Breathing involves the exchange of gases in the lungs, a process which occurs by diffusion. The oxygen is then transported throughout the body. Carbon dioxide is the waste gas produced by respiration.

Respiration and the process of diffusion

Respiration is the process by which cells obtain energy from glucose and oxygen. During this process, glucose and oxygen enter the body cells, while waste products like carbon dioxide and water are released. The exchange of these substances occurs through the process of diffusion.

What is diffusion?

Diffusion is the movement of particles from an area of high concentration to an area of low concentration. It is a passive process that does not require energy. In the context of respiration, diffusion allows for the exchange of gases and other substances between the cells and their surrounding environment.

The role of diffusion in respiration

During respiration, glucose and oxygen need to enter the body cells, while carbon dioxide and water, which are waste products, need to be removed from the cells. This exchange occurs through diffusion.

1. Glucose and oxygen entering the cells:
- Glucose is a sugar molecule that serves as a fuel for cellular respiration. It is transported into the cells through the process of diffusion.
- Oxygen, which is needed for the production of energy, is also transported into the cells by diffusion. Oxygen molecules move from areas of high concentration (such as the lungs or gills) to areas of low concentration (the cells) through the process of diffusion.

2. Carbon dioxide and water leaving the cells:
- Carbon dioxide is a waste product of cellular respiration. It is produced within the cells and needs to be removed. Carbon dioxide molecules move from areas of high concentration (the cells) to areas of low concentration (such as the lungs or gills) through the process of diffusion.
- Water, another waste product of respiration, is also removed from the cells by diffusion. It moves from areas of high concentration (the cells) to areas of low concentration (such as the kidneys or sweat glands) through the process of diffusion.

The incorrect options:

- Osmosis is the movement of water molecules across a semi-permeable membrane from an area of lower solute concentration to an area of higher solute concentration. It is not involved in the exchange of glucose, oxygen, carbon dioxide, and water during respiration.
- Effusion is the process by which gas molecules escape through a small hole into a vacuum. It is not relevant to the exchange of substances during respiration.
- Plasmolysis is the shrinkage of a cell's cytoplasm due to water loss. It is not directly related to the exchange of substances during respiration.

Therefore, the correct answer is option 'C': Diffusion.