2.4.11 Adaptations for Rapid Transport

Key Adaptations for Rapid Transport:

1. Increased Surface Area:

• Structures such as microvilli (found on epithelial cells in the small intestine) provide a large surface area to enhance the rate of transport processes like diffusion and active transport.
• Example: Microvilli increase absorption of glucose and amino acids in the ileum.

2. Thin Exchange Surfaces:

• Thin membranes or epithelial layers reduce the diffusion distance, speeding up transport.
• Example: The alveoli in the lungs and capillaries have thin walls for efficient gas exchange.

3. Rich Blood Supply:

• Dense networks of capillaries maintain a steep concentration gradient by constantly transporting absorbed substances away and delivering substances to cells.
• Example: Nutrients absorbed in the ileum are transported into the bloodstream.

4. Concentration Gradients:

• Systems maintain steep gradients for substances like oxygen, carbon dioxide, and glucose:
• Ventilation in lungs maintains a gradient for oxygen and carbon dioxide.
• Sodium-potassium pumps in co-transport create ion gradients for glucose uptake.

5. Specialised Transport Proteins:

• Carrier proteins and channel proteins in the membrane ensure rapid and selective transport:
• Facilitated diffusion relies on specific channel proteins for ions like Na⁺ or K⁺.
• Active transport uses carrier proteins for substances like glucose.

6. Energy Supply:

• Cells involved in active transport (e.g., epithelial cells) contain numerous mitochondria to produce ATP, which powers processes like the sodium-potassium pump.

• Example: Epithelial cells in the ileum use ATP for glucose absorption.

7. Water Movement:

• Aquaporins (specialised channel proteins) increase the rate of osmosis by allowing water to move more quickly through the membrane.
• Example: Kidney cells use aquaporins for water reabsorption.

Examples of Adaptations in Different Systems:

8. Small Intestine:

• Microvilli increase the surface area for nutrient absorption.
• Rich blood supply in villi maintains concentration gradients.

9. Lungs:

• Alveoli provide a large surface area and thin walls for rapid gas exchange.
• Ventilation ensures a steep gradient for oxygen and carbon dioxide.

10. Root Hair Cells:

• Thin extensions increase surface area for water and mineral uptake.
• Active transport of ions maintains a water potential gradient for osmosis.