Many plants’ adaptations are
designed to minimise water loss and balance the amount of water in their cells.
This is hugely significant and important as many of a plant’s life processes
require water. Plants are autotrophs’ and are able to make their own food by
photosynthesis. The equation for photosynthesis is;
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As shown, plants need water in
order to complete the process and produce glucose, the sugar they use to create
energy. If plants don’t have access to water, or ways of conserving it, their
cells won’t be able to complete this process and create food for the plant. As
this would lead to the plant dying, plants have adaptations which allow it to
control water loss and therefore ensure processes such as photosynthesis can be
carried out. Photosynthesis isn’t the only reason plants need water, for mesophytes
and hydrophytes, water is needed to support their structures. As plants don’t
have skeletons, the cell walls and vacuoles in their cells provide support.
When the cells’ vacuoles are turgid and full of water, the plant is able to
stand upright. For hydrophytes, the water often supports the plant itself. Water
is also necessary for keeping the cells’ membranes moist which allows for
efficient gas exchange. Water is also used to control the temperature of the
plant. Without water, plants’ cells wouldn't be able to function or produce substances such as glucose, which the cells need to survive.
The
issue plants face when it comes to water conservation is transpiration. As
water evaporates from the plant’s leaves and stomata, more water moves up the plant to
replace the molecules lost. This is due to cohesion; water molecules are
attracted to each other. They stick together to make a chain and as water
evaporates from the plant’s leaves and stem, more molecules are pulled up to
fill the space the evaporated water has left. Unfortunately for some plants, this means they are nearly always losing water. Transpiration is the main cause
of water movement in plants yet there are other smaller factors contributing to
this movement. Root pressure pushes water up the plant and capillary action
means that water sticks to the sides of the xylem and is pulled upwards. Although
transpiration results in a loss of water from the plant, it also helps keep the
plant cool and allows for movement of water and other minerals around the plant.
The rate of transpiration increases when a plant's stomata are exposed to high winds and hot or dry environments, as there is a high water concentration gradient between the inside of the plant, and its environment. This means that as there is less water outside of the plant, the H20 molecules will automatically diffuse into this low concentration area in an attempt to reach an isotonic state. Subsequently, the higher the concentration gradient, the more water the plant lose.
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