Positive and negative feedback in cell signallingSpec C2.1.14
In short
Cell signalling pathways are regulated by feedback. In negative feedback the response reduces the original stimulus, so the signal decreases and conditions stay stable, as when insulin lowers blood glucose and so less insulin is secreted. In positive feedback the response increases the stimulus, amplifying the signal, as when high oestradiol late in the follicular phase increases GnRH secretion.
| Feature | Negative feedback | Positive feedback |
|---|---|---|
| Effect of the response on the stimulus | Reduces it | Increases it |
| Result | Signal is damped; conditions return towards a set point | Signal is amplified; a rapid, large change |
| How it ends | Continuous, keeps things stable | Needs an outside event to stop the cycle |
Negative feedback example: insulin
A rise in blood glucose stimulates insulin secretion. Insulin signalling makes cells take up glucose, so blood glucose falls. Lower glucose reduces insulin secretion, so the signal switches itself off.
Positive feedback example: oestradiol and GnRH
Late in the follicular phase, the growing follicle keeps oestradiol concentration high. Oestradiol now increases GnRH secretion by the hypothalamus, instead of inhibiting it as it does at lower concentrations. More GnRH raises FSH and LH, which stimulate the follicle to secrete even more oestradiol. The cycle builds to the LH surge and ends with ovulation.
Linking question: in what ways is negative feedback evident at all levels of biological organization? Here it acts on a signalling pathway; in C3.1 it controls heart rate and ventilation rate, and in D3.3 it keeps body temperature and blood glucose near their set points.
Quick check
HL only What term does the IB use for a signalling chemical that binds to a receptor?
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A ligand.
HL only Which marine bacterium is the example of quorum sensing?
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Vibrio fischeri, which becomes bioluminescent at high population density.
HL only What is the second messenger in the epinephrine pathway?
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Cyclic AMP (cAMP).
HL only Which amino acid in the insulin receptor is phosphorylated?
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Tyrosine.
HL only Where are the receptors for steroid hormones?
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Inside the cell, in the cytoplasm or nucleus.
Written and checked against the IB Biology HL specification · Updated October 2026