NCERT Solutions for Class 9 Science Chapter 5
The Fundamental Unit of Life
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-61
Questions No-1
How do substances like CO2 and water move in and out of the cell? Discuss.
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Carbon dioxide (CO₂) moves in and out of the cells by the process of diffusion. Diffusion involves movement of molecules from higher concentration to lower concentration across the plasma membrane. Water moves in and out of the cells by osmosis. Osmosis is the movement of water or solvent through a semipermeable membrane from a solution of lower concentration of solutes to a solution of higher concentration of solutes to which the membrane is relatively impermeable. Both diffusion and osmosis are physical or mechanical processes and do not require spending of energy for their performance by the cells.
The cell membrane is selectively permeable and regulates the movement of substances in and out of the cell.
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 by the process of diffusion when the concentration of O₂ inside the cell is low as compared to its surroundings.
Movement of water:
Water moves from a region of high concentration to a region of low concentration through the plasma membrane. The plasma membrane acts as a semi-permeable membrane, and this movement of water is known as osmosis. However, the movement of water across the plasma membrane of the cell is affected by the amount of substance dissolved in water.
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