Question

How do substances like CO₂ and water move in and out of the cell? Discuss.

Answer 1

The cell membrane is selectively permeable and regulates the movement of substances in and out of the cell.

1. Movement of CO₂: CO₂ is produced during cellular respiration. Therefore, it is present in high concentrations inside the cell. This CO₂ must be excreted out of the cell. In the cell’s external environment, the concentration of CO₂ is low as compared to that inside the cell. Therefore, according to the principle of diffusion, CO₂ moves from a region of higher concentration (inside the cell) towards a region of lower concentration (outside the cell). Similarly, O₂ enters the cell through diffusion when the concentration of O₂ inside the cell is low compared to its surroundings.
2. Movement of water: Water moves from a region of high concentration to a region of low concentration through the plasma membrane, which acts as a semi-permeable membrane. This water movement is known as osmosis. However, the movement of water across the cell's plasma membrane is affected by the amount of substance dissolved in water.