Question

Which of the following molecules would diffuse through a cell membrane?
(A) Water
(B) Glycogen
(C) Haemoglobin
(D) Catalase

Answer 1

Hint: The cell membrane is also known as the plasma membrane. It separates the interior and exterior of a cell. It allows the cell to interact with its surroundings in a controlled way. It consists of lipids, proteins, and carbohydrates. These carbohydrates are attached to lipids and proteins.

Complete Step by Step Answer:
The cell membrane is semi-permeable in nature and only small molecules can pass through it. However, large molecules or highly charged molecules do not pass through it. Of the given options, water is a small uncharged polar molecule. Hence, water can easily diffuse through a cell membrane.
Correct Option: (A) Water.

Additional Information: The molecule can pass through the cell wall in two ways: passive transport and active transport. Passive transport occurs down the potential gradient, that is, from higher concentration to lower concentration. ATP is not required during passive transport as it occurs spontaneously. Active transport occurs down the potential gradient, that is, from lower concentration to higher concentration. ATP is required during active transport as the molecule moves against the potential gradient during active transport.

Note: Glucose is a large molecule. So, it will not diffuse through the cell membrane. However, it can pass through the cell membrane by passing through channel proteins. The process of the passing of haemoglobin through the cell membrane is a highly complex phenomenon. Catalase is an enzyme present in living organisms that catalyses hydrogen peroxide into water and oxygen. It cannot diffuse through the cell membrane.