Chapter 9, Problem 8STP

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.It also helps in maintaining homeostasis.

Answer to Problem 8STP

Correct answer :

The correct answer is optionD. proteins

Explanation of Solution

Explanation/justification for the correct answer :

OptionD. proteins- An important property of plasma membrane is selective permeability, by which a membrane allows some substances to pass through while keeping others out. This property is important to the survival of a cell. Proteins that are found on the outer surface of plasma membrane called receptors transmit signals to the inside of the cell. Some proteins span the entire membrane and act as tunnels through which certain substances enter and exit the cell. These transport proteins contribute to the selective permeability of the plasma membrane. They transport the needed substances and waste materials through the membrane.

Hence this option is correct.

Explanation for incorrect answer :

Option A. carbohydrates- The carbohydrates are attached to the proteins and stick out from the plasma membraneto define the cell’s characteristics and help cells identify signals. They do not contribute to the selective permeability of the plasma membrane.So, this is an incorrect option.

Option B. ions- Ions do not contribute to the selective permeability of the plasma membrane. So, this is an incorrect option.

Option C. minerals- Minerals do not contribute to the selective permeability of the plasma membrane. So, this is an incorrect option.