National 4/5 Biology

1. National 4/5 Biology Diffusion and Osmosis

2. We are learning to • Describe osmosis in relation to practical examples • Relate what we learn through the experiments to osmosis in animal cells

3. Osmosis Lab • You are going to set up 4 different experiments between you • Follow your instructions carefully your group members depend on you to do things properly

4. Experiment 1 • Vanilla or peppermint in a balloon • Using 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 knot the end • Leave for 20 minutes

5. Experiment 2 • Collect two boiling tubes • Place distilled water in tube 1 • Place salty water in tube 2 • Cut two cylinders of potato using cork borers take note of their appearance and their weight • Place one cylinder into each boiling tube • Leave for 30minutes

6. Experiment 3 • You 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 cells • Isotonic – has the same concentration of water as the cells • Hypotonic – has more water than the cells • Remember water moves from a high water concentration to low water concentration

7. Experiment 4 • Observe the information about the sultanas • Using the following words define what state the cells are in • Plasmolysed – 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

8. Round Robin • Share all the information from your experiment with your group • Each person takes a turn and no one interrupts whilst they speak – 2 minutes each • Once finished you can ask questions about what they did and what they found out

9. Place mat • You have been given a large piece of paper • Draw 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

10. Conclusions • Water moves by osmosis from a high water concentration to a low water concentration • If 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

11. Osmosis in plant cells Vacuole has become swollen and pushes the cell contents against the cell wall 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

12. 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?