National 5 Biology Diffusion and Osmosis

We are learning to

Describe osmosis in relation to practical examples

Relate what we learn through the experiments to osmosis in animal cells

Osmosis LabYou are going to set up 4 different

experiments between youFollow your instructions carefully your group

members depend on you to do things properly

Experiment 1Vanilla or peppermint in a balloonUsing a dropper place two drops of vanilla or

peppermint inside a deflated balloon without getting any on the outside.

Inflate the balloon slightly and place inside a bag and not the end

Leave for 20minutes

Experiment 2Collect two boiling tubesPlace distilled water in tube 1Place salty water in tube 2Cut two cylinders of potato using cork borers

take note of their appearance and their weight

Place one cylinder into each boiling tubeLeave for 30minutes

Experiment 3You have three beakers in front of you each

with different solutions and an egg with the shell removed

Try to decide what type of solution you have in each beaker based on the following:

Hypertonic – has less water than the cellsIsotonic – has the same concentration of

water as the cellsHypotonic – has more water than the cellsRemember water moves from a high water

concentration to low water concentration

Experiment 4Observe the information about the sultanasUsing the following words define what state

the cells are inPlasmolysed – vacuole has shrunk and

cytoplasm and membrane have shrunk away from the cell wall

Turgid – vacuole is swollen pushing cytoplasm and cell membrane against the cell wall

In each case state if water has moved into the cells or out of the cells

Round RobinShare all the information from your

experiment with your groupEach person takes a turn and no one

interrupts whilst they speak - 2minutes eachOnce finished you can ask questions about

what they did and what they found out

Place matYou have been given a large piece of paperDraw out the placemat as follows

Each member of the group has two minutes to write down the important points raised in the experiments

Now as a group decide what the main points should be and write them in the centre

ConclusionsWater moves by osmosis from a high water

concentration to a low water concentrationIf a solution is hypertonic to the cells then

the cells will lose water and become plasmolysed

If a solution is isotonic to the cells then the cells will remain unchanged

If a solution is hypotonic to the cells then the cells will gain water and become turgid

Osmosis in plant cells

The vacuole has shrunk and cytoplasm has come away from cell wall due to loss of water

No change to cell due to equal water concentrations

Vacuole has become swollen and pushes the cell contents against the cell wall

Osmosis in animal cells

Cells have shrunk due to loss of water

No change to cells – concentration of water is equal

Cells have swollen and burst due to gain of water - why?