IGCSE Biology: Coordination and Response

Overview

• Chapter 14 focuses on coordination and response in the human body.
• Covers five main parts: electrical impulses, nervous system roles, reflex arc, pupil reflex, and synapses.

Nervous System

Key Concepts

• Electrical impulses travel along neurons.
• Nervous system consists of:
  • Central Nervous System (CNS): Brain and spinal cord, acts as control center.
  • Peripheral Nervous System (PNS): Nerves and neurons coordinating bodily functions.

Neurons

• Motor Neuron: Cell body at one end, insulated by myelin sheath, nerve endings at the other.
• Sensory Neuron: Smaller cell body in the middle, dendrites at one end, axon terminal at the other.
• Relay Neuron: Shorter, branched, cell body at one end.

Reflex Actions

• Reflex Arc: Automatic response mechanism to stimuli, involving sensory, relay, and motor neurons.
• Synapse: Gap between neurons where neurotransmitters facilitate impulse transmission.

Eye Function

Structure of the Eye

• Key parts: Cornea, iris, lens, retina, optic nerve.
• Pupil Reflex: Adjusts eye to high or low light intensity.
  • Radial muscles contract in low light, circular muscles in high light.

Accommodation

• Adjustments for near and distant vision.
• Ciliary muscles contract for near objects, relax for distant ones.

Hormones

Key Hormones

• Adrenaline: Produced in adrenal glands, prepares body for action.
• Insulin: Produced in pancreas, reduces blood glucose.
• Testosterone & Estrogen: Development of male and female sexual characteristics.

Hormonal Systems

• Endocrine System: Slow chemical messaging system using hormones.
• Comparison with nervous system:
  • Speed: Nervous is faster.
  • Messaging: Nervous uses electrical, endocrine uses chemical.
  • Duration: Hormonal effects last longer.

Homeostasis

Blood Glucose Regulation (Gluco-regulation)

• Insulin lowers blood glucose, glucagon raises it.
• Diabetes: Inability to regulate glucose effectively.

Temperature Regulation (Thermoregulation)

• Vasodilation: Blood vessels widen in heat.
• Vasoconstriction: Blood vessels narrow in cold.

Tropic Responses

Plant Responses

• Gravitropism: Growth in response to gravity.
  • Positive: Roots grow downwards.
  • Negative: Shoots grow upwards.
• Phototropism: Growth in response to light.
  • Positive: Shoots grow towards light.

Use of Hormones as Weed Killers

• Hormones disrupt normal growth, selectively kill weeds.

Exam Tips

• Be familiar with definitions and processes, such as synaptic transmission and hormone functions.
• Use diagrams for visual understanding, especially for processes like gluco-regulation and thermoregulation.

Practice Questions

• Engage with past exam questions for better understanding and preparation.