Mass transport

Diffusion

The free net movements of particles from an area of high concentration to low concentration

Why does small organisms rely on diffusion

Diffusion is sufficient as they have a high SA:Vol ratio, short diffusion distance and low metabolic demands

Why do organisms need a mass flow transport system

Diffusion is insufficient as they have a large SA:Vol ratio and high metabolic demands

Features of a mass flow transport system

Large exchange surfaces

A system of vessels

A one way system

A pump

A suitable transport medium

Adaptable rate of transport

Large exchange surfaces (mass flow transport)

Gets materials into and out of the transport system

A system of vessels (mass flow transport system)

Carry substances around the body, sometimes along specific routes

A one way system (mass flow transport)

Ensures substances like glucose and waste move in the right direction

Pump (mass flow transport system)

Maintains concentration gradient by moving materials fast enough to meet organisms needs

Suitable transport medium (mass flow transport)

A fluid that’s flow to carry substances

Adaptable rate of transport (mass flow transport)

Matches supply to changing needs of the organisms

Open circulatory systems (insects)

Blood circulates in large body spaces

Lower pressure and less precise so blood cannot be directed

Closed circulatory system (most animals)

Blood is contained within vessels

Pressure can be increased and blood cannot be directed

Single circulation (fish)

Blood passes through the heart ONCE

Blood loses pressure crossing the gill capillaries so it reaches organs slower

Double circulation (mammals)

Blood passes through the heart TWICE

Pulmonary and systemic circulation

Keeps oxygenated and deoxygenated blood separate maximising oxygen delivery