PREVIOUSLY ASKED IN:
WBPSC Miscellaneous Preliminary 2019
Answer
nitrates, nitrites and urea
Explanation
Nitrogen is a crucial macronutrient for plant growth. Plants cannot absorb free atmospheric nitrogen directly. They absorb it from the soil primarily in the form of inorganic nitrates (NO3-) and nitrites (NO2-). Additionally, plants can also absorb urea directly through their roots or foliage when applied as a fertilizer (though soil microbes often convert it first into ammonium and then nitrates). Therefore, nitrates, nitrites, and urea represent the usable forms.
Key Points
- > Nitrogen is a major component of chlorophyll, the compound by which plants use sunlight energy to produce sugars.
- > Rhizobium bacteria in the root nodules of leguminous plants help fix atmospheric nitrogen.
- > Deficiency of nitrogen causes the yellowing of leaves, a condition known as Chlorosis.
- > Urea was the first organic compound artificially synthesized in a laboratory (by Friedrich Wöhler).
- > Insectivorous plants (like the Pitcher plant) trap insects specifically to fulfill their nitrogen requirements in nitrogen-poor soils.
Additional Information
Essential Mineral Nutrients in Plants
| Nutrient Type | Examples | Primary Function |
|---|---|---|
| Macronutrients | Nitrogen (N), Phosphorus (P), Potassium (K) | Overall growth, cell structure, root development |
| Macronutrients | Magnesium (Mg) | Core component of the chlorophyll molecule |
| Micronutrients | Iron (Fe), Zinc (Zn), Manganese (Mn) | Enzyme activation, electron transport |
| Micronutrients | Boron (B) | Carbohydrate transport |
Memory Tips
- NPK Fertilizers: Stand for Nitrogen, Phosphorus, and Potassium – the primary macronutrients.
- Remember: Plants synthesize proteins, they DO NOT absorb intact proteins from the soil.