To prevent blood flowing back after each heartbeat. They ensure that the blood flows only in one direction (back to the heart).
Four; the upper atmosphere, the atmosphere, the mantle, and the core.
Answer:
Secondary succession is the series of community changes which take place on a previously colonized, but disturbed or damaged habitat. Examples include areas which have been cleared of existing vegetation (such as after tree-felling in a woodland) and destructive events such as fires.
The dissolved sugars produced in the leaves of a maple tree move to the roots through the<em><u> phloem</u></em>. It is a tissue that transports nutrients to where it is needed
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Well yes, but a dichotomous key can be used to classify just about anything you want.
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