stomata physiology

Question 1

What is the role of stomata in plant physiology?

Answer 1

• Stomata regulate the exchange of carbon dioxide (CO₂) and water vapour (H₂O).
• 90% of atmospheric exchange occurs through stomata.
• Stomata control evapotranspiration and CO₂ uptake.

Question 2

What is the structure of stomata?

Answer 2

• Composed of two guard cells and surrounding subsidiary cells.
• Together, they form the stomatal complex.
• Stomata shape and distribution vary across species.

Question 3

What is the stomatal index?

Answer 3

It is the ratio of the number of stomata to the total number of epidermal cells.

Question 4

How do stomata develop and specialize?

Answer 4

• Asymmetric division of epidermal cells forms the guard cells.
• Specialization leads to functioning guard cells and recruitment of subsidiary cells.
• Adaptations occur in morphology, density, and distribution of stomata.

Question 5

How do guard cells function to regulate stomatal opening and closing?

Answer 5

• Guard cells act as hydraulic valves, opening when they increase in volume due to osmotic uptake.
• Stomatal closure is triggered by water loss and reduced hydrostatic pressure in guard cells.

Question 6

How do stomata open?

Answer 6

• K+ ions enter guard cells, driven by an electrochemical gradient.
• Cl- and malate also enter, creating an osmotic force that draws water into the cell, causing expansion and pore opening.
• Sucrose is transported from mesophyll cells to guard cells, contributing to osmotic pressure and energy supply.

Question 7

How do stomata close?

Answer 7

• Ca2+ ions enter guard cells and cytosolic pH changes.
• These triggers cause K+ efflux, reducing osmotic pressure and causing water to leave the guard cells.

Question 8

What methods are used to study guard cell physiology?

Answer 8

• Electrophysiology (e.g., patch clamp)
• Pharmacology
• Genetics
• Imaging techniques

Question 9

What factors regulate stomatal opening and closing?

Answer 9

• Internal CO₂ concentration: High CO₂ leads to stomatal closure.
• Light: Blue light causes stomatal opening, with phytochrome and cryptochrome involved in mediating the effect.
• Water vapour: Water loss triggers stomatal closure.
• Abscisic acid (ABA): Mediates stomatal closure during water stress.

Question 10

How is stomatal opening and closing controlled by the circadian rhythm?

Answer 10

• Stomata of C3 and C4 plants open during the day and close at night.
• Stomata of CAM plants open primarily at night.