The guard cell prevents water loss in leaves.
Some xerophytic plants have tiny leaves to reduce the amount of water lost during transpiration.
Sometimes the amount of water is not sufficient to complete a proper photosynthesis cycle and the heat from the light dries up the leaves pre maturely and they die. Some leaves are simply more sensitive to light and heat and curl up to avoid too much damage.
Plants use waxy substances on their leaves to help reduce transpiration, the evaporation of water from plants. The wax helps to keep water in the plant as to not dehydrate the plant.
Because lower epidermis remains away from the light and in the absence of light the water loss through transpiration is minimized.
Well, stomata are the pores through which leaves breathe. These are also the pores through which transpiration takes place (Transpiration is the loss of excess water- just like in us, only we call it sweating). So if these pores were on the top of the leaf where sunlight falls directly, then there would be a lot of loss of water through evaporation and it is definitely not good to lose so much water. So in order to reduce the chance of losing lot of water, these stomatal pores are in the lower leaf.
Most xerophytic plants have waxy coating on epidermal cells of leaves to minimize water loss by transpiration. For this reason these plants also have sunken stomato gaurded by trichomes etc.
To reduce transpiration
Leaves of an oak tree fall off during summer because the oak tree is trying to save the water and minerals of the tree. i.e. the tree is trying to reduce the amount of transpiration which takes place through heavy sunlight. So by getting rid of leaves the amount of transpiration reduces and the oak tree won't die.
To protect it from predators in the desert.(: and to reduce the rate of transpiration. In many cases the thorn are formed by the modification of shoot , Thus eliminating the leaves hence the free surface to minimize the transpiration.)
It has needle-like leaves to reduce water loss through transpiration. It has a sloping shape to prevent accumulation of snow.
An antitranspirant is a substance applied to plant leaves in order to reduce transpiration.
defence. the cacti leaves are the thorns...
to reduce the high rate of transpiration and it reduce the chances of blockage of stomata by small tiny particles of soil which are present in atmosphere.
Transpiration.
The needle like leaves have a smaller surface area. Thus ,the stomata ut contains is smaller and lesser as conpared to other stomatas in leaves in different places . Therefore ,with lesser stomatas,the amount of water loss during transpiration is lesser.
Reduce loss of water through transpiration / evaporation.
Sometimes the amount of water is not sufficient to complete a proper photosynthesis cycle and the heat from the light dries up the leaves pre maturely and they die. Some leaves are simply more sensitive to light and heat and curl up to avoid too much damage.
Transpiration in plants is regulated by sunshine, temperature and humidity. If you increase humidity in the air, the rate of transpiration will go down. Another approach to reduce transpiration in crop plants is application of certain chemicals like cycosil to close the stomata during sunshine.