Chapter 7, Problem 15A

Summary Introduction

Introduction:

A cell is a structural and functional unit of an organism. Every cell is surrounded by a protective covering called plasma membrane. It controls the entry and exit of substances into and out of the cell. This property is called selective permeability.

Answer to Problem 15A

C. increasing the number of cholesterol molecules

Explanation of Solution

Explanation/justification for the correct answer :

C. increasing the number of cholesterol molecules- Cholesterol molecules are nonpolar and are positioned among the phospholipids in such a way that they prevent the fatty acid tails of the phospholipid bilayer from sticking together. This causes fluidity in the plasma membrane. If the number of cholesterol molecules is increased, the fluidity of plasma membrane will increase.

Hence this option is correct.

Explanation for incorrect answer :

A. decreasing the temperature- This will not affect the fluidity of the plasma membrane. So, this is an incorrect option.

B. increasing the number of proteins- Proteins help in transport of substances and waste materials through the plasma membrane. Fluidity is caused by the cholesterol molecules. So, this is an incorrect option.

D. increasing the number of unsaturated fatty acid- Cholesterol which is a type of lipid contributes to the fluidity of plasma membrane. Unsaturated fatty acid cannot cause fluidity. So, this is an incorrect option.