Organisms exchange substances with their environment

• What is metabolic rate?


  amount of energy uses up by an organism within a given period of time
• Describe the tracheal system of an insect

  • spiracles = pores on surface that can open to allow diffusion
  • tracheae = large tubes full of air that allow diffusion
  • tracheoles = smaller branches from tracheae, permeable to allow gas exchange with cells
• How is a tracheal system of an insect adapted for gas exchange?

  1. Tracheoles have thin walls so short diffusion pathway
  2. high numbers of highly branched tracheoles so short diffusion distance to cells and large SA
  3. tracheae provide tubes of air so fast diffusion
  4. contraction of abdominal muscles change pressure in body causing air to move in and out maintains conc gradient
  5. fluid in end of tracheoles drawn into tissues by osmosis during exercise - diffusion is faster through air to gas exchange system
• Terrestrial insect adaptations to limit water loss

  Thick waxy cuticle increases diffusion distance so less water loss

  spiracles can open and close to allow gas exchange but reduce water loss

  hairs around spiracles trap moist air reducing water gradient so less water loss
• How are fish hills adapted for gas exchange?

  • Made of many filaments covered with lamellae to increase SA for diffusion
  • Thin lamellae wall so short diffusion distance between water and blood
  • Lamellae have large number of capillaries to removes O2 and bring CO2 quickly so maintains conc gradient
• Counter current system 


  1. blood and water flow in opposite directions through/over lamellae
  2. so oxygen conc gradient always higher in water than blood
  3. so maintains a concentration gradient of O2 between water and blood
  4. for diffusion along whole length of lamellae
• How are the leaves of dicotyledonous plants adapted for gas exchange?

  • Many stomata large SA for gas exchange
  • spongy mesophyll contains air spaces which allows large SA for gases to diffuse through
  • Thin so short diffusion distance
• Structural and functional adaptations in xerophytic plants that allow gas exchange while limiting water loss


  • Thicker waxy cuticle increases diff distance so less evaporation
  • sunken stomata in pits/rolled leaves/hairs which trap water vapour and protect stomata from wind. Therefore reduces conc gradient so less evaporation
  • spines/needles which reduce SA to Vol ratio
• What’s the gross structure of the human gas exchange system?


  Trachea, Bronchi, Bronchioles, Lungs, Alcello, capillary network surrounding alveoli
• What are the alveolar epithelium adaptations which make it efficient for gas exchange

  • flattened cells/1 cell thick for short diffusion pathway
  • folded so large surface area
  • permeable so allows diffusion of O2 / CO2
  • moist - gases can dissolve for diffusion
  • good blood supply from large network of capillaries so maintains conc gradient
• How does had exchange occur in the lungs?

  O2 diffuses from alveolar air space into blood down its conc gradient across alveolar epithelium then across capillary endothelium
• What’s the importance of ventilation?

  Brings air containing higher conc of oxygen and removes air with lower conc of oxygen maintaining conc gradients
• Whats the process of inspiration?

  1. Diaphragm muscles contract and flattens
  2. external intercostal muscles contract and internal intercostal muscles relax so the ribcage is pulled up and out
  3. increasing volume and decreasing pressure in thoracic cavity
  4. air moves into lungs down pressure gradient
• What’s the process of expiration?

  1. diaphragm relaxes and moves upwards
  2. external intercostal muscles relax and internal intercostal muscles contract and ribcage moves down and in
  3. decreasing vol and increasing pressure in thoracic cavity
  4. air moves out of lungs down pressure gradient
• Why is expiration normally passive at rest?

  internal intercostal muscle do not normally need to contract as expiration is aided by elastic recoil in alveoli
• How do different lung diseases reduce rate of gas exchange?

  • thickened alveolar tissue (fibrosis) increases diffusion distance
  • alveolar wall breakdown reduces surface area
  • reduce lung elasticity so lungs expand and recoil less which reduces conc gradient of O2 and CO2
• How do different ling diseases affect ventilation?

  • reduces lung elasticity so lungs expand and recoil less reducing volume of air in each breath (tidal vol) and reducing maximum vol of air breathed out in one breath (forced vital capacity)
  • narrow airways reduce airflow in and out of lungs (asthma) reducing maximum vol of air breathed in 1 sec (forced expiratory vol)
  • reduced rate of gas exchange increasing ventilation rate to compensate for reduced oxygen in blood
• Why do people with lung disease experience fatigue?

