The difference in concentration between two areas
The system of organs including the nose, mouth, trachea, bronchi, bronchioles and alveoli through which air is taken into the body
Cells that cover the internal and external surfaces of organs
A micro-organism that causes disease.
The spreading out of the particles of a gas or any substance in solution down a concentration gradient
Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus
The tiny air sacs which make up the structure of the lungs. The site of gaseous exchange.
A group of cells in an organism that are specialised to work together to carry out a particular function.
A structure with a particular function which is made up of different tissues.
The glucose used in cellular respiration comes from the food you eat which is broken down in your digestive system. It passes into the blood by diffusion and is carried around your body to the cells. The oxygen needed by the cells comes into the body in the air moved into the breathing system. It passes into the blood by diffusion and is carried around the body by the circulatory system. The oxygen moves into the cells from the blood down a concentration gradient.
The carbon dioxide produced during cellular respiration is poisonous so it must not be allowed to build up in the cells. It passes into the blood stream by diffusion down a concentration gradient and is carried back to the lungs in the blood. There the carbon dioxide passes into the air by diffusion and is removed from the body in the air which is breathed out.
In a small, single celled organism such as an Amoeba, simple diffusion is enough to supply the needs of the cell. Useful substances such as oxygen can diffuse in from the surroundings and waste products can diffuse out fast enough for the organism to survive successfully.
However as organisms get bigger the surface area to volume ratio gets smaller. As a result simple diffusion is no longer enough. The surface area is not large enough for sufficient diffusion to take place, particularly in active organisms which need a lot of oxygen and make a lot of carbon dioxide. A specialised breathing system linked to a transport system becomes necessary.
The link between size and surface area:volume ratio
A specialised breathing system makes sure that oxygen is brought into the body and carbon dioxide is removed. The breathing system is also known as the respiratory system but this can cause confusion. Respiration takes place in the cells and breathing takes place in the airways and the lungs - they are not the same thing.
A simple model of the human breathing system
The structures of the breathing system are closely related to their function: