Science
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Chapter 5: The Fundamental Unit of Life
Class: IX
Exercise number 61
Question 1
How do substances like CO2 and water move in and out of the cell? Discuss.
Answer 1
In cells the membrane regulates the movement of substances from and to the cell and this cell membrane is selectively permeable.
Movement of CO2:
CO2 is produced as a result of cellular respiration. Inside the cell the concentrations of CO2 is high and must be excreted out of the cell. The concentration of CO2 in the external environment of cell is low as compared to that inside the cell. So CO2 moves from cell (higher concentration region) to external environment (lower concentration region). O2 enters the cell through the same process of diffusion.
Movement of water:
Water moves from the higher concentrated region to lower concentrated region through the semi permeable membrane, known as plasma membrane and this movement of water is called as osmosis. The movement of water through the plasma membrane of the cell is also affected by the amount of substance dissolved in water.
Question 2
Why is the plasma membrane called a selectively permeable membrane?
Answer 2
The cell membrane or plasma membrane is called as a selectively permeable membrane because it controls the movement of substances in and out of the cell. This means plasma membrane allows the movement of only some substances through it and prevents the movement of some other materials.
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