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(a) During the day photosynthesis takes place in the guard cells, due topresence of light; there is formation of sugars/glucose
in the guard cells; accumulation of sugars in the guard cells raises their osmotic pressure; this makes the guard cells to gain
water by osmosis from the neighbouring epidermal cells; these cells become turgid and bulge; causing the stomata to open;
During the night there is no photosynthesis due to the absence of light; no sugar formation in the guard cells; the osmotic
pressure of the guard cells decrease; guard cells lose water by osmosis to the neighbouring epidermal cells; they become
flaccid and their walls shrink; making the stomata to close; Total 12mks; maximum 10mks.
OR
Describe the mechanism of opening and closing of the stomata using the photosynthetic theory.
Opening
-In the guard cells there are chloroplasts; which carry out photosynthesis in the presence of light; (in the day)
-During photosynthesis glucose is produced in the guard cells; this increases osmotic pressure; compared to the neighbouring epidermal cells; water then moves into the guard cells by osmosis; and increases their turgidity;
-The inner walls of guard cells are thicker than the outer walls; so outer walls stretch more than the inner walls causing guard cells to bulge outwards causing the stomata to open;
Closing
-During the night when there is no light; no photosynthesis takes place in the guard cells; Glucose in the guard cells is converted into starch; this lowers the osmotic pressure of the guard cells than the neighbouring cells;
-Water is then drawn away from the guard cells by osmosis; into the neighbouring cells, making them to be flaccid;
- Thinner outer wall shrink and the curvature of the thicker inner wall reduces; then the stomata closes;
(b) Regulation of blood sugar.
When the blood sugar rises, it is detected by the hypothalamus; which stimulates the pancreas; to release insulin; through the
blood the insulin gets to the liver; where it stimulates the conversion of excess glucose to glycogen and fats which are stored;
the insulin also enhances rapid breakdown of glucose in the muscle cell; these events leads to a fall in blood sugar back to
normal; When the blood sugar is low, the hypothalamus; stimulate the pancreas to release glucagon; which via the
bloodstream; get to the liver, where it stimulates the liver to convert glycogen to glucose; and fats to glucose; there is also less
breakdown of glucose in the cells; leading to a rise in the blood sugar level back to the norm
gregorymasila answered the question on February 23, 2018 at 12:08
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