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Overview of Biological Communication and Homeostasis

May 30, 2025

Miss Esteric Biology - OCR Module 5: Communication, Homeostasis, and Energy

Introduction

  • The video comprehensively covers OCR Module 5: Communication, Homeostasis, and Energy.
  • It offers resources like flashcards for key terms and marking points for A-level Biology.

Homeostasis

  • Definition: Maintenance of a constant internal environment via physiological control systems.
  • Negative Feedback Loop:
    • Most common mechanism; deviation from set limits is detected by receptors.
    • Mechanisms are triggered to revert conditions to set limits.
    • Example: Thermoregulation involves the nervous system and sometimes hormones.
  • Positive Feedback:
    • Rare, increases deviation from the set limit; example is childbirth with hormone oxytocin.

Thermoregulation

  • Importance: Maintains enzyme activity for metabolic reactions.
  • Ectotherms vs. Endotherms:
    • Ectotherms (e.g., fish, amphibians) regulate temperature through behavior and limited physiological responses.
    • Endotherms use the nervous system to regulate temperature through mechanisms like sweating and vaso-(constriction/dilation).
    • Behavioral adaptations are also used by both ectotherms and endotherms.

Excretion as Homeostatic Control

  • Metabolic Waste Products:
    • Carbon dioxide from respiration, excreted via lungs.
    • Nitrogenous waste (urea, ammonia, uric acid) from amino acids.
  • Liver's Role:
    • Converts ammonia to urea, detoxifies substances, stores glucose as glycogen.

Liver Structure and Function

  • Blood supply through hepatic artery, vein, and portal vein.
  • Lobules: Functional units of the liver.
  • Hepatocytes: Liver cells with high metabolic activity (e.g., production of bile).
  • Kupffer Cells: Engulf pathogens in the liver.

Kidney Function

  • Nephrons: Functional units for filtration and reabsorption.
  • Key Processes: Ultra-filtration, selective reabsorption, maintenance of ion gradients.
  • Hormonal Control:
    • ADH regulates water reabsorption in response to blood water potential.

Urine and Diagnostics

  • Used to diagnose conditions like diabetes and pregnancy using hormone detection.

Neurons and Nervous System

  • Types of Neurons: Sensory, relay, motor.
  • Myelination: Accelerates impulse conduction.
  • Action Potential: Generation through ion movement; refractory period ensures discrete impulses.

Synapses

  • Neurotransmitter Release: Triggers new action potential in postsynaptic neuron.
  • Summation: Spatial and temporal for reaching threshold for action potential.

Hormonal Communication

  • Endocrine System: Hormones secreted into blood, widespread and long-lasting effects.

Adrenal Glands

  • Hormones: Adrenaline, noradrenaline, cortisol, aldosterone, androgens.

Pancreas and Blood Glucose Regulation

  • Insulin and Glucagon: Manage blood glucose levels.
  • Second Messenger Model: Mechanism of glucagon and adrenaline.

Plant Responses

  • Responses to Herbivores: Physical (thorns) and chemical (alkaloids, pheromones) defenses.
  • Responses to Abiotic Stress: Leaf loss, stomatal control, day-length sensitivity.
  • Tropisms: Growth-directed by light, gravity, and water.

Photosynthesis

  • Chloroplast Structure: Thylakoid membranes, stroma.
  • Light-Dependent Reactions: Use light to produce ATP and reduced NADP.
  • Calvin Cycle: Light-independent reactions producing glucose.

Limiting Factors

  • Affect rate of photosynthesis (e.g., light, CO2, temperature).

Respiration

  • ATP Uses: Energy for cellular processes like active transport and muscle contraction.
  • Aerobic Respiration Stages: Glycolysis, Link Reaction, Krebs Cycle, Oxidative Phosphorylation.
  • Anaerobic Respiration: Occurs without oxygen, produces less ATP.

Respiratory Substrates

  • Types: Carbohydrates, lipids, proteins can all be used.
  • RQ Values: Indicate type of substrate and respiration (aerobic/anaerobic).

Respirometer

  • Device to measure respiration rates by oxygen/carbon dioxide exchange.

This guide provides a comprehensive overview of the key topics in OCR Module 5, focusing on the important concepts and functions within homeostasis, neurons, plant and animal responses, and photosynthesis and respiration.

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