volume and surface area

• As organisms increase in size their SA:V ratio decreases
• • The large surface area allows for maximum absorption of nutrients and gases and secretion of waste products
• • The greater volume results in a longer diffusion distance to the cells and tissues of the organism
• • For larger, multicellular organisms the distance between the surface of the organism to its centre is relatively long
• • Transport systems in animals include:
  • The blood and circulatory system - carries the necessary substances around the body
• • Transport systems in plants include:
  • The xylem - moves water and mineral ions from roots to shoots
  • The phloem - moves sugars and amino acids to where they are needed in the plant
• • Large, multicellular organisms like humans have relatively small surface areas (SA) in comparison to their volumes
  • This is why larger organisms need exchange surfaces within their transport systems to carry out diffusion, osmosis and active transport at a sufficient rate
• • Exchange surfaces in animals include:
  • The lungs and alveoli for gas exchange
  • The small intestines and villi for absorption of digested food
• • Exchange surfaces in plants include:
  • Roots and root hairs where mineral ions and water are absorbed
  • The leaves for gas exchange
• how to increase efficiency of exchange:

  • Having a large surface area to increase the rate of transport
  • A barrier that is as thin as possible to separate two regions, to provide as short a diffusion path as possible for substances to move across
• • The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface
• summary of diffusion factors table

  A) greaterr

  B) faster

  C) higher

  D) kinetic

  E) greater