Question

Stomata opens during the day and closes during the night because

• A. Enzymes convert starch into sugar during the night
• B. Photosynthesis takes place during daytime only
• C. Formation of sugar increases osmotic concentration of cell sap which results in absorption of water which provide turgidity to guard cells
• D. None of the above

Answer 1

The correct option is C Formation of sugar increases osmotic concentration of cell sap which results in absorption of water which provide turgidity to guard cells

During the day, due to the presence of sunlight, photosysnthesis occurs which results in the formation of sugars. These sugars increase the solute concentration and lowers the water potential inside the cell. Thus resulting in the diffusion of water into the cell through osmosis. This increases the cell's volume and turgor pressure. Therefore, ​​​​​​​the two guard cells lengthen by bowing apart from one another and result in the opening of stomata that leads to exchange of gasses.
During the night, photosynthesis does not occur. Hence the water potential inside the cells increase and water diffuses out of the cells. THis results in the closing of the stomata.