Question

a student notices that animal cells behave differently when exposed to solutions that are hypotonic compared to certain fungi, plant, and bacterial cell. the animal cell lyses while the other three do not. what structural difference accounts for the unique way animal cells react when exposed to water.
a cell membranes made of different phospholipids
b rigid cell walls that prevent the expansion of the cells
c glycoproteins attached to the membrane that repel the water
d cholesterol molecules embedded in the membrane to remove excess water

Explanation:

• Option A: Cell membranes of all these cells (animal, fungal, plant, bacterial) have phospholipids as a major component. The difference in phospholipids is not the reason for the observed behavior.
• Option B: Fungal, plant, and bacterial cells have rigid cell walls. In a hypotonic solution, water enters the cells (by osmosis). The rigid cell - wall exerts a counter - pressure (turgor pressure) that prevents the cell from bursting (lysis). Animal cells lack a cell wall. When water enters animal cells in a hypotonic solution, there is no such rigid structure to prevent the cell from expanding beyond its capacity, leading to lysis.
• Option C: Glycoproteins on the membrane are mainly involved in cell - cell recognition, adhesion, etc., and not in repelling water to prevent lysis.
• Option D: Cholesterol in the membrane is involved in maintaining membrane fluidity (especially in animals) and does not have a role in removing excess water to prevent lysis.

Answer:

B. Rigid cell walls that prevent the expansion of the cells