Transcript How has this cactus adapted to the desert environment?

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
temperatures in
the desert?
How does it
cope with the
high
evaporation
rates?
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 waxy skin
protects from
evaporation and
sun burn
The cactus has
spikes instead of
leaves, so it
doesn’t lose as
much water from
evaporation.
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.