Quorum sensing at Higher Level: An AHL statement: chemical signalling between cells of a bacterial population.
Practise this as you read
- Describe quorum sensing.
- Identify an example: bioluminescence in Vibrio fischeri.
Free preview
This is the free notes preview
You're reading the free notes. Aimnova Pro unlocks the full study experience — and you can try it with your first topic free to keep:
- FlashcardsLock in vocabulary and key terms with spaced repetition.
- Practice questionsAnswer exam-style questions and get instant AI marking.
- Mock exams & past-paper vaultSit full mocks and see exactly how examiners award marks.
- Personalised study planA daily plan built around your exam date and weak areas.
The big idea: In quorum sensing, bacteria of one population signal to each other. Each cell releases a small signalling molecule and has receptors for it. Only when the population is dense does the signal reach a threshold concentration, and then the same genes switch on in every cell at once.
The points to remember
- Each bacterium releases a signalling molecule and has receptors for it.
- Few bacteria: the signal diffuses away, so its concentration stays low.
- Many bacteria: the signal accumulates.
- Past a threshold, it binds the receptors and switches genes on.
- All the cells respond together, so the population acts as one.
Remember it as: Enough voices, then everyone acts.
Real example: the glowing squid. Vibrio fischeri lives in the light organ of the Hawaiian bobtail squid. Packed densely there, the bacteria build up the signal and switch on their genes for bioluminescence. The squid's glow at night hides its shadow from predators below. The same bacteria free in seawater are too spread out to glow.
Trap: A single bacterium does not glow just because it has the genes: the signal must reach the threshold, which needs a dense population.
Know your predicted grade
Take timed mock exams and get detailed feedback on every answer. See exactly where you're losing marks.
How it is asked: Expect a statement MCQ (which example shows quorum sensing, or what triggers the response) or a Describe question on how quorum sensing works.
Describe how quorum sensing controls bioluminescence in Vibrio fischeri.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.