Chapter 9, Problem 8A

Summary Introduction

Introduction:

A cell grows until it reaches its size limit, then it either stops growing or divides. Most cells are less than 100µm in diameter. There are several factors that influence the small size of a cell. The ratio of surface area to volume is the key factor that limits the size of a cell. Surface area of a cell refers to the area covered by the plasma membrane through which the nutrients and wastes must pass through. The volume refers to the space taken up by the contents of the cell.

Answer to Problem 8A

Correct answer :

The correct answer is option B. decreases

Explanation of Solution

Explanation/justification for the correct answer:

Option B. decreases- As a cell grows, its volume increases much more rapidly than the surface area. So if the volume of a cell increases, the plasma membrane expands. The relative amount of surface area available to transport nutrients per unit volume of cell decreases proportionally. Hence, the ratio of surface area to volume decreases. By remaining small cells have a higher ratio of surface area to volume and they can sustain themselves more easily. Hence this option is the correct option.

Explanation for incorrect answer:

Option A. increases−As a cell grows, its volume increases much more rapidly than the surface area. So if the volume of a cell increases its surface area decreases proportionally. Hence, the ratio of surface area to volume decreases. Hence, this is not the correct option.

Option C. stays the same- As a cell grows, its volume increases much more rapidly than the surface area. So if the volume of a cell increases its surface area decreases proportionally. Hence, the ratio of surface area to volume decreases. Hence this is not the correct option.

Option D. reaches its limit- As a cell grows, its volume increases much more rapidly than the surface area. So if the volume of a cell increases its surface area decreases proportionally. Hence, the ratio of surface area to volume decreases. Hence this is not the correct option.