Xerophytes

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Xerophytic Adaptations
Xerophytes are plants that are adapted to conditions that make transpiration
extremely fast e.g. hot, dry and windy conditions. They usually live in deserts or sand
dunes which are both very windy environments which receive very little precipitation
which is lost to the environment very quickly.
Xerophytes usually have adapted leaves in order to minimise water loss as this where
transpiration mainly happens. Adaptations include:
A thick cuticle; to stop water from evaporating out of plants, they've
developed a thick, waxy, waterproof cuticle which doesn't allow the water out
as much as normal cuticles
Rolling up of leaves; since the stomata are mostly located in the lower
epidermis which is on the underside of the leaf, when the leaf is folded, it traps
still air. Water can collect here, therefore there's no water potential gradient
between the stomata and the air, so water can't evaporate out
Hairy leaves; the hairiness of some leaves mean that water is trapped on the
tiny hairs, reducing the water potential gradient, limiting water loss yet again
Stomata in pits or grooves; the stomata been located in pits or grooves in a
plant means that water is collected in these pits, again reducing the water
potential gradient, meaning transpiration is harder to carry out
Reduced surface area to volume ratio of the leaves; a low surface area to
volume ratio means that materials are harder to diffuse and get to cells, and so
water is harder to evaporate and transpire from cells NB This however
affects the rate of photosynthesis due to a smaller surface area.
Cacti
Cacti are the best known xerophytes, inhabiting deserts
in the Americas, Africa and Sri Lanka. They are very
specialized organisms which can thrive in the driest areas
in the world.
Cacti have no true leaves but instead have spikes which
reduce the surface area available for water to be lost.
Spikes also conserve water by trapping a layer of air to
the plant, to lower the water potential gradient so water
does not diffuse out, as well as collect water when there
is moisture in the air which then drips to the ground to be
collected by the extensive root network. The spikes offer protection against
herbivores and provide shade to the plant, lowering the temperature to limit
evaporation.
Many Cactuses are also very small and round. This means there is a
very low SA:V ratio meaning the rate of diffusion is low due to
very small surface area. The stems of cactuses are where most of

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Cacti also have a different way of transpiring. They only open their stomata during the
night when temperatures are very cool and so water loss is minimized. CO2 is absorbed
during the night and is stored as malic acid in the vacuole of the mesophyll cells. The
malic acid is then moved to the chloroplasts during the day and turned back into CO2
for photosynthesis.…read more

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