GCSE · Geography · AQA · Spec 8035

Plant and animal adaptations in hot deserts

Almost no rain, and scorching heat. Most living things can't survive a hot desert, yet cacti, camels and fennec foxes thrive there. Their secret: every feature solves a problem.

Sort it: problem → solution

Which desert problem does each feature solve?

A hot desert gets less than 250 mm of rain a year, the little that falls evaporates quickly, and the heat is extreme. Each feature below is an adaptation that helps something survive there. Tick every problem it helps with. Some features tackle two problems, and not every feature fits these three.

A Too little water
B Extreme heat
C Strong winds, blowing sand or grazing animals

Fennec fox's large ears
Being active at night and resting by day
Burrowing deep underground
Camel: tolerates dehydration and makes very concentrated urine
Cactus spines instead of leaves
Thick, waxy skin
Fleshy, swollen stem
Wide, shallow roots
A long tap root, 7–10 m deep
Seeds with tough outer coats
Camel's long eyelashes and hairy ears
Camel's wide feet

Look closer

Built for drought: a desert plant up close

View: Roots: spread wide. Showing 6 layers: Ground, Fleshy stem, Stored water, Waxy skin, Spines, Shallow roots

View

Layers

Explore

Tap a part · peel the skin · switch the roots

Some desert plants spread wide, shallow roots just under the surface. They soak up as much rain as possible before it evaporates, and they anchor the plant against strong winds.

A cactus body shown with the two root plans that different desert plants use.

Process · Closed loop

The ephemeral's race against the drought

Tap each stage in turn, and notice where the loop starts again.

Stage 01

Rain falls

After a long dry spell, rain finally falls. Buried in the dry ground, seeds have been waiting for exactly this.

Watch out: The adult plant doesn't survive the dry spell. Its seeds do.

Two ways for a plant to beat the drought

XerophytesvsEphemerals

Start with the top row: it's the difference that matters most.

Focus

The strategy

Xerophytes

Hoard it: cut water loss right down and store water in the plant's tissues

Ephemerals

Race it: grow only after rain and finish the life cycle fast

The insight

This is the one to remember. A xerophyte makes its water last; an ephemeral makes the most of the water while it lasts.

When it grows

Xerophytes

Survives long periods without rain on the water it has stored

Ephemerals

Only in the few weeks after rain has fallen

What gets through the dry spell

Xerophytes

The plant itself

Ephemerals

Only its tough-coated seeds

Examples

Xerophytes

Cacti, agave, the Joshua tree

Ephemerals

The Arizona desert poppy

Myth-buster

What's really in a camel's hump?

Camels can survive in hot deserts for long periods without drinking. Plenty of people point to the hump to explain how.

Which is closest to what you think the hump stores?

Water. It's a water tank the camel drinks from when it's thirsty.Fat. It's an energy reserve the camel uses when food is scarce.Both. Some water for when it's thirsty and some food for when it's hungry.

How sure are you?

I'm sureI think soI'm guessing

Water. It's a water tank the camel drinks from when it's thirsty.

This is a common misconception

This is the famous myth, and it's wrong: there's no water in the hump at all. The camel handles thirst in other ways. It tolerates high rates of dehydration, it can take on large volumes of water when it does drink, and it makes highly concentrated urine so very little water is wasted.

Fat. It's an energy reserve the camel uses when food is scarce.

This matches the evidence

Spot on. The hump stores fat, which the camel uses as nourishment when there's little to eat. That matters in hot deserts, where vegetation is very sparse, and it lets camels go for long periods without food. Its thick, leathery lips help on the food side too: they let it eat spiny cacti and other spiky plants.

Both. Some water for when it's thirsty and some food for when it's hungry.

This is a common misconception

Half right, which makes this one sneaky. The hump is a food reserve (stored fat), but it holds no water. For water, the camel relies on tolerating dehydration, drinking large volumes at once and making very concentrated urine.

Hump = fat = food reserve. Water is handled by the rest of the camel: it tolerates dehydration, drinks a lot at once and makes concentrated urine.

Exam practice

Put it into words

Describe how one named plant and one named animal are adapted to survive in hot deserts. [4 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

Names a plant adaptation, e.g. spines instead of leaves, thick waxy skin, a fleshy water-storing stem, wide shallow roots or a long tap root. (1 mark)
Says how that plant adaptation helps, e.g. spines have a smaller surface area, so less water is lost by transpiration. (1 mark)
Names an animal adaptation, e.g. the fennec fox's large ears, a camel's highly concentrated urine, or being nocturnal. (1 mark)
Says how that animal adaptation helps, e.g. large ears release body heat, so the fox stays cool. (1 mark)

Model answer

A cactus has thick, waxy skin, which reduces the amount of water it loses, and a fleshy stem that stores water so it survives long periods without rain. A camel produces highly concentrated urine, which conserves water, so it can survive for longer without drinking.

