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-2
Why is the plasma membrane called a selectively permeable membrane?
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The cell membrane or the plasma membrane is known as a selectively permeable membrane because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.
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Plasma membrane is called selectively permeable membrane because it allows the movement of only selected molecules across it and not all of them.
The plasma membrane is called a selectively permeable membrane because it selectively allows certain substances to pass through while restricting others. Here’s why:
1. Controlled Passage: It regulates the entry and exit of substances.
2. Selective Entry: Small, uncharged molecules can pass freely, while larger molecules or ions require specialized channels or transporters.
3. Protein Channels: Specific proteins in the membrane act as gateways, allowing only certain substances to pass based on size, charge, or recognition.
4. Regulation of Environment: It maintains the right balance of substances inside the cell and prevents the entry of harmful substances.
5. Homeostasis Maintenance: This selective permeability helps cells maintain a stable internal environment for optimal functioning.
Overall, the plasma membrane’s selective permeability is vital for controlling what enters and exits the cell, ensuring a suitable environment for cellular processes while safeguarding against harmful substances.