Exchange Summary

• Describe the relationship between the size and structure of an organism and its SA: V

  As size increases, SA: V tends to decrease

  More thin/ flat/ elongated structures increase SA: V
• How is SA:V calculated?

  Divide surface area (size length x side width x number of sides) by volume (length x width x depth)

  
• Suggest an advantage of calculating SA: mass for organisms instead of SA:V

  Easier/ quicker to find/ more accurate because irregular shapes
• What is metabolic rate? Suggest how it can be measured

  amount of energy used up by an organism within a given period of time

  Often measured by oxygen uptake - as used in aerobic respiration to make ATP for energy release
• Explain the relationship between SA:V and metabolic Rate

  As SA : V increases (smaller organisms), metabolic rate increases because

  Rate of heat loss per unit body mass increases

  So organisms need a higher rate of respiration

  To release enough heat to maintain a constant body temperature (replace lost heat)
• Explain the adaptation that facilitate exchange as SA:V reduces in larger organisms

  Changes to body shape (long/ thin)

  • Increases SA:V and overcomes (reduces) long diffusion distance / pathway

  Development of systems, such as a specialised surface / organ for gaseous exchange (lung)

  • Increases (internal) SA:V and overcomes (reduces) long diffusion distance / pathway
  • Maintain a concentration gradient for diffusion (by ventilation/ good blood supply
• Explain how the body surface of a single- celled organism is adapted for gas exchange

  Thin, flat shape and large surface area to volume ratio

  Short diffusion distance to all parts of cell - rapid diffusion (O2 / CO2)
• Describe the tracheal system of an insect

  Spiracles= Pores on surface that can open / close to allow diffusion

  Trachea= large tubes full of air that allow diffusion

  Tracheoles = smaller branches from tracheae, permeable to allow gas exchange with cells
• Explain how an insect's tracheal system is adapted for gas exchange

  Tracheoles have thin walls

  • so short diffusion distance to cells

  High numbers of highly branched tracheoles

  • creates a large SA so short diffusion distance to cells

  Trachae provide tubes full of air for fast diffusion

  Contraction of abdominal muscles (abdominal pumping)

  • changes pressure in body, causing air to move in/ out
  • maintains concentration gradient for diffusion

  Fluid in end of tracheoles drawn into tissues by osmosis during exercise (lactate produced in anaerobic respiration lowers wp of cells)

  • As fluid is removed, air fills tracheoles

  So rate of diffusion to gas exchange surface increases as diffusion is faster through air
• Explain structural and functional compromises in terrestrial insects that allow efficient gas exchange while limiting water loss

  Thick waxy cuticle/ exoskeleton - increases diffusion distance so less water loss

  Spiracles can open to allow gas exchange AND close to reduce water loss

  Hairs around spiracles - trap moist air, reducing WP gradient so less water loss
• Explain how the gills of fish are adapted for gas exchange

  Gills made of many filaments covered with many lamellae

  Increase surface area for diffusion

  Thin lamellae wall/ epithelium

  So short diffusion distance between water/ blood

  Lamellae have a large number of capillaries

  Remove O2 and bring CO2 quickly so maintains concentration gradient
• Describe counter current flow in the gills of fish

  1. Blood and water flow in opposite directions through/ over lamellae
  2. So oxygen concentration always higher in water (than blood near)
  3. So maintains a concentration gradient of O2 between water and blood
  4. For diffusion along whole length of lamellae
• Why can the flow of gases in fish not be parallel?

  If parallel flow, equilibrium would be reached so oxygen wouldn't diffuse into blood along the whole gill plate
• Explain how the leaves of plants are adapted for gas exchange

  Many stomata (high density) - Large surface area for gas exchange (when opened by guard cells)

  Spongy Mesophyll contains air spaces - Large SA for gases to diffuse through

  Thin - short diffusion distances
• Sate the structure of a leaf

  Waxy cuticle

  Upper epidermis

  Palisade Mesophyll

  Spongy Mesophyll

  Lower Epidermis

  Stoma

  Guard Cells

  
• Explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss

  Thicker waxy cuticle

  • Increases diffusion distance so less evaporation

  Sunken stomata in pits / rolled leaves / hairs

  • 'Trap' water vapour / protect stomata from wind
  • So reduced water potential gradient between leaf/ air
  • So less evaporation

  Spines/ needles

  • Reduces surface area to volume ratio
• Explain the essential features of the alveolar epithelium that make it adapted as a surface for surface for gas exchange

  1 cell thick- short diffusion distance

  Folded- large surface area

  Permeable - allows diffusion of O2 / CO2

  Moist - Gases can dissolve for diffusion

  Good blood supply from large network of capillaries - maintains concentration gradient
• Describe how gas exchange occurs in the lungs

  Oxygen diffuses from alveolar air space into blood down its concentration gradient

  Across alveolar epithelium then across capillary endothelium
• Explain the importance of ventilation

  Brings in air containing higher conc of oxygen and removes air with lower conc of oxygen

  Maintaining concentration gradients
• Describe Inspiration (breathing in)

