Animals: Exchange of Materials

Topic: Animals - Exchange of Materials

• In multicellular organisms, cells are specialised to carry out different functions and form different tissues and organs. One main function of specialised cells is the exchange of materials.

• The exchange of materials in animals happens through a variety of processes: diffusion, osmosis and active transport.

• Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration.

• Osmosis is the movement of water molecules through a partially permeable membrane from an area of high water concentration to an area of low water concentration.

• Active transport moves substances against a concentration gradient, from an area of low concentration to an area of high concentration. It requires energy, provided by respiration.

• The surface area to volume ratio is fundamental to the exchange of materials. Small cells have a larger surface area to volume ratio, which allows materials to move into and out of the cell more quickly.

• The respiratory system in mammals demonstrates how animals maximise the efficiency of gas exchange. Through breathing, oxygen enters the lungs and gets absorbed by the alveoli. The oxygen then binds to the red blood cells and is transported to different parts of the body.

• The alveoli are designed to maximise the diffusion of gas. They have a large surface area, a moist, thin wall and a rich supply of blood vessels.

• The circulatory system facilitates the transport of materials through the body. The heart pumps blood around the body, supplying oxygen and nutrients to cells, and removing waste products like carbon dioxide.

• In fish, gills allow for effective gas exchange. Water containing oxygen flows over the gills, and as it does so, oxygen diffuses into the blood in the gill capillaries, whilst carbon dioxide diffuses out into the water.

• The surface area of the intestines in animals is increased through the presence of villi. This maximises the absorption of digested food.

Remember to:

Understand the differences between diffusion, osmosis and active transport, and when each is used in the body.
Know the structure of the respiratory and circulatory systems and how they contribute to the exchange and transport of materials.
Understand the role and structure of the alveoli and gills in gas exchange.
Learn about how the intestines maximise the absorption of food.