What it shows
Dry seeds take up water through their seed coat by imbibition, swelling and gaining weight. By weighing dry and soaked pulses at fixed times you plot how fast and how much they absorb, and why soaking helps cooking and sprouting.
The science
Dry seeds contain proteins and starch that attract water. Water enters through the seed coat and the tiny hole called the micropyle, and the seed swells. The embryo uses this water to start germination, and the water also softens the seed so it cooks in less time.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A handful each of chana, rajma and moong
- Three bowls
- Plain water
- A kitchen scale (to 1 g) or letter balance
- A tea strainer
- A notebook with a table
- A cloth for blotting
Safety
For this project: Wash hands after handling the pulses and do not eat raw soaked rajma, which must be boiled well by an adult.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Weigh 20 g of each dry pulse and write down the weights.
Put each in its own bowl with plenty of water, and label the bowls.
After three hours drain one bowl through the strainer, pat the seeds dry and weigh them again.
Return the seeds to the water and repeat the weighing every three hours for 12 hours, and once more the next morning.
Calculate the percentage gain for each time as the gain divided by the starting weight times 100.
Draw a line graph of percentage gain against time for the three pulses.
Measure the width of five seeds before and after soaking to show the swelling.
What you should see
Each pulse gains roughly 80 to 120 percent in weight in a night, that is it about doubles, with most of the gain in the first six hours. The graph rises quickly at first and then flattens.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What is imbibition?
The soaking up of water by dry seed parts.
02Why do seeds swell?
Water fills their cells.
03Why does soaking save cooking time?
The soft, water-filled seeds heat through faster.
04Why must rajma be boiled well?
Raw rajma has a natural toxin that boiling destroys.
Take it further
Soak seeds in warm water and in cold water and compare how fast they absorb.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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