140. Match the components of List I with List II.
List I                                                                              List II
A. Legume                                                                   I. Frankia
B. Azolla                                                                      II. Azorhizobium
C. Sugarcane                                                             III. Anabaena
D. Actinorhizal                                                         IV. Acetobacter
(a) A-I, B-III, C-II, D-IV
(b) A-II, B-III, C-I, D-IV
(c) A-II, B-III, C-IV, D-I
(d) A-II, B-IV, C-I, D-III

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Symbiotic Relationships and Nitrogen Fixation in Plants

Plants require nitrogen to grow, but nitrogen in its atmospheric form (N₂) is not directly usable by most plants. Some plants, however, have formed symbiotic relationships with nitrogen-fixing bacteria to meet their nitrogen needs. These relationships are vital for maintaining soil health and plant productivity. Let’s explore how different plants engage with nitrogen-fixing bacteria to aid in nitrogen fixation.

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Key Symbiotic Relationships in Plants

1. Legumes and Rhizobium Bacteria

   • Symbiotic Relationship: Legumes such as beans, peas, and lentils form a symbiotic relationship with Rhizobium bacteria. These bacteria reside in the root nodules of legumes and fix nitrogen from the atmosphere into a form that the plant can use.

   • Bacteria: Azorhizobium (correct answer) helps in nitrogen fixation in legumes.

2. Azolla and Anabaena

   • Symbiotic Relationship: Azolla, a water fern, has a mutualistic relationship with Anabaena, a nitrogen-fixing cyanobacterium. This symbiosis is particularly important in rice paddies, where the Azolla-Anabaena system adds nitrogen to the soil and increases rice yields.

   • Bacteria: Anabaena (correct answer) forms a symbiotic relationship with Azolla.

3. Sugarcane and Acetobacter

   • Symbiotic Relationship: Sugarcane can form a relationship with Acetobacter bacteria that help in fixing nitrogen. These bacteria provide nitrogen to the sugarcane, enhancing its growth.

   • Bacteria: Acetobacter (correct answer) supports nitrogen fixation in sugarcane.

4. Actinorhizal Plants and Frankia

   • Symbiotic Relationship: Actinorhizal plants, such as alder trees, form a symbiotic relationship with Frankia, a nitrogen-fixing actinobacterium. This relationship helps these plants thrive in nitrogen-deficient soils.

   • Bacteria: Frankia (correct answer) helps actinorhizal plants in nitrogen fixation.

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Correct Answer:

(b) A-II, B-III, C-I, D-IV

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Conclusion

Nitrogen fixation is a crucial process that supports plant growth and soil fertility. Understanding the relationships between plants and nitrogen-fixing bacteria, such as Rhizobium, Anabaena, Acetobacter, and Frankia, highlights the importance of symbiosis in agriculture and ecosystems. These bacteria not only help plants obtain essential nutrients but also contribute to healthier soils and more sustainable farming practices.