Exchange systems

• Trachea


  Supported by rings of cartilage which prevents it from collapsing during pressure changes
• Breathing ventilation


  The flow of air in and out of the lungs
• Inspiration


  1. Diaphragm contracts and becomes flat

  2. External intercostal muscles contract

  3. Pulls ribs up and out

  4. Increases volume of the thorax and lungs - elastic walled alveoli stretches
• Expiration


  1. Diaphragm relaxes and becomes dome shaped

  2. External intercostal muscles relax

  3. Pulls ribs down and in

  4. Decreases volume of the thorax and lungs - elastic walled alveoli shrinks by elastic recoil
• Alveoli


  • Many small rounded alveoli - increases surface area
  • Many branching capillaries - increases surface area
  • Single layer of flattened epithelial cells - short diffusion pathway
  • Ventilation and circulation of blood ensures a gradient for O2 and CO2
  • Red blood cells have a larger diameter than capillary so they squeeze through - more time for exchange of gases
• Tidal volume


  The volume of air in each breath
• Ventilation rate


  Number of breaths per minute
• Minute ventilation


  Tidal volume x breathing rate
• Forced expiratory volume (FEV)


  The volume of air that can be expelled in 1 second
• Forced vital capacity (FVC)


  Maximum volume of air that can be breathed out after a deep breath in
• Gills


  • Covered by the operculum
  • Each gill filament has many lamellae which are covered in capillaries and made of a single layer of epithelial cells
  • The fish breathes in water through the mouth, it flows over the gills
• Gas exchange in fish


  1. Deoxygenated blood flows across each gill filament and then across the lamellae through capillaries

  2. O2 diffuses from water into blood at the lamellae

  3. Blood and water flow in opposite directions - the counter current mechanism

  4. Ensures blood continually meets with a higher oxygen concentration so diffusion can occur across the whole length of lamellae

  5. Oxygenated blood flows along gill filaments to body cells

  6. CO2 diffuses from blood to water
• Insect gas exchange


  • Insects are small and have a high SA:V which could cause them to lose lots of water
  • They have a waterproof exoskeleton
  • Hairs around spiracles to reduce evaporation
  • Close spiracles if they lose too much water
• Insect gas exchange


  1. Air diffuses into trachea when spiracles are open

  2. Trachea branches into smaller tubes called tracheoles which are directly connected to muscle tissue / cells (no blood system)

  3. Gas exchange occurs where air tubes meet cells

  4. O2 diffuses down a concentration gradient to respiring cells and CO2 diffuses out

  5. Insects use rhythmic abdominal movements to move air in and out of spiracles
• At rest


  • Water fills ends of tracheoles
  • O2 travels slower in water so decreases at over which O2 can diffuse into muscle cells as there's less contact with muscle cells
  • Less O2 diffuses in
• During high respiration


  • Cells release substances such as lactate which are soluble and lower the water potential in the muscle
  • Water moves from the tracheoles to the muscle cells by osmosis
  • Increases the surface area over which diffusion rate increases
• Plant gas exchange


  • Waxy waterproof cuticle allows very little gas exchange
  • Stomata are pores in the lower epidermis of leaves, surrounded by 2 guard cells
  • Numerous stomata with small diameter increases rate of diffusion
  • Leaves are thin providing a short diffusion pathway
  • Respiration and photosynthesis maintain concentration gradients for CO2 and O2
  • Numerous mesophyll cells provide a high surface area
  • Mesophyll cells have air spaces around them so gases can diffuse faster
  • Diffuse across cell wall and membrane of mesophyll cells
  • Water enters the guard cells to make them turgid which opens the stomata
  • If the plant starts to get dehydrated, the guard cells lose water and become flaccid which closes the pores
• In daylight


  • CO2 diffuses into cells for photosynthesis
  • Respiration also occurs
  • Rate of photosynthesis is greater than rate of respiration
• During night


  • No photosynthesis as no light is available
  • O2 diffuses in for respiration and CO2 diffuses out as a waste product
• Xerophytes


  • Adapted to survive in particularly dry conditions
  • Have a thick cuticle so less water can escape
  • Leaves may roll up so the stomata on the lower epidermis are not exposed to the outside, reducing the water potential gradient and water loss
  • Leaves may have hairs to trap a layer of moist air near the surface of the leaves to reduce the water potential gradient
  • Stomata may be in pits and grooves
  • Leaves have a small surface area to volume ratio
• Digestion


