Chapter 14: Coordination and Response - IGCSE Biology

Introduction

• Focus on coordination and response, a key chapter with frequent exam questions.
• Central theme: Nervous system and its functions.

Nervous System

• Purpose: Allows the body to respond to environmental changes, coordinated usually by the brain as part of the Central Nervous System (CNS).
  • Reflex actions: Rapid responses bypassing the brain.
• Receptors and Effectors:
  • Receptors: Specialized cells detecting stimuli and turning them into electrical impulses, found in sense organs (ear, eye, skin).
  • Effectors: Body parts producing responses (e.g., muscle contraction, gland hormone release).

Neurons

• Types of Neurons:
  • Sensory Neurons: Carry signals from receptors to CNS.
  • Relay Neurons: Transmit messages within the CNS.
  • Motor Neurons: Carry signals from CNS to effectors.
• Neuron Structure:
  • Axons: Carry impulses away from cell body.
  • Dendrites: Pick up signals and impulses.
  • Myelin Sheath: Insulates nerve fibers, speeding impulse transmission.

Central Nervous System vs. Peripheral Nervous System

• CNS: Brain and spinal cord, coordinating responses to stimuli.
• PNS: Connects CNS to body, involving sensory and motor neurons.

Voluntary and Involuntary Reactions

• Reflex Actions: Automatic and rapid responses to minimize damage, following a reflex arc.
• Synapses: Junctions between neurons, ensuring one-way impulse travel, involving neurotransmitters.

Sense Organs: The Eye

• Structure: Includes cornea, pupil, lens, iris, optic nerve, retina, and fovea.
• Functions:
  • Cornea: Refracts light.
  • Iris: Controls light entry.
  • Lens: Focuses light.
  • Retina: Contains light receptors.
  • Optic Nerve: Transmits signals to the brain.
• Photoreceptor Cells:
  • Rods: Sensitive to dim light, black and white vision.
  • Cones: Sensitive to color, concentrated in fovea.
• Pupil Reflex: Involuntary response adjusting pupil size according to light intensity.
• Accommodation: Lens shape adjustment for focusing light.

Endocrine System

• Hormones: Chemical substances altering target organ activities, produced by glands (adrenal, pituitary, pancreas, testes, ovaries).
• Key Hormones and Functions:
  • Adrenaline: Prepares body for action (respiratory/circulatory effects).
  • Insulin: Lowers blood glucose levels.
  • Testosterone/Estrogen: Secondary sexual characteristics development.

Nervous vs. Endocrine System

• Differences:
  • Nervous: Rapid, short-term effects via electrical impulses.
  • Endocrine: Slower, longer-lasting effects via hormones.
• Similarities: Both involved in survival.

Homeostasis

• Maintenance of a constant internal environment.
  • Negative Feedback: Corrects deviations (e.g., temperature regulation).
• Blood Sugar Regulation:
  • High: Pancreas secretes insulin (glucose to glycogen).
  • Low: Pancreas secretes glucagon (glycogen to glucose).
• Diabetes:
  • Type 1: Insufficient insulin, requiring management through diet and insulin injections.

Coordination and Response in Plants

• Plant Hormones and Tropisms:
  • Auxin: Influences shoot/root growth in response to light (phototropism) and gravity (geotropism).
• Phototropism: Growth towards light for photosynthesis.
• Geotropism: Root growth towards gravity for moisture access.
• Etiolation: Plant growth in darkness, leading to structural changes.
• Weed Killers: Use synthetic hormones to disrupt plant growth.

Conclusion

• Coordination and response encompass complex systems in both animals and plants, critical for survival and adaptation.