Topic 3

• Surface area to volume ratio: The surface area of an organism divided by its volume the larger the organism, the smaller the ratio
• Factors affecting gas exchange:

  • diffusion distance
  • surface area
  • concentration gradient
  • temperature
• Ventilation:

  • Inhaling and exhaling in humans
  • controlled by diaphragm and antagonistic interaction of internal and external intercostal muscles
• Inspiration:

  • External intercostal muscles contract and internal relax
  • pushing ribs up and out
  • diaphragm contracts and flattens
  • air pressure in lungs drops below atmospheric pressure as lung volume increases
  • air moves in down pressure gradient
• Expiration:

  • External intercostal muscles relax and internal contract
  • pulling ribs down and in
  • diaphragm relaxes and domes
  • air pressure in lungs increases above atmospheric pressure as lung volume decreases
  • air forced out down pressure gradient
• Passage of gas exchange:

  • Mouth / nose -> trachea -> bronchi -> bronchioles -> alveoli
  • crosses alveolar epithelium into capillary endothelium

  
• Why large organisms need specialised exchange surface?

  • They have a small surface area to volume ratio
  • higher metabolic rate - demands efficient gas exchange
  • specialised organs e.g. lungs / gills designed for exchange
• Fish gill anatomy:

  • Fish gills are stacks of gill filaments
  • each filament is covered with gill lamellae at right angles

  
• How fish gas exchange surface provides large surface area?

  • Many gill filaments covered in many gill lamellae are positioned at right angles
  • creates a large surface area for efficient diffusion
• How tracheal system provides large surface area:

  • Highly branched tracheoles
  • large number of tracheoles
  • filled in ends of tracheoles moves into tissues during exercise so larger surface area for gas exchange
• Fluid-filled tracheole ends:

  • Adaptation to increase movement of gases
  • when insect flies and muscles respire anaerobically - lactate produced
  • water potential of cells lowered, so water moves from tracholes to cells by osmosis
  • gases diffuse faster in air
• How do insects limit water loss:

  • Small surface area to volume ratio
  • waterproof exoskeleton
  • spiracles can open and close to reduce water loss
  • thick waxy cuticle - increases diffusion distance so less evaporation
• Dicotyledonous plants leaf tissues:

  • Key structures involved are mesophyll layers
  • (palisade and spongy mesophyll)
  • stomata created by guard cells

  
• Gas exchange in plants:

  • Palisade mesophyll is site of photosynthesis
  • oxygen produced and carbon dioxide used creates a concentration gradient
  • oxygen diffuses through air space in spongy mesophyll and diffuse out stomata
• Role of guard cells:

  • swell - open stomata
  • shrink - closed stomata
  • at night they shrink, reducing water loss by evaporation

  
• Xerophytic plants:

  • Plants adapted to survive in dry environments with limited water (e.g. marram grass/cacti)
  • structural features for efficient gas exchange but limiting water loss
• Adaptations of xerophyte:

  • Adaptations to trap moisture to increase humidity -> lowers water potential inside plant so less water lost via osmosis:
  • sunken stomata
  • curled leaves
  • hairs
  • thick cuticle reduces loss by evaporation
  • longer root network
• Locations of carbohydrate digestion: Mouth -> duodenum -> ileum
• Locations of protein digestion: Stomach -> duodenum -> ileum
• Endopeptidases:

  • Break peptide bonds between amino acids in the middle of the chain
  • creates more ends for exopeptidases for efficient hydrolysis

  
• Exopeptidases: Break peptide bonds between amino acids at the ends of polymer chain
• Membrane-bound dipeptidases: Break peptide bond between two amino acids
• Digestion of lipids:

  • Digestion by lipase (chemical)
  • emulsified by bile salts (physical)
  • lipase produced in pancreas
  • bile salts produced in liver and stored in gall bladder
• Role of bile salts:

  • Emulsify lipids to form tiny droplets and micelles
  • increases surface area for lipase action - faster hydrolysis
• Micelles: Water soluble vesicles formed from fatty acids, glycerol, monoglycerides and bile salts
• Lipid absorption:

  • Micelles deliver fatty acids, glycerol and monoglycerides to epithelial cells of ileum for absorption
  • cross via simple diffusion as lipid-soluble and non-polar
• Lipid modification:

  • Smooth ER reforms monoglycerides / fatty acids into tryglycerides
  • golgi apparatus combines tryglycerides with proteins to form vesicles called chylomicrons
• How lipids enter blood after modification:

  • Chylomicrons move out of cell via exocytosis and enter lacteal
  • lymphatic vessels carry chylomicrons and deposit them in bloodstream
• Glucose and amino acids are absorbed via co-transport in the ileum

  
• Haemoglobin(Hb):

  • Quaternary structure protein
  • 2 alpha chains
  • 2 beta chains
  • 4 associated haem groups in each chain containing Fe2+
  • transports oxygen
• Affinity of haemoglobin: The ability of haemoglobin to attract / bind to oxygen
• Saturation of haemoglobin: When haemoglobin is holding the maximum amount of oxygen it can hold
• Loading / unloading of haemoglobin:

  • Binding/detachment of oxygen to haemoglobin
  • also known as association and disassociation
• Oxyhaemoglobin dissociation curve:

  • oxygen is loaded in regions with high partial pressures (alveoli)
  • unloaded in regions of low partial pressure (respiring tissue)

  
• Oxyhaemoglobin dissociation curve shifting left:

  • Hb would have a higher affinity for oxygen
  • load more at the same partial pressure
  • becomes more saturated adaptation in low-oxygen environments
  • e.g. llamas/ in foetuses
• Bohr effect:

  • High carbon dioxide partial pressure
  • causes oxyhaemoglobin curve to shift to the right
• Oxyhaemoglobin dissociation curve shifting right:

  • Hb has lower affinity for oxygen
  • unloads more at the same partial pressures
  • less saturated
  • present in animals with faster metabolisms that need more oxygen for respiration e.g. birds/rodents
• Closed circulatory system: Blood remains within blood vessels
• Name different types of blood vessels: Arteries, arterioles, capillaries, venules and veins
• Capillary endothelium:

  • Extremely thin
  • one cell thick
  • contains small gaps for small molecules to pass through (e.g. glucose, oxygen)