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Adaptations of plants to the availability of water (Cacti (Cacti are…
Adaptations of plants to the availability of water
Terrestrial plants
For land based plants water loss can be an issue due to their need to have their stomata remain open during the day for photosynthesis to occur.
A waxy cuticle on the leaf prevents water loss via evaporation from the epidermis
Stomata found under the surface of the leaves to prevent direct heating by sunlight
Stomata close at night when there is no sunlight
Deciduous plants loose their leaves in the winter when water is less available for photosynthesis.
Marram grass
Adapted for harsh, dry, sandy conditions where there is low water availability. Named a xerophyte due to its adaptation to arid conditions.
Leaf is rolled longitudinally so that air is trapped between the leaf preventing water loss with a humid air layer (reduced diffusion water potential between the air and the leaf).
Thick waxy cuticle on the outer side of the leaf to prevent upper epidermis evaporation.
Stomata are on the inside of the rolled leaf so they are protected by the enclosed air space.
Spongy mesophyl is very dense, very few air spaces - less surface area for water loss.
Cacti
Cacti are succulents - they store water within their stems which becomes fleshy and swollen. The stem is often ribbed or fluted to allow for expansion when water is stored inside the stem.
Leaves are spines. This reduces the surface area of the leaves. When the total leaf surface area is reduced, less water is lot via transpiration.
Stem is green - filled with chlorophyll pigment for photosynthesis.
Wide spreading roots to ensure efficient rain water capture in sandy conditions where surface water is quick to soak away.
Hydrophites
Plants that live in the water - they have easy access to water,but are faced with other issues of getting oxygen to their submerged tissues.
Large air spaces within the leaf.This allows high buoyancy preventing the leaf from becoming submerged in water.
Stomata are on the upper epidermis, ensures they are constantly exposed to sunlight. Allows constant gas exchange.
Leaf stem has many large air spaces. This helps with buoyancy, but also allows for oxygen to diffuse quickly to the roots for aerobic respiration
How do they transpire?
For hydrophites due to their water based environemnt they have ti adapt to be able to maintain the transpiration flow to ensure mineral ions can be transported throughout the plant. Many plans contain specialised structures at the tips of their leaves called hydathodes. these structures can release water droplets which then evaporate from the leaf surface.
Other xerophytic features:
Closing the stomata when water availability is low will reduce water loss from the plant and reduce the water take up needed.
Some plants have low water potential inside their leaf cells. This is done by having a very high concentration of salt within the cells. This reduced rate of evaporation of water from the cells surface.
Long tap root that can reach underground for lower level water table stores of water such as aquifers