Description

COORDINATION AND IRRITABILITY — Comprehensive Study Notes
A-Level Biology — Form Five (TIE Syllabus, Revised Edition 2024)

A comprehensive, exam-ready resource covering nervous and hormonal coordination, sensory receptors, plant responses, and phytohormones — all in one clearly organized document.

📘 What’s Inside
1. Meaning of Coordination and Irritability

Clear definitions: irritability, coordination, stimulus, receptor, and effector

Five reasons why coordination matters, including homeostasis

The general response pathway (stimulus → detection → integration → action → change) with a hot-object reflex example

2. Nervous Coordination in Mammals

Nervous system divisions table: CNS, PNS, somatic, and autonomic

Labelled motor neurone diagram with all parts explained (dendrites, axon, myelin sheath, nodes of Ranvier, terminals)

Three neurone types compared: sensory, relay, and motor

Action potential fully explained in five stages — resting potential, depolarisation, repolarisation, refractory period, and restoration

Labelled action potential graph (depolarisation, repolarisation, hyperpolarisation)

Saltatory vs. continuous conduction explained

Synaptic transmission in six steps with labelled synapse diagram

Brain regions table: cerebrum, cerebellum, medulla oblongata, hypothalamus, thalamus, and spinal cord

Sympathetic vs. parasympathetic table (fight or flight vs. rest and digest)

3. Reflex Actions and Reflex Arcs

Definition and five-step reflex arc pathway

Withdrawal reflex worked example

Four reflex types: unconditioned, conditioned, spinal, and cranial

Reflex vs. voluntary action comparison table

4. Sensory Receptors

Classification by stimulus: mechanoreceptors, thermoreceptors, chemoreceptors, photoreceptors, nociceptors, and osmoreceptors — with examples

Classification by location: exteroceptors, interoceptors, and proprioceptors

Five receptor properties: specificity, sensitivity, adaptation, transduction, and receptive field

The human eye — labelled diagram, structures table, rods vs. cones comparison table, accommodation explained, and the pupil reflex

The human ear — structures table and the full hearing pathway

5. Hormonal Coordination in Mammals

Features of hormonal coordination and the endocrine system

Major endocrine glands table — hypothalamus, pituitary, thyroid, parathyroid, adrenal cortex/medulla, pancreas, ovaries, and testes

Negative feedback diagram and explanation

Blood glucose control fully diagrammed — insulin and glucagon in negative feedback loops

Selected hormones explained: ADH, thyroxine, adrenaline, insulin, glucagon, oestrogen, and progesterone

Diabetes mellitus table: Type 1 vs. Type 2 causes and features

6. Coordination in Plants

How plants coordinate without a nervous system

Plant responses table: tropism, nastic movement, and tactic response

All five tropisms explained: phototropism, gravitropism, hydrotropism, thigmotropism, and chemotropism

Labelled phototropism diagram showing auxin redistribution

Labelled gravitropism diagram comparing root and shoot responses

Nastic movements: thigmonasty (Mimosa), photonasty, and thermonasty

Tropism vs. nastic movement comparison table

7. Plant Hormones (Phytohormones)

Major plant hormones table: auxins, gibberellins, cytokinins, abscisic acid, and ethylene — with actions and applications

Auxin and apical dominance with labelled diagram

Hormone interactions explained (auxin–cytokinin balance, gibberellin–ABA opposition, ethylene interactions)

Six agricultural applications with a caution about concentration and timing

8. Nervous and Hormonal Coordination Compared

Comparison table across messenger, transport route, and speed

9. Homeostasis and Coordination

Definition and the role of receptors, control centres, and effectors

Homeostatic control table covering temperature, blood glucose, water potential, and calcium

10. Practical and Experimental Skills

Six-step protocol for investigating phototropism

Protocol for investigating Mimosa touch response

Variables explained: independent, dependent, controlled, and reliability measures

11. Key Terms for Examination Revision

Complete glossary

12. Examination Questions

18 short-answer questions covering every subtopic

6 essay/structured questions with multi-part mark allocations

13. Suggested Answer Points

Model answer guide for selected questions plus essay technique guidance

14. Source and Scope Note

Notes aligned to TIE Biology for Advanced Secondary Schools, Chapter Four, with transparency about the scanned source

✅ Why This Guide Works
Six labelled diagrams — motor neurone, action potential, synapse, eye, phototropism, and gravitropism

Every process shown in numbered steps — action potential, synaptic transmission, reflex arc, and hearing pathway

All major comparison tables — sympathetic/parasympathetic, rods/cones, reflex/voluntary, tropism/nastic, nervous/hormonal

Homeostasis integrated — glucose, temperature, water, and calcium all in one table

Practical experiments included — with variables and reliability guidance

Exam-focused — 18 short-answer questions, 6 structured essays, and model answer points

Complete coverage — from neurone structure to plant hormone applications in a single document

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