The movement of substances

Define diffusion as the movement of particles from an area of high concentration to an area of low concentration.
Explain how factors such as concentration gradient, temperature, and surface area affect the rate of diffusion.
Provide examples of diffusion occurring in living organisms (plants and animals) and relate these to specific structures where diffusion is maximised.

Diffusion is the process by which particles move from an area of high concentration to an area of low concentration.
This movement occurs naturally due to the random motion of particles.
Diffusion can happen in any gas or liquid.
Diffusion happens in organisms but also happens in more obvious places like when the smell of cooking food leaves the kitchen and spreads to the rest of the house.

Diffusion of smell particles away from hot toast

Concentration gradient: The greater the difference in concentration between two areas, the faster diffusion will occur.
Temperature: Higher temperatures increase the kinetic energy of particles, leading to faster diffusion.
Surface area: A larger surface area allows for more particles to move across a boundary, increasing the rate of diffusion.

Diffusion allows oxygen to move from the air into the plant cells.
- Stomata, tiny pores found on the underside of leaves, allow for the exchange of gases between the plant and the atmosphere.
Diffusion helps to transport water and nutrients from the roots to the rest of the plant.
- The root hairs of plants have a large surface area to maximize the absorption of water and nutrients from the soil.

The lungs are vital organs for gas exchange in animals.
- Oxygen from the air diffuses into the blood, while carbon dioxide diffuses out of the blood and into the air.
- This process is essential for maintaining the body's oxygen supply and removing waste gases.
The small intestine is where most of the nutrients from food are absorbed into the bloodstream.
- Digested nutrients, such as sugars, amino acids, and fatty acids, diffuse across the walls of the small intestine and into the blood.
The large surface area, along with the constant movement of blood, ensures efficient diffusion in the lungs and small intestine.

Diffusion: The net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient, due to random motion.
Concentration: A measure of how much of a substance is present in a given volume.
Concentration gradient: The difference in concentration between two areas.
Surface area: The total area of the outer surface of an object or structure; a larger surface area allows for faster diffusion across a boundary.
Gas exchange: The process where gases like oxygen and carbon dioxide move between an organism and its environment, often by diffusion (e.g., in the lungs).

Plan and carry out a simple experiment to investigate one factor (e.g., temperature) that affects the rate of diffusion using materials like coloured substances in water or agar jelly.
Compare diffusion with other transport processes in cells and organisms, such as osmosis and active transport, highlighting the differences and similarities.