Lesson focus: Plants need mineral ionA tiny charged particle of a mineral, such as nitrate, that plants take up from the soil. in small amounts because those ions supply elements used to build essential molecules and structures.
Explain the roles of nitrateA mineral ion that plants take from the soil to make amino acids and proteins., magnesiumA mineral plants take from the soil and need to make chlorophyll., phosphateA mineral that plants take from the soil to help roots grow and make DNA. and potassiumA mineral that plants take from the soil to help flowers, fruit and leaves stay healthy. ions and evaluate evidence for mineral deficiency.
Build on earlier learning
Investigating photosynthesisThe previous lesson treated water, light, temperature and carbon dioxide as factors. Mineral supply is another condition affecting growth and photosynthetic capacity.
Practical
Mineral deficiency in plants
- Grow seedlings in solutions each missing one mineral, plus a complete solution.
- Keep light, temperature and volume the same.
- Compare leaf colour and growth after two weeks.
Record: A table of each solution and its symptoms.
You will be successful when you can…
- State roles of four mineral ions.
- Link deficiency to affected molecules.
- Distinguish correlation from diagnosis.
- Design a controlled mineral investigation.
Words that carry the science
- mineral ion
- A charged element-containing particle absorbed from soil solution or nutrient solution.
- nitrate
- A nitrogen-containing ion used to make amino acids and other nitrogenous compounds.
- magnesium
- A mineral ion whose atoms form part of chlorophyll molecules.
- phosphate
- A phosphorus-containing ion used in DNA, membranes and ATP-related molecules.
- potassium
- An ion involved in enzyme activity, osmoregulation and stomatal function.
- chlorosis
- Abnormal yellowing caused by reduced chlorophyll or chloroplast function.
Connect each mineral ion to molecules, symptoms and evidence
01Mineral ions supply elements for construction
nitrateA mineral ion that plants take from the soil to make amino acids and proteins. ions supply nitrogen for amino acids, proteins and nucleic acids. magnesiumA mineral plants take from the soil and need to make chlorophyll. ions supply magnesium used in chlorophyll. phosphateA mineral that plants take from the soil to help roots grow and make DNA. contributes phosphorus to DNA, phospholipids and energy-transfer molecules. potassiumA mineral that plants take from the soil to help flowers, fruit and leaves stay healthy. supports many enzymes and guard-cell function.
mineral ionA tiny charged particle of a mineral, such as nitrate, that plants take up from the soil. are not plant “food”. Plants make organic molecules by photosynthesis, but they need ions as raw materials and regulators.
02Symptoms are clues, not unique diagnoses
Nitrate shortage commonly reduces growth because protein synthesis is constrained. Magnesium shortage can cause chlorosisWhen leaves turn yellow because they are not making enough chlorophyll. because less chlorophyll is produced. Phosphate shortage can restrict root and shoot growth, while potassium shortage can affect leaf margins and water regulation.
Similar symptoms can result from disease, root damage, unsuitable pH, waterlogging or multiple deficiencies. Position on old or young leaves can add evidence because ions differ in mobility, but diagnosis still needs controlled testing.
03Hydroponic comparisons isolate one ion
Grow genetically similar seedlings in complete nutrient solution and solutions lacking one named ion. Keep light, temperature, solution volume, pH, aeration and starting size controlled. Include several plants per treatment and measure growth and leaf colour objectively.
A treatment lacking all minerals is not a sufficient control experiment for identifying one ion because many variables differ. The strongest comparison changes only the target ion while replacing its accompanying counter-ion appropriately.
Plants and mineral ions
Plants make glucose by photosynthesis, but to make other substances they also need mineral ions, absorbed from the soil water by the root hair cells. Grow seedlings in solutions each missing one mineral and compare them with a control.
Controls
Heights are illustrative. Fertilisers replace the mineral ions that crops remove from the soil.
Infer a mineral limitation cautiously
Older leaves become yellow while new growth is small in one hydroponic treatment.
- Identify chlorosis as reduced green pigment.
- Magnesium is part of chlorophyll, so magnesium shortage is one hypothesis.
- Nitrate shortage can also reduce growth and chlorophyll production.
- Compare with single-ion omission treatments and check pH and roots before deciding.
How to make the reasoning visible: Use symptoms to generate a hypothesis, then use controlled comparisons to distinguish explanations.
Interpret mineral-omission evidence
The values are illustrative means after four weeks.
| Treatment | Mean dry mass / g | Mean chlorophyll index | Main observation | Interpretation |
|---|---|---|---|---|
| Complete solution | 4.8 | 42 | Healthy green growth | Reference |
| No nitrate | 2.0 | 24 | Small, pale plants | Nitrogen limitation supported |
| No magnesium | 3.4 | 15 | Strong chlorosis | Chlorophyll link supported |
| No phosphate | 2.7 | 35 | Restricted roots and shoots | Phosphorus limitation supported |
| No potassium | 3.1 | 31 | Leaf-edge damage | Potassium limitation supported |
Why use dry mass rather than fresh mass?
Why must pH be monitored?
Check your understanding
Answer from memory, then check against the suggested answer.
Which ion supplies nitrogen for amino acids?
Which mineral element is part of chlorophyll?
What is chlorosis?
Explain why adding more fertiliser may fail to increase crop yield.
Explain why a nitrate-deficient plant may contain less chlorophyll even though nitrate is not part of the chlorophyll molecule.
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A plant is grown in soil lacking nitrate ions and magnesium ions.
Explain how a lack of nitrate ions reduces growth.
(2)Explain how a lack of magnesium ions reduces growth.
(2)Suggest why symptoms alone may not prove a deficiency.
(1)Total for this question: 5 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., make a chain from the missing ion to a molecule, then to a process, then to growth.