Tag: biology

Transpiration occurs through stomata. The opening and closing of stomatal pore depends on the turgidity of guard cells. When guard cells become turgid the stomata open and when guard cells become flaccid the stomata close. 

During stomatal opening starch gets converted to organic acids, like malic acid. The dissociation of organic acid increases proton concentration. The protons move out of guard cells and to maintain electrical neutrality potassium ions move into the guard cells. The inflow of potassium ions results in a drop in water potential in guard cells, due to which water moves into guard cells making them turgid and stomata open.

According to the most widely accepted theory of stomatal opening and closing, potassium ions are involved in turgor movement of guard cells. Inflow of potassium ions decreases water potential in guard cells, which leads to inflow of water. Consequently guard cells swell and stomatal pore opens. When potassium ions move out, these events are reversed and stomatal pore closes.

Transpiration is the process of loss of water, in vapour form, through stomata. The process depends on the turgidity of guard cell. An increase in turgidity of guard cells opens stomatal pore, whereas a decrease in turgidity of guard cells closes stomatal pore. The change in turgidity of guard cells is brought about by reversible influx and efflux of potassium ions.

Starch is osmotically inactive and does not contribute to decrease in water potential. Conversion of starch to organic acids like malic acid promotes uptake of ions like potassium. This decreases water potential and helps in uptake of water. Thus making guard cells turgid and opening of stomata.

Changes in turgidity of guard cells, regulate the opening and closing of stomata. When guard cells are turgid, stomatal pore opens and when guard cells are flaccid stomatal pore closes.

Potassium ions movement into and out of guard cells is related to the turgidity and consequent opening and closing of stomatal pore.

Guard cells have chloroplast, on exposure to light, there is synthesis of sugar in guard cells. The increase in sugar concentration causes water to move in from surrounding cells, thus making guard cells turgid. Increase in turgidity of guard cells leads to stomatal opening.

Amophila are xerophytic grasses, which show rolling of leaf as a xerophytic adaptation to conserve water. Nerium leaves show multilayered epidermis, thick layer of cuticle and sunken stomata, but do not show rolling of leaves. Melia is not a xerophyte.