Osmosis + diffusion 1.15 - 1.17

How are substances transported

diffusion, osmosis, active transport

Definition of diffusion

net movement of particles from an area of higher concentration to an area of lower concentration

Definition of osmosis

The net movement of water particles from an area of high water potentially to an area of low water potential across a partially permeable membrane

Active transport definition

The movement of particles across a membrane against a concentration gradient from an area of lower to an area of higher concentration, using energy transferring during respiration

Core Practical: Investigate osmosis in potatoes

1- prepare sucrose solutions of different concentrations ranging from pure water to very concentrated sucrose

2- use a cork borer to cut a potato into same sized pieces

3- divide the cylinders into groups of 3 and use a mass balance to measure the mass of each group

4- place one group in each solution

5- leave the cylinders in the solution for at least 40 mins ( making sure they all get the same time)

6- remove the cylinders and pat dry gently with a paper towel. This removes excess water so the final mass is accurate.

7- weigh each group again and record results

8- The only thing changed in the experiment is the sucrose solution concentration, everything else must be kept the same for good results.

Percentage gain and loss of mass in osmosis

(end mass - start mass) / start mass x 100