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Acute diseases are sudden, severe, and short term only. They quickly appear and worsen without warning and they disappear. Examples of this are flu or colds.
Chronic diseases, on the other hand, are long-developing diseases. The symptoms have been present for long time and it worsens as time progresses. Examples of this are Osteoporosis and heart disease.
The answer is commensalism.
<span>Commensalism is a relationship between two organisms in which only one of them has benefit, and the other one is not affected (it has no harm or benefit).
</span>In this example, clownfish has the benefit - it is protected from predators by sea anemones. <span>The sea anemone isn't harmed and doesn't benefit from this relationship. Hence, this is the example of commensalism.</span>
A contractile vacuole works just the same as the name suggests, in that it expands and contracts. The point of the contractile vacuole is to pump water out of the cell through a process called osmoregulation, the regulation of osmotic pressure. It occurs in freshwater protists, but mainly in the kingdom Protista as a whole.