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When plants suffer from deficiency diseases, they do not have enough mineral ions. This can be investigated in science experiments by measuring the growth of barley seedlings.

Method:

1. Sow ten barley seeds onto cotton wool in a petri dish. Add 10 cm³ of distilled water, seal using tape to avoid water loss through evaporation and place on a sunny windowsill to germinate. Repeat with three other petri dishes.
2. About one week after germination, open each petri dish, pour out any distilled water and add 10 cm³ of the following solutions:
   • Petri dish 1 - Distilled water
   • Petri dish 2 - Culture solution containing magnesium sulfate and potassium nitrate
   • Petri dish 3 - Culture solution containing magnesium sulfate (deficient in nitrogen)
   • Petri dish 4 - Culture solution containing potassium nitrate (deficient in magnesium)
3. Replace all petri dishes on the window sill and leave for two weeks.
4. Open each petri dish and carefully remove each seedling from the cotton wool.
5. Dry in an oven and record the total dry mass of each set of ten seedlings.

Results:

Conclusions: