Exchange and transport in plants
Plants, like animals, need an internal transport system in order to move substances around.
- Water and mineral ions are absorbed by the roots
- Plants synthesise food in the leaves through the process of photosynthesis
Key words:
Stomata (stoma = singular) - Openings in the underside of leaves that allow gases to enter and leave Guard cells - cells which border the stomata and control their opening and closing Cuticle - waxy coating to the topside of leaves that help reduce water loss Translocation - the movement of dissolved sugars in the phloem Transpiration - the loss of water from the leaf by evaporation and diffusion Phloem - the living transport tissue in the plant which carries sugars Xylem - the non-living transport tissue in the plant which carries water |
Just like animals, plants exchange materials with their environment, as indicated above.
For more details about the specifics of these forms of exchange, see the page on Cellular Transport In trees and woody plants, the xylem makes up the bulk of the wood, whereas the phloem forms a ring just under the layer of bark. Young saplings are often chewed by rabbits and deer. This results in the destruction of the phloem, meaning the transportation of glucose cannot take place and the plant dies
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Transpiration
As discussed above, water vapour is lost from the leaves by evaporation and then diffusion out from the stomata. This loss of water is called transpiration. As the water is lost, more water is 'pulled up' through the plant from the roots via the xylem, a bit like a straw.
The continuous movement of water from root to leaves through the xylem, and then out of the stomata is called the transpiration stream.
As discussed above, water vapour is lost from the leaves by evaporation and then diffusion out from the stomata. This loss of water is called transpiration. As the water is lost, more water is 'pulled up' through the plant from the roots via the xylem, a bit like a straw.
The continuous movement of water from root to leaves through the xylem, and then out of the stomata is called the transpiration stream.
The rate of transpiration is affected by the rate of photosynthesis:
Therefore, warm sunny conditions = more photosynthesis = more transpiration In addition, transpiration will be increased by any conditions that increase the rate of evaporation and diffusion of water. This means hot, dry and windy conditions |
Make sure you understand the adaptations that plants have made in order to reduce water loss. Check out the Adaptations page to help you (look at the 'Adaptations Revision Notes' document)
Science in action!
This is a potometer. It is a very simple piece of kit that can be used to measure the rate of transpiration. Make sure you understand how it works.