Unit Overview
Control and Coordination
CIE A-Level BiologyΒ· 5 min read π n/a
1. Unit at a Glance
This unit follows a clear learning arc, starting from the cellular basis of nervous communication in animals, building up to whole system responses, then covering hormonal control in both animals and plants. We begin with the fundamental unit of the nervous system (the neurone), then learn how signals travel along and between neurones. We apply this knowledge to the mammalian eye, then compare nervous control to the slower, long-range hormonal system, before finishing with coordination in plants that lack a nervous system entirely.
This unit includes the following sub-topics:
Neurone structure
Covers the structure and function of motor, sensory and relay neurones in mammalian nervous systems.
β β β± 4 min
Nerve impulse propagation
Explains resting potential, action potential generation and propagation along myelinated and unmyelinated axons.
β β β β β± 6 min
Synaptic transmission
Describes how signals are transmitted across cholinergic synapses and how chemicals/drugs affect this process.
β β β β β± 6 min
Reflex arcs
Outlines the structure and function of reflex arcs and their role in rapid protective responses.
β β β± 3 min
Eye structure and photoreception
Covers mammalian eye structure, rod/cone cell function, and light detection by visual pigments.
β β β β± 5 min
Hormonal communication
Compares hormonal and nervous control, and covers mechanism of steroid and non-steroid hormone action.
β β β β± 5 min
Plant growth regulators
Explains the role of auxins and other regulators in plant tropisms and growth coordination.
β β β β± 4 min
2. Common Pitfalls
Wrong move:
Confusing the characteristics of nervous and hormonal control
Why:
Exam questions frequently ask for direct comparisons, so mixing these up loses easy marks
Correct move:
Remember: nervous = fast, specific, short-lived effect; hormonal = slow, widespread, long-lived effect
Wrong move:
Reversing sodium and potassium ion movement during action potentials
Why:
This is one of the most frequently exam errors on this topic
Correct move:
Depolarization = ions flow into the neurone; Repolarization = ions flow out of the neurone
3. Quick Reference Cheatsheet
Key Concept | Unit-Level Summary |
|---|---|
Resting potential | ~-70 mV, maintained by pump: 3 out, 2 in |
Action potential | All-or-nothing event: depolarization to ~+40 mV followed by repolarization |
Saltatory conduction | Impulse jumps between nodes of Ranvier in myelinated axons, speeds transmission |
Synaptic transmission | Calcium influx triggers neurotransmitter release into the synaptic cleft |
Rod vs cone cells | Rods: high sensitivity, low acuity, non-colour; Cones: low sensitivity, high acuity, colour |
Nervous vs hormonal | Nervous: electrical/chemical signaling; Hormonal: only chemical signaling via blood |
Auxin function | Promotes cell elongation in shoots, causes phototropism via differential growth |
What's Next
Begin your study of this unit with the first sub-topic on neurone structure, which lays the critical cellular foundation for all topics on nervous communication that follow. After you complete all sub-topics in this unit on control and coordination, you will move on to the next unit on homeostasis, which builds on the coordination concepts you learn here to explore how organisms maintain stable internal conditions.