Gas Exchange in Plants

1
Gas Exchange in Plants

• Structure and function of stomata and guard cells

2
Structure and function of stomata

• Generally stomata open during day and close
  during the night. The guard cells on each side of
  the stoma pore control the size of the poor by
  changing their shape.

3
Structure and function of stomata

• Make your own clear and labelled diagram of the
  stomata and guard cells from p28 of Systems
  Their Maintenance
• The process of drawing these structures will help
  you learn them!

4
Structure and function of stomata

• If water enters the guard cells, they swell up
  and the stoma pore opens.
• If water leaves the guard cells, they become
  flaccid and the stoma pore closes.

5
Structure and function of stomata

• These changes are thought to be due to a
  reversible uptake and loss of potassium ions by
  the guard cells.

6
Structure and function of stomata

• During the day the chloroplasts inside the guard
  cells photosynthesise.
• As a result they produce ATP, which fuels an
  active transport mechanism that takes up
  potassium ions from the surrounding epidermal
  cells.

7
Structure and function of stomata

• This lowers the water potential in the guard
  cells and water enters by osmosis, the guard
  cells become turgid and the stoma pore opens.

8
Structure and function of stomata

• At night the chloroplasts in the guard cells do
  not photosynthesise.
• Less ATP is available for the active uptake of
  potassium ions, which then leave the guard cells
  by diffusion.

9
Structure and function of stomata

• The loss of the potassium ions raises the water
  potential of the guard cell, water passes out
  into the epidermal cells, which have a more
  negative water potential.
• The guard cells become flaccid and the stoma pore
  closes.