How does the cell membrane control movement of substances?

The cell membrane controls the movement of substances in and out of the cell through its selectively permeable nature, allowing only certain molecules to pass while restricting others.

It is composed of a phospholipid bilayer with embedded proteins that facilitate transport.

Mechanisms of transport across the cell membrane:

1. Diffusion

• Movement of substances from higher to lower concentration

• Does not require energy

• Example: movement of oxygen and carbon dioxide

2. Facilitated diffusion

• Uses protein channels or carriers

• Helps larger or charged molecules (like glucose) cross the membrane

• No energy required

3. Osmosis

• Movement of water across a semi-permeable membrane

• Occurs from higher water concentration to lower water concentration

4. Active transport

• Moves substances against the concentration gradient (low to high)

• Requires energy (ATP)

• Uses specific transport proteins

5. Endocytosis and exocytosis

• Endocytosis: intake of large particles by engulfing

• Exocytosis: removal of materials from the cell

Importance:

• Maintains internal balance (homeostasis)

• Regulates nutrient intake and waste removal

• Protects the cell from harmful substances

In simple terms: The cell membrane acts like a gatekeeper, allowing needed substances in and removing waste while maintaining balance inside the cell.