The short answer
Chemical messengers, feedback loops, and the key idea: a hormone's mechanism depends on whether it can cross the cell membrane.
Written and checked by GAMSAT tutors — not AI-generated.
Try the reasoning style
We treat forgetting as a failure — a lapse to be patched with reminders and records. Yet a mind that kept everything could not think; it would drown in the undifferentiated noise of every moment it had ever lived. To forget is not so much to lose information as to decide, mostly without our noticing, what was never worth keeping.
The author's argument relies most directly on which unstated assumption?
Pick an option to see how the tutor reasons to the answer — not just whether you were right.
Not quite — the answer is B.
Work backwards from the conclusion: a mind that ‘kept everything’ supposedly ‘could not think.’ That only follows if thinking means leaving most of experience out — so B is the premise the argument quietly rests on. A raises reliability, which the passage never weighs; C contradicts ‘mostly without our noticing’; D smuggles in a claim about intellect the passage never makes. The question rewards finding the hidden premise, not recalling a fact.
The endocrine system sends hormones through the blood — slower than nerves, but far-reaching and long-lasting. A hormone only affects cells with the right receptor (its "target" cells). The single most useful GAMSAT idea here is that how a hormone works depends on whether it can cross the cell membrane.
Solubility decides the mechanism
Steroid hormones are lipid-soluble → they cross the membrane and bind receptors inside the cell, then switch genes on/off. Effects are slow but long-lasting. Peptide/amine hormones are water-soluble → they can't cross the membrane, so they bind surface receptors and trigger second messengers (like cAMP). Effects are fast but short-lived.
Steroid vs peptide hormones
Steroid (lipid-soluble)
- Cross the cell membrane
- Bind INTRACELLULAR receptors
- Alter gene transcription
- Slow onset, lasting effect
- e.g. testosterone, cortisol, oestrogen
Peptide / amine (water-soluble)
- Cannot cross the membrane
- Bind SURFACE receptors
- Use second messengers (cAMP)
- Fast onset, short-lived
- e.g. insulin, adrenaline, glucagon
The classic question
GAMSAT loves to give you a "novel" hormone and tell you it's lipid-soluble (or that it acts via a surface receptor) and ask you to deduce the rest. Lipid-soluble ⇒ intracellular receptor ⇒ changes gene expression. Water-soluble ⇒ surface receptor ⇒ second messenger. Reason from the solubility.
Negative feedback (the thyroid axis)
Hypothalamus
Releases TRH, signalling the pituitary.
Pituitary
Releases TSH, signalling the thyroid.
Thyroid
Releases thyroid hormone (T3/T4), which speeds metabolism.
The loop closes
Rising T3/T4 inhibits the hypothalamus and pituitary — turning its own production down. That's negative feedback keeping levels stable.
Worked example
A newly discovered hormone is found to bind a receptor on the OUTSIDE of its target cells. Is it more likely lipid-soluble or water-soluble, and will its effects be fast or slow?
Check yourself
A steroid hormone (lipid-soluble) most likely exerts its effect by:
Key takeaways
- Hormones travel in blood and act only on cells with the matching receptor.
- Lipid-soluble (steroid) ⇒ cross membrane ⇒ intracellular receptor ⇒ change gene expression ⇒ slow, lasting.
- Water-soluble (peptide/amine) ⇒ surface receptor ⇒ second messenger (cAMP) ⇒ fast, short.
- Most hormone systems are kept stable by negative feedback.
- Reason from solubility — it tells you receptor location, mechanism and speed.
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