Cell Membrane MCQs Quiz | Class 9

This Class IX Science quiz covers Unit II: Organization in the Living World, specifically focusing on the Cell Membrane (Subject Code 086). The questions address the structure, function, and the selectively permeable nature of the plasma membrane. Test your knowledge on how substances move in and out of cells, check your score instantly, and download the PDF answer key for revision.

Understanding the Cell Membrane

The cell membrane, also known as the plasma membrane, is a vital component of all living cells. It separates the contents of the cell from its external environment. In Class 9 Science, understanding the structure and function of this membrane is fundamental to Unit II: Organization in the Living World.

1. Structure and Composition

The plasma membrane is extremely delicate, thin, elastic, and living. It is primarily composed of organic molecules called lipids and proteins. The flexibility of the membrane allows certain organisms, like Amoeba, to engulf food from the external environment, a process known as endocytosis.

2. Selectively Permeable Nature

One of the most important characteristics of the cell membrane is that it is selectively permeable. This means it allows the entry and exit of some materials while preventing the movement of others. This regulation is crucial for maintaining the internal balance (homeostasis) of the cell.

3. Transport Mechanisms

Substances move across the membrane primarily through two physical processes:

  • Diffusion: The spontaneous movement of a substance (like carbon dioxide or oxygen) from a region of high concentration to a region of low concentration. This is essential for gaseous exchange.
  • Osmosis: The movement of water molecules through a selectively permeable membrane from a region of high water concentration to a region of low water concentration.

4. Effect of Solutions on Cells

Depending on the concentration of water surrounding the cell, osmosis can cause the cell to swell, shrink, or stay the same size.

Solution Type Condition Effect on Cell
Hypotonic Surrounding medium has higher water concentration than the cell. Cell gains water and swells (becomes turgid).
Isotonic Surrounding medium has exactly the same water concentration as the cell. No net movement of water; cell size remains the same.
Hypertonic Surrounding medium has lower water concentration than the cell. Cell loses water and shrinks (plasmolysis in plants).

Quick Revision Facts

  • The cell membrane is the outermost covering in animal cells.
  • In plant cells, the cell membrane is found inside the rigid cell wall.
  • Viruses lack any membranes and hence do not show characteristics of life until they enter a living body.