Chapter 7, Problem 33A

Summary Introduction

To explain:

The difference and the relation between given terms.

Introduction : One of the main functions of cells is transport of substances. This is called cellular transport. There are different ways by which substances move in and out of the cell. These include osmosis, diffusion and active transport.

Answer to Problem 33A

Differences between active transport and facilitated diffusion can be summarized in the following table:

Active transport	Facilitated diffusion
1. It is a fast movement of molecules.	It is a slow movement of molecules.
2. It involves movement of molecules from a region of low concentration to a region of high concentration.	It involves movement of molecules from a region of high concentration to a region of low concentration.
3. It requires energy in the form of ATP.	It does not require energy.
4. It involves movement of large molecules like proteins, complex sugars etc.	Ions and small molecules move by this method.
5. It helps in maintaining homeostasis.	It helps in maintaining dynamic equilibrium of gases, water and ions.

Both active transport and facilitated diffusion are methods of cellular transport.

Explanation of Solution

Facilitated diffusion: Besides water cells also need to transport small molecules and ions like chloride ions and sugars. For this, cells use transport proteins to move ions across plasma membrane. By this method cells use channel proteins to move molecules into the cell and uses carrier proteins to move substances out of the cell. It involves movement of molecules from a region of high concentration to a region of low concentration, so it does not need any energy. This method is also called passive transport.

Active transport: It involves movement of molecules from a region of low concentration to a region of high concentration. This movement of substances is against the concentration gradient. Hence it requires input of energy in the form of ATP. It occurs with the help of carrier proteins called pumps. Some pumps move one type of substance in only one direction while some move two substances in either same direction or in opposite direction. Active transport helps in maintaining homeostasis.

Both these methods help in transport of substances and wastes into and out of the cell.