Transpiration Flashcards
What are stoma surrounded by
Two guard cells
Two key features of guard cells
-cellulose cell wall on the inner side of the guard cellos thicker than rest of cell.
-some of the cellulose microfibrils in the cell wall are arranged in ring shapes
Where does CO2 diffuse from
Diffuses into the lead through stomata.
-in light conditions the stomata open allowing co2 to diffuse into leaf.
-light conditions trigger solutes such as the potassium ion to be transferred into the guard cells- this lowers water potential of the interior of the guard cells- water moves into guard cells by osmosis, causing guard cells to swell-turgid.
What do the rings of cellulose prevent in the guard cell
Prevent guard cells from expanding widthwise, instead they expand lengthwise, thickened cell walls prevent guard cells from expanding evenly, forcing guard cells to develop a curve shape- allows stoma to open between the guard cells
What happens when stomata are open
Water vapour can diffuse out of leaf- could cause plant to dry out
-at night when the plant stops photosynthesis the stomata close to reduce water loss.
What happens in a drought
-level of water in soil can fall-roots send a hormonal signal to leaves- this hormone triggers guard cells to lose their turgidity, causing stomata to close- reduce water loss-no photosynthesis, small price to pay, plant might die.
How does light intensity affect transpiration
-As we increase light intensity, the rate of transpiration increases. Because increasing light intensity increases the number of open stomata, allowing more water vapour to diffuse out the leaf.
-At high light intensities the rate of transpiration no longer increases, almost all stomata will be open.
How does relative humidity affect transpiration
-relative humidity tells us the concentration of water vapour in the air as a percentage of the maximum possible. For example 100% relative humidity means that the concentration of water vapour is as high as possible.
-If relative humidity outside the leaf increases, means there is a smaller concentration gradient between the inside of the leaf and the outside.- Reduces rate of transpiration.
How does temperature affect transpiration
The rate of transpiration is increased by temperature
-water molecules have more kinetic energy, greater rate of evaporation of water from the internal surfaces of the leaf
-relative humidity of the external air decreases
-therefore the concentration gradient of water vapour between the inside of the leaf and external air increases at higher temperatures-increases rate of transpiration
How does wind affect the rate of transpiration
-when water vapour moves out of the stomata during transpiration, that water vapour can build up around the external surface of the leaf, the effect of this is to reduce the concentration gradient for water vapour between the inside of the leaf and the outside- this reduces the rate of transpiration
-wind removes the water vapour as it diffuses out of the leaf, because air movements increase the concentration gradient of water vapour, this increases rate of transpiration.
How does level of water in soil affect transpiration
Reduced rate of transpiration- drought.
