Q1. [3] deep thorough-understanding
A farmer notices that even after providing adequate water, sunlight, and carbon dioxide, his crop plants show stunted growth and pale yellow leaves. He suspects a deficiency of certain soil minerals. Explain why mineral elements absorbed from the soil are essential for a plant's autotrophic nutrition even though they are not used directly to synthesise carbohydrates during photosynthesis.
Generated by claude-sonnet-4-6 · 2026-06-26 01:00 · grounding rag
Model Answer
Although photosynthesis requires only CO₂, water, sunlight, and chlorophyll to produce carbohydrates, plants still need minerals from the soil for other essential life processes that support autotrophic nutrition.
- Nitrogen (as nitrates/nitrites) is essential for synthesising proteins and other compounds needed for growth and body-building.
- Magnesium is a component of chlorophyll; without it, chlorophyll cannot be formed, so photosynthesis itself fails — explaining the pale yellow (chlorotic) leaves.
- Phosphorus and iron are needed for synthesising important biological molecules and enzymes.
Thus, minerals are indispensable raw materials for building the plant body and enabling photosynthesis, even though they do not directly form carbohydrates.
Source: Chapter 5, Section 5.2.1 Autotrophic Nutrition
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Explanation
- The key insight examiners want: minerals ≠ carbohydrate synthesis, but they are still essential for body-building (proteins) and for making chlorophyll (so photosynthesis can even occur).
- Always link the symptom (stunted growth = nitrogen/protein deficiency; yellow leaves = magnesium/chlorophyll deficiency) to the mineral — this shows applied understanding.
- Quote the textbook examples: nitrogen → proteins; nitrogen taken as inorganic nitrates/nitrites or via bacteria. Mention magnesium explicitly since the question gives the chlorosis clue.
- Do not write a full essay; 3 marks = 3 distinct points clearly stated.