of the leaves. Massive amounts of gaseous exchange takes place in the leaves through these pores for the purpose of photosynthesis. But it is important to note here that exchange of gases occurs across the surface of stems, roots and leaves as well. Since large amounts of water can also be lost through these stomata, the plant closes these pores when it does not need carbon dioxide for photosynthesis.
The opening and closing of the pore is a function of the guard cells. The guard cells swell when water flows into them, causing the stomatal pore to open. Similarly the pore closes if the guard cells shrink. Take two healthy potted plants which are nearly the same size.
Keep them in a dark room for three days. Now place each plant on separate glass plates. Place a watch-glass containing potassium hydroxide by the side of one of the plants. The potassium hydroxide is used to absorb carbon dioxide.
Cover both plants with separate bell-jars as shown in Fig. . . Use vaseline to seal the bottom of the jars to the glass plates so that the set-up is air-tight.
Keep the plants in sunlight for about two hours. Pluck a leaf from each plant and check for the presence of starch as in the above activity. Do both the leaves show the presence of the same amount of starch? What can you conclude from this activity?
Figure . Figure . Figure . Figure .
Figure . (a) Open and (b) closed stomatal pore