The keystone species is the one at the bottom of the pyramid, if we look at it like a pyramid. If the grass dies, then the deer cannot get food and die, and the predator cannot eat and dies, and the whole ecosystem can fall apart.
Substances that are made up of only one type of atom.
Plants stomata allow it to transpire and is also a mechanism used to 'suction' or 'pull' the water through the xylem