Which of the following hormones requires a cell surface receptor for its action?

(a) Adrenaline

(b) Progesterone

(c) Growth factors

(d) All of the above

This question has two correct answers: (a) Adrenaline and (c) Growth factors.

The need for a cell surface receptor is determined by a molecule's ability to cross the cell's lipid membrane. Water-soluble molecules cannot pass through and therefore require a surface receptor, while lipid-soluble molecules can diffuse through and typically bind to intracellular receptors.

Analysis of the Options

• (a) Adrenaline: This hormone, also known as epinephrine, is an amine hormone. It's polar and water-soluble, meaning it cannot cross the cell membrane. It must bind to G-protein coupled receptors on the cell surface to trigger a response.
• (b) Progesterone: This is a lipid-soluble steroid hormone. Its nonpolar structure allows it to easily diffuse across the cell membrane and bind to a receptor inside the cell (an intracellular receptor).
• (c) Growth factors: This is a class of signaling molecules, most of which are proteins or peptides. Like adrenaline, they are water-soluble and too large to pass through the cell membrane. They bind to enzyme-linked receptors on the cell surface. Because both adrenaline and growth factors are water-soluble and cannot enter the cell, they both require cell surface receptors for their action.