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Photosynthetic theory;
During the day, guard cells carry out photosynthesis manufacturing glucose; This increases the
osmotic pressure of the sap vacuole; which becomes higher than that of the neighbouring
epidermal cells; guard cells therefore take in water by osmosis; and become turgid; the outer
thin wall stretches easily; pulling the thicker inner wall outwards; thus the stomata opens;
At night, there is no light hence no photosynthesis takes place; plant cells respire using up more
glucose; the osmotic pressure of the sap vacuole of the guard cells reduces; becoming lower
than the neighbouring epidermal cells; the guard cells lose water by osmosis; to adjacent
epidermal cells; they then become flaccid; pulling together the thick inner walls; and stomata
closes;
Enzymatic inter-conversion between starch and glucose/sugar;
At day time, plants continuously use carbon (IV) oxide for photosynthesis; leading to an
increase in the pH of the guard cells; this causes starch to be converted to sugar/glucose; the
glucose increases the osmotic pressure of the guard cells; hence water is taken in by osmosis;
the cells become turgid and bulge outwards; causing the stomata to open;
At night, no photosynthesis occurs but respiration takes place; carbon (IV) oxide accumulates
in guard cells;lowering the pH; the low pH favours conversion of glucose into starch; starch is
osmotically inactive;this lowers the osmotic pressure of guard cells; guard cells therefore lose
water by osmosis to the adjacent epidermal cells; become flaccid; pulling together the thick
inner walls; and the stomata closes;
Active ion exudation;
During the day, there is an accumulation of potassium and sodium ions; as a result of
active pumping of the ions by the ATP formed through photosynthesis; carbon (IV) oxide
fixation occurs in the guard cells; the guard cells become turgid; and stomata open;
At night, before the stomata close, the ions diffuse out of the guard cells into epidermal cells;
the osmotic pressure of guard cells is lowered; they lose water to epidermal cells by osmosis;
and become flaccid; thereby closing the stomata;
Kavungya answered the question on May 13, 2021 at 13:17
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