OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

What are receptor molecules responsible for?

1. Passing impulses to muscle fibers

2. Releasing neurotransmitters

3. Absorbing oncoming transmitter substances

4. Generating heat for the neuron

The correct answer is: Absorbing oncoming transmitter substances

Receptor molecules are specialized proteins located on the surface of cells that bind to specific substances, such as neurotransmitters, hormones, or other signaling molecules. When these transmitters bind to receptor molecules, they typically trigger a response within the cell, which can lead to various physiological effects, such as changes in cell behavior, communication between cells, or signal transmission in the nervous system. This binding process is crucial for allowing cells to interpret and respond appropriately to their environment, making option C the correct choice. The other options pertain to different functions in the nervous system. Passing impulses to muscle fibers involves the role of motor neurons and their connection to muscles, rather than receptor molecules directly. Releasing neurotransmitters is a function of neurons themselves, particularly at the synapse, where neurotransmitters are secreted to propagate signals. Generating heat for the neuron is not a function associated with receptor molecules; instead, neurons generate heat as a byproduct of metabolic activities, not through receptor interactions. Thus, recognizing the specific role of receptor molecules in receiving and responding to signaling molecules clarifies why option C is accurately identified.