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Unit 3: Homeostasis and Disease

12 dot points, in syllabus order. Each dot point has a focused answer, with exam-style questions and worked answers where available.

What are the different types of disease-causing agents and how do they spread between people?

Classify pathogens and the diseases they cause, describe modes of transmission, and use epidemiological terms such as incidence, prevalence and reservoir to describe the spread of disease

Pathogens and transmission. Types of pathogens with named diseases, the modes of disease transmission, and the epidemiology terms used to describe how disease spreads through a population.

7 min read →

How do vaccines protect a whole community, and why are antibiotics losing their power against bacteria?

Explain how immunisation produces artificial active immunity, how herd immunity protects a population, and how antibiotic use and resistance affect the control of infectious disease

Disease control. How vaccines create artificial active immunity and memory cells, how herd immunity protects a population, and how antibiotics work and why resistance evolves.

7 min read →

How does the body keep blood glucose steady between meals and after eating a sugary snack?

Explain how blood glucose concentration is regulated by negative feedback, including the roles of the pancreas, insulin and glucagon and the liver

Blood glucose regulation. The islets of Langerhans, the antagonistic action of insulin and glucagon, the liver as the main effector, and how the negative feedback loop runs in both directions.

7 min read →

How is the nervous system divided up so that some responses are voluntary and others run automatically?

Describe the organisation of the nervous system into central and peripheral divisions, and the somatic and autonomic (sympathetic and parasympathetic) divisions and their roles in homeostasis

How the nervous system is organised. The central and peripheral divisions, the somatic and autonomic systems, and the antagonistic sympathetic and parasympathetic branches in homeostasis.

6 min read →

How do hormones coordinate slow, widespread and sustained responses across the body?

Describe how endocrine glands secrete hormones that regulate target cells, using thermoregulation and blood glucose regulation as examples

Endocrine system. How hormones reach target cells, steroid versus protein hormone action, and worked negative-feedback loops for blood glucose and thyroxine.

8 min read →

How does the body hold its core temperature near 37 degrees whether it is freezing or sweltering outside?

Explain how the body regulates core temperature by negative feedback, including the role of the hypothalamus, thermoreceptors and the effectors that control heat loss and heat gain

Thermoregulation. The hypothalamus and thermoreceptors, the effectors for heat loss (sweating, vasodilation) and heat gain (shivering, vasoconstriction), and the four routes of heat transfer.

7 min read →

How does the body defend itself against pathogens and remember the ones it has already met?

Describe the lines of defence against pathogens, including non-specific defences and the specific immune response with B and T lymphocytes

Immunity. Pathogen types, the three lines of defence, humoral and cell-mediated responses, memory cells, and active versus passive immunity.

9 min read →

How does the body keep its internal environment stable when conditions outside keep changing?

Explain how stimulus-response models and negative feedback maintain a stable internal environment within tolerance limits

Homeostasis. The stimulus-response model, the receptor-control centre-effector pathway, why negative feedback dominates, and how to write a feedback loop in the exam.

7 min read →

How does a nerve cell turn a stimulus into an electrical signal that travels the length of an axon?

Explain the resting membrane potential, the generation and propagation of the action potential, the all-or-none principle, the refractory period and saltatory conduction

Nerve impulse. The resting potential and sodium-potassium pump, depolarisation and repolarisation, the all-or-none principle, the refractory period, and how myelin produces saltatory conduction.

7 min read →

What happens to the body when homeostatic control mechanisms fail or are overwhelmed?

Explain how disease, malfunction of feedback systems and environmental factors disrupt homeostasis, using named examples such as diabetes

Disrupted homeostasis. Causes of disease, feedback failure, diabetes type 1 and 2, and how disrupted variables damage cells.

8 min read →

How do the kidneys keep the water and salt content of the blood constant whether you drink a litre of water or sweat it out?

Explain how body fluid composition is regulated, including the role of the kidney and nephron, antidiuretic hormone and aldosterone in osmoregulation by negative feedback

Osmoregulation. The nephron and the three stages of urine formation, the role of antidiuretic hormone in water balance, and aldosterone in salt balance, all as negative feedback.

8 min read →

How does the nervous system detect change and respond within a fraction of a second?

Describe the structure and function of neurons, the transmission of nerve impulses, synaptic transmission and the reflex arc in homeostatic control

Nervous system. Neuron structure, the action potential and saltatory conduction, synaptic transmission with neurotransmitters, and the reflex arc.

8 min read →