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Measurement at home

Osmosis

Incredible edible expanding vegetables

How much can vegetables ‘grow’ in 90 minutes?

• Do all vegetables change size by the same amount through osmosis?
• How does water salinity affect change in vegetable size?

Estimated time: 30 minutes + 90 minute wait between measurements.
No prior knowledge needed.

Risks

• Don’t eat the samples.

Equipment required

• a range of vegetables and fruit: carrot, potato, melon, apple, etc.
• Peeler and knife (with responsible user)
• Ruler
• Small bowls
• Water
• Table salt
• Measuring jug
• Weighing scales (or teaspoon)
• Timer (or clock)
• Paper and pencil for results.

Steps

Watch the video

1. Put 200 ml of water in each bowl. Add 10 g of salt (about two level teaspoons) to one bowl. You can label bowls, though taste can probably identify which is which! If you have many samples you may need more bowls.
2. Peel vegetables. Cut each into pieces of 1 cm square cross section and as long as possible. Cut the ends squarely. Assemble pieces in two rows identical in length and number (as in the image below). It helps to make the length an exact number of centimetres. Record total row length.
3. Put one set of pieces in each bowl. Pieces of different vegetables can be in the same bowl as long as they are easy to identify and none are touching.
4. Leave for 90 minutes.
5. Remove pieces from the bowl a set at a time. Reassemble into a row and record its new length.
6. Convert the change in length to a percentage: % change = 100% x (start length end length) / start length.
7. Enter results below

Thoughts, tips and information

SI measurement units

• metre (m) for length
• second (s) for time

Challenge Topics

Measurement Science, Maths, Biology.

• It’s important to have the same number of total surfaces (edges and ends) and ensure they are all exposed to the water.
• If left for longer, do the length changes continue?
• How does salt amount and time effect the result?
• Osmosis enables plant roots to draw water from soil and kidneys to function.