  1. Diaphragm contracts and flattens
  2. External Intercostal muscles contract pulling ribs upwards and outwards while internal intercostal muscles relax
  3. Increasing volume and decreasing pressure in thoracic cavity
  4. Air moves into lungs down pressure gradient
• Describe Expiration (breathing out)

  1. Diaphragm relaxes and curves
  2. Internal Intercostal muscles relax and ribs are pulled downwards and inwards while external intercostal muscles relax
  3. Decreasing volume and increasing pressure (above atmospheric) in thoracic cavity
  4. Air moves out of lungs down pressure gradient
• Suggest why expiration is normally passive at rest

  Internal intercostal muscles do not normally need to contract

  Expiration aided by elastic recoil in alveoli
• Suggest how different lung diseases reduce the rate of gas exchange

  Thickened alveolar tissue (fibrosis) - increases diffusion distance

  Alveolar wall breakdown - reduces surface area

  Reduce lung elasticity - Lungs expand / recoil less - reduces concentration gradient of O2 / CO2
• Describe the role of red blood cells and haemoglobin (Hb) in oxygen

  Red Blood Cells contain lots of Hb

  • No nucleus and biconcave - more space for Hb, High SA:V and short diffusion distance

  Hb associates with oxygen at gas exchange surfaces (lungs) where partial pressure of oxygen (pO2) is high

  This forms oxyhaemoglobin which transports oxygen

  • Each can carry 4 oxygen molecules, one at each Haem group

  Hb dissociates from oxygen near cells where pO2 is low
• Describe the Structure of Haemoglobin

  Protein with a quaternary structure

  Made of 4 polypeptide chains

  Each chain contains a Haem group containing an iron ion (Fe2+)
• Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve

  Areas with low pO2 - respiring tissues

  • Hb has a low affinity for oxygen
  • So oxygen readily unloads with Hb
  • So % saturation is low

  Areas with high pO2 - gas exchange surfaces

  • Hb has high affinity for oxygen
  • So oxygen readily loads with Hb
  • So % saturation is high

  
• Explain how the cooperative nature of oxygen binding results in an S - shaped oxyhaemoglobin dissociation curve

  1. Binding of first oxygen changes tertiary/ quaternary structure of haemoglobin
  2. This uncovers Haem group binding sites, making further binding of oxygens easier
• Describe evidence for the cooperative nature of oxygen binding

  A low pO2 as oxygen increases there is a slow increase in % saturation of Hb with oxygen - when first oxygen is binding

  At higher pO2 as oxygen increases there is a rapid increase in % saturation of Hb with oxygen - showing it has got easier for oxygens to bind
• What is the Bohr effect?

  Effect of CO2 concentration on dissociation of oxyhaemoglobin - curve shifts to right
• Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin


  1. Increasing blood CO2 due to increased rate of respiration
  2. Lowers blood pH (more acidic)
  3. Reducing Hb's affinity for oxygen as quaternary structure changes slightly
  4. So faster unloading of oxygen to respiring cells at a given pO2

  
• Describe evidence for the Bohr effect

  At a given pO2 % saturation of Hb with oxygen is lower
• Explain the advantage of the Bohr effect

  More dissociation of oxygen - faster aerobic respiration - more ATP produced
• Explain why different types of haemoglobin can have different oxygen transport properties

  Different types of Hb are made of polypeptide chains with slightly different amino acid sequences

  Resulting in different quaternary structures

  So they have different affinities for oxygen
• Explain how organisms can be adapted to their environment by having Hb with a higher affinity for O2

  More O2 associates with Hb more readily

  At gas exchange surfaces where pO2 is lower

  Organisms in low O2 environments - high altitudes, underground or foetuses
• Explain how organisms can be adapted to their environment by having Hb with a lower affinity for O2

  Curve shift right

  More O2 dissociates from Hb more readily

  At respiring tissues where more O2 is needed

  Organisms with high rates of respiration / Metabolic rate (may be small or active)
• Describe the Hb curve

  Curve shifts to left - Hb has higher affinity for O2

  Curves shifts to right- Hb has lower affinity for O2

  
• Describe the general pattern of blood circulation in a mammal

  1. Deoxygenated blood in right side of heart pumped to lungs, oxygenated returns to left side
  2. Oxygenated blood in left side of heart pumped to rest of body, deoxygenated returns to right
• Suggest the importance of a double circulatory system

  Prevents mixing of oxygenated/ deoxygenated blood

  So blood pumped to body is fully saturated with oxygen for aerobic respiration

  Blood can be pumped to body at a higher pressure (after being lower from lungs)

  Substances taken to/ removed from body cells quicker / more efficiently
• Draw a diagram to show the general pattern of blood circulation in a mammal, including the names of key blood vessels

  1

  
• Name the blood vessels entering and leaving the heart and lungs

  Vena Cava- transports deoxygenated blood from respiring body tissues to the heart

  Pulmonary Artery - transports deoxygenated blood from the heart to lungs

  Pulmonary vein - transports oxygenated blood from lungs to the heart

  Aorta - transports oxygenated blood from heart to respiring body tissues