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I. All cyanobacteria are N2-fixers II....

I. All cyanobacteria are `N_2`-fixers
II. The main sources of biofertilizers are bacteria, fungi and cyanobacteria
III. Azospirillum and Azotobacter are symbiotic `N_2`-fixers.
IV. Microbes like bacteria and many fungi can be grown on nutritive media to form colonies but they cannot be seen with the naked eyes.

A

All are correct

B

All are wrong

C

only I, III and IV are wrong

D

Only II is wrong

Text Solution

AI Generated Solution

The correct Answer is:
To analyze the statements provided in the question, we will evaluate each one for its correctness based on our knowledge of microbiology and biofertilizers. ### Step-by-Step Solution: 1. **Statement I: All cyanobacteria are N₂-fixers.** - Cyanobacteria, also known as blue-green algae, are known for their ability to fix atmospheric nitrogen (N₂) into a usable form for plants. Thus, this statement is **correct**. 2. **Statement II: The main sources of biofertilizers are bacteria, fungi, and cyanobacteria.** - Biofertilizers are indeed derived from living microorganisms, and the main sources include bacteria (like Rhizobium), fungi (like mycorrhiza), and cyanobacteria. Therefore, this statement is also **correct**. 3. **Statement III: Azospirillum and Azotobacter are symbiotic N₂-fixers.** - Azospirillum and Azotobacter are both nitrogen-fixing bacteria, but they are not symbiotic. Azospirillum is known to associate with the roots of plants, while Azotobacter is free-living in the soil. Therefore, this statement is **incorrect**. 4. **Statement IV: Microbes like bacteria and many fungi can be grown on nutritive media to form colonies, but they cannot be seen with the naked eye.** - It is true that bacteria and fungi can be cultivated on nutritive media to form colonies, but these colonies can often be seen with the naked eye, depending on their size and the medium used. Hence, this statement is **incorrect**. ### Summary of Statements: - **I: Correct** - **II: Correct** - **III: Incorrect** - **IV: Incorrect** ### Final Answer: - The correct statements are I and II, while III and IV are incorrect.
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