Chapter 7, Problem 19STP

Summary Introduction

To access:

Transport proteins are needed to move certain substances against a membrane.

Introduction:

The cell membrane is the outer boundary of the cell and helps to regulate the entry and exit of molecules, ions or solutes. It is selectively permeable and so it lets some substance to pass through more rapidly and other substances more slowly.

Explanation of Solution

As the cell membrane is a selectively permeable membrane, it checks the influx and out flux of substances or molecules. Small molecules such as water, oxygen and carbon dioxide can pass directly through the lipid bilayer in the cell membrane. In case of larger molecules, charged molecules for example, glucose, a specific transport protein facilitates the movement.

A concentration gradient exists which allow the larger molecules to diffuse into the cells but these materials are repelled by the hydrophobic parts of the cell membrane. The transport protein allows them to diffuse by carrying these materials to the interior of the cell.

The transport protein act as either channels or carriers for the material which may be regulated or unregulated.

Conclusion

In addition to the water molecules, ions, the cell requires some other molecules like glucose, to carry out vital activities. The large molecules do not readily move inside the cell but they require special transporters.