) structural. 2) behavioural. 3) physiological. 4) behavioural. 5) structural. 6) physiological. 7) physiological. 8) structural. 9) behavioural. 10) structural. 11) acclimatisation (within one life, not inherited). 12) Variation: some moths were darker; selection: on dark bark, birds caught pale moths more often; inheritance: dark colour was passed to offspring; over generations dark moths became the majority.
Download the adaptations chart (PDF)
Where to get help
A 1-on-1 online science class with a tutor who holds a master's degree in science, for grades 3 to 10, Key Stage 2 and GCSE, the Australian years and CBSE Class 7 to 10: adaptations sorted with the three test questions on the shared screen, natural selection written in the four-step form the mark scheme wants, and the exam questions practised by type. The recording and notes after every class, the same tutor every week, US$10 to $13 an hour. The biology page has the courses; the free 30-minute first class is a real lesson, usually on the homework the child brings.
Questions parents ask
1What is an adaptation?
2What are the three types of adaptation?
3What is an example of a structural adaptation?
4What is the difference between a behavioural and a physiological adaptation?
5How do adaptations arise?
See how we teach this, 1-on-1 online →
Shobha
Founder and lead tutor, Science with Shobha
Teaching maths, science and English to children online since 2018. 500+ students, 20+ tutors, families in nine countries.