biology module 3

• Exchange surfaces in organisms

  • Have many similar adaptations to make substances such as oxygen and carbon dioxide can exchange across the surfaces as efficiently as possible
  • Small organisms like amoeba have a very large surface area compared to their volume and simple diffusion is sufficient to meet their metabolic needs
  • Large organisms have a smaller surface area compared to their volume, higher metabolic rates, and require adaptations to increase the efficiency of exchange across their surface
• Adaptations to increase efficiency of exchange

  • Provide large surface area
  • Maintain concentration gradient
  • Reduce diffusion pathway
• Mammalian gas exchange system structures

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
• Alveoli


  • Provide large surface area
  • Short diffusion distance
  • Concentration gradient maintained by ventilation
• Ventilation


  1. Diaphragm contracts, external intercostal muscles contract, internal intercostal muscles relax - increases volume and decreases pressure, air flows in

  2. Diaphragm relaxes, external intercostal muscles relax, internal intercostal muscles contract - decreases volume and increases pressure, air flows out
• Spirometer measurements


  • Vital capacity - maximum volume of air inhaled and exhaled
  • Tidal volume - air inhaled and exhaled at rest
  • Residual volume - volume of air always remaining in lungs
  • Breathing rate - number of breaths per minute
  • Ventilation rate - tidal volume x breathing rate
• Gas exchange in fish

  • Less oxygen dissolved in water than in air
  • Ventilation - water flows over gills
  • Gas exchange - across gill filaments and lamellae
  • Concentration gradient maintained by counter-current flow mechanism
• Gas exchange in insects

  • Tracheal system with spiracles, tracheae, and tracheoles
  • Large surface area from many branching tracheoles
  • Short diffusion distance from thin tracheal walls
  • Concentration gradient maintained by respiration and abdominal muscle contraction/relaxation
• Types of circulatory systems

  • Open (invertebrates)
  • Closed (vertebrates and some invertebrates)
• Open circulatory system


  Transport medium (hemolymph) pumped directly into body cavity, few transport vessels, transports food and waste but not gases
• Closed circulatory system


  Transport medium (blood) remains in blood vessels, can exchange gases and small molecules, transports oxygen and carbon dioxide
• Single closed circulatory system

  Blood passes through heart once per cycle, one circuit (e.g. fish)
• Double closed circulatory system

  Blood passes through heart twice per cycle, two separate circuits (e.g. mammals, birds)
• Pigmented protein


  For example, hemoglobin
• Single closed circulatory system

  • Blood passes through the heart once per cycle
  • Only one circuit that the blood takes
• Single closed circulatory system

  • Fish
• Single closed circulatory system

  1. Blood passes through two sets of capillaries immediately after being pumped out of the heart

  2. Blood flows through capillaries in the gills to become oxygenated

  3. Blood flows through capillaries delivering the blood to the body before returning it back to the heart
• Single closed circulatory system would not enable efficient gas exchange for mammals but it does work for fish because they have that counter current flow mechanism
• Double closed circulatory system

  • Blood passes through the heart twice per cycle
  • Two separate circuits the blood would take
• Double closed circulatory system

  • Birds and most mammals
• Double closed circulatory system

  1. One circuit is blood vessels carrying blood from the heart to the lungs for gas exchange

  2. Second circuit is blood vessels carrying the blood from the heart to the rest of the body to deliver oxygen, nutrients and collect waste
• Blood vessels


  • Arteries
  • Arterials
  • Capillaries
  • Venules
  • Veins
• Capillaries


  • Form capillary beds (many branched capillaries connected)
  • Narrow diameter to slow down blood flow and maximise diffusion
  • Made up of only one layer of squamous epithelial cells with small gaps to enable tissue fluid formation
• Hydrostatic pressure


  Pressure exerted by a liquid
• Oncotic pressure


  Tendency of water to move into the blood by osmosis
• Tissue fluid formation


  1. High hydrostatic pressure at arterial end of capillary forces out water and small molecules

  2. Liquid forced out is called tissue fluid
• Tissue fluid reabsorption


  1. Decreased hydrostatic pressure and increased oncotic pressure at venule end of capillary causes net movement of liquid back into capillaries

  2. Remaining tissue fluid absorbed into lymphatic system as lymph
• Mammalian heart


  • Organ made of cardiac muscle
  • Cardiac muscle is myogenic and never fatigues
  • Surrounded by inelastic pericardial membranes
• Left ventricle


  • Thicker muscular wall to contract with more force and pump blood at higher pressure
• Right ventricle


  • Thinner cardiac muscle wall as it doesn't need to contract with as much force
• Atria


  • Cardiac muscle is much thinner as they don't need to contract with much force
• Cardiac cycle


  1. Diastole (Atria and ventricles relaxing)

  2. Atrial systole (Atria contracting)

  3. Ventricular systole (Ventricles contracting)
• Cardiac output


  Volume of blood which leaves one ventricle in one minute, calculated as heart rate x stroke volume
• Control of cardiac cycle

  1. Sinoatrial node releases wave of depolarization across Atria

  2. Atrioventricular node releases wave of depolarization to ventricles

  3. Bundle of His and Purkinje fibres conduct depolarization to ventricle walls
• Electrocardiogram (ECG)


  Measures differences in electrical activity in skin caused by heart's electrical activity
• Abnormal heart rhythms


  • Tachycardia (over 100 bpm)
  • Bradycardia (under 60 bpm)
  • Fibrillation (irregular rhythm)
  • Ectopic heartbeats (additional beats)
• Hemoglobin


  Globular protein responsible for transporting oxygen
• Myoglobin


  Protein found in muscle tissues, made of one polypeptide chain
• Oxyhemoglobin dissociation curve


  Shows percentage saturation of hemoglobin with oxygen at different partial pressures of oxygen
• High partial pressure of oxygen

  Hemoglobin has high affinity and is highly saturated