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Q58 (IAS/2022) Environment & Ecology › Ecology & Ecosystem Basics › Biogeochemical cycles Official Key

Which of the following are nitrogen-fixing plants ? 1. Alfalfa 2. Amaranth 3. Chickpea 4. Clover 5. Purslane (Kulfa) 6. Spinach Select the correct answer using the code given below :

Result
Your answer: —  ·  Correct: A
Explanation

The correct answer is Option 1 (1, 3 and 4 only). Nitrogen fixation is a biological process where certain plants, primarily belonging to the Leguminosae (Fabaceae) family, host Rhizobium bacteria in their root nodules to convert atmospheric nitrogen into ammonia.

  • Alfalfa (1), Chickpea (3), and Clover (4) are all leguminous plants. They are well-known for their symbiotic relationship with nitrogen-fixing bacteria, making them essential for soil fertility and crop rotation.
  • Amaranth (2) belongs to the Amaranthaceae family and does not fix nitrogen.
  • Purslane (5) (Portulaca oleracea) and Spinach (6) (Spinacia oleracea) are non-leguminous leafy vegetables that lack the biological mechanism to fix atmospheric nitrogen; instead, they are heavy consumers of soil nitrogen.

Since only Alfalfa, Chickpea, and Clover possess nitrogen-fixing capabilities, Option 1 is the only scientifically accurate choice.

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Q. Which of the following are nitrogen-fixing plants ? 1. Alfalfa 2. Amaranth 3. Chickpea 4. Clover 5. Purslane (Kulfa) 6. Spinach Select th…
At a glance
Origin: Mixed / unclear origin Fairness: Moderate fairness Books / CA: 5/10 · 0/10
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This is a classic 'Identify the Legume' test disguised as a science question. Standard texts (NCERT Geography, Shankar Environment) explicitly list Alfalfa, Clover, and Chickpea as nitrogen fixers. The strategy is binary: Is it a legume (pulse/fodder)? Yes = Fixer. Is it a leafy vegetable (Spinach/Amaranth)? No = Consumer.

How this question is built

This question can be broken into the following sub-statements. Tap a statement sentence to jump into its detailed analysis.

Statement 1
Is alfalfa (Medicago sativa) a nitrogen-fixing plant?
Origin: Direct from books Fairness: Straightforward Book-answerable
From standard books
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
Presence: 5/5
“Te nitrogen cycle involves the major constituent of the atmosphere, (78.084 per cent of each breath we take). Nitrogen is also an important element in the formation of organic molecules, especially proteins, and therefore is essential to living processes. A simplifed view of the nitrogen cycle is portrayed in Fig. 1.9. Te vast atmospheric reservoir is however inaccessible directly to most organisms. Te key link to life is provided by nitrogen-fxing bacteria, which live principally in the soil and are associated with the roots of certain plants. For example, the legumes such as alfalfa, beans, clover, pulses, peas, soybeans, green-manuring crops and peanuts.”
Why this source?
  • Explicitly lists alfalfa among legumes associated with nitrogen-fixing bacteria.
  • Connects legumes (including alfalfa) to root-associated nitrogen fixation used in agriculture.
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Presence: 4/5
“Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant. The influence of large animals like ants, termites, earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil that comes out of their body changes.”
Why this source?
  • Defines nitrogen fixation by Rhizobium in root nodules of leguminous plants.
  • Shows the mechanism by which leguminous hosts obtain fixed nitrogen from bacteria.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
Presence: 4/5
“& srnrul<zrR ". N ,- / & f. -.:.:u' ,\SACADEMY *d6#.,r'' tufYl' 'J *w{d )/ uY./ include free living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root-nodule plants (e.g., Rhizobium) as well as blue-green algae (e.g., Anabaena, Spirulina). Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialized bacteria: Nitrosomonas bacteria promote transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.”
Why this source?
  • Describes symbiotic nitrogen-fixing bacteria living in association with leguminous plants.
  • Names groups of free-living and symbiotic nitrogen fixers relevant to legumes.
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