Water is not a organic molecule
Sugar and salt are examples of soluble substances. Substances that do not dissolve in water are called insoluble. Sand and flour are examples of insoluble substances.
Chalk is insoluble - it does not dissolve in water.
Membrane proteins can function as enzymes to speed up chemical reactions, act as receptors for specific molecules, or transport materials across the cell membrane. Carbohydrates, or sugars, are sometimes found attached to proteins or lipids on the outside of a cell membrane.
Answer:
A. to enter a cell at a specific receptor site.