The cell has to use active transport when it's trying to transport material against the concentration gradient. (from low to high concentration) Or, if a molecule is too big to diffuse through the cell membrane, it must be moved through using a carrier protein.
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Answer:
um....if you got the passage how we spposed to tell you.
Explanation:
Number of people per square mile.
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Answer:
False. It occurs about every 24 hours.
Explanation:
A circadian rhythm is a natural, internal process that regulates the sleep-wake cycle and repeats roughly every 24 hours.