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Understanding Coordination and Response in Biology

May 5, 2025

IGCSE Biology - Coordination and Response (Chapter 14)

Overview

  • Chapter Coverage: Coordination and response.
  • Parts of Study: Electrical impulses, nervous system structure, reflex actions, synapses, sense organs.

Nervous System

Key Concepts

  • Definition: Electrical impulses travel along neurons.
  • Parts:
    • Central Nervous System (CNS): Brain and spinal cord.
    • Peripheral Nervous System (PNS): Nerves and neurons.
  • Actions:
    • Involuntary Actions: Not under conscious control (e.g., reflexes).
    • Voluntary Actions: Under conscious control.
  • Nerve Impulse: Electrical signal passing along neurons (nerve cells).

Types of Neurons

  1. Motor Neuron: Cell body at one end, covered by myelin sheath, ends in nerve endings.
  2. Sensory Neuron: Smaller cell body in the middle, dendrites at one end, axon terminal at the other.
  3. Relay Neuron: More branched, synaptic endings, shorter axon.

Reflex Arc

  • Definition: Automatic and rapid integration of stimuli with responses.
  • Process: Stimulus → Receptor → Sensory Neuron → CNS (Relay Neuron) → Motor Neuron → Effector.
  • Synapse: Junction between neurons, neurotransmitters pass impulses.

Synapses

  • Function: Ensure one-way impulse travel.
  • Events at Synapse: Impulse arrives, vesicles release neurotransmitters, neurotransmitter diffuses across synapse.
  • Impact of Drugs: Affect neurotransmitter function, e.g., heroin.

Sense Organs

The Eye

  • Parts: Cornea, iris, lens, retina, optic nerve.
  • Functions:
    • Cornea: Refracts light.
    • Iris: Controls light entry.
    • Lens: Adjusts focus.
    • Retina: Contains light receptors (rods and cones).
  • Pupil Reflex: Adjusts pupils for light intensity.
  • Accommodation: Eye adjusts for near/distant objects.

Receptors

  • Rods: Black and white vision, low light.
  • Cones: Color vision, high light intensity.

Hormones

  • Definition: Chemical substances produced by glands, carried in blood.
  • Examples:
    • Adrenaline: Prepares for action (adrenal gland).
    • Insulin: Reduces blood glucose (pancreas).
    • Testosterone/Estrogen: Development of sexual characteristics.

Adrenaline Effects

  • Increases pulse rate, converts glycogen to glucose, increases breathing rate, blood diversion.

Nervous vs. Hormonal System

  • Nervous System: Quick, localized, electrical impulses.
  • Hormonal System: Slow, widespread, chemical messengers.

Homeostasis

Gluco Regulation

  • Insulin: Lowers blood glucose.
  • Glucagon: Raises blood glucose.
  • Diabetes: Imbalance in glucose regulation.

Thermoregulation

  • Adaptations: Insulation, sweating, shivering.
  • Vasodilation/Vasoconstriction: Blood vessel adjustments for heat regulation.

Tropic Responses

  • Gravitropism: Plant growth response to gravity.
  • Phototropism: Plant growth towards light.
  • Weed Killers: Hormones used to control plant growth.

Exam Practice

  • Muscle & Eye Questions: Review antagonistic muscles and eye structure.

This chapter involves a detailed understanding of biological coordination and response mechanisms, with emphasis on both the nervous and hormonal systems, along with practical applications and adaptations in organisms.

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