Cells and organs must communicate. This SL lesson covers C2.2 Neural signalling, C3.1 Integration of body systems and C3.2 Defence against disease.
You will follow the nerve impulse and synapse, compare nervous and hormonal control, and see how the body defends itself.
Work through each screen, answer the questions as you go (some are wordy, some are calculations) and collect ⭐ stars. Press Start when you are ready.
A neuron maintains a resting potential (about −70 mV) by pumping ions. A strong enough stimulus reaches threshold and triggers an action potential — a rapid depolarisation that sweeps along the axon.
Action potentials are all-or-none: above threshold they are always the same size. Myelin speeds conduction by saltatory (node-to-node) jumping.
Where two neurons meet, the impulse crosses a synapse chemically. The arriving impulse triggers release of a neurotransmitter (e.g. acetylcholine) that diffuses across the gap and binds receptors on the next neuron.
Synapses ensure one-way transmission and allow signals to be summed and integrated.
The body is coordinated by two interacting systems:
Control centres (such as the brain) use feedback to keep the internal environment stable — a theme continued in homeostasis.
Sort each process by the type of defence (or not a defence).
Innate defences act fast and non-specifically: skin and mucous barriers, blood clotting, and phagocytes that engulf pathogens.
Adaptive immunity is specific: B-lymphocytes make antibodies against a pathogen's antigens, and memory cells give a faster, stronger response next time (the basis of vaccination and herd immunity).
Antibiotics treat bacteria, not viruses; overuse selects for antibiotic-resistant strains.
Match each term to its correct description.
C2.2: resting and action potentials; all-or-none; synapses use neurotransmitters
C3.1: nervous (fast) and endocrine (slow) systems interact via feedback
C3.2: innate vs adaptive immunity; antibodies and memory cells; antibiotic resistance
Skills: speed = distance / time for nerve conduction
Press Finish to see your score.
You have worked through Theme C: Interaction — Signalling & Body Systems for IB Diploma Biology. 🎉
Your stars: 0 / 0
Next: test yourself in the Evaluate stage Confidence Quiz, then lock it in with Verify.