Question

Unicellular symbiotic organisms improve yield of legumes by

• A. Fixing atmospheric nitrogen without colonising roots of host plant
• B. Fixing atmospheric nitrogen and colonising roots of host plant
• C. Inducing the host plant to absorb more phosphorus
• D. Stimulating the host plant to become tolerant to drought

Answer 1

Answer: (B)

Fixing atmospheric nitrogen and colonising roots of host plant

Symbiotic nitrogen fixing bacteria form a mutually beneficial association with the plants. The bacteria obtain food and shelter from plants. In return, they give a part of their fixed nitrogen to the plants. The most important of the symbiotic nitrogen fixing bacteria is Rhizobium. It forms nodule on the roots of legume plants. They develop the ability to fix nitrogen only when they are present inside the root nodules. In the nodule cells, bacteria (bacteroids) lie in groups surrounded by membrane of the host which is lined by a pink-red pigment called leghaemoglobin. So, the correct answer is 'Fixing atmospheric nitrogen and colonising roots of host plant'.