plants

Question 1

importance of stomata

Answer 1

-allow gaseous exchange of carbon dioxide for photosynthesis and o2 for respiration
-regulate transpiration
-control water loss by the plants
-creates transpirational pull when water is lost
-transpiration has a cooling effect on the plants

Question 2

explain the opening and closing of stomata

Answer 2

 In the potassium ion accumulation hypothesis, the opening of stomata is associated
with the influx of K+
ions into the guard cells from the epidermal cells.
 At day, blue light increases the activity of proton pumps in the membrane of guard
cells.
 The proton pumps use ATPs to transport H+
ions out of guard cells.
 When H+ are pumped out, K+
ions diffuse into guard cells through channel proteins
to maintain electron potential.
 Accumulations of K+
ions causes water potential to decrease and water is drawn
into the cells by osmosis.
 The guard cells become turgid and curve inwards more allowing stoma to open.
 During peak transpiration, water stress occurs and plant releases abscisic acid,
which is a phytohormone, which will trigger the closure of stomatal aperture.
 Potassium ions move from guard cells to subsidiary epidermal cells, resulting in a
decrease in [K+
] in guard cells.

Question 3

Describe the structure of stomata

Answer 3

 The inner wall of guard cell is thicker than outer wall
 The expansion of outer wall is more than inner wall when turgid
 This causes guard cell to bend outwards
 The opening of guard cells increase length of guard cell but not in width (guard cell is held by
lateral force by microfibrils)
 Guard cells allow gaseous exchange and water loss
 Guard cells are surrounded by subsidiary cell