Plant Nutrition

1. The process of degradation of humus by some microorganisms and release

The process of degradation of humus by some microorganisms and release of inorganic nutrients is known as

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eutrophication
mineralization
humification
stratification
This question was previously asked in
UPSC CISF-AC-EXE – 2024
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The correct answer is B) mineralization.
Mineralization is the process by which organic matter, such as humus, is decomposed by microorganisms into inorganic nutrients (minerals) like nitrates, phosphates, and sulfates. These inorganic nutrients are then available for uptake by plants.
Humification is the process of formation of humus, a stable form of organic matter, from the decomposition of plant and animal residues. Eutrophication is the enrichment of water bodies with nutrients. Stratification refers to the layering of soil or water bodies. Mineralization is a key part of nutrient cycling in ecosystems.

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2. Which one of the following nutrients is *not* available in

Which one of the following nutrients is *not* available in fertilizers?

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Iron
Nitrogen
Phosphorus
Potassium
This question was previously asked in
UPSC CISF-AC-EXE – 2020
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The question asks which nutrient is *not* available in fertilizers among the given options. All listed options (Iron, Nitrogen, Phosphorus, Potassium) are essential plant nutrients and are available in various types of fertilizers. Nitrogen, Phosphorus, and Potassium are primary macronutrients commonly found in NPK fertilizers, which form the bulk of the fertilizer industry. Iron is a micronutrient, required in smaller quantities, but is also available in specific micronutrient fertilizers (e.g., iron chelates) and is often included in complete fertilizer blends.
While all options are plant nutrients and can be found in fertilizers, Nitrogen, Phosphorus, and Potassium are the primary macronutrients (needed in large quantities) and form the basis of most common fertilizers. Iron is a micronutrient (needed in smaller quantities).
The phrasing of the question is potentially misleading, as Iron is indeed available in fertilizers. However, in the context of multiple-choice questions where one option must be selected, and considering the prominence of N, P, and K as the main components of standard fertilizers compared to Iron which is a micronutrient supplement, Iron might be considered the intended answer if the question is implicitly distinguishing between macronutrients and micronutrients in the context of bulk fertilization, despite the poor wording. Given the options, Iron is the least likely to be a major component of a general fertilizer compared to N, P, and K.

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3. Which of the following are nitrogen-fixing plants ? Alfalfa Amarant

Which of the following are nitrogen-fixing plants ?

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  1. Alfalfa
  2. Amaranth
  3. Chickpea
  4. Clover
  5. Purslane (Kulfa)
  6. Spinach

Select the correct answer using the code given below :

1, 3 and 4 only
1, 3, 5 and 6 only
2, 4, 5 and 6 only
1, 2, 4, 5 and 6
This question was previously asked in
UPSC IAS – 2022
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The nitrogen-fixing plants among the given options are Alfalfa, Chickpea, and Clover.
– Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃) or related nitrogenous compounds. In agriculture, this is primarily done by bacteria, notably Rhizobia, which live symbiotically in the root nodules of leguminous plants.
– Alfalfa (Medicago sativa) is a legume and fixes nitrogen.
– Amaranth (Amaranthus spp.) is not a legume and does not fix nitrogen.
– Chickpea (Cicer arietinum) is a legume and fixes nitrogen.
– Clover (Trifolium spp.) is a legume and fixes nitrogen.
– Purslane (Kulfa) (Portulaca oleracea) is not a legume and does not fix nitrogen.
– Spinach (Spinacia oleracea) is not a legume and does not fix nitrogen.
Nitrogen-fixing plants play a crucial role in natural ecosystems and agriculture by increasing soil fertility. They are often used in crop rotation and as cover crops. While legumes are the most common examples of symbiotic nitrogen fixers, certain other plants (like Alnus) also host nitrogen-fixing bacteria (like Frankia).

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4. Depending on the requirements, plant nutrients are classified as micro

Depending on the requirements, plant nutrients are classified as micronutrients and macronutrients. Which one of the following is an example of a macronutrient?

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Manganese
Copper
Magnesium
Chlorine
This question was previously asked in
UPSC CAPF – 2022
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The correct answer is C) Magnesium.
Plant nutrients are classified as macronutrients or micronutrients based on the quantity required by the plant. Macronutrients are needed in relatively large amounts, while micronutrients are needed in very small amounts. The primary macronutrients are Nitrogen (N), Phosphorus (P), and Potassium (K). Secondary macronutrients include Calcium (Ca), Magnesium (Mg), and Sulfur (S). Manganese (Mn), Copper (Cu), and Chlorine (Cl) are classified as micronutrients.
Magnesium is a component of chlorophyll, essential for photosynthesis, and activates many enzymes. Its requirement by plants is relatively high compared to micronutrients.

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5. Which one of the following elements is present in the green pigment of

Which one of the following elements is present in the green pigment of leaves ?

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Magnesium
Iron
Calcium
Copper
This question was previously asked in
UPSC CAPF – 2017
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Magnesium is present in the green pigment of leaves (chlorophyll).
– The green pigment in leaves is called chlorophyll.
– Chlorophyll molecules are crucial for photosynthesis, the process by which plants convert light energy into chemical energy.
– The core structure of the chlorophyll molecule is a porphyrin ring, similar to the heme group in hemoglobin, but with a central magnesium atom coordinating the nitrogen atoms, whereas hemoglobin has iron at its center.
While iron is essential for the synthesis of chlorophyll, it is not a structural component of the chlorophyll molecule itself. Magnesium is the central metal ion within the chlorophyll structure. Calcium is important for cell wall structure and signaling, and copper is a cofactor in various enzymes.

