Question

in a cell, what is the function of the cell membrane?
a. it generates energy for the cell.
b. it controls the entry and exit of substances.
c. it removes waste and stores ingested food.
d. it only maintains the cell shape.

Explanation:

• Option A: Energy generation in cells (e.g., ATP production) is done by mitochondria, not the cell membrane. So A is incorrect.
• Option B: The cell membrane is a selectively permeable barrier. It regulates what substances can enter or exit the cell, allowing necessary materials in and waste or harmful substances out (or restricting their entry). This matches the function of the cell membrane.
• Option C: Waste removal and food storage (in some cases, like vacuoles in plant cells for storage) are not primary functions of the cell membrane. Lysosomes and vacuoles are more involved in waste handling and storage, so C is incorrect.
• Option D: Maintaining cell shape is a function of structures like the cell wall (in plant cells) or the cytoskeleton. The cell membrane's main role isn't just shape maintenance, so D is incorrect.

Answer:

B. It controls the entry and exit of substances.