Biology unit guide
Human physiology
Digestion, blood glucose, immunity, the kidney, neurones, hormones and reproduction.
Unit 5 is where negative feedback appears again and again, and recognising that is most of the unit. Blood glucose, osmoregulation and thermoregulation are the same logical structure with different hormones and organs. Students who learn the pattern once and slot the details in find this unit short; students who learn each system separately find it the longest in the course.
Topics in this unit
What gets examined
- Negative feedback as a general mechanism, applied to glucose, water balance and temperature.
- Insulin and glucagon: which cells release them, what they do, and what happens when the mechanism fails.
- The kidney nephron: where filtration, reabsorption and osmoregulation occur, and the role of ADH.
- Primary and secondary immune responses, and why vaccination produces lasting protection.
- Resting potential, action potential, and transmission across a synapse.
- Hormonal control of the menstrual cycle and the feedback loops involved.
How to revise it
Learn negative feedback once as a template
Change detected, response triggered, change reversed, receptor detects return to normal. Then fill in the hormone and organ for each system. Three topics become one.
Follow the nephron in order
Glomerulus, proximal tubule, loop of Henle, distal tubule, collecting duct - and what happens at each. Questions almost always name a location, so the sequence is the map.
Explain the action potential as ion movement
Sodium in for depolarisation, potassium out for repolarisation, pump restores resting potential. Naming the ion and its direction is where the marks are.
Contrast the two immune responses
The secondary response is faster and larger because memory cells already exist. That comparison is the answer to most vaccination questions.
Where marks get lost
- Swapping insulin and glucagon, or saying insulin raises blood glucose.
- Describing feedback as positive when the response reverses the change.
- Placing selective reabsorption in the glomerulus rather than the proximal tubule.
- Saying antibodies destroy pathogens directly rather than marking them for destruction.
- Confusing depolarisation with repolarisation when describing an action potential.
Practise this unit
Reading about a unit only goes so far. Work through real IB-style questions on it, with mark schemes.