  Cells receive less oxygen -> rate of aerobic respiration reduced so less ATP made
• What’s the difference between correlations and causations?

  correlation = change in one variable reflected by a change in another - identified on a scatter graph

  Causation = change in one variable causes a change in another variable
• What happens during digestions?

  Large biological molecules hydrolysed to smaller molecules that are small enough to be absorbed across cell membranes into blood
• Describe the digestion of starch in mammals

  • Amylase hydrolyses starch to maltose
  • membrane bound Maltese hydrolyses maltose to glucose
  • hydrolysis of glycosidic bond
• Describe the digestion of disaccharides in mammals

  • membrane bound disaccharidases hydrolyse disaccharides into 2 monosaccharides

  e.g maltase - maltose to glucose and glucose

  sucrase - sucrose to glucose and fructose

  lactase - lactose to glucose and galactose

  • hydrolysis of glycosidic bond
• Describe the digestion of lipids in mammals

  • bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets
  • this increases SA for lipids for increases lipase activity
  • lipase (made in pancreas) hydrolyses lipids to monoglycerides and fatty acids by hyrdolysing ester bond

  
• Describe the digestion of proteins by a mammal

  Endopeptidases hydrolyse internal peptide bonds within polypeptide to make smaller peptides so more SA for exopeptidases

  Exopeptidases hydrolyse terminal peptide bonds at ends of polypeptide into single amino acids

  membrane bound dipeptidases hydrolyse peptide bonds between a dipeptide into 2 amino acids
• Why are membrane bound enzymes important in digestion

  Located on cell membranes of epithelial cells lining ileum and maintain conc gradients for absorption
• Absorption of amino acids and monosaccharides

  
• Describe the absorption of lipids by a mammal including micelles

  • micelles contain bile salts, monoglycerides and fatty acids and make monoglycerides and fatty acids more soluble in water
  • monoglycerides/fatty acids absorbed by diffusion
  • Triglycerides reformed in epithelial cells and aggregate into globules
  • globules coated with proteins forming chulomicrons which are then packaged into vesicles
  • vesicles move to cell membrane and leave via exocytosis

  enter lymphatic vessels and eventually return to blood circulation
• What red blood cells and haemoglobin role in oxygen transport

  • red blood cells contain lots of haemoglobin-no nucleus, Biconcave, high SA:V, short diffusion path
  • Hb associates with O2 where partial pressure of O2 is high
  • this forms oxyhaemoglobin which transports O2
  • Hb dissociates from O2 near cells where pO2 is low
• Structure of haemoglobin


  • protein with a quaternary structure
  • made of 4 polypeptide chains
  • each chain contains a haem group containing iron ion
• O2 in comparison to oxyhaemobglobin

  
• What is the Bohr effect?

  effect of CO2 conc on dissociation of oxyhaemoglobin

  
• Advantage of Bohr effect:

  more dissociation of oxygen so faster aerobic respiration so more ATP produced
• Why do different haemoglobin have different oxygen transport properties?

  • Different Types of Hb are made of polypeptide chains with slightly different amino acid sequence resulting in different tertiary shape so different affinities for oxygen
• How organisms can b adapted to their environment

  
• What’s the general pattern of blood circulation in a mammal?

  closed double circulatory system
• Deoxygenated blood in right side of heart pumped into lungs, oxygenated returns to left side

  Oxygenated blood in left side of the heart pumped to rest of body, deoxygenated returns to right
• What’s 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 higher pressures so substances taken and removed from body cells quicker more efficiently
• Pattern of blood circulation

  
• Blood vessels entering and leaving heart:

  Vena cava: deoxygenated blood from tissues to heart

  pulmonary artery: deoxygenated blood from heart to lungs

  pulmonary vein: oxygenated blood from lungs to heart

  aorta: oxygenated blood from heart to respiring body tissues
• Which blood vessels are connected to kidneys?


  renal arteries: oxygenated blood to kidneys

  renal veins: deoxygenated blood to vena cava from kidneys