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A-Level Revise Aid: This resource is designed to support your revision and may contain errors. If you find a discrepancy with your class teaching, your teacher is correct -- please let us know at alevelrevise@scott.scottrix.co.uk.

Homeostasis and the Nervous System

Year 1 / ASYear 2 / A-Level All Boards (AQA, Edexcel, OCR, WJEC, CCEA) AQA

A-Level Biology revision: Homeostasis and the Nervous System. Learning objectives, key points, worked examples and practice questions across AQA, Edexcel, OCR, WJEC and CCEA.

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πŸ“Œ Key Points

Key Fact: Negative feedback: deviation -> correction (e.g. blood glucose, temp, water); Positive: amplifies (e.g. oxytocin in childbirth)
Key Fact: Kidney: cortex/medulla; nephron (Bowman's capsule, PCT, loop of Henle, DCT, collecting duct); ADH: increases water permeability of DCT/CD; Loop: counter-current multiplier creates medullary gradient
Key Fact: Neurones: sensory, relay, motor; Resting potential -70mV (Na⁺/K⁺ pump, K⁺ leak); Action potential: depolarisation (Na⁺ in), repolarisation (K⁺ out), refractory period
Key Fact: Synapse: Ca^2⁺ -> vesicle fusion -> neurotransmitter -> receptor -> depolarisation; Summation: temporal/spatial
Key Fact: Hormones: insulin (Ξ²-cells, lowers glucose), glucagon (Ξ±-cells, raises glucose), adrenaline (fight/flight), thyroxine (metabolic rate); Diabetes: type 1 (no insulin), type 2 (insulin resistance)

🎯 Learning Objectives

  • Explain homeostasis: set point, receptors, effectors, negative/positive feedback
  • Detail kidney structure and osmoregulation (ADH, loop of Henle)
  • Describe nervous system: CNS/PNS, neurone types, resting/action potential, synapses
  • Explain hormonal control: endocrine glands, insulin/glucagon, adrenaline, thyroxine
  • Understand temperature regulation: hypothalamus, vasodilation/constriction, sweating, shivering

πŸ’‘ Worked Example

Exam-Style Question

Question: Describe how the loop of Henle creates a water potential gradient in the kidney medulla

Model Answer:

Descending limb: permeable to water, impermeable to ions -> water leaves by osmosis. Ascending limb: impermeable to water, active Na⁺/Cl⁻ transport out -> filtrate diluted, medulla concentrated. Counter-current multiplier: flow in opposite directions maintains gradient

❓ Practice Questions

Model answers are being added progressively - questions marked ✗ don't have one yet. Cross-check with your teacher or the official mark scheme.

Questions:

  • Define homeostasis✗ answer coming soon
  • Explain action potential phases✗ answer coming soon
  • How does insulin lower blood glucose?✗ answer coming soon
  • Role of hypothalamus in thermoregulation✗ answer coming soon
  • Difference between type 1 and type 2 diabetes✗ answer coming soon

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