A-Level Biology: Homeostasis and Response
Suggested Lesson-by-Lesson Breakdown
This is a suggested teaching sequence for the A-level Biology topic Homeostasis and Response. It is based on common content across AQA, OCR, and Edexcel specifications, but the exact order and emphasis may vary by exam board.
Lesson 1: Introduction to Homeostasis
Focus: what homeostasis is and why organisms need it.
Core content:
- definition of homeostasis
- maintenance of stable internal conditions
- importance of controlling temperature, blood glucose, blood pH, and water potential
- overview of receptors, coordination systems, and effectors
Lesson outcome: students can explain why stable internal conditions are necessary for survival and enzyme activity.
Lesson 2: Negative Feedback and Control Systems
Focus: how the body restores conditions to a set range.
Core content:
- negative feedback as the main control mechanism
- departure from the norm and corrective responses
- difference between negative and positive feedback
- examples of homeostatic control systems
Lesson outcome: students can describe a negative feedback loop and apply it to biological examples.
Lesson 3: Stimuli, Receptors and Responses
Focus: how organisms detect change in the internal and external environment.
Core content:
- stimuli and response pathways
- role of receptors in detecting specific changes
- effectors such as muscles and glands
- simple responses including reflexes, taxes, and kineses
Lesson outcome: students can trace the pathway from stimulus to response.
Lesson 4: The Nervous System and Neurone Structure
Focus: how neurones are adapted for communication.
Core content:
- sensory, relay, and motor neurones
- structure of a myelinated neurone
- role of myelin and nodes of Ranvier
- organisation of nervous pathways
Lesson outcome: students can compare neurone types and relate structure to function.
Lesson 5: Resting Potential and Action Potentials
Focus: how nerve impulses are generated and transmitted.
Core content:
- resting potential
- role of sodium and potassium ions
- depolarisation and repolarisation
- all-or-nothing principle
- refractory period and speed of conduction
- saltatory conduction in myelinated neurones
Lesson outcome: students can explain how an action potential is formed and moves along an axon.
Lesson 6: Synapses and Neuromuscular Junctions
Focus: how signals pass between cells.
Core content:
- structure of a synapse
- role of neurotransmitters such as acetylcholine
- steps in synaptic transmission
- summation and inhibition
- comparison between synapses and neuromuscular junctions
Lesson outcome: students can describe how information passes across a synapse and why transmission is one-way.
Lesson 7: Muscles as Effectors
Focus: how skeletal muscles produce a response.
Core content:
- muscles acting in antagonistic pairs
- gross structure of skeletal muscle
- actin, myosin, ATP, and calcium ions
- sliding filament theory
- fast and slow twitch fibres
Lesson outcome: students can explain how muscle contraction occurs and why muscles are effective biological effectors.
Lesson 8: Control of Heart Rate
Focus: how heart activity is coordinated and adjusted.
Core content:
- myogenic nature of the heart
- SAN, AVN, bundle of His, and Purkyne tissue
- roles of pressure receptors and chemoreceptors
- autonomic nervous system control of heart rate
Lesson outcome: students can explain how heart rate changes in response to internal conditions.
Lesson 9: Hormonal Communication and Blood Glucose Control
Focus: endocrine control of internal conditions.
Core content:
- differences between nervous and hormonal communication
- roles of insulin, glucagon, and adrenaline
- glycogenesis, glycogenolysis, and gluconeogenesis
- role of the liver in blood glucose regulation
- type 1 and type 2 diabetes
Lesson outcome: students can describe how blood glucose concentration is controlled by negative feedback.
Lesson 10: Osmoregulation and the Kidney
Focus: maintenance of blood water potential.
Core content:
- meaning of osmoregulation
- role of the hypothalamus, pituitary gland, and ADH
- structure of the nephron
- ultrafiltration and selective reabsorption
- loop of Henle and water reabsorption in collecting ducts
Lesson outcome: students can explain how the kidney and ADH help maintain water balance.
Lesson 11: Plant Responses
Focus: response mechanisms in plants.
Core content:
- plant growth responses to stimuli
- phototropism and gravitropism
- role of IAA in roots and shoots
- how plant responses differ from animal nervous responses
Lesson outcome: students can explain how plant hormones control directional growth.
Lesson 12: Required Practicals, Data Skills and Revision
Focus: applying theory to experiments and exam questions.
Core content:
- investigating movement responses in animals
- glucose testing and colorimetry practicals
- analysis of data linked to pulse rate, reflexes, and homeostatic control
- synoptic links across nervous, hormonal, and homeostatic processes
Lesson outcome: students can apply content knowledge to practical, data-handling, and exam-style questions.
Board note: AQA includes especially detailed content on receptors, heart rate, nerve impulses, synapses, muscle contraction, blood glucose, and blood water potential. OCR places this material mainly in Module 5: Communication, homeostasis and energy. Edexcel Biology A (SNAB) spreads it mainly across Topic 7: Run for your Life and Topic 8: Grey Matter.
Sources
AQA A-level Biology specification
OCR Biology A specification at a glance
Pearson Edexcel Biology A specification