A Keystone species is the one whose presence regulates the species composition and functioning of the ecosystem. These species are mostly present in less number but have profound effect on the ecosystem.
Example: Saguaro cactus is keystone species of desert. It produces large number of fruits in hottest period of summer. Hence it provides food and shelter to other desert species such as rats and snake.
Cyto means cell and skeleton is self explanatory, therefore, cytoskeleton provides shape of the cell, like normal human skeleton provides shape for us by carrying muscles.
Cellular respiration that proceeds in the absence of oxygen is anaerobic respiration. Cellular respiration that proceeds in the presence of oxygen is aerobic respiration. Anaerobic respiration evolved prior to aerobic respiration.
