B3.3 - Concentration Gradients

Concentration gradients are necessary for gas exchange due to

differences in the concentration

In gas exchange (concentration gradient)

• Oxygen is high in the air/water, but low in blood

• CO2 is high in the blood, but low in air/water 

Concentration gradient is maintained through

• Blood pumping/flow

• Ventilation

• Structural adaptations

Blood flow

moving of blood through the exchange surface carries oxygenated blood away from the exchange surface, and brings deoxygenated blood to the exchange surface

blood flow in fish

is a concurrent exchange → blood flow moves in the opposite direction to water flow, which maintains the concentration gradient along the gill

Ventilation

process of moving air or water across the gas exchange surface which
1. brings fresh oxygen
2. removes CO2

Ventilation in mammals occurs through

negative pressure breathing → diaphragm contracts, moving down, ribcage expands, intercostal muscles contract
→ increases volume of thoratic cavity, pressure decreases

Ventilation in fish

water flows over gills in an unidirectional manner

together, processes ensures

that fresh oxygen is available and CO2 is removed, which sustains the necessary concentration gradient