Osmosis, Diffusion, Active Transport

• Diffusion


  The spreading out of particles resulting in a net movement from an area of higher concentration to an area of lower concentration
• Molecules that move in and out of cells by diffusion

  • Oxygen
  • Carbon dioxide
  • Urea
• Cells need oxygen for respiration


  Oxygen moves into the cell by diffusion
• Respiration produces carbon dioxide

  Carbon dioxide moves out of the cell by diffusion
• Urea is a waste product produced inside cells


  Urea diffuses out of the cells into the blood plasma
• Factors affecting the rate of diffusion

  • Difference in concentrations (concentration gradient)
  • Temperature
  • Surface area of the membrane
• Greater concentration gradient


  Faster diffusion
• Higher temperature


  Greater rate of diffusion
• Larger surface area of the cell membrane


  Greater rate of diffusion
• Osmosis


  The diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Dilute solution


  • Contains a high concentration of water
  • Contains a low concentration of solute (e.g. sugar)
• Concentrated solution


  • Contains a low concentration of water
  • Contains a high concentration of solute (e.g. sugar)
• Osmosis


  Water diffuses from the dilute solution to the concentrated solution through a partially permeable membrane
• Animal cell in water

  Water moves into the cell by osmosis, causing the cell to expand and potentially burst
• Animal cell in concentrated solution


  Water moves out of the cell by osmosis, causing the cell to shrink
• Plant cell in water

  Water moves into the cell by osmosis, causing the cell to become turgid (swollen)
• Plant cell in concentrated solution


  Water moves out of the cell by osmosis, causing the cell to become flaccid (shrunken)
• The cell wall prevents the plant cell from bursting when water moves in by osmosis
• Active transport


  Moves substances from a more dilute solution to a more concentrated solution, against the concentration gradient, requiring energy from respiration
• Diffusion


  Particles move down the concentration gradient, does not require energy from respiration
• Active transport


  Particles are moved against the concentration gradient, requires energy from respiration
• Active transport in animals

  • Cells lining the human small intestine transport sugars like glucose from the lumen (lower concentration) into the cell (higher concentration)
• Cells lining the human small intestine

  • Have many mitochondria to provide the energy for active transport
• Active transport in plants

  • Root hair cells transport ions like magnesium from the soil (lower concentration) into the cell (higher concentration)
• Root hair cells


  • Have many mitochondria to provide the energy for active transport
• Plants need magnesium to make chlorophyll in the leaves