Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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Question: If two populations do not mate and produce fertile offspring, separate species result.

Answer: If two populations do not mate and produce fertile offspring, what results?


Question: Most have cells that are not able to exchange gases with the outside environment do multicellular organisms need transport systems.

Answer: Why do multicellular organisms need transport systems?


Question: The cell membrane consists of two adjacent layers of phospholipids.

Answer:
The cell membrane consists of two adjacent layers of what?