Two halves for each organism: the feature, then how it helps. A feature on its own is only half an answer.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Every feature is an answer to a problem: too little water, too much heat, or wind, sand and hungry grazers.

What you need to know

An adaptation is an evolutionary change in structure or function that improves an organism's chance of survival in its environment.
Hot deserts are hard to live in because of the lack of precipitation (under 250 mm a year, which evaporates quickly) and the extreme heat.
Animals stay cool by releasing heat (the fennec fox's large ears) or by avoiding it (being nocturnal, burrowing deep underground).
Camels cope with scarce water by tolerating dehydration, taking on large volumes of water and producing highly concentrated urine.
Xerophytes, such as cacti, agave and the Joshua tree, cut water loss and store water; ephemerals grow, flower and seed within a few weeks of rain.

The big picture

Hot deserts are brutal: under 250 mm of rain a year that evaporates quickly, plus extreme heat. The plants and animals that live there are highly specialised, and every adaptation answers a particular problem. Animals keep cool with features like the fennec fox's large ears, or avoid the heat by being nocturnal or burrowing. Camels cope with little water by tolerating dehydration, drinking large volumes and making concentrated urine; their hump stores fat, not water. Plants take one of two routes: xerophytes such as cacti cut water loss and store water, while ephemerals race through their life cycle in the few weeks after rain.

Key points

1Match every adaptation to the problem it solves: lack of water, extreme heat, or wind, blowing sand and grazing animals.

2Some adaptations do two jobs: cactus spines cut water loss and deter grazers; wide, shallow roots catch rainfall and anchor the plant against strong winds.

3A camel's hump stores fat as an energy reserve for when food is scarce. It does not store water.

4Camels' thick leathery lips let them eat spiny plants, long eyelashes and hairy ears keep out blowing sand and dust, and wide feet stop them sinking into sand.

5Cacti have spines instead of leaves, thick waxy skin and fleshy water-storing stems; some desert plants have wide, shallow roots and others long tap roots reaching 7–10 m down.

6Ephemerals complete their life cycle in a few weeks after rain (the Arizona desert poppy takes about five weeks), then die; their tough-coated seeds survive until the next rain.

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Worked example

Problem

Explain one way the fennec fox is adapted to survive the extreme heat of a hot desert.

⚠ Watch out

Saying a camel's hump stores water. It stores fat, an energy reserve for when food is scarce. The camel copes with the lack of water by tolerating dehydration, drinking large volumes when it can and producing highly concentrated urine.

🧠

Memory hook

Hoard it or race it: xerophytes hoard water, ephemerals race the rain. And the camel's hump? A packed lunch, not a water bottle.

✓

Check yourself

Cover the page. Name one adaptation for the lack of water, one for the heat and one that does two jobs, then say how each one helps the organism survive.

Flashcards

(14)

What is an adaptation?

An evolutionary change in structure or function that improves an organism's chance of survival in its environment.

Why can most plants and animals not survive in hot deserts?

The lack of precipitation (under 250 mm of rain a year, which evaporates quickly) and the extreme heat.

Name two behaviours desert animals use to avoid the heat.

Being nocturnal (active at night, resting by day) and burrowing deep underground, where it is cooler.

Give three ways a camel copes with a lack of water.

It tolerates high rates of dehydration, takes on large volumes of water when it drinks, and produces highly concentrated urine.

What does a camel's hump store, and why?

Fat, an energy reserve used as nourishment when food is scarce. It does not hold water.

How do a camel's lips, eyelashes and hairy ears help it?

Thick leathery lips let it eat spiny cacti; long eyelashes and hairy ears protect it from strong winds and blown sand and dust.

Why do camels have wide feet?

To spread their weight so they don't sink into the sand, which reduces the energy they use.

What is a xerophyte? Give three examples.

A plant adapted to arid conditions that uses, and stores, the little water available. Examples: cacti, agave, the Joshua tree.

What two jobs do cactus spines do?

Their small surface area reduces water lost by transpiration and evaporation, and they protect the cactus from grazing animals.

How do a cactus's stem and skin help it survive?

The fleshy stem stores water for long periods without rain; the thick, waxy skin reduces water loss.

Wide, shallow roots or a long tap root: what does each do?

Wide, shallow roots catch rainfall before it evaporates and anchor the plant against wind. A long tap root reaches 7–10 m down to water underground.

What is an ephemeral plant?

A plant that grows, flowers and makes seeds within a few weeks of rain, then dies as the water dries up. Its tough-coated seeds survive until the next rain.

How quickly does the Arizona desert poppy complete its life cycle?

It grows, flowers and produces seeds within about five weeks of rainfall.

Xerophyte versus ephemeral: what's the key difference?

Xerophytes survive by greatly reducing water loss and storing water; ephemerals have very rapid life cycles that happen only after rain.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Which desert problem does each feature solve?

The ephemeral's race against the drought

What's really in a camel's hump?

Put it into words

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