IGCSE Biology: Coordination and Response

Chapter Overview

• Focus on chapter 14: Coordination and Response
• The chapter covers electrical impulses, nervous system roles, reflex actions, synapses, sense organs, and hormones

Nervous System

• Key Components:
  • Central Nervous System (CNS): Brain and spinal cord; acts as control center
  • Peripheral Nervous System: Nerves and neurons regulating bodily functions
• Types of Neurons:
  • Motor Neuron: Cell body at one end, myelin sheath, nerve endings
  • Sensory Neuron: Cell body in the middle, dendrites, axon terminal
  • Relay Neuron: Branched, shorter axon, synaptic endings
• Nerve Impulse: Electrical signal passing along neurons (nerve cells)

Reflex Actions

• Definition: Automatic and rapid responses to stimuli
• Involuntary Actions vs. Voluntary Actions:
  • Involuntary: Not under conscious control
  • Voluntary: Conscious decisions
• Reflex Arc: Involves sensory, relay, and motor neurons; quick response to protect the body
• Synapse: Gap between neurons where neurotransmitters diffuse

The Eye and Vision

• Eye Structure: Cornea, iris, lens, retina, optic nerve
• Pupil Reflex: Adjusts for high/low light intensity
  • Low Light: Radial muscles contract, pupil dilates
  • High Light: Circular muscles contract, pupil constricts
• Accommodation: Adjusts for near/distant objects
  • Near Object: Ciliary muscles contract, lens becomes thicker
  • Distant Object: Ciliary muscles relax, lens becomes thinner
• Light Receptors:
  • Rods: Low detailed, black and white images, low light
  • Cones: Detailed, colorful images, high light

Hormones

• Definition: Chemical substances produced by glands, carried by blood
• Hormones and Functions:
  • Adrenaline: Prepares body for action
  • Insulin: Reduces blood glucose
  • Testosterone/Estrogen: Development of sexual characteristics
• Adrenaline Effects: Increased pulse, conversion of glycogen to glucose, rapid breathing

Nervous vs. Hormonal Systems

• Nervous System: Quick, electrical impulses, localized response
• Hormonal (Endocrine) System: Slow, chemical messages, widespread effects

Homeostasis

• Definition: Maintenance of constant internal environment
• Gluco Regulation:
  • Insulin lowers blood glucose by converting it to glycogen
  • Glucagon raises blood glucose by converting glycogen back
• Thermoregulation:
  • Vasodilation: Blood vessels widen, increase heat loss
  • Vasoconstriction: Blood vessels narrow, reduce heat loss
• Diabetes: Dysfunction in gluco regulation, type 1 due to insulin cell death

Tropic Responses in Plants

• Gravitropism: Growth response to gravity
  • Positive: Downward growth (roots)
  • Negative: Upward growth (shoots)
• Phototropism: Growth response to light
  • Positive: Towards light (shoots)
  • Negative: Away from light
• Plant Hormones as Weed Killers: Accelerate growth unsustainably to kill plants

Exam Practice Questions

• Understanding and identifying the function of muscles and eye parts in response to actions

These notes summarize the essential topics in Chapter 14 of IGCSE Biology, focusing on coordination and response mechanisms in organisms.