Discuss the importance of oxygen to all living organisms, and describe how three different organisms-human, flatworm, and fern-obtain the oxygen they need.

Oxygen is the most essential element for the survival of all living things. Oxygen supports life on earth and without oxygen, ther would probably be no life on earth. Oxygen is used for all metabolic functions in living organisms: human gets their oxygen supply directly from plants and few blue-green algae. Oxygen then is taken by the lungs and is supplied throughout the body. Flatworm gets oxygen from their skin or from their host organism; fern is a green plant which prepares oxygen through photosynthesis.