Gas Exchange

• What is the function of a respiratory system?

  Provides a gas exchange surface between the air and the blood.
• How is oxygen carried in the blood?

  Bound to haemoglobin in red blood cells.
• How is carbon dioxide carried in the blood?

  In the plasma (mainly)
• How do oxygen and carbon dioxide move from the air to the blood/the blood to respiring cells?

  Diffusion
• Which is the organelle where aerobic respiration takes place?

  Mitochondria
• What is the word and symbol equation of aerobic respiration?

  glucose + oxygen -> water + carbon dioxide + ATP

  C6H12O6 + 6 O2 -> 6 H2O + 6 CO2 + ATP
• Why do mammals require a specialised respiratory system?

  A large volume of oxygen is needed for a large number of cells to maintain the high levels of aerobic respiration. This high rate of respiration is required to provide the energy needed for high metabolic rates (chemical reactions such as protein synthesis), movement, active transport, cell division, and to maintain a constant body temperature (birds also must do this).
• As the site of an organism increases, does surface area to volume ratio (SA:V) increase or decrease?

  Decrease
• What problems occur as a result of the level of SA:V ratio in larger organisms?

  A low SA:V ratio means there is a lower rate of gas exchange without a gas exchange surface. Therefore the organism will have a lower metabolic rate, meaning it will likely not have enough energy.
• What problems occur as a result of the level of SA:V ratio in smaller organisms?

  A high SA:V ratio means that there is a high rate of gas exchange. Therefore the organism will have a high metabolic rate, meaning in order to maintain this, the organism will have to eat a lot.
• Why is there a maximum size that a cell can be?

  Distance into the cell for diffusion cannot be too large and SA:V ratio cannot be too low, otherwise gas exchange/exchange in general will not be sufficient.
• Why is there a minimum size that a mammal can be?

  Mammals need to maintain an internal body temperature, so they must be large enough so that they do not struggle to eat enough to do this.
• Describe a graph of how surface area changes as volume increases.

  As volume increases, surface area increases.

  The graph is linear.
• What do organisms need to exchange with their environment?

  Materials, nutrients, excretory products and heat
• What determines the rate at which exchange can take place?

  Size and shape
• As well as surface area to volume ratio, what other factor affects rate of exchange when considering larger/smaller organisms?

  Diffusion pathway - the distance to cover once inside the organism
• In hotter climates, are warm blooded animals typically larger or smaller than those in colder climates?

  Smaller - larger SA:V ratio so heat loss is greater
• What shape will greatly decrease the diffusion pathway?

  Flat and thin
• When does SA:V ratio/diffusion pathway not have as much effect on an organism?

  If it is relatively inactive (e.g. a sea anemone)
• What is Fick's Law?

  Rate of diffusion is proportional to:

  $\frac{surface\ area\times difference\ in\ concentration}{length\ of\ diffusion\ pathway}$
• What is a specialised gas exchange surface?

  A specific structure that is adapted for the exchange of materials with the environment (e.g. alveoli in the lungs)
• What three factors increase rate of diffusion?

  . large surface area

  . short diffusion pathway

  . steep concentration gradient
• Why is a specialised gas exchange surface often an internal structure?

  So that it is not easily damaged and to prevent large amounts of water loss.
• What is the gas exchange surface of a fish?

  Gills
• How does gas exchange occur in a fish?

  Water enters the mouth and moves to the gills within the opercular cavity before leaving via the opercular valve at the inside of the fish's head.

  This is a continuous ventilation system.
• What role does a ventilation mechanism play in gas exchange?

  Maintain a steeper concentration gradient at the gas exchange surface for a faster rate of diffusion.
• Why does a fish require a continuous ventilation system as opposed to a tidal ventilation system?

  Water has a low dissolved oxygen concentration - continuous flow allows for more efficient gas exchange. Water is also more dense than air, so cannot be moved as easily.
• How many gills are on each side of a fish's head?

  4
• What is the structure of a gill?

  Down the centre is a gill bony arch, with gill rakers on one side to catch particles in the water and feather-like gill filaments on the other side. There are two sets of gill filaments attached the arch at right angles to each other. This is so water can flow over both sets at the same time, maximising gas exchange.
• What are gill filaments?

  Feather-like structures on the gills of a fish which increase the surface area for a higher rate of diffusion.
• What are lamellae?

  Additional structures on gill filaments that increase surface area further. They have walls one cell thick for a short diffusion pathway and capillary beds within them which provides good blood flow to maintain a steep concentration gradient.
• How are capillaries adapted for gas exchange?

  Their walls are one cell thick made of endothelial cells which are also flattened. This provides a short diffusion pathway for a faster rate of diffusion. They are also narrow which slows down the speed of the blood, allowing more time for diffusion.
• In fish, how does the direction of the flow of water compare to the flow of blood and what is the advantage of this?

  They flow in opposite directions in a counter-current mechanism.

  If they flowed in the same direction, equilibrium would eventually be reached and so oxygen concentration in the blood would be limited to 50%.

  As they flow in opposite directions, this maintains a concentration gradient for oxygen from the water into the blood. This is maintained along the whole length of the gill filament.
• What are spiracles?

  Small holes in an insect's abdomen and/or thorax through which air enters and leaves.

  They can be opened when internal oxygen concentration is too low and closed to prevent water loss by evaporation.
• How does the oxygen travel to respiring tissues in an insect?

  Oxygen enters via the spiracles, diffuses through the trachea and many tracheoles and then diffuses directly into respiring cells.
• How is a large surface area provided in an insect's gas exchange?

  The trachea splits into many highly-branched tracheoles with many ends.
• How is a short diffusion pathway provided in an insect's gas exchange?

  Tracheole walls are one cell thick.
• How is a steep concentration gradient maintained in an insect's gas exchange?

  Respiration in the insect's tissues:

  The oxygen is used immediately in aerobic respiration within the respiring cells, producing then a high concentration of carbon dioxide. This carbon dioxide then moves out of the tracheoles via ventilation. This maintains a high oxygen concentration in the tracheoles and a high concentration of CO2 in the respiring cells for diffusion.
• What do flying insects require more of?

  Oxygen for higher rates of aerobic respiration to release greater amounts of energy for rapid muscle contraction.

  They will likely begin respiring anaerobically which produces lactic acid which must be removed with oxygen at rest.
• What is DGC?

  A discontinuous gas-exchange cycle

  Some insects have spiracles that close for long periods of time (several hours or even days) and open occasionally for only a few minutes.

  One hypothesis suggests that this is due to preventing water loss.

  Gibbs and Johnson found that insects using DGC has the lowest metabolic rate. (Continuous was highest and cyclic was intermediate)