3.4.1 Features of Mass Transport

Key Features of Mass Transport Systems:

1. Transport Medium:

• A liquid that carries substances around the body (e.g., blood in animals).

2. Pressure Gradient:

• Movement occurs due to differences in pressure within the system (e.g., blood pressure in arteries vs veins).

3. Specialised Vessels:

• Vessels like arteries, veins, and capillaries ensure directed and controlled flow of the transport medium.

4. Exchange Surfaces:

• Mass transport systems are connected to surfaces where exchange occurs (e.g., capillaries in tissues or alveoli in the lungs).

5. Mechanisms to Maintain Flow:

• E.g., the heart pumps blood in animals, creating the force needed to sustain mass transport.

Mass Transport in Animals:

1. Blood Circulation:

• Blood transports oxygen, carbon dioxide, nutrients, hormones, and waste products.
• The system is closed and uses specialised vessels (arteries, veins, and capillaries).

2. Double Circulatory System:

• Mammals have two circuits:
• Pulmonary circulation: Blood flows between the heart and lungs.
• Systemic circulation: Blood flows between the heart and the rest of the body.

3. Heart:

• Acts as a pump to maintain blood flow.
• Creates a pressure gradient for efficient transport.

Mass Transport vs Diffusion:

Feature	Mass Transport	Diffusion
Distance	Transports substances over long distances.	Limited to short distances.
Speed	Fast due to pressure gradients.	Slow as it depends on concentration gradients.
Control	Directional and regulated.	Passive and less controlled.

Why Mass Transport is Necessary:

1. Large Size of Organisms:

• Multicellular organisms have small surface area to volume ratios, making diffusion insufficient for transport.

2. High Metabolic Rates:

• Cells require a constant supply of oxygen and nutrients and removal of carbon dioxide and other waste products.

3. Specialised Transport Needs:

• Specific substances like hormones and immune cells need to be delivered to target areas efficiently.

Comparison with Mass Transport in Plants:

• Xylem:
  • Transports water and dissolved minerals from roots to leaves via transpiration (a passive process).
• Phloem:
  • Transports sugars and organic molecules from sources (e.g., leaves) to sinks (e.g., roots) via translocation (an active process).

Key Terms:

1. Mass Transport:

• The bulk movement of substances over long distances through a system of vessels or tubes.

2. Pressure Gradient:

• The difference in pressure that drives the movement of the transport medium.

3. Circulatory System:

• The network of the heart, blood, and vessels in animals.

4. Transpiration:

• The movement of water through plants, from roots to leaves, driven by evaporation.

5. Translocation:

• The movement of sugars and nutrients in plants through the phloem.