topic 3

• Exchange surface


  Specialised surface that arises as the size of the organism, and its surface area to volume ratio increases
• Features of an efficient exchange surface

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


  1. Fish opens mouth

  2. Lowers floor of buccal cavity to enable water flow in

  3. Closes mouth, raising buccal cavity floor to increase pressure

  4. Water forced over gill filaments by pressure difference between mouth and opercular cavities

  5. Operculum acts as valve and pump to let water out and pump it in
• Spiracles


  Small openings of tubes (trachea or tracheoles) that supply insects with gases
• Gas exchange in plants

  • Leaves have many small holes called stomata to allow gases to enter and exit
  • Air spaces in leaves allow gases to move around and come into contact with photosynthesising cells
• Mammalian gaseous exchange system

  • Lungs are lobed structures with large surface area in chest cavity
  • Rib cage protects lungs and lubricating substance prevents friction during inflation/deflation
  • Intercostal muscles and diaphragm control ventilation

  
• Inspiration


  1. External intercostal muscles contract, internal relax, ribs raise

  2. Diaphragm contracts and flattens

  3. Volume in thorax increases, pressure decreases, air forced into lungs
• Expiration


  1. Internal intercostal muscles contract, external relax, ribs lower

  2. Diaphragm relaxes and raises

  3. Volume in thorax decreases, pressure increases, air forced out of lungs
• Spirometer


  Device used to measure lung volumes and breathing rate

  
• Lung volumes


  • Vital capacity
  • Tidal volume
  • Residual volume
  • Inspiratory reserve volume
  • Expiratory reserve volume
• Digestion


  Hydrolysis of large biological molecules into smaller molecules that can be absorbed
• Digestive enzymes


  • Amylases
  • Maltases
  • Sucrases
  • Lactases
  • Lipases
  • Endopeptidases
  • Exopeptidases
  • Dipeptidases
• Emulsification


  Process that increases the surface area of lipids and speeds up their digestion by lipases
• Absorption of digested products

  1. Amino acids absorbed by facilitated diffusion through carrier molecules, co-transported with Na+

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


  Water soluble globular protein with haem groups that can bind and transport oxygen

  
• Partial pressure of oxygen

  Affects the affinity of haemoglobin for oxygen - higher partial pressure increases affinity, lower partial pressure decreases affinity

  
• Dissociation curves illustrate the changes in haemoglobin-oxygen affinity

  
• 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


  After binding the first oxygen molecule, it becomes easier for the other oxygen molecules to bind
• Fetal haemoglobin


  Has a higher affinity for oxygen compared to adult haemoglobin

  
• Presence of carbon dioxide

  Decreases the affinity of haemoglobin for oxygen

  
• Bohr effect


  Carbon dioxide creates slightly 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

  The heart has two pumps - one pumps blood to the lungs to be oxygenated, 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
• Cardiac cycle


  1. Cardiac diastole (atria and ventricles relax)

  2. Atrial systole (atria contract)

  3. Ventricular systole (ventricles contract)