Among all the functions of plasma membrane, transport of substances across it is considered the most important

CBSE Class 9 CBSE Class 9 Science
1

Among all the functions of plasma membrane, transport of substances across it is considered the most important. Explain, how does the transport of substances facilitated across this membrane occur the cell?

2

The transport of substances across plasma membrane occurs by either with expenditure of energy, i.e. active transport or without energy expenditure, i.e. passive transport.

  1. By Diffusion The spontaneous movement of a substance (solid, liquid or gas) from a region of its higher concentration to a region of its lower concentration is called diffusion. It is a passive process. For example, CO2 as waste accumulates in higher concentration inside the cell. In the cell’s external environment, the concentration of CO2 is lowered compared to inside of the cell.
    Due to this difference in the concentration, CO2 moves out of the cell by the process of diffusion. Similarly, O2 enters the cell by the process of diffusion, when the level or concentration of O2 inside the cell decreases.
  2. By Osmosis Osmosis is defined as the passage of water from a region of high water concentration to a region of low water concentration, i.e. along a concentration gradient through a semipermeable membrane. It is an active process, e.g. absorption of water by plant roots.
    The flow of water depends upon the type of medium or solution surrounding the cell.