Consider the following statements about Rhizobium bacteria: 1. They live in the root nodules of leguminous plants. 2. They have a parasitic relationship where they harm the plant. 3. They convert atmospheric oxygen into liquid nitrogen. Which of the statements given above is/are correct?

The correct option is (a). Explanation Rhizobium is a genus of soil bacteria capable of fixing atmospheric nitrogen. It establishes a specific biological association with leguminous plants, playing a vital role in soil fertility and the nitrogen cycle. Statement-wise Analysis: - Statement 1 is Correct: Rhizobium bacteria reside in the roots of leguminous plants (such as peas, beans, and lentils). They induce the formation of specialized structures called root nodules, where the bacteria proliferate and function. - Statement 2 is Incorrect: The relationship between Rhizobium and the leguminous plant is symbiotic (mutualistic), not parasitic. In this association, both partners benefit: the bacteria provide fixed nitrogen to the plant, and the plant provides nutrients (sugars) and shelter to the bacteria. A parasitic relationship involves harm to the host, which is not the case here. - Statement 3 is Incorrect: The primary function of Rhizobium is to convert atmospheric nitrogen ($N_2$) into ammonia ($NH_3$) or related nitrogenous compounds that the plant can absorb and utilize. It does not convert atmospheric oxygen into liquid nitrogen. Key Takeaway: Rhizobium facilitates biological nitrogen fixation through a mutualistic relationship with leguminous plants, converting inert atmospheric nitrogen into ammonia within root nodules.

NCERT Class 8 Science — Chapter 2: Microorganisms : friend and foe

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Consider the following statements about Rhizobium bacteria:

They live in the root nodules of leguminous plants.
They have a parasitic relationship where they harm the plant.
They convert atmospheric oxygen into liquid nitrogen.

Which of the statements given above is/are correct?

Official previous-year question

Verified 1 Aug 2026.

Options

A1 only
B2 only
C1 and 3 only
D1, 2 and 3

Did you get this right?

Solution

The correct option is (a).

Explanation

Rhizobium is a genus of soil bacteria capable of fixing atmospheric nitrogen. It establishes a specific biological association with leguminous plants, playing a vital role in soil fertility and the nitrogen cycle.

Statement-wise Analysis:

Statement 1 is Correct: Rhizobium bacteria reside in the roots of leguminous plants (such as peas, beans, and lentils). They induce the formation of specialized structures called root nodules, where the bacteria proliferate and function.
Statement 2 is Incorrect: The relationship between Rhizobium and the leguminous plant is symbiotic (mutualistic), not parasitic. In this association, both partners benefit: the bacteria provide fixed nitrogen to the plant, and the plant provides nutrients (sugars) and shelter to the bacteria. A parasitic relationship involves harm to the host, which is not the case here.
Statement 3 is Incorrect: The primary function of Rhizobium is to convert atmospheric nitrogen ($N_2$) into ammonia ($NH_3$) or related nitrogenous compounds that the plant can absorb and utilize. It does not convert atmospheric oxygen into liquid nitrogen.

Key Takeaway:
Rhizobium facilitates biological nitrogen fixation through a mutualistic relationship with leguminous plants, converting inert atmospheric nitrogen into ammonia within root nodules.

Your note

More from Chapter 2: Microorganisms : friend and foe

With reference to microorganisms, consider the following statements: 1. They are classified into four major groups: bacteria, fungi, protozoa, and algae. 2. They can survive only in moderate climates and die in ice-cold or hot spring environments. 3. Some microorganisms are unicellular, while others are multicellular. Which of the statements given above is/are correct?

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Which one of the following characteristics distinguishes viruses from other microorganisms?

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Consider the following statements regarding the habitat of microorganisms: 1. They are found in air, water, and soil but not inside the bodies of animals. 2. They can exist freely as well as grow on other organisms. 3. They are capable of surviving in deserts and marshy lands. Which of the statements given above is/are correct?

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Which one of the following human diseases is caused by a protozoan pathogen?

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Consider the following pairs of microorganisms and their classification: 1. Aspergillus : Algae 2. Paramecium : Protozoa 3. Penicillium : Fungi 4. Spirogyra : Bacteria How many of the above pairs are correctly matched?

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Keep practising Chapter 2: Microorganisms : friend and foe

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The correct option is (a).

Explanation

Statement-wise Analysis:

Statement 1 is Correct: Rhizobium bacteria reside in the roots of leguminous plants (such as peas, beans, and lentils). They induce the formation of specialized structures called root nodules, where the bacteria proliferate and function.
Statement 2 is Incorrect: The relationship between Rhizobium and the leguminous plant is symbiotic (mutualistic), not parasitic. In this association, both partners benefit: the bacteria provide fixed nitrogen to the plant, and the plant provides nutrients (sugars) and shelter to the bacteria. A parasitic relationship involves harm to the host, which is not the case here.
Statement 3 is Incorrect: The primary function of Rhizobium is to convert atmospheric nitrogen ($N_2$) into ammonia ($NH_3$) or related nitrogenous compounds that the plant can absorb and utilize. It does not convert atmospheric oxygen into liquid nitrogen.