each stoma is surrounded by
two guard cells
feature of outside facing cell walls of guard cells
thick
feature of adjacent facing cell walls of guard cells
thin
guard cells have bands of
cellulose microfibrils
true or false
guard cells have plasmodesmata
false
describe the CSM of the guard cells
often folded and contains many channel and carrier proteins
describe the contents of the cytoplasm
there is a high density of chloroplasts and mitochondria and several small vacuoles
describe the chloroplasts of guard cells
have thylakoids but with few grana
describe the mitochondria of guard cells
have many cristae
when do stomata open
when they gain water by osmosis and become turgid
what is required for inward osmosis to happen in the guard cells
a decrease in water potential
mechanism to open stomata (1)
in response to light, ATP-powered proton pumps in the guard cell CSM actively transport hydrogen (H+) ions out of the guard cell
mechanism to open stomata (2)
this leaves the inside of the guard cells negatively charged compared to the outside
mechanism to open stomata (3)
causes channel proteins in the guard cell CSM to open allowing potassium (K+) ions to move down the electrochemical gradient and enter the guard cells
what is an electrochemical gradient
the combination of the electrical gradient and concentration gradient
mechanism to open stomata (4)
influx of potassium ions increases the solute concentration inside the guard cells lowering the water potential inside the cells
mechanism to open stomata (5)
water now enters the guard cells by osmosis through aquaporins in the CSM and accumulate in the vacuoles increasing their size
mechanism to open stomata (6)
this increases the turgor pressure of the guard cells causing the stoma to open
what is the function of the cellulose microfibrils
only allow guard cells to increase in length not diameter
what is the importance of having thick outside facing and thin adjacent cell facing cell walls
thin walls bend more easily than thick walls causing the guard cells to become curved, opening the stoma
mechanism to close stomata (1)
after certain environmental stimuli are detected, the proton pumps in the guard cell CSM stop actively transporting H+ ions out of the guard cell
mechanism to close stomata (2)
the potassium ions leave the guard cells
mechanism to close stomata (3)
water potential gradient is now reversed and water leaves the guard cell by osmosis
mechanism to close stomata (4)
this causes the guard cell to become flaccid, closing the stomata