Answer and Explanation:
- Cell communication: proteins are necessary to allow cells to interact with each other through signaling and coordinate their activities.
- Transport: there are various types of proteins that help transport particles across the membrane. They include channel proteins (passive transport) and carrier proteins (can be passive or active transport).
- Cell to cell recognition: membrane proteins are needed to help distinguish which particles are part of the cell ("self") and thus helpful, as opposed to potentially harmful substances.
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