Distinguish hormone delivery from a specific target response
Explain why widespread circulation does not mean identical activity in every organ.
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall electrical impulses, blood transport, gland secretion and the distinction between a stimulus and a body response.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Does hormone delivery alone prove a target response?
What you will learn
- Separate arrival from recognition
- Use source and target roles in a new model
Distinguish hormone delivery from a specific target response
| Feature | Meaning |
|---|---|
| Circulation | Can deliver the chemical widely |
| Target | Recognises the signal and alters activity |
| Multiple targets | Do not remove specificity |
| Non-response | Delivery alone does not prove an activity change |
Separate arrival from recognition
Blood circulation can carry a hormone widely. Arrival near an organ, however, is not the same as a response by that organ. A specific target has cells able to recognise the hormone and alter their activity. This distinction explains why a blood-borne signal can produce coordinated changes in selected targets instead of making every tissue do the same thing.
Use a supplied model with three organs: the chemical reaches all three, but only two have the stated suitable recognition mechanism. Those two are the specific targets in that model. The third is supplied with blood but has no stated response to this hormone. Do not infer target identity merely from the presence of a blood vessel or from the organ being closest to the gland.
Use source and target roles in a new model
One hormone can influence more than one specific target organ. Adrenaline can change heart activity and contribute to pupil and breathing responses. More than one target does not remove specificity: the changes remain linked to cells that respond to the signal. Conversely, the producing gland is identified by production, not by the largest response drawn on a graph.
When explaining an unfamiliar route, first identify the gland that releases the chemical, then name blood as the carrier, and finally state which supplied organs change activity. Receptor recognition is supporting background; a full account of molecular signalling is not required here. Keep any conclusion tied to the information actually supplied about response.
Pause and explain
A gland releases H and only organs M and N respond in a supplied model. Which are targets?
Worked example
A hormone reaches P, Q and R; only P and R respond. Identify its targets.
Show the worked solution
- Circulation reaches all three.
- The stated activity changes identify P and R as specific targets.
Answer P and R are the specific target organs; arrival at Q alone does not establish a response.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain why blood carriage does not imply the same response in every organ.
Give me a hint
Distinguish circulation and recognition.
Compare my reasoning
- Blood delivers the chemical widely.
- Specific target cells recognise it and change activity.
Blood can carry a hormone widely, but only specific responsive targets alter their activity; delivery is not identical response.
Look for these in your work
- State widespread carriage
- Explain specificity
Gland A produces H. H reaches B, C and D, but only B and D change activity. Identify source and targets.
Give me a hint
Use production for source and response for targets.
Compare my reasoning
- A is the producing gland.
- B and D are the specific target organs.
Source: gland A. Specific targets: B and D. Delivery to C does not establish its response.
Look for these in your work
- Identify source
- Identify both targets
A student says two different organ responses prove that two different hormones must be involved. Evaluate this using adrenaline.
Give me a hint
A single chemical can have more than one target.
Compare my reasoning
- Adrenaline can affect the heart and contribute to other fight-or-flight responses.
- Different responsive targets do not require different hormones.
The conclusion is not justified. A single hormone such as adrenaline can alter activity in more than one specific target organ.
Look for these in your work
- Use a hormone example
- Reject the unsupported one-target rule
Common mistakes
- Calling every blood-supplied organ an identical target.
- Assuming there can be only one target per hormone.
What can you explain now?
A gland releases H and only organs M and N respond in a supplied model. Which are targets?
Compare with the explanation
M and N
They show the supplied specific responses.
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Make it stick
Explain specificity when one hormone reaches several organs.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.