  Large biomolecules are broken down into smaller molecules that can easily be transported around the body
• Protein digestion


  1. Endopeptidases act to hydrolyse peptide bonds inside a protein

  2. Exopeptidases act to hydrolyse peptide bonds at the end of protein molecules, removing single amino acids

  3. Dipeptidases act to separate the 2 amino acids that make up a dipeptide by hydrolysing the peptide bond between them
• Amylase


  Catalyses the conversion of starch into maltose, involving the hydrolysis of glycosidic bonds
• Lipase


  Catalyses the breakdown of lipids into monoglycerides and fatty acids, involving the hydrolysis of ester bonds in lipids
• Bile salts


  Produced in the liver and emulsify lipids, causing lipids to form small droplets which increases the surface area available for lipases to work on
• Absorption of digestion products


  1. Monosaccharides like glucose are absorbed by active transport with Na+ via a co-transport protein

  2. Fructose is absorbed via facilitated diffusion through a carrier protein

  3. Monoglycerides and fatty acids form micelles which release them across the membrane of the intestinal epithelial cells

  4. Amino acids are absorbed via co-transport with Na+, actively transported out of the intestinal epithelial cells into the blood, creating a concentration gradient
• Haemoglobin


  • Consists of 4 polypeptide chains (quaternary structure)
  • Joins to 4 oxygen molecules
  • Contains 4 heme groups, each has an iron
  • Oxygen joins with haemoglobin to form oxyhaemoglobin
  • Found in red blood cells
• Oxyhaemoglobin dissociation curve


  • Shows the percentage saturation of haemoglobin with oxygen at different partial pressures of oxygen (PO2)
  • Haemoglobin has a higher affinity for oxygen at high PO2 (e.g. in alveoli)
  • Haemoglobin has a lower affinity for oxygen at low PO2 (e.g. in respiring tissues)
• Bohr effect


  • The dissociation curve shifts to the right at higher partial pressures of CO2 (PCO2)
  • Oxygen unloading is faster when PCO2 is higher at respiring tissues where oxygen is needed
  • Increasing PCO2 decreases haemoglobin affinity for oxygen by decreasing blood pH
• Circulatory system


  • Closed double circulatory system - blood passes through the heart twice for each complete circulation of the body
  • Pulmonary circulation - deoxygenated blood in right side of heart pumped to lungs, oxygenated blood returns to left side
  • Systemic circulation - oxygenated blood in left side of heart pumped to tissues/organs, deoxygenated blood returns to right side
• Blood vessels


  • Coronary arteries deliver oxygenated blood to cardiac muscle
  • Aorta takes oxygenated blood from heart to respiring tissues
  • Vena cava takes deoxygenated blood from respiring tissues to heart
  • Pulmonary artery takes deoxygenated blood from heart to lungs
  • Pulmonary vein takes oxygenated blood from lungs to heart
  • Renal arteries take deoxygenated blood to kidneys
  • Renal veins take deoxygenated blood from kidneys to vena cava
• Heart structure


  • Atrioventricular valves prevent backflow of blood from ventricles to atria
  • Semilunar valves prevent backflow of blood from arteries to ventricles
  • Left ventricle has a thicker muscular wall to generate higher blood pressure for oxygenated blood to travel around the body
  • Right ventricle has a thinner muscular wall to generate lower blood pressure for deoxygenated blood to travel to the lungs
• Arteries


  • Carry blood from heart to rest of body at high pressure
  • Have a thick smooth muscle layer to contract and push blood along, controlling blood flow and pressure
  • Have an elastic tissue layer to stretch
• Pulmonary artery


  Takes deoxygenated blood from the heart
• Pulmonary vein


  Takes oxygenated blood from the lungs to the heart
• Renal artery


  Takes deoxygenated blood to the kidneys
• Renal vein


  Takes deoxygenated blood from the kidneys to the vena cava
• Atrioventricular valves


  • Prevent backflow of blood from ventricles to atria
• Semilunar valves


  • Prevent backflow of blood from arteries to ventricles
• Left ventricle has a thicker muscular wall


  Generates higher blood pressure for oxygenated blood to travel greater distance around the body