(a) How do guard cells regulate the opening and closing of stomatal pores? (b) Two similar green plants are kept separately in oxygen-free containers, one is 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) Plants kept in continuous light will live longer because the light helps in the process of photosynthesis and also exchange of gases takes place easily. The respiration process takes place and hence the plant n continuous light will live longer.