Animal cells are bathed in an isotonic fluid, and plant and bacteria cells have a
cell wall. What does this protect the cell
membrane from?

Plant cell has cell wall.It protects the cell membarane from wheather,wind.It need cell wall because it is not moving.

a wall located the outside of cell membrane provides the cell support and protection against mechanical stress or damage from osmotic rapture and lysis...

Explanation:

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).