CBSE Questions for Class 11 Medical Biology Mineral Nutrition Quiz 11 - MCQExams.com

Frankia is a Gram-positive species of actinomycete filamentous bacterium that lives in symbiosis with actinorhizal plants of the genus Alnus. It is a nitrogen-fixing bacterium and forms nodules on the roots of non-leguminous trees. 

Thus, the correct answer is 'Frankia.'

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'.

Correct Option: A

Explanation:

In the picture

• P represents soil particles: Since the image depicts a root system, the outer layer shows soil.
• Q represents root hair: The elongated, yellow structures are root hair and they play an important role in nutrient and water absorption.
• R represents bacteria: Various microbes such as nitrogen-fixing bacteria can be found in the soil near plant roots.

Hence, the correct option is P – Soil Particles, Q – Root hair, R - Bacteria 

Correct Option: A

Explanation:

• Molecular nitrogen which is present within the air can't be utilized directly by plants, it has to be converted into compounds before utilization.
• Rhizobium species are included in the Symbiotic organic process which occurs on the roots of leguminous plants.
• But to make nodules so on, convert it into compound nitrogen, non-leguminous plants like Alnus are involved.
• The best example involved in nodule formation is actinomycetes called Frankia.

In principle, the reduction of N2 to NH3 is a six-electron process.

However, the biological reaction always generates at least 1 mol of H2 in addition to 2 mol of NH3 for each mole of N≡N. Hence, an input of two additional electrons is required.

In most nitrogen-fixing microorganisms, the eight high-potential electrons come from reduced ferredoxin, generated by photosynthesis or oxidative processes. Two molecules of ATP are hydrolyzed for each electron transferred. Thus, at least 16 molecules of ATP are hydrolyzed for each molecule of N2 reduced.

Again, ATP hydrolysis is not required to make nitrogen reduction favorable thermodynamically. Rather, it is essential to reduce the heights of activation barriers along the reaction pathway, thus making the reaction kinetically feasible.

Here four ammonia molecules have to be produced from two nitrogen molecules, so (16 X 2) = 32 ATP will be hydrolysed. 

So the correct option is '32'.