Transpiration
When the plant opens its stomata to let in carbon dioxide, water on the surface of the cells of the The plant tissue in a leaf which has loosely packed cells and air spaces between them to allow gas exchange. and Plant tissue containing closely packed cells in the upper layer of a leaf. The process in which a liquid changes state and turns into a gas. and When particles spread out from a region of higher concentration to a region of lower concentration. out of the leaf. This process is called The loss of water from leaves by evaporation through the stomata..
Water is drawn from the Narrow, hollow, dead tubes with lignin, responsible for the transport of water and minerals in plants. to replace the water that has been lost from the leaves.
Water molecules inside the xylem cells are strongly attracted to other water molecules. There is strong cohesion between the molecules because of The strongest type of van der Waals force that arises through a dipole-dipole attraction when hydrogen atoms are covalently bonded to highly electronegative nitrogen, oxygen or fluorine atoms.. A continuous column of water is therefore pulled up the stem in the transpiration stream by evaporation from the leaves.
As water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots.
Transpiration is an unavoidable consequence of A chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy. Oxygen is produced as a by-product of photosynthesis. Algae subsumed within plants and some bacteria are also photosynthetic. - only five per cent of the water taken up by the plant is used for photosynthesis - but does have its purposes:
- provides the water for photosynthesis
- transports Naturally occurring, inorganic chemical substances. Minerals are necessary for both plant and animal health.
- cools the leaf as water evaporates
- provides water that keeps the cells Having turgor - enlarged and swollen with water., which supports herbaceous plants
Water uptake and transport across the root
Root hairs are single-celled extensions of Cells of the epidermis, the outer covering layer of an organism. in the root. They grow between soil particles and absorb water and minerals from the soil.
Water enters the root hair cells by The movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.. This happens because soil water has a higher water potential than the cytoplasm of the root hair cell. Minerals enter by The transport of molecules against their concentration gradient from a region of low concentration to a region of high concentration..
A summary of water uptake, water transport and transpiration:
Factors affecting transpiration
The rate of transpiration is affected by several factors. These include:
- temperature
- humidity
- air movement
- light intensity
The table below explains how factors increase the rate of transpiration:
| Factor | Change in factor that increases transpiration rate | Explanation |
| Temperature | Increases | An increase in temperature increases evaporation, so the rate of diffusion of water from inside the leaf to outside increases |
| Humidity | Decreases | A decrease in humidity reduces the concentration of water molecules outside the leaf, so the rate of diffusion of water from inside the leaf to outside increases |
| Air movement | Increases | An increase in air movement removes water vapour from outside the leaf, so the rate of diffusion of water from inside the leaf to outside increases |
| Light intensity | Increases | An increase in light intensity generally increases the number of open stomata, so the rate of diffusion of water from inside the leaf to outside increases |
| Factor | Temperature |
|---|---|
| Change in factor that increases transpiration rate | Increases |
| Explanation | An increase in temperature increases evaporation, so the rate of diffusion of water from inside the leaf to outside increases |
| Factor | Humidity |
|---|---|
| Change in factor that increases transpiration rate | Decreases |
| Explanation | A decrease in humidity reduces the concentration of water molecules outside the leaf, so the rate of diffusion of water from inside the leaf to outside increases |
| Factor | Air movement |
|---|---|
| Change in factor that increases transpiration rate | Increases |
| Explanation | An increase in air movement removes water vapour from outside the leaf, so the rate of diffusion of water from inside the leaf to outside increases |
| Factor | Light intensity |
|---|---|
| Change in factor that increases transpiration rate | Increases |
| Explanation | An increase in light intensity generally increases the number of open stomata, so the rate of diffusion of water from inside the leaf to outside increases |
Question
What conditions will decrease the rate of transpiration?
Decrease in temperature, increase in humidity, no or reduced air movement and low light intensity.