Chapter 36 - 4 Flashcards
Regulation of Transpiration
What are some pros of leaves having large surface areas?
Increases CO2 absorption and O2 excretion.
What are some cons of leaves having large surface areas?
It increases water loss.
How are these pros and cons of leaves having high large surface areas evened out?
The stomata has guard cells that open and close the pore which helps to balance water loss and gas exchange.
Where are stomata’s located?
Underside of leaves.
What percent of leaf surface area is the stomata?
1-2% 95% of water loss is through stomata.
What do guard cells do?
Change diameter of stomata pore regualting water loss.
How are stomata numbers controlled?
They are genetically controlled for maximum photosynthesis. Desert plants have fewer stomata.
Are also environmentally controlled.
What are some examples of stomata’s being environmentally controlled.
High light and low CO2 during leaf development leaves to more stomata . High CO2 decreases stomata during leaf development. Plants have less stomata now then 1977 due to global warming and increased CO2.
What coordinates the stomata pore size mainly?
Hydration. More hydrated cells are more turgid. The orientation of cellulose in cell walls of guard cells causes the cell to bow outward when hydrated, opening the pore.
What happens if a guard cell is dehydrated?
The guard cells stop bowing and become flaccid. This makes the pore smaller.
What is the role of potassium in stomata?
Omsosis is driven by the uptake and loss of potassium from guard cells. When potassium is moved into the cell water follows.
Why are stomata closed at night?
No light means no photosynthesis which means there is no need for CO2. It prevents water loss.
What are the 3 cues that stimulate opening at dawn of hydrated stomata?
Light - stimulates active transport of H out of guard cells and promotes transport of K and H2O into guard cells.
CO2 Depletion - photosynthesis
Internal clock of Guard cells - circadian rhythms in guard cells cause stomata to open every 24 hours. (even when it is dark)
What stimulates the closing of the stomata?
Decrease of Light
Dehydration
Rising Temp
How do environmental stresses affect stomata closing?
High temperature and wind dehydrate the plant. The guard cells cells become less turgid, closing the stomata.
Drought/low soil moisture cause roots to produce abscisic acid (ABA) a hormone that stimulates guard cells to remove potassium and water to close stomata. This indirectly reduces photosynthesis but keeps the plant alive.
