How are these animals and plants linked?

Hint: What do you know about ecosystems?

A desert food chain:

Draw a desert food chain in your book.

Objectives

• All students must be able to draw a simple desert food chain.

• Most students should be able to give an example of a real desert plant and explain two adaptations

• Some students should be able to explain desert food chains and webs in detail.

STRIPE:

• Reflective learner - Present your learning in different ways when sharing your work with different groups of people

Syllabus key ideas:

• 5.1 Ecosystems in hot deserts are finely balanced.

• 5.2 Plants have adapted to survive in hot deserts.

What is the difference between a food chain and a food web?

• A food chain only follows just one path as animals find food. eg: A hawk eats a snake, which has eaten a frog, which has eaten a grasshopper, which has eaten grass.

• A food web shows the many different paths plants and animals are connected. eg: A hawk might also eat a mouse, a squirrel, a frog or some other animal. The snake may eat a beetle, a caterpillar, or some other animal. And so on for all the other animals in the food chain.

• A food web is several food chains connected together.

Task 1

• Your teacher will give you some cards with different desert plants and animals on them and some string.

• Use these to create a food web similar to the one on the next slide.

• What would happen to this web if one of the plants or animals in it disappeared?

A desert food web

So how do plants survive in the harsh desert environment?

How does this cactus cope with the lack of water in the desert? How does it

cope with the high evaporation rates?

How does it cope with the high temperatures in the desert? How does this

cactus protect itself from animals that want to eat it?

Note these key terms in your book:

• Xerophytes – plants that have adapted to survive in very dry conditions

• Dormant – when plants stop growing, for example in a drought

• Ephemerals – plants that grow, flower and produce seeds within just a few weeks (following rain)

Barrel cactus

• The shallow roots spread out around the plant to absorb moisture from rain or dew

• The stomata (pores) are opened at night to exchange gasses for photosynthesis

• This reduces the water lost out of the stomata

• Inside the cactus is a mass of water-storing tissue

• The cactus is covered with a thick waxy layer to prevent water loss and protect the plant from burning in the sun

Cistanche

• This plant is leafless, so can’t photosynthesise

• It gets its ‘food’ by tapping the roots of other plants

• This means that it is a parasite

Living stones

• These plants are camouflaged, so animals don’t eat them

• They are succulents – they store water in their leaves

• They grow with all but the tips of their leaves in the ground

• The surrounding soil and stones protect them from the sun

• They grow in southern Africa

Fire thorn branch

• Grows in deserts of SW USA

• Sheds its leaves to conserve moisture in dry times

• After rains new leaves grow among the spines

• If the ground is wet enough it flowers

Welwitschia

• This plant has only two frayed strap like leaves

• It has a huge tap root which may be 1m wide at the top

• It grows on gravel plains in the Namib desert

• It may live for a thousand years or more

Haworthia

• Grow in places with some shade

• Only the tips of the leaves poke above the surface

• In droughts the plant shrinks into the ground

Date palm

• Long roots to reach water

• Grown at an oasis• Small leaves reduce

water loss• Dates are nutritious

and don’t rot

Task 2

• Choose one of the plants you have just seen and collect a photograph of it from your teacher

• Draw the plant, filling a page, in your exercise book

• Annotate (label) the plant to explain how it is adapted to the desert environment

Example:

The giant saguaro can store tonnes of water in its stems

The cactus has spikes instead of leaves, so it doesn’t lose as much water from evaporation.

The waxy skin protects from evaporation and sun burn

Reflection

• Are some of you willing to present your sketches to the rest of the class, explaining how it has adapted to the desert environment.

• Class vote for most informative sketches – award merits

• When might annotated sketches be useful in an exam?

Have we achieved our objectives?

• All students must be able to draw a simple desert food chain.

• Most students should be able to give an example of a real desert plant and explain two adaptations

• Some students should be able to explain desert food chains and webs in detail.