exhange surfaces

• what are the three main factors which impact the need for an exchange system?

  Size

  Surface area to volume ratio

  Level of activity
• how does size impact the need for an exchange system?


  Small organisms like single-celled organisms have cytoplasm close to the environment they live in diffusion will provide enough oxygen and nutrients to keep the cells alive and active. Multicellular organisms may have several layers of cells which makes diffusing oxygen or nutrients very difficult which makes the organism need a specialized exchange system
• What is the significance of a small surface area and a small volume in a smaller organism?

  Small organisms have a small Surface Area- and a small volume. the SA is large compared to the volume so they have a large Surface Area: Volume ratio. This means that their surface area is large enough to supply all their cells with enough oxygen
• what is the significance of a large surface area and a large volume in an organism?


  As size increases, volume rises quicker than the surface area. This means that the surface area will be smaller than the volume- meaning that an organism will need a specialised system to supply enough oxygen for all metabolic needs.
• how does the level of activity in an organism impact the need for an exchange system?


  Some organisms are more active than others- metabolic activity uses more energy from food and requires oxygen to release the energy through aerobic respiration. the cells of ana active organism need good supplies of oxygen and nutrients to supply the energy for movement; this need for energy is increased in ectotherms which need to keep themselves warm.
• What are the features of a good exchange system?


  Thin barriers

  Large surface area

  Good blood supply
• generally speaking, why is a large surface area needed for a good exchange surface?


  Provides more space for molecules to pass through- often achieved by folding the membranes and walls involved.
• generally speaking, why is a thin barrier needed for a good exchange surface?


  Reduce the diffusion distance- the barrier also needs to be permeable ton the substances that are being exchanged.
• generally speaking, why is a good blood supply needed for a good exchange surface?


  Fresh supplies can be brought to one side and keeping the concentration high- can also remove molecules from the demand side to keep the concentration low. this is important to maintain a steep concentration gradient so that diffusion can occur rapidly.