Different groups of animals have evolved different organs to take in oxygen and send out carbon dioxide; but they all have certain common characters. Mention four such characters.

Different organisms have different ways of obtaining oxygen from the surrounding atmosphere and releasing carbon dioxide to the atmosphere but they all share:

• Process of diffusion-for the gas exchange

• The circulatory system within the respiratory organs (rich in blood capillaries)

• The respiratory surface-thin and can be increased

• Protection of respiratory organs.