The following image shows the concentration-response curves of three agonists acting at the same receptor on the same tissue preparation.
From the concentration-response curves A, B and C below:

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The question refers to an image showing concentration–response curves for three agonists A, B, and C acting at the same receptor in the same tissue, but no numerical data or visual details from the curves are provided in the text.
To analyze the options properly, we need to connect statements to two key concepts in pharmacology: potency and efficacy (intrinsic activity).

- Potency: how much drug is required to produce a given effect. It is reflected by the EC50 (the concentration producing 50% of the maximal effect). A more potent drug has a leftward-shifted curve (lower EC50) compared with another.
- Efficacy (intrinsic activity): the maximum effect a drug can produce, relative to a full agonist. A partial agonist has a lower Emax than a full agonist, even at saturating concentrations, whereas a full agonist can achieve Emax close to the maximal response observed with the system.
- Intrinsic activity value of 1: in classic receptor theory, an intrinsic activity (or efficacy) of 1 corresponds to a full agonist capable of eliciting the maximal possible response in the system; values less than 1 indicate partial agonism.

Now, evaluating each option in light of these concepts:

Option 1: "drug A is a partial agonist"
- Without seeing the A curve’s plateau relative to B and C (Emax) we cannot confirm whether A has a reduced maximal effect. If A’s Emax is noticeably lower than B and C, this would support A being a partial agonist; if A reaches a similar Emax to B and C, this would argue against A being partial. The statement could be true in some curve configurations, false in others, so a decision requires the plotted Emax values.

Option 2: "drug B is more potent than drug A"
- This depends on the EC50 values for A and B. If B’s curve is shifted left of A’s (lower EC50), B is more potent. If B’s EC50 is the same or higher (curve not left of A), then B is not more potent. Since potency is a property inferred from the horizontal position of the curve, we need the actual EC50 data from the plots to judge.

Option 3: "drug C has intrinsic activity value of 1"
- An intrinsic activity of 1 implies C is a full agonist. This would be supported if C’s Emax equals the maximal response achievable in this tissue with a known full agonist, and if C’s efficacy matches that standard. However, without comparing C’s Emax to that reference or knowing whether any curve reaches the system’s maximum, we cannot confirm intrinsic activity = 1 from the text alone.

Option 4: "drug A has greater intrinsic efficacy than drug C"
- This asserts that A’s Emax exceeds C’s Emax. Again, to verify, we would compare the plateau levels of A and C at saturating concentrations. If A’s curve reaches a higher maximum than C, this would be correct; if they plateau at the same level or if C exceeds A, then it would be incorrect. The needed data are not provided here.

In summary, because the actual concentration–response curves are not visible in the provided text, none of the four statements can be definitively judged true or false based solely on the information given. Each option relies on specifics about Emax and EC50 that require direct reference to the curves. Conceptually, the distinctions hinge on: (a) whether A’s Emax is smaller than full, (b) whether B’s curve is shifted left relative to A, (c) whether C achieves a full agonist Emax (intrinsic activity of 1), and (d) whether A’s Emax surpasses C’s. Without the curves, these remain unresolved conjectures based on general principles rather than definitive conclusions from the data.

PCOL2021 2025 Module 1 Practice Quiz

The following image shows the concentration-response curves of three agonists acting at the same receptor on the same tissue preparation. From the concentration-response curves A, B and C below:

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