3.1 Main Inorganic Nutrients
Learn how plants obtain essential inorganic nutrients, how these nutrients are classified, and how Knop's culture solution is used to study nutrient deficiency.
Learning Objectives
- Identify and classify inorganic nutrients required by plants into macronutrients and micronutrients.
- Explain the specific functions of each macronutrient and micronutrient in plant growth and metabolism.
- Identify and describe the deficiency effects caused by the lack of specific macronutrients and micronutrients in plants.
- Describe the composition and preparation of a complete Knop's culture solution.
- Explain the experimental setup and method to investigate the effects of nitrogen, phosphorus, and potassium (NPK) ratios on the growth of seedlings.
Classification of Main Inorganic Nutrients & Knop's Solution Apparatus
Plants absorb inorganic nutrients from air, water and soil mineral salts. These nutrients are divided into macronutrients and micronutrients, and their roles can be studied using Knop's culture solution.
Macronutrients
Needed in large amounts: C, H, O, N, K, Ca, Mg, P, S.
Micronutrients
Needed in trace amounts: Cl, Fe, Mn, B, Zn, Cu, Ni, Mo.
Knop's Solution
Complete nutrient medium used to study deficiency symptoms.
Short Explanation
What are inorganic nutrients?
Plants require inorganic nutrients from their surroundings to synthesise essential organic compounds such as carbohydrates and proteins. These nutrients are absorbed from air, water, and soil mineral salts.
Macronutrients
Required in large quantities. Carbon, hydrogen and oxygen are obtained readily from air and water, while the rest are absorbed as dissolved mineral salts from the soil.
Micronutrients
Required in small or trace quantities. They act mainly as enzyme activators and cofactors in photosynthesis, respiration and hormone synthesis.
Deficiency symptoms
A deficiency in any nutrient disrupts metabolic functions and leads to distinct visible symptoms such as chlorosis, stunted growth, or leaf margin yellowing.
Knop's culture solution
A complete nutrient solution formulated in 1859 by Wilhelm Knop. It contains all essential macronutrients and trace elements needed for healthy plant growth.
Try to Answer First
Answer in your mind, then press “Check Answer”.
State the difference between macronutrients and micronutrients, and give two examples of each.
Why must the culture bottles in Knop's solution experiment be wrapped with black paper?
Explain why a corn seedling lacking magnesium displays yellowing between mature leaf veins.
Common Mistakes
- Confusing the deficiency symptoms of nitrogen, potassium, and magnesium: nitrogen deficiency causes general chlorosis starting on older leaves; potassium deficiency causes yellowing along leaf edges; magnesium deficiency causes interveinal chlorosis on mature leaves.
- Forgetting to replace both the cation and anion appropriately when preparing nutrient-deficient solutions. For example, omitting \(\text{Ca(NO}_3)_2\) requires adding \(\text{CaCl}_2\) so that calcium is still supplied while nitrogen is eliminated.
- Stating that carbon, hydrogen, and oxygen are absorbed as mineral salts through fertilisers, when they are actually obtained from carbon dioxide in the air and water from the soil.
- Assuming the air pump in Knop's experiment is to supply carbon dioxide for photosynthesis; it actually supplies oxygen to the roots for aerobic respiration.
Concept Misunderstandings
Micronutrients are less important than macronutrients because they are needed in tiny amounts.
Micronutrients are just as essential for plant survival as macronutrients; a lack of any micronutrient such as zinc, boron, or iron causes severe abnormalities, metabolic disruption, or plant death.
Chlorosis is caused exclusively by a lack of sunlight.
Chlorosis is the loss or failure of chlorophyll synthesis, which is frequently caused by a deficiency of chemical elements required for its structure or synthesis, such as nitrogen, magnesium, iron, or sulphur.
Plant roots absorb all nutrients by passive diffusion alone.
Roots actively transport mineral ions against concentration gradients, which requires ATP generated by aerobic cellular respiration — hence the necessity of an air pump in hydroponic culture.
Summary
- Plant nutrients are categorised into macronutrients (C, H, O, N, K, Ca, Mg, P, S) and micronutrients (Cl, Fe, Mn, B, Zn, Cu, Ni, Mo).
- C, H, and O form the structural basis of organic compounds and are rarely deficient.
- N, P, and K (NPK) are critical fertiliser components: N promotes chlorophyll and protein synthesis; P aids root development, nucleic acids, and ATP; K regulates turgidity and enzyme activation.
- Calcium forms the middle lamella and cell wall; magnesium forms the core of the chlorophyll molecule.
- Micronutrients act primarily as enzyme activators and cofactors in photosynthesis, respiration, and hormone synthesis.
- Knop's solution is a complete nutrient medium used to study deficiency symptoms; key experimental precautions include aeration and opaque wrapping to inhibit algae growth.
Short Activity
Objective: identify nutrient functions, deficiency symptoms and Knop's solution experiment details.
A. Objective Quiz
Which of the following macronutrients is the central structural component of the chlorophyll molecule?
In an experiment studying nutrient deficiencies using Knop's culture solution, what is the primary purpose of connecting an air pump to the culture bottle?
B. Fill in the Blanks
Culture bottles in a nutrient solution experiment are covered with black paper to avoid the growth of .
The yellowing of plant leaves resulting from a failure to synthesise chlorophyll due to nutrient deficiency is called .
C. Matching / Drag and Drop
Drag each nutrient deficiency to its characteristic symptom. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Nutrient Deficiency to Its Symptom
Write the correct nutrient deficiency next to each symptom.
| Characteristic Symptom | Nutrient Deficiency |
|---|---|
| 1. Yellowing (chlorosis) occurring mainly on matured leaves, followed by underlying leaves falling off | |
| 2. Poor, unhealthy root growth with dark green, dull leaves and red or purple spots on older leaves | |
| 3. Disrupted protein synthesis with premature death and yellowing along leaf edges | |
| 4. Death of terminal buds, abnormal growth, and leaves that become thick, rolled up, and fragile |
Answer choices: Nitrogen deficiency • Phosphorus deficiency • Potassium deficiency • Boron deficiency
