Biology physics and maths tutor

• how does an organisms Size relate to its surface area to volume ratio?

  The larger the organism the lower the surface area to volume ratio
• how does SA/v ratio affect transport of molecules

  The lower the SA/V ratio the further molecules must travel to reach partsof an o organism.
• Larger organisms require specialised gas exchange surfaces due to a small surface area to volume ratio, diffusion being insufficient to provide all cells with oxygen, large organisms being more active
• 5 features of an efficient gas exchange surface

  • folds for a large surface area
  • good blood supply for maintaining a steep diffusion gradient
  • moist for gasses to dissolve
  • thin for a short diffusion pathway
  • permeable for gasses to diffuse in
• describe the gas exchange mechanism in a unicellular organism

  • simple diffusion
  • thin cell membrane provides short diffusion distance
• describe the gas exchange mechanism in flatworms

  • flat structure provides a large surface area and reduces diffusion distance
  • simple diffusion
• describe the gas exchange mechanism in earthworms

  • slow moving and low metabolic rate to they require little oxygen
  • circulatory system for the transport of oxygen
  • rely on external surface for gas exchange
• ventilation is the movement of fresh air into a space and stale air out of a space to maintain a steep concentration gradient of oxygen and carbon dioxide
• gill filaments are the main site of gas exchange in fish, they have gill lamellae which provide a large surface area and good bloody supply for gas exchange
• explain inspiration in a fish

  • mouth opens and operculum closes
  • mouth floor lowers and pressure inside mouth decreases
  • water moves into mouth because external pressure is greater then internal pressure
• explain expiration in a fish

  • mouth closes and operculum opens
  • mouth floor raises, increasing the pressure in the mouth and decreasing the volume
  • water is forced out of the operculum as the internal pressure is greater than the external pressure
• counter current flow is where blood and water flow in opposite directions across the gill plate, maintaining a concentration gradient across the entire gill plate
• how is counter current flow used to maintain a steep diffusion gradient?

  • water is always next to blood of a lower oxygen concentration
  • keeps rate of diffusion constant and enables 80% of oxygen to be absorbed
• parallel flow is where blood and water flow in the same direction across the gill plate
• main features of an insects gas transport system:

  • spiracles - small external openings along the thorax and abdomen through which air enters and air and water leave
  • tracheae - large tubes supported by rings of chitin
  • tracheoles - smaller branches dividing off tracheae
• adaptations of the insect tracheal system:

  • spiracles can open and close to regulate diffusion
  • bodily contractions speed up movement of air through spiracles
  • highly branched tracheoles provide a large surface area
  • impermeable cuticle reduces water loss by evaporation