Which set of functions is directly controlled by the cell membrane

active transport, recognition of chemical messages, protection

The plasma membrane, also called the cell membrane refers to a double layer of the proteins and lipids, which envelopes a cell and distinguishes the cytoplasm from its surrounding environment. It is selectively permeable, which signifies that it only allows some of the molecules to move in and move out.  

All the cells possess a cell membrane, and it performs certain set of functions like determination of chemical messages, active transportation, and protection. All these set of activities plays an essential role in the survival of the cell.  

fairly constant

Explanation:

Respiration produces carbon dioxide which is used by plants for photosynthesis reducing the amount of carbon dioxide in the atmosphere