3.3.1-3.3.2 SA: Vol and gas exchange

• Examples of products that are exchanged

  1. Respiratory gases
  2. Nutrients (glucose , amino acid , vitamins , minerals )
  3. Excretory products
  4. Heat
• surface area

  Total area of organism exposed to an external environment
• Volume

  Total internal volume of an organism
• Where do exchanges take place in an organism

  On the surface of the organism
• Where are materials exchanged used up

  They are absorbed and used by the cells that mostly make up its volume
• What’s relationship between SA:Vol of organism and diffusion

  Increasing surface area to volume ratio increases the rate of diffusion
• Describe relationship between size and surface area to volume ratio

  As size increased an organisms Surface area to volume ratio decreased as volume increases at much faster rate than surface area
• Explain why very small organisms like amoeba can meet gas exchange requirements by diffusion across the cell surface membrane only

  1. Larger surface area : volume ratio
  2. Short diffusion pathway so gas can penetrate to all part easily
• What is the possible disadvantage of a large surface area to volume ratio?

  Higher rate of heat loss as it’s easier to lose heat so they need a higher metabolic rate so respire faster to replace lost heat and maintain body temperature
• Explain why larger organism like fish and mammal need specialised gas exchange systems

  1. Small surface area to volume ratio
  2. So not enough surface area to supply by diffusion as it’s too slow as they have a longer diffusion pathway
  3. Larger surface Area to volume ratio can be provided with lungs and gills
• Why is the specialised exchange system inside an organism?

  It’s very thin so is easily damaged and dehydrated
• 4 features of specialised gas exchange system

  1. Large surface area
  2. very thin surface
  3. selectively permeable
  4. movement of environmental medium
• Which has higher oxygen concentration air or water

  Air
• Why do smaller organism have higher metabolic rate

  As they have larger surface area to volume ratio so lose heat more faster as it’s easier to lose so the High metabolic rate allows them to respire faster to release heat energy that can replace lost heat to maintain body temper
• How can animal reduce its heat loss

  By having a large body size which more compact so it has smaller surface area to volume ratio reducing heat loss
• What’s rate of heat loss determined by

  Surface