Chapter 11, Problem 1STP

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 1STP

Correct answer :

The correct answer is option A. the ability of oxygen to diffuse into the cell

Explanation of Solution

Explanation/justification for the correct answer:

Option A. the ability of oxygen to diffuse into the cell- 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 movement of substances can be managed more easily in small cells. Plasma membrane is selectively permeable. Once inside the cell, the substances move by diffusion. Diffusion over large distances is slow and inefficient because it depends on random movement of molecules and ions. Therefore, cells remain small to maximize the ability of diffusion.

Hence this option is the correct option.

Explanation for incorrect answer:

Option B. the amount of energy produced in the cell − 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. Diffusion over large distances is slow and inefficient because it depends on random movement of molecules and ions. Therefore, cells remain small to maximize the ability of diffusion. The amount of energy produced is not affected by this.

Hence, this is not the correct option.

Option C. the diffusion of proteins through the cells- Diffusion over large distances is slow and inefficient because it depends on random movement of molecules and ions. Therefore, cells remain small to maximize the ability of diffusion. Gases move by diffusion and not proteins.

Hence this is not the correct option.

Option D. the rate of protein synthesis in the cell- Diffusion over large distances is slow and inefficient because it depends on random movement of molecules and ions. Therefore, cells remain small to maximize the ability of diffusion. Protein synthesis does not depend on size of the cell.

Hence this is not the correct option.