transport

• what is diffusion?


  the net movement of particles from an area of higher concentration to an area of lower concentration
• what are the 3 main factors affect that affect the rate of diffusion?

  • concentration gradient
  • temperature
  • surface area
• what is concentration gradient?


  larger gradient

  faster diffusion
• what is temperature in diffusion?


  higher temperature = faster diffusion
• what is sruface area in diffusion?


  larger surface area = faster diffusion
• give examples of substances transported by diffusion in lungs and kidney.


  • lungs; oxygem diffused into the blood from lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient
  • kidney; urea diffuses from cells into blood plasma so it can be excreted in urine
• how are single-celled organism adapted for diffusion?


  • large surface area to volume ratio
  • maximises the rate of diffusion of molecules to meet the organisms needs
• how is surface area to volume ratio calculated?


  surface area = number of sides x side length x side width
• what 4 factors increase the effectiveness of a gas exchange surface?


  • large surface area
  • thin membrane - short diffusion path
  • efficient blood supply
  • ventilation
• what is osmosis?


  the movement of water from a dilute solution to a concentrated solutions through a partially permeable membrane
• what is meant when a solution is isotonic to a cell?


  the concentrations of the external and internal solutions are the same
• what is meant when a solution is hypotonic to a cell?


  the concentration of the external solution is lower than that of internal solution
• what may happen when an animal cell is placed in a very hypertonic solution?


  water moves into the cell causing it to burst
• how do plant leaves and stems remain rigid?

  water moves in by osmosis causing the vacuole to swell and the cytoplasm to press against the cell wall
• what may happen when a plant cell is placed in a very hypertonic solution?


  water moves out of the cell by osmosis and the vacuole and cytoplasm decreases in size

  the cell membrane may pull away from the cell wall, causing the cell to become plasmolysed
• what is active transport?


  the movement of molecules from a more dilute solution to a more concentrated solution against a concentrated gradient, using energy from respiration
• how do plant root hair cells use active transport?


  root hair cells use active transport to take mineral ions from a more dilute solution in soils