Final answer:
The size of a graded potential is directly proportional to the stimulus intensity (A), with larger stimuli causing larger membrane potential changes, which may lead to an action potential if they summate effectively.
Step-by-step explanation:
The size of a graded potential is directly proportional to the stimulus intensity. Graded potentials are local changes in the neuron's membrane potential, and these changes, whether depolarization or hyperpolarization, depend on the size of the stimulus. A more intense stimulus will trigger a larger graded potential, causing a more significant change in membrane voltage.
For example, testing warmer water will cause only a slight change in a thermoreceptor, while hotter water will result in a much larger change in the membrane potential. Graded potentials are crucial because they can summate and potentially bring a neuron to the threshold required to fire an action potential, leading to downstream effects such as muscle contractions or gland secretions.