All cells contain cell membranes. which of the following describes the composition of cell membranes?
a. cell membranes are composed of carbohydrate chains, which allow all materials to enter and leave the cell.
b. cell membranes are composed of cellulose, which provides rigidity for the cell.
c. cell membranes are composed of cytoplasm, which allows proteins to be excreted by the cell.
d. cell membranes are composed of lipid molecules, which provide a flexible structure.

1. environmental factors, such as ph and temperature, can affect the function of an enzyme. a. true b. false 2. which of the following is an organic molecules (ex. vitamins) that an enzyme? a. coenzyme b. product c. active site d. substrate 3. how do enzymes effect the speed of a chemical reaction? a. they speed it up b. they slow it down c. they have no effect on the speed of a reaction 4. during a chemical reaction, an enzyme is used up so that it can only be used one time. a. true b. false 5. which of the following results from a chemical reaction that is catalyzed by an enzymes? a. active site b. product c. substrate d. coenzyme