movement of substances

• diffusion: the net movement of particles from an region of high concentration to an region of low concentration, down a concentration gradient
• osmosis: the net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane
• active transport: the movement of particles, using energy, from a region of lower concentration to a region of higher concentration, against a concentration gradient, through a partially permeable membrane
• concentration gradient: difference in concentration between a region of higher concentration of a substance and a region of lower concentration
• water potential: tendency of water molecules to move from one region to another
• factors affecting rate of diffusion:

  1. SA:V ratio: larger SA:V ratio, greater area for substances to pass through, faster rate of diffusion
  2. temperature: molecules have more kinetic energy, move faster and diffuse faster
  3. steepness of concentration gradient
  4. distance
• adding animal cell into a solution

  solution with high water potential: bursts

  solution with low water potential: crenated
• adding plant cell into a solution

  solution with high water potential: turgid

  solution with low water potential: flaccid

  solution with very low water potential: plasmolysed
• concentration gradient: the difference in concentrations between two regions
• how does the distance between 2 substances affect the rate of diffusion?

  the shorter the diffusion distance, the less time is needed for the substance to travel, and hence the rate of diffusion is higher
• What is the relationship between the surface area-to-volume ratio and the rate of diffusion?

  The greater the surface area-to-volume ratio, the higher the rate at which substances move in and out of the cell