2.2 Nutrient Requirements in Plants
Plants require essential mineral nutrients for healthy growth, development and reproduction. These nutrients are classified as macronutrients or micronutrients based on the quantity needed, and a deficiency in any essential nutrient produces specific symptoms.
Learning Objectives
- Classify plant nutrients into macronutrients and micronutrients.
- State the functions of macronutrients and micronutrients in plant growth and development.
- Identify and describe the deficiency effects of nitrogen, phosphorus, and potassium on plant growth.
- Explain the setup and experimental controls used to study macronutrient deficiencies in plants using culture solutions.
Comparison of Healthy Plant vs. Nitrogen, Phosphorus, and Potassium Deficiencies
Distinctive symptoms appear on the stem, upper leaves, lower leaves, roots and reproductive parts.
Short Explanation
Essential Plant Nutrients
Plants require macronutrients in large quantities and micronutrients in small quantities. Both groups are equally essential for healthy growth, development and reproduction.
Mineral elements are absorbed from the soil or from a culture solution. The quantity required determines whether an element is classified as a macronutrient or a micronutrient.
Macronutrients
Required in large quantities. Examples: nitrogen, phosphorus, potassium, magnesium, calcium, sulphur, oxygen, carbon and hydrogen.
Micronutrients
Required in small quantities. Examples: boron, iron, copper, molybdenum, manganese and zinc.
Functions of Macronutrients
| Macronutrient | Functions |
|---|---|
| Nitrogen | Synthesises protein, chlorophyll, enzyme and nucleic acid. Helps the growth of branches and leaves. Increases the production of fruits and seeds. |
| Phosphorus | Synthesises protein and nucleic acid. Promotes cell division for the production of flowers and fruits. |
| Potassium | Synthesises protein. Promotes plant cell division. Strengthens resistance to infectious diseases. |
| Magnesium | Important component in chlorophyll. |
| Calcium | Synthesises spindle fibres during cell division. Helps growth of meristem at tips of shoots and roots. |
| Sulphur | Synthesises protein and chlorophyll. Helps development of fruits. Promotes plant cell division. |
| Oxygen | Involved in plant cell respiration to produce energy. |
| Carbon & Hydrogen | Build sugar or starch during photosynthesis. Build cellulose. |
Functions of Micronutrients
| Micronutrient | Functions |
|---|---|
| Boron | Synthesises chlorophyll and cell wall. Helps the formation of fruits and seeds. |
| Iron | Helps growth of young tree parts. Helps cell respiration. |
| Copper | Involved in photosynthesis and respiration. |
| Molybdenum | Synthesises protein. Helps growth of plants. |
| Manganese | Involved in photosynthesis and respiration. Helps formation of amino acid. |
| Zinc | Helps synthesis of protein and formation of chlorophyll. Helps formation of leaves. |
Effects of Nitrogen, Phosphorus and Potassium Deficiency
| Plant Feature | Healthy Plant | Nitrogen Deficiency | Phosphorus Deficiency | Potassium Deficiency |
|---|---|---|---|---|
| Plant Growth & Stem | Normal plant growth; strong stem | Stunted plant growth; weak stem | Stunted plant growth, slow to grow and mature; weak stem | Stunted plant growth, dies before reaching maturity; weak stem |
| Leaves at Top | Small and light green | Smaller and fall easily | Smaller and purplish | Have brown spots, curled ends, and chlorosis |
| Leaves at Bottom | Bigger and dark green | Pale green or yellow (chlorosis / lacking chlorophyll) | Bluish green, curled, with brown edges | Wilt and have dead tissues around the edges |
| Flowers & Fruits | Normal production | Production is stunted | Production stops | Production of flowers is reduced, production of fruit stops |
| Root Growth | Normal growth | Normal growth | Growth deteriorates | Growth is reduced |
Experiment 2.2: Studying Macronutrient Deficiency
Aim: To study the effects of macronutrient (nitrogen, phosphorus, and potassium) deficiency on plant growth.
Hypothesis: Deficiency of macronutrients (nitrogen, phosphorus, and potassium) stunts plant growth.
Variables: Manipulated — type of culture solution (complete, without nitrogen, without phosphorus, without potassium). Responding — growth of plant. Constant — volume of culture solution, size and type of seedlings, light, and temperature.
Key procedures and precautions: Seedlings are placed in boiling tubes wrapped in black paper to prevent light from entering and stop the growth of green algae. The culture solution is aerated for 5 minutes every day using an air pump to provide oxygen for root respiration. The culture solution is replaced once a week with fresh culture solution of the same type to replenish nutrients and maintain nutrient concentration. The setup is placed in a bright place with sunlight for photosynthesis.
Try to Answer First
Answer in your mind, then press “Check Answer”.
What is the difference between macronutrients and micronutrients?
What are the specific symptoms observed on the lower leaves of a plant deficient in nitrogen?
Why are the boiling tubes wrapped in black paper in Experiment 2.2?
Common Mistakes
- Confusing the deficiency symptoms of nitrogen and phosphorus. Phosphorus deficiency causes leaves to turn purplish at the top and bluish green with brown edges at the bottom, not pale yellow.
- Stating that root growth deteriorates in nitrogen deficiency. In a nitrogen-deficient plant, root growth remains normal, whereas root growth deteriorates in phosphorus deficiency and is reduced in potassium deficiency.
- Forgetting to aerate the culture solution during hydroponic experiments. Roots require dissolved oxygen for cellular respiration to absorb nutrients actively.
Concept Misunderstandings
Micronutrients are less important than macronutrients because plants only need them in tiny amounts.
Both macronutrients and micronutrients are equally essential for plant survival and normal development. The terms “macro” and “micro” refer only to the quantity needed, not their importance.
Wrapping boiling tubes in black paper is done to keep the roots warm.
Wrapping the tube in black paper is strictly to prevent sunlight penetration, thereby inhibiting algae from growing and competing for nutrients.
Summary
- Plants require macronutrients in large quantities and micronutrients in small quantities.
- Nitrogen is vital for vegetative growth and chlorophyll synthesis.
- Phosphorus is needed for nucleic acids and root/flower development.
- Potassium is needed for enzyme activation and disease resistance.
- Deficiency in any of these three elements impairs plant development, producing distinct leaf discolourations, stunted root or shoot growth, and failure to produce fruits or flowers.
Short Activity
A. Objective Quiz
1 Which of the following macronutrients is a primary component of chlorophyll and causes chlorosis when deficient?
2 A farmer observes that his crops have stunted growth, small purplish top leaves, and deteriorating root systems. Which nutrient is most likely deficient in the soil?
B. Fill in the Blanks
3 In a culture solution experiment, air is pumped daily into the boiling tube to supply for root respiration.
4 Plants deficient in potassium develop leaves with spots at the top and dead tissues around the edges of the bottom leaves.
C. Drag and Drop: Match the Nutrient to Its Function
Drag each nutrient to its correct function. On a phone, tap an answer first, then tap a matching box. Tap the Answer Choices area to return a selected item.
C. Match the Nutrient to Its Function
Write the correct nutrient next to each function.
| Function in Plant | Nutrient |
|---|---|
| 1. Synthesises spindle fibres during cell division and helps growth of meristem | |
| 2. Synthesises chlorophyll and cell wall, and helps formation of fruits and seeds | |
| 3. Promotes plant cell division and strengthens resistance to infectious diseases | |
| 4. Helps growth of young tree parts and helps cell respiration |
Answer choices: Calcium • Boron • Potassium • Iron