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6. The three primary soil micro-nutrients are

The three primary soil micro-nutrients are

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carbon, oxygen and water
copper, cadmium and carbon
nitrogen, phosphorus and potassium
boron, zinc and magnesium
This question was previously asked in
UPSC CAPF – 2013
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The correct option is C. Nitrogen, Phosphorus, and Potassium are the three primary macronutrients required by plants.
Plants require various nutrients from the soil for healthy growth. These are broadly classified into macronutrients (needed in larger quantities) and micronutrients (needed in smaller quantities). The three most crucial macronutrients, often called primary nutrients, are Nitrogen (N), Phosphorus (P), and Potassium (K). While the question asks for “micro-nutrients”, option C lists the standard “primary” nutrients. Given the options, NPK is the only plausible set of primary nutrients listed.
Other macronutrients include Calcium (Ca), Magnesium (Mg), and Sulfur (S). Micronutrients include Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo), and Chlorine (Cl). Option D lists some micronutrients, but NPK are universally referred to as the primary nutrients. The question’s wording “primary soil micro-nutrients” might be slightly imprecise, potentially intending to ask for primary nutrients or listing common soil nutrients from which to choose the primary ones. In the context of soil fertility and fertilizers, NPK are the standard primary nutrients.

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7. A plant having yellow leaves with dead spots has the deficiency of

A plant having yellow leaves with dead spots has the deficiency of

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Potassium
Magnesium
Nitrate
Phosphate
This question was previously asked in
UPSC NDA-2 – 2016
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A plant having yellow leaves with dead spots likely has a deficiency of Potassium.
Potassium (K) is a mobile nutrient in plants. Deficiency symptoms typically appear first in older leaves because the plant translocates potassium to younger, growing tissues. Common symptoms of potassium deficiency include chlorosis (yellowing) along the margins and tips of older leaves, which progresses inwards. As the deficiency worsens, these yellow areas often develop into necrotic spots (dead tissue), giving the appearance of scorched or brown margins and tips.
Magnesium (Mg) deficiency also causes chlorosis but typically results in interveinal chlorosis (yellowing between the veins while the veins remain green). Nitrate (Nitrogen) deficiency causes general yellowing of the entire leaf, starting with older leaves. Phosphate (Phosphorus) deficiency can cause stunted growth and sometimes purplish discoloration, especially on stems and the undersides of leaves, but not typically yellowing with marginal necrosis.

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8. Which one of the following is a known metallophyte for Fe?

Which one of the following is a known metallophyte for Fe?

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Eichhornia crassipes
Miconia lutescens
Astragalus acemosus
Mentha arvensis
This question was previously asked in
UPSC Geoscientist – 2023
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Eichhornia crassipes (Water Hyacinth) is well-known for its ability to accumulate various heavy metals, including Iron (Fe), Copper (Cu), Cadmium (Cd), Lead (Pb), Mercury (Hg), Nickel (Ni), and Zinc (Zn), from contaminated water. It is widely studied and used in phytoremediation efforts for metal-contaminated aquatic environments.
– Metallophytes are plants tolerant of or able to accumulate high levels of heavy metals.
– Eichhornia crassipes is a prominent example of a plant used for phytoremediation, including the removal or accumulation of iron.
– Miconia species are often associated with nickel accumulation; Astragalus species with selenium accumulation.
Phytoremediation is a process using plants to remove, detoxify, or immobilize environmental pollutants, including heavy metals. While the term metallophyte is often used for terrestrial plants on metalliferous soils, the concept extends to aquatic plants with similar capabilities in water.

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9. Which one among the following is not a micronutrient for plants ?

Which one among the following is not a micronutrient for plants ?

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Iron
Manganese
Magnesium
Chlorine
This question was previously asked in
UPSC CDS-2 – 2024
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Magnesium is a macronutrient for plants, required in relatively large quantities, whereas Iron, Manganese, and Chlorine are micronutrients, required in smaller quantities.
Plant nutrients are classified into macronutrients and micronutrients based on the amount required by the plant for healthy growth.
Essential macronutrients include Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, and Sulfur. Essential micronutrients include Iron, Manganese, Zinc, Copper, Boron, Molybdenum, and Chlorine.

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10. Which set of vegetables is underground stem or modified stem of a

Which set of vegetables is underground stem or modified stem of a plant?

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Potato, artichoke, round gourd
Onion, garlic, carrot
Potato, onion, garlic
Potato, garlic, turnip
This question was previously asked in
UPSC CDS-1 – 2024
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Potato (tuber), onion (bulb), and garlic (bulb) are all considered modified underground stems. A potato tuber is a swollen underground stem used for storage. An onion bulb is a short, modified stem surrounded by fleshy leaves. A garlic bulb is similar, consisting of a central stem with cloves that are modified leaves/buds.
Potato, onion, and garlic are examples of vegetables that are modified underground stems adapted for storage or reproduction.
Carrots and turnips are examples of taproots used for storage, not stems. Artichoke is a flower bud, and round gourd (Tinda) is a fruit.

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