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biology 0610printed 246 · PDF 246
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printed 246 · PDF 246
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● Some examples include gills for fish, streamlined bodies and
different types of enzymes.
● Some plants contain adaptive features to help them survive in an
environment where water is scarce. These are known as
xerophytes.
● Other plants contain adaptive features to help them survive in a
water-dense environment. These are called hydrophytes.
Adaptive features of xerophytes
● Xerophytes often have closed stomata. This is because plants
lose most water as water vapor through the stomata. If they close
the stomata, transpiration of water almost completely stops.
● The leaves of xerophyte plants are covered with a thick waxy
cuticle which makes them waterproof.
● Xerophytes contain hairs on their leaves. These trap a layer of
moist air next to the leaf. The moist air reduces the diffusion
gradient for water vapor from the leaf into the air so less water
vapor diffuses out of the leaf.
● Most xerophytes have sunken stomata on the undersides of
leaves. The lower surface is cooler than the upper one due to less
contact with sunlight so less water will evaporate.
● The xerophytes usually contain few stomata and they are often
sunk into deep pits in the leaves. When water wafer diffuses out
through the stomata it collects in the air trapped in the pits. This
reduces the diffusion gradient so less water vapor diffuses out of
the leaf.
● Xerophytes have very small and barely visible leaves, often in
the form of spines. The spines are sharp and prevent hungry and
thirsty animals eating the plant and the small surface area of the
leaves allows less diffusion of water outside.
● Usually desert plants also have deep or spreading roots so that
they can seek out water deep down in the soil or over a wide area.