The molecules that convert extracellular signals into intracellular signals are:

• A. Neurotransmitters.
• B. Hormones.
• C. Cell surface receptors.
• D. Intracellular receptors.

Answer: (C)

Verified step by step guidance

1. Understand the role of cell surface receptors: These are proteins located on the cell membrane that bind to external signaling molecules, such as hormones or neurotransmitters, initiating a cellular response.
2. Recognize that cell surface receptors are crucial for signal transduction: They convert extracellular signals into intracellular signals, allowing the cell to respond appropriately to changes in its environment.
3. Differentiate between cell surface receptors and intracellular receptors: While cell surface receptors are located on the cell membrane, intracellular receptors are found within the cell and typically bind to signaling molecules that can cross the cell membrane.
4. Consider the types of molecules that interact with cell surface receptors: These include hormones and neurotransmitters, which are unable to cross the cell membrane and thus rely on these receptors to transmit their signals into the cell.
5. Conclude that cell surface receptors are the correct answer for converting extracellular signals into intracellular signals, as they are specifically designed to facilitate this process by binding to external molecules and triggering internal cellular responses.