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Introduction to ecosystems
Introduction to ecosystems

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1.3 Filtering food from the ocean

As you learned earlier, the oceans are rich in nutrients in the form of very small and microscopic organisms. A whole range of animals make a living by filtering the small organisms from the surrounding water. Professor Mimi Köehl describes the problems that filter feeders have and helps you to visualise them.

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Activity 2

In Week 3 you learnt about size and shape in relation to animals and temperature. Now, think about the size and shape of organisms that live in a fluid medium. Give some examples of the particular problems that they encounter as a consequence of the physical properties of the fluid.

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Water is more viscous than air. It is also denser. For small organisms the water is very sticky, so because of their size it is like living in honey rather than water. Single cell organisms that swim using a whip-like strand called a flagellum can’t move by beating it backwards and forwards, but need to use a corkscrew motion, as described by Dr Tett in the video ‘Investigating phytoplankton' (Section 4.1.1). You might also have thought of problems of buoyancy. Fins that provide lift, such as those of sharks, counteract the tendency for the body to sink as it is denser than water.