(a) How do guard cells regulate opening and closing of stomatal pores?
(b) Two similar green plants are kept separately in oxygen free containers, one in dark and the other in continuous light. Which one will live longer? Give reasons.<

(a) The guard cells regulate the opening and closing of stomatal pores by the osmosis process. When water flows into the guard cells, they swell up and the curved surface causes the stomata to open. When the guard cells lose water, they shrink and become flaccid and straight thus closing the stomata.

(b) Plant kept in continuous light will live longer because the light helps in the process of photosynthesis. This is because photosynthesis will not take place in the absence of light. Hence, the plant kept in dark will live shorter as compared to the plant kept in the light. Also, gaseous exchange and respiration take place easily.