Read the following paragraph and answer the question. Give ONLY the answer, no other words or explanation.

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Answer: <most likely answer, as short as possible>.

Paragraph: 
Passive transport occurs when a substance passes through the cell membrane without needing any energy to pass through. This happens when a substance moves from an area where it is more concentrated to an area where it is less concentrated. Concentration is the number of particles of a substance in a given volume. Let's say you dissolve a teaspoon of salt in a cup of water. Then you dissolve two teaspoons of salt in another cup of water. The second solution will have a higher concentration of salt.


Question: When substances pass through the cell membrane without needing any energy what is it called?
passive transport
Passive transport.