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(a) Describe the photosynthetic theory of opening and closing of the stomata. (b) Describe the regulation of blood sugar level in man.

(a) Describe the photosynthetic theory of opening and closing of the stomata.
(b) Describe the regulation of blood sugar level in man.

Answers

gregory
(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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