Chapter 8, Problem 3STP

Summary Introduction

Introduction :

Transportation of molecules through the cell membrane mainly depends upon the concentration and size of molecules across the membrane. If the size of the molecule is very large or molecules are moving against the concentration gradient, then additional energy is required for transportation.

Answer to Problem 3STP

Correct answer :

The correct answer is option (B) diffusion.

Explanation of Solution

Explanation/justification for the correct answer :

Diffusion: It is the process in which ions or molecules move from their higher concentration to their lower concentration through the plasma membrane and hence does not require the input of additional energy.

Explanation for incorrect answer :

Option (A) Active Transport: It is the movement of molecules across the cell membrane by using cellular energy. In this process, molecules move from their lower concentration to higher concentration through the plasma membrane. Molecules move against the concentration gradient, and to do so energy is required.

Option (C) Endocytosis: It is the process by which cells engulf large molecules with the help of vesicles formation. It is an energy-dependent process.

Option (D) Exocytosis: It is an energy-dependent process where cells expel material from within the cells into the extracellular fluid. Here, intracellular vesicles fuse with the plasma membrane and dump the material outside of the cell.