Which of these describes the function of the cell membrane? 1. Maintaining homeostasis
2. Cell division
3. Producing energy
4. Protein synthesis

It maintains homeostasis by controlling what gets in and out of the cell so the answer is 1.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products