Answer:
As they produce food by the process of photosynthesis which cannot be done by anyone else. Plants use chlorophyll, CO2 and H2O in photosynthesis( which is a biochemical process). Plants became a cause of life on earth. Hence plants are the ultimate source of food on earth.
The stomata of leaves are surrounded by guard cells. The guard cells help the leaves to regulate the rate of transpiration of water from the leaves by opening and closing the stomata. When water enter the guard cells, they swell and bulge and this makes the stomata to open. So, with high water pressure, the guard cells will stimulate the stomata to open. The reverse will be the case if the water pressure is low.
Germ cell's I believe. These are cells that includes half your genome in order to reproduce.
