General Resources



Subject Guide

Biology Guide.pdf

Command Terms

Glossary of Command Terms

Prescribed Lab Practicals

Lab Practicals



May 2019 Revision Sessions

Human & Animal Physiology

DNA, RNA, Cellular Respiration & Photosynthesis

Spiky's Study Notes


Additional Resources



Prox's Diagram Corner

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Diagrams provided by @Proxentauri#6434

Human & Animal Physiology (Topics 6, 11 & Option D)

Myogenic Control of the Heart Beat

  1. Bloods flows into interior & superior vena cava
  2. Sinoatrial (SA) node sends out electrical signal which causes cardiac muscle of atria to contract
  3. Blood in right atrium is forced into right ventricle via tricuspid valve
  4. Atrioventricular (AV) node receives signal from SA node and sends electrical signal to Bundle of His
  5. Signal from Bundle of His causes Perkinje fibres in right ventricular wall to contract
  6. After right ventricle contracts, blood flows to the pulmonary valve, which sends blood to lung where it is oxygenated
  7. Oxygenated blood comes back to the left atrium via the pulmonary vein
  8. SA node triggers atria to contract, sending the blood to the left ventricle via bicuspid valve
  9. From left ventricle, blood is sent to the rest of body via aorta

Regulation of Heart Rate

  • Heart rate is moderated through sympathetic and parasympathetic (vagus) nerve
  • From the medulla oblongata of brain to heart, nerve impulses are sent through sympathetic nerves
  • Parasympathetic nerves send information about oxygen levels and pH of blood to medulla
  • Medulla sends nerve impulses to the heart to increase/decrease heart rate
  • Medulla releases epinephrine via sympathetic nerve to increase heart rate or sends acetylcholine via parasympathetic nerve to decrease heart rate

Lung Structure

  • Air enters respiratory system through nose or mouth and passes through pharynx to trachea
  • Air travels down trachea until it divides into two bronchi which lead to lungs
  • Inside each lung, bronchi divide into many smaller airways called bronchioles, greatly increasing surface area
  • Each bronchiole contains a cluster of air sacs called alveoli, where gas exchange with bloodstream occurs
    • Alveoli have specialized structural features to facilitate gas exchange with blood:
      • Have very thin epithelial layer (one cell thick) to minimize diffusion distance of gasses
      • Spherical in shape to maximize surface area
      • Surrounded by a rich capillary network
      • Internal surface covered with a layer of fluid (surfactant) as dissolved gases are better able to diffuse into bloodstream

Mechanism of Breathing & Respiratory Muscles

  • Inspiration (inhaling) and expiration (exhaling) are controlled by two sets of antagonistic (working oppositely) muscle groups
    • During inspiration:
      • Diaphragm muscles contract, causing the diaphragm to flatten and increasing the volume of the thoracic cavity
      • External intercostals contract, pulling ribs upwards and outwards (expanding chest)
      • When volume of lungs increase, pressure in lungs decreases
      • Gases will move from areas of high pressure to low pressure, hence air will move into the lungs
    • During expiration:
      • Diaphragm muscles relax, reducing volume of the thoracic cavity
      • Internal intercostal muscles contract, pulling ribs inwards and downwards (reducing breadth of chest)
      • When volume of lungs decreases, pressure in lungs increases
      • Gases will move from areas of high pressure to low pressure, hence air will move out of the lungs


  • Spermatogenesis describes the production of sperm in the seminiferous tubules of the testes
    • Process begins at puberty when the germ-line epithelium of the seminiferous tubules divides by mitosis to form spermatogonia
    • These cells then undergo a period of cell growth to become primary spermatocytes
    • Primary spermatocytes undergo a first meiotic division to form two secondary spermatocytes
    • Secondary spermatocytes undergo a second meiotic division to form four haploid daughter cells called spermatids
    • Spermatids then undertake a process of differentiation in order to become functional sperm cells
  • Spermatogenesis is a lifelong, uninterrupted process that happens continuously

Nucleic Acids (Topics 2 & 7)