4. To be considered a fossil an
organism must have lived only during a short
part of Earth's history; many fossils of the
organism must be found in rock layers; the
fossil must be found over a wide area of
Earth; the organism must be unique.

light dependent reactions:

light independent reactions:

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the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.