2.4.10 Active Transport & Co-transport

Active Transport:

1. Definition:

• The movement of molecules or ions from an area of low concentration to an area of high concentration, against the concentration gradient.

2. Key Features:

• Requires energy in the form of ATP.
• Involves carrier proteins in the membrane, which change shape to transport substances across.

3. Examples:

• The sodium-potassium pump:
• Pumps 3 sodium ions out and 2 potassium ions in to maintain ion balance in cells.
• Uptake of mineral ions by plant root cells.

Co-transport:

1. Definition:

• A process where the movement of one molecule or ion down its concentration gradient facilitates the movement of another molecule or ion against its concentration gradient.

2. Example: Glucose and Sodium in the Ileum:

• Step 1: Sodium-potassium pump actively transports sodium ions out of the epithelial cell into the blood, reducing the sodium concentration inside the cell.
• Step 2: Sodium ions move from the lumen of the ileum into the epithelial cell by facilitated diffusion through a co-transport protein.
• Step 3: As sodium moves into the cell, it carries glucose or amino acids with it against their concentration gradient.
• Step 4: Glucose and amino acids move into the bloodstream by facilitated diffusion through a different protein.

Comparison of Active Transport and Co-transport:

Feature	Active Transport	Co-transport
Energy requirement	Requires ATP.	Indirectly depends on ATP (for ion pumps).
Direction of movement	Against the concentration gradient.	One molecule moves down its gradient, allowing another to move against.
Proteins involved	Uses carrier proteins.	Uses co-transport proteins.
Example	Sodium-potassium pump.	Glucose and sodium in the ileum.

Importance of Active Transport & Co-transport:

1. Active Transport:

• Maintains ion gradients (e.g., in nerve impulses).
• Enables uptake of nutrients like minerals in plants.

2. Co-transport:

• Allows efficient absorption of glucose and amino acids in the small intestine.
• Essential for energy production and nutrient uptake.