Movement In and Out of Cells

• Diffusion: the movement of molecules from a region of high concentration to a region of low concentration down the concentration gradient.
• Diffiusion results in random movement of molecules until equilibrium is reached
• The diffusion of gases and solutes is important as without it, molecules which are needed for life, for example glucose and oxygen for respiration, would not be able to get to the places they are needed. Water is needed as a solvent
• Factors influencing faster diffusion:

  • Larger concentration gradient
  • Higher temperature
  • Smaller surface area
• Osmosis: movement of water molecules from a region of high water potential to a region of low water potential, through a partially permeable membrane
• Conc. of solute outside cell = conc. inside cell → no change in size
• Conc. of solute outside cell > conc. inside cell → cell shrinks (Plasmolysis)
• Conc. of solute outside cell < conc. inside cell → cell swells (Turgid)
• In plants:

  • Increasing solute concentration inside of cell causes cell to become turgid, vacuole fills up.
  • Decreasing solute concentration inside of cell causes cell to become flaccid, losing water and vacuole gets smaller. Cell body shrinks, pulling away from cell wall
• In animals:

  • increasing solute concentration inside of cell can cause cell to explode as a result of it having too much water, crenation.
• Active Transport: movement of particles through a cell membrane, from a region of lower concentration to a region of higher concentration against a concentration gradient, using energy released during respiration
• Active transport is needed when an organism wants to optimize the amount of nutrients it can take up - ion uptake by root hairs and uptake of glucose by epithelial cells of villi.