2 (d) Movement of substances into and out of cells

diffusion

the net movement of particles from an area of higher concentration to an area of lower concentration, down a concentration gradient

osmosis

the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration

active transport

the movement of particles against a concentration gradient, from an area of lower concentration to an area of higher concentration, using energy released during respiration

Four factors that affect the movement of substances

• surface area to volume ratio

• distance

• temperature

• concentration gradient

explain how distance affects the movement of substances

• if substance only have a short distance to move, then they’ll move in and out of cells faster

explain how termperature affects the movement of substances

• as the particles in a substance get warmer they have more energy - so they move faster

• this means as temperature increases, substances move in and out of cells faster

explain how concentration gradient affects the movement of substances

• substances move in and out of a cell faster if there’s a big difference in concentration between the inside and outside of the cell

• if there are lots more particles on one side, there are more there to move across

• this only increase the rate of diffusion and osmosis, it doesnt affect the rate of active transport

investigate diffusion in a non-living system

1. make agar jelly with phenolphtalein and dilute sodium hydroxide

2. put dilute hydrochloric acid in a beaker

3. cut out cubes from the jelly and put them in the beaker of acid

4. if you leave the cubes for a while, they’ll eventually turn colorless as the acid diffuses into the agar jelly and neutralizes the sodium hydroxide

investigate osmosis in living system

1. cut potato into identical cylinders and get some beakers with different sugar solutions in them

2. one should be pure water, another should be a very concentrated sugar solution

3. measure the length of the cylinders

4. then leave a few cylinders in each beaker for half an hour

5. then take them out and measure length again

6. if cylinders have drawin water by osmosis, they’ll be a bit longer

7. if water has been drawn out, they’ll have shrunk a bit

investigate osmosis in non living system