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• Exchange surfaces


  • Large surface area
  • Thin to ensure short distance for substances to cross
  • Good blood supply/ventilation to maintain steep gradient
• Ventilation in fish


  1. Fish opens mouth

  2. Lowers floor of buccal cavity

  3. Closes mouth, raising buccal cavity floor

  4. Operculum acts as valve and pump to let water out and pump it in
• Insect gas exchange


  • No transport system, oxygen transported directly to tissues via spiracles and tracheal system
  • Gases move by diffusion, mass transport from muscle contraction, and volume changes in tracheoles
• Plant gas exchange


  • Leaves have stomata to allow gases to enter and exit
  • Air spaces in leaves allow gases to move and contact photosynthesising cells
• Mammalian gaseous exchange system

  • Lungs are lobed structures with large surface area in chest cavity that can inflate
  • Rib cage protects lungs and has muscles to raise and lower it
  • Diaphragm separates lungs from abdomen

  
• Airflow into and out of lungs

  1. Air enters through nose, trachea, bronchi, bronchioles

  2. Gaseous exchange occurs in alveoli walls
• Trachea, bronchi, bronchioles


  • Held open by cartilage rings
  • Lined with ciliated epithelium and goblet cells
  • Bronchioles have smooth muscle and elastic fibres
• Alveoli


  • Very thin, only one cell thick
  • Surrounded by capillaries also one cell thick
  • Large number (300 million) giving 70m2 surface area
• Structures and functions of mammalian gaseous exchange system

  • Cartilage - supports trachea and bronchi, prevents lung collapse
  • Ciliated epithelium - moves mucus to prevent infection
  • Goblet cells - secrete mucus to trap bacteria and dust
  • Smooth muscle - controls airway diameter
  • Elastic fibres - control air flow
• Ventilation - inspiration


  1. External intercostal muscles contract, diaphragm contracts

  2. Increases thoracic volume, lowers pressure, air forced in
• Ventilation - expiration


  1. Internal intercostal muscles contract, diaphragm relaxes

  2. Decreases thoracic volume, increases pressure, air forced out
• Spirometer


  Device to measure lung volumes and breathing rate

  
• Lung volumes


  • Vital capacity - max air inhaled/exhaled
  • Tidal volume - air breathed in/out at rest
  • Residual volume - air always present in lungs
  • Inspiratory/expiratory reserve volumes - additional air that can be inhaled/exhaled

  
• Digestion


  Hydrolysis of large molecules into smaller absorbable ones
• Digestion of macromolecules


  • Carbohydrates - amylases, maltases, sucrases, lactases
  • Lipids - lipases, emulsified by bile salts
  • Proteins - endopeptidases, exopeptidases, dipeptidases
• Absorption


  1. Amino acids - facilitated diffusion with Na+ co-transport

  2. Monoglycerides and fatty acids - diffuse into epithelial cells, reformed into triglycerides, transported in lymph
• Haemoglobin


  • Globular protein with haem groups that can bind 4 oxygen molecules
  • Affinity for oxygen varies with partial pressure - high in lungs (loading), low in respiring tissues (unloading)

  
• Dissociation curves


  Illustrate the changing affinity of haemoglobin for oxygen

  
• Haemoglobin


  Globular protein which consists of two beta polypeptide chains and two alpha helices. Each molecule forms a complex containing a haem group.
• Haemoglobin


  • Carries oxygen in the blood as oxygen can bind to the haem (Fe2+) group
  • Each molecule can carry four oxygen molecules
• Partial pressure of oxygen

  Affects the affinity of oxygen for haemoglobin

  
• Partial pressure of oxygen increases

  Affinity of haemoglobin for oxygen increases

  
• Loading


  Oxygen binds to haemoglobin in the lungs
• Unloading


  Oxygen is released from haemoglobin in respiring tissues
• Dissociation curves


  Illustrate the change in haemoglobin saturation as partial pressure changes

  
• Haemoglobin saturation


  Affected by its affinity for oxygen

  
• Partial pressure is high

  Haemoglobin has high affinity for oxygen and is highly saturated

  
• Partial pressure is low


  Haemoglobin has low affinity for oxygen and is less saturated

  
• Binding of first oxygen molecule

  Increases affinity of haemoglobin for oxygen
• Positive cooperativity


  Binding of first oxygen molecule changes shape, making it easier for other oxygen molecules to bind
• Fetal haemoglobin


  Has higher affinity for oxygen than adult haemoglobin
• Presence of carbon dioxide

  Decreases the affinity of haemoglobin for oxygen
• Bohr effect


  Carbon dioxide creates acidic conditions which change the shape of haemoglobin, making it easier for oxygen to be released
• In large organisms, diffusion alone is not enough to supply substances like oxygen, glucose and other molecules to cells
• Common features of a circulatory system

  • Suitable medium (blood)
  • Means of moving the medium (heart)
  • Mechanism to control flow (valves)
  • Close system of vessels

  
• Closed double circulatory system

  Heart has two pumps - one pumps blood to the lungs, the other pumps oxygenated blood around the body
• Heart


  • Made up of two pumps, each with two chambers (atrium and ventricle)
  • Atrium is thin-walled and elastic, ventricle has thick muscular wall
• Atrioventricular valves


  Left (bicuspid) and right (tricuspid) valves between atria and ventricles
• Main blood vessels connected to the heart

  • Aorta
  • Pulmonary artery
  • Pulmonary vein
  • Vena cava

  
• Sinoatrial node


  Region of specialised fibres in the right atrium that acts as the pacemaker of the heart