transportation in cells

• what is diffusion?


  the net movement of particles from an area of higher concentration to an area of lower concentration
• What three factors affect the rate of diffusion?

  concentration gradient, temperature, surface area
• give examples of substances transported by diffusion the lungs and kidney

  lungs: oxygen diffuses into blood from the lungs and carbon dioxide diffuses into the lungs from the blood, both down their concentration gradient.
• how are single-celled organisms adapted for diffusion?

  they have a large surface area to volume ratio - maximises the rate of diffusion of molecules to meet the organism's needs.
• how is surface area to volume ratio calculated?

  surface ares divided by volume
• what four factors increase the effectiveness of gas exchange surface?


  large surface area, thin membrane, efficient blood supply, ventilation
• what is osmosis?


  the movement of water from a dilute solution to a concentrated solution through a partially permeable membrane.
• how do plant leaves and stems stay rigid?

  water moves in by osmosis, causing the vacuole to swell and the cytoplasm to press against the cell wall.
• what is active transport?

  movement across a cell membrane against concentration gradient (using energy)
• how do plant root hair cells use active transport?

  take up mineral ions from a more dilute solution in soils.