Chapter 9, Problem 4A

Summary Introduction

Introduction:

A cell grows until it reaches its size limit, then it either stops growing or divides. Most cells undergo division. Cell division helps a cell to reproduce and makes the organism grow and heal certain injuries. Most cells are less than 100µm in diameter. There are several factors that influence the small size of a cell.

Answer to Problem 4A

Correct answer :

The correct answer is option C. As cells grow, their ratio of surface area to volume increases

Explanation of Solution

Explanation/justification for the correct answer:

Option C. As cells grow, their ratio of surface area to volume increases- 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. As a cell grows, its volume increases much more rapidly than the surface area. Hence, the ratio of surface area to volume decreases and not increases. 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. Cells remain small to enable communication−The cell size affects the cell’s ability to communicate instructions for cellular functions. If the cell becomes too large, it becomes impossible to send signals to various organelles. Hence, this is not the correct option.

Option B. Large cells have difficulty diffusing nutrients rapidly enough- The movement of substances can be easily managed in a small cell than in a large cell. Plasma membrane is selectively permeable so it controls the transport of materials. Once inside the cell, substances move by diffusion. Diffusion over large distance is slow and inefficient.so the cells remain small to maximize the ability of diffusion and motor proteins to transport nutrients and waste products. Hence this is not the correct option.

Option D. Transportation of wastes becomes a problem for large cells- The movement of substances can be easily managed in a small cell than in a large cell. Plasma membrane is selectively permeable so it controls the transport of materials. As the cell grows, it has difficulty in expelling wastes out of the cell. So, the cells remain small to maximize the ability to transport waste products. Hence, this is not the correct option.