Plant Nutrients Part Deux…

Shortages of different minerals produce different symptoms. (The picture above is from the wonderful but sadly now defunct Tomato Headquarters website – one day the tomatoes will overthrow their oppressors!) It illustrates the visible changes that occur in the leaves due to different deficiencies. Unsurprisingly, a shortage of magnesium leads to pale coloured leaves – magnesium is the key mineral present in chlorophyll. The differences between the various conditions are quite subtle in some cases so it is not always obvious what the cause of the problem is. There are many important trace nutrients and a variety of symptoms.

It should be possible to design an experiment to establish what deficiency is causing any given set of symptoms. The first thing to do is to make an observation. Look at the picture of a maize plant (above) – the problem should be obvious. The edges of the leaves are yellowy brown and shrivelled.

The next step is to propose a hypothesis – this is a suggested explanation for the problem that can be tested scientifically. I know that nitrogen deficiency can cause leaves to turn yellow so my hypothesis is going to be, “The maize is suffering from a shortage of nitrate in the soil”. How would you go about testing this claim?

We need to set up a controlled experiment and ensure that it is a fair test. There are various approaches that you might take but you need to compare two sets of plants, one set acting as a control and the other as your test subjects. In a laboratory or greenhouse (anywhere you can control all the conditions) randomly assign a dozen small maize plants into two groups A & B. Group A (the control) gets everything that a young plant needs; warmth, light, water, carbon dioxide and soil with a perfect balance of nutrients.  Group B has identical conditions except that the soil has reduced nitrate. The two groups are compared over time. Group A should grow perfectly and Group B will show signs of deficiency. If the leaves resemble those in the picture then that supports your hypothesis.

Farmers need to be particularly alert to their soil conditions and how their crops are growing.

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Questions…

1. Name a metal element that is an essential mineral for humans.
2. Suggest a good dietary source for the mineral.
3. What role does this mineral play in the body?
4. What is the main soil condition that determines the availability of mineral nutrients?
5. Name a variable that would need to be controlled in the experiment described above.
6. How could you make the experiment described above more reliable?
7. The maize in the photograph was not in fact suffering from nitrogen deficiency. What mineral is it missing?
8. What does the word reduction mean in the context of the video?
9. Water enters the root cells of plants passively. Give an example of active transport in root cells.