17. What is a cell membrane? A. A thin flexible barrier around the cell that regulates transport.
B. A rigid cover that provides support for the cell.
C. Converts solar energy to chemical energy.
D. The place where light energy, water and carbon dioxide are used.​

Compare and contrast the adaptations of free-living flatworms and parasitic flatworms

Animal bodies (and even plant bodies for that matter) are complex enough that life couldn't exist without enzymes. enzymes are usually large, complex biological catalysts that are expensive to make. enzymes speed up the rate of chemical reactions without being used up during the reaction (they can be reused many times). they are highly specific in the reactions they regulate. knowing what enzymes are and how they function, why does this explain why complex life forms could not exist if there were no enzymes.

What is the difference between an igneous, sedimentary and metamorphic rock