To study the effect of salt solutions of different concentrations on the germination and growth of cress seeds. These are written instructions to accompany the video on the main toxicology page here.
You will need
- Cress seeds
- Table salt (sodium chloride)
- Measuring jug
- Kitchen scales or measuring spoons
- Cut two sheets of kitchen roll into four equal strips and fold each one twice to make 8 squares for soaking up salt solution. Label the squares (with a biro or pencil) as 0, 0.1, 0.2, 0.25, 0.3, 0.35, 0.4 and 0.5.
- Prepare your ‘stock solution’ (0.5 M NaCl) by adding 29 g of table salt to 1 litre of tap water in a measuring jug. NB: 29 g is approximately 1 level tablespoon + 1 level teaspoon.
- Soak your paper that is labelled ‘0.5’ in the 0.5 M stock solution and lay in a large flat container, e.g. a roasting tray.
- Soak your paper that is labelled ‘0’ in plain tap water and place in the tray.
- Prepare the other salt solutions by dilution using a measuring spoon or cup:
- 0.4 M: mix 4 parts of stock solution with 1 part of water.
- 0.35 M: mix 7 parts of stock solution with 3 parts of water.
- 0.3 M: mix 3 parts of stock solution with 2 parts of water.
- 0.25 M: mix 1 part of stock solution with 1 part of water.
- 0.2 M: mix 2 parts of stock solution with 3 parts of water.
- 0.1 M: mix 1 part of stock solution with 4 parts of water.
- Soak your other square paper pieces in the appropriate solution and place them in the flat container.
- Count 25 cress seeds onto each square.
- Cover the container with cling film and seal around the edge with sticky tape to avoid evaporation.
- Leave the cress seeds for ~1 week. The results on this page were obtained after 6 days.
- Count and record the number of seeds that have germinated from each sample. If you can see only a tiny bit of root you can still count it as germinated.
- Measure the shoot length of the seedlings and record your data. If there is no shoot, record it as 0.
- You can then calculate a mean shoot length for each salt concentration and also a standard deviation.