← Young Researchers ScienceOsmosis and germination30 minutesStd 9–12

Salt Against Seeds

✨ Your graph shows the precise saltiness at which life simply stops starting.

Five saucers of seeds at rising salt concentrations with shorter and fewer shoots as the salt increases, beside a dose-response graph of percentage germinated against grams of salt per hundred millilitres falling from ninety-five per cent to zero. — How it works

🧰 You need

fifty dried green gram or mung seeds
five saucers lined with cotton wool
salt and a kitchen scale
a measuring cup for water
a marker and a ruler

⚠️ Do not eat the treated seeds, and wash your hands after handling the solutions.

👀 What you will see

The plain water dish germinates almost every seed, usually within two days. Germination falls as salt rises, and the strongest dish may produce nothing at all. Shoots in the salty dishes are shorter and thinner even when they do germinate.

🧪 Do it

Label the five saucers 0, 1, 2, 4 and 8 grams of salt per 100 millilitres of water, and mix each solution.
Put ten seeds from the same packet on the damp cotton wool in each saucer.
Add the same measured volume of the matching solution to each saucer, and keep them side by side in the same light and temperature.
Top up each saucer daily with its own solution, using the same volume for all five.
Count and record the number of germinated seeds in each saucer every day for seven days.
On day seven measure the shoot length of every germinated seed and calculate the mean per saucer.
Plot percentage germinated against salt concentration and describe the shape of the curve.

💡 Why it happens

A seed must absorb water before it can germinate, and water crosses the seed coat by osmosis, the movement of water across a partly permeable membrane from a weaker to a more concentrated solution. Salty water outside the seed is more concentrated, so water enters more slowly and, above a certain concentration, is even drawn out of the seed. Germination therefore falls as concentration rises, giving a dose-response curve rather than a sudden switch. The same effect ruins farmland when over-irrigation leaves salt behind in the soil, a problem called salinisation.

🔁 Now try this

Add a sixth dish at 16 grams per 100 millilitres, then use your graph to estimate the concentration that halves germination.

🤔 Think about it

Mangroves grow with their roots in salt water, so what must they be doing that these seeds cannot?

🧘 Ask the Acharya

“Mangroves grow with their roots in salt water, so what must they be doing that these seeds cannot?” — ask him and he will explain it from your own chapters.

Ask Guru →

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