surface area to volume ratio

• Active and passive transport of materials/ions moving in and out of cells and cell organelles

  Explain
• Diffusion and facilitated diffusion of materials/ions moving in and out of cell


  Explain
• Movement of water particles (osmosis) through the cell membrane and the effects on the cell


  Explain
• Phagocytosis and pinocytosis in eukaryotic cells

  Describe
• Surface area to volume ratio

  Significance for cells
• When cells grow, their volume increases as does their surface area
• Volume is calculated as a cube and surface is calculated as a square, thus the ratio between surface area and volume (SA:V) decreases as the cell grows
• Small cell


  • Larger surface area to volume ratio than a cell of the same shape
• Larger surface area to volume ratio of a cell

  • Faster the rate at which substances move into and out of a cell
• Larger organisms must have smaller cells
• Surface area to volume ratio

  • Microvilli
  • Neurons
  • Root hair cells
  • Cristae
  • Red blood cells
• Organ level


  Surface area to volume ratio examples (microvilli, neurons, root hair cells, cristae, red blood cells)
• Organism level


  Elephants have large ears which are thin (small volume) and wide (large surface area), allowing rapid heat loss to stop overheating in their hot environments
• Red blood cells have a large surface area in proportion to their volume
• Air entering lungs


  1. Goes through smaller and smaller tubes until it reaches alveoli

  2. Oxygen from air enters blood, carbon dioxide from body goes into air

  3. Alveoli are very tiny but there are 300,000,000 in each lung
• The body needs all 600 million alveoli in the lungs to get enough oxygen into the blood
• Redesign a 4cm cube cell to have a volume of 64cm3 but a larger surface area


  Record the SA:V ratio for each cell
• Eskimos are short, rounded people with small ears and other external appendages


  • African blacks are tall and slender
• Mouse eats more food (weight for weight) than a cat

  Mouse will lose more heat energy per kilo than a cat because it has a higher SA:Vol ratio, so it must eat more per kilo to compensate
• Mittens are warmer than gloves

  Mittens have a lower SA:Vol ratio than fingered gloves, so heat loss is less
• Dog hangs its tongue out when hot


  To increase its surface area and increase the area where moisture can evaporate and take heat energy away from its body
• Person crosses their legs and folds their arms when cold

  Effectively reduces their SA:Vol ratio
• Lung tissue is divided into alveoli rather than each bronchiole remaining as a tube


  Alveoli are like little bags, bags have sides and an end, tubes have sides only
• Arteries divide into arterioles and finally capillaries


  To increase the contact between blood and the wall of the vessel carrying it, resulting in greater exchange of substances into and out of the blood