IGCSE Biology 0610 - 3.1 Diffusion

Objective: Describe the importance of diffusion of gases and solutes in living organisms.

What is Diffusion?

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. This movement continues until the concentration of particles is uniform throughout the system.

Importance of Gas Diffusion

Many living organisms require a continuous supply of gases, such as oxygen and carbon dioxide. Diffusion is the primary mechanism for the exchange of these gases.

• Oxygen uptake in animals: In animals, oxygen diffuses from the lungs (where the concentration is high) into the blood (where the concentration is lower). This oxygen is then transported to the body's cells.
• Carbon dioxide removal from animals: Carbon dioxide, a waste product of respiration, diffuses from the blood (where the concentration is high) into the lungs. It is then exhaled from the body.
• Gas exchange in plants: Plants also rely on diffusion for gas exchange. Carbon dioxide diffuses into the leaves from the atmosphere, and oxygen diffuses out.

Importance of Solute Diffusion

Solutes, such as nutrients and water, also move through biological systems via diffusion.

• Nutrient uptake in roots: In plants, mineral ions (nutrients) diffuse from the soil (where they are present at a higher concentration) into the root cells.
• Water uptake in roots: Water also moves into root cells by diffusion, following the uptake of mineral ions.
• Absorption in the small intestine: Nutrients absorbed from digested food in the small intestine diffuse from the intestinal cells into the blood.
• Waste removal: Some waste products can also be removed from cells by diffusion.

Factors Affecting Diffusion Rate

Factor	Effect on Diffusion Rate
Concentration Gradient	Steeper gradient = Faster diffusion
Temperature	Higher temperature = Faster diffusion (increased kinetic energy)
Surface Area	Larger surface area = Faster diffusion
Distance	Shorter distance = Faster diffusion
Medium	Diffusion is faster in gases than in liquids, and faster in liquids than in solids.

Summary

Diffusion is a vital process for the survival of living organisms, enabling the efficient transport of essential gases and solutes across membranes and within tissues. The rate of diffusion is influenced by several factors, including concentration gradient, temperature, surface area, distance, and the medium through which the particles are moving.