Experiments: Investigating Factors Affecting Rate of Diffusion and Osmosis

Question 1

agar cube experiment

Answer 1

• agar cubes of different sizes can be used to demonstrate the relationship between SA:V ratio and rate of diffusion
• the cubes contain alkali and an indicator - they are placed in an acid
• as the acid diffuses into the cube it reacts with the alkali - this neutralisation turns the indicator colourless
• the smallest cube becomes colourless the quickest

Question 2

potato chip experiment

Answer 2

• potato chips can be placed in sucrose or salt solutions of different concentrations
• osmosis will occur until the water potential of the tissue and solution are the same, this causes a mass change
• if the solution has a higher water concentration, water will move into the potato chip and the mass will increase
• if the solution has a lower water concentration, water will move out of the potato chip and the mass will decrease
• this method can be used to determine the water potential of the potato - if there is no change in mass, the concentration of the solution is the same as the concentration of the cytoplasm

Question 3

visking tube experiment

Answer 3

• visking tubes only allow small soluble molecules to pass through, therefore, osmosis can occur
• you can change the concentration of the sucrose solution or the temperature of the water to investigate the effect on osmosis
• the height the liquid rises in a set time will increase if osmosis is faster

Question 4

onion cell practical

Answer 4

• we can also use thin sections of onion cells to study the effects of osmosis
• the cells soaked in pure water are turgid
• the cells soaked in concentrated salt or sugar solution are plasmolysed