RG size and surface area

• what do organisms need to exchange with their environment?

  substances
• what do cells need to take in?

  oxygen and nutrients
• why do cells need to take in oxygen?

  for aerobic respiration
• what WASTE PRODUCTS do cells need to excrete?

  carbon dioxide and urea
• why does heat need to be exchanged?

  because most organisms need to stay at roughly the same temp, so heat needs to be exchanged
• what do smaller animals have?

  higher surface area : volume ratio
• what do multicellular organisms need?

  exchange organs

  mass transport systems
• what does an organism need to do\?

  supply every one of its cells with substances (eg glucose for respiration)

  and remove waste products from every cell to avoid damaging itself
• what can substances do in single-celled organisms?


  diffuse directyl into or out of the cell across the cell-surface membrane
• why is the diffusion rate quick in single-celled organisms?

  due to the small distances the substances need to travel
• What is diffusion across the outer membrane like in multicellular animals?

  too slow
• why is diffusion across the outer membrane in multicellular animals TOO SLOW?

  • Some cells are deep within the body - big distance between them and the outside environment
  • large animals - low SA:V ratio- it is difficult to exchange enough substances to supply a large volume of animal through a small outer surface
• IN MAMMALS, what does 'mass transport' usually refer to?

  the circulatory system
• what does the circulatory system use blood to do?

  carry glucose and oxygen around the body
• what does mass transport in plants involv?

  the transport of water and solutes into the system in the xylem and phloem