What it shows
Salt in irrigation water stops seeds from taking up water. Germination counts across different salt strengths show why saline groundwater harms crops.
The science
Water moves into a seed by osmosis, from low to high concentration of dissolved substances. If the water outside is very salty, little or no water enters, and a root may even lose water. So high salinity delays or prevents germination and reduces growth.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Mung or wheat seeds
- Five petri dishes or plates with cotton or tissue
- Table salt and a kitchen scale
- A measuring cup
- Labels and a notebook
- A ruler
Safety
For this project: Wash hands after handling seeds. Do not taste the solutions, and wipe up spills so the floor is not slippery.
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.
All the safety rulesStep by step
8 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.
Make solutions of 0, 0.5, 1, 2 and 4 grams of salt in 100 ml of water.
Line five dishes with cotton and place ten seeds in each.
Pour 10 ml of a different solution into each dish and label them.
Keep the dishes in the same place and moisten them with the same solution each day.
Count germinated seeds every day for a week.
Measure the shoot lengths after seven days.
Calculate the germination percentage for each concentration.
Plot germination percentage against salt strength.
What you should see
Germination falls as the salt strength rises, and the highest strength shows few or no sprouts. The curve shows the limit the seeds tolerate.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is osmosis?
The movement of water through a membrane towards a more concentrated solution.
2Why is salty soil bad for crops?
Plants cannot take up water easily.
3What is the control here?
The 0 gram dish with plain water.
4Where is salinity a problem in India?
In coastal areas and some irrigated lands.
Take it further
Compare a salt-tolerant seed such as barley with a sensitive one such as bean.
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.
Free ebooks for this project
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