specialised exchange surfaces (a,b) Flashcards Preview

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Why is diffusion sufficient to supply the needs of single celled organisms?

  • metabolic activity of a single-celled organism is usually low, so oxygen demands and carbon dioxide production of the cell are relatively low
  • SA:V of the organism is large

Why is diffusion not sufficient to supply the needs of multicellular organisms?

  • they have higher metabolic activity as they use lots of energy for movement etc
  • as an organism increases in size, its SA:V ratio decreases
  • distances that substances need to travel from the outside to reach the cells get longer

Features of efficient exchange surfaces

  • increased surface area - e.g. root hair cells
  • thin layers - so short diffusion distances so fast and efficient process - e.g. alveoli
  • good blood supply - gives steeper concentration gradient so faster diffusion - constant delivery of substances to and from the exchange surface e.g. alveoli or gills
  • ventilation - helps maintain concentrations + make processes more efficient e.g. alveoli or gills