AP Biology : Cellular Communications and Junctions

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Understand Types Of Signaling, Receptors, And Signaling Molecules

Which type of ligand is water soluble, and thus unable to enter a cell?

Possible Answers:

steroid hormones

Nitric oxide

Small, hydrophobic ligands

Water-soluble ligands

Correct answer:

Water-soluble ligands

Explanation:

 The membrane of the cell is a phospholipid bilayer, which allows hydrophobic molecules to diffuse through it. Small, hydrophobic ligands are able to diffuse through the plasma membrane. Nitric oxide is lipophilic, readily dissolving in lipids, and can diffuse across the plasma membrane. Steroid hormones are hydrophobic, and can thus diffuse across the plasma membrane. Water-soluble ligands cannot diffuse across the plasma membrane to enter a cell.

 

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