Transpiration
- Created by: Eleanor Izzard
- Created on: 02-01-13 12:39
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- Transpiration
- the loss of water vapour by evaporation from aerial parts of the plant
- Transpiration Stream
- as water leaves the xylem in the leaf, it must be replaced below. Water moves up the Xylem from the roots to replace the water lost
- Useful to the plant:
- water is required to enable cells to grow and elongate
- water is required in the leaf for photo-synthesis
- water keeps the cells turgid
- evaporation of water can keep the plant cool
- the flow of water can carry useful minerals up the plant
- Measuring Rate
- Potometer can be used to estimate the rate of water loss
- actually measures the rate of water uptake but about 99% of water taken up is lost in transpiration
- important that there are no air bubbles
- water lost by the leaf is replaced from the water in the capillary tube
- the movement of the meniscus at the end of the water column can be measured
- to study different environmental conditions on the rate of transpiration, you can place the equipment in different situations
- Potometer can be used to estimate the rate of water loss
- Altering Factors
- Light - in light stomata open for gaseous exchange
- Cuticle - waxy reduces evaporation
- Water Availability - if there is little water in the soil then the water cannot be replaced so water loss is reduced when stomata are closed or when leaves shed water
- Wind - carries water vapour away that have just diffused out of the leaf - maintaining high water potential gradient
- Number, size and position of Stomata - lower surface, water is lost less readily
- Relative Humidity - higher decreases water loss, smaller water potential gradient
- Number of Leaves - more = more surface area over which vapour can be lost
- Temperature - increased increases water loss
- 1.increase rate of evaporation from the cell surfaces so that the water potential in the leaf rises
- increase the rate of diffusion through the stomata as they have more kinetic energy
- decrease the water vapour potential in the air, allowing more rapid diffusion
- Water Loss
- If water loss by transpiration is greater than water uptake from the roots, the plant cells will lose turgidity
- the leaves of woody plants will wilt and the plant will eventually die
- non woody plants will wilt and die
- If water loss by transpiration is greater than water uptake from the roots, the plant cells will lose turgidity
- How does it occur
- water enters the leaves in the xylem and passes to the mesophyll cells by osmosis and evaporates from the surface to from water vapour
- the spongy mesophyll cells have large air spaces between them that help the water vapour to diffuse through the leaf tissue
- As vapour collects in these air spaces, the water vapour potential rises, and once to above outside the leaf, water molecules will diffuse outside the leaf
- the stomata make an esy route out of the leaf, as they are open during the day
- As vapour collects in these air spaces, the water vapour potential rises, and once to above outside the leaf, water molecules will diffuse outside the leaf
- the spongy mesophyll cells have large air spaces between them that help the water vapour to diffuse through the leaf tissue
- 1. osmosis from the xylem to mesophyll cells
- 2. evaporation from the surface of the mesophyll cells into the intercellular spaces
- 3. diffusion of water vapour from the intercellular spaces out through the stomata
- 2. evaporation from the surface of the mesophyll cells into the intercellular spaces
- water enters the leaves in the xylem and passes to the mesophyll cells by osmosis and evaporates from the surface to from water vapour
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