transport in and out of cells

• Active transport

  1. Moves from an area of low concentration to high concentration

  2. Requires energy from respiration
• Active transport


  • Allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil
  • Allows sugar molecules to be absorbed to plant root hairs from lower concentrations in the gut into the blood, which has a higher concentration
• Osmosis


  The diffusion of water from a dilute to a concentrated solution through a partially permeable membrane
• Water may move across cell membranes by osmosis
• Diffusion

  The net movement of particles from an area of higher concentration to an area of lower concentration until they are spread out
• Diffusion happens in

  • Oxygen and carbon dioxide diffuse during gas exchange in lungs, gills, and plant leaves
  • Urea diffuses from cells into the blood plasma for excretion by the kidney
  • Digested food molecules from the small intestine diffuse to the blood
• Factors affecting diffusion

  • Difference in concentration (concentration gradient)
  • Temperature
  • Surface area of a membrane
• A single celled organism has a large surface area to volume ratio which allows enough molecules to diffuse in and out to meet the cell's needs
• Adaptations in multicellular organisms

  • Rich blood supply to maintain the concentration gradient
  • Large surface area
  • Thin surface
  • Surfaces kept moist so substances can dissolve and diffuse faster
  • Ventilation occurs to speed up gaseous exchange