Nitrogen Cycle and Microorganisms

Nitrogen fixation is a crucial process where atmospheric nitrogen is converted into usable compounds by microorganisms. Although nitrogen makes up 78% of the atmosphere, it is not directly usable by most living organisms. Through nitrogen fixation, bacteria such as Rhizobium in leguminous plants convert nitrogen into ammonium ions, which plants can use. This symbiotic relationship enriches the soil, benefiting plant growth even after the plants die.

What is the primary role of nitrogen in living organisms?

• It acts as a catalyst in metabolic reactions.

• It provides energy for cellular processes.

• It is a key component of DNA, RNA, and proteins.

• It forms the structure of cell walls.

What percentage of the Earth's atmosphere is nitrogen?

• 78%

• 90%

• 50%

• 21%

What is the process called when atmospheric nitrogen is converted into nitrogen compounds?

• Respiration

• Transpiration

• Photosynthesis

• Nitrogen fixation

Which microorganisms aid in the conversion of atmospheric nitrogen into ammonium ions?

• Viruses

• Algae

• Fungi

• Microorganisms

What is the role of Rhizobium bacteria in leguminous plants?

• They fix nitrogen in the roots.

• They provide structural support.

• They aid in water absorption.

• They help in photosynthesis.

Where do Rhizobium bacteria reside in leguminous plants?

• In the nodules of the roots

• In the stems

• In the flowers

• In the leaves

What compound is formed first when nitrogen combines with hydrogen?

• Ammonia

• Nitric oxide

• Nitrite

• Nitrate

What is the function of leghemoglobin in nitrogen fixation?

• It transports nitrogen to the leaves.

• It combines with oxygen to promote nitrogenase activity.

• It converts nitrogen into proteins.

• It stores nitrogen in the roots.

What happens to the nitrogen in the soil after the plant dies?

• It evaporates into the atmosphere.

• It decomposes into other elements.

• It is absorbed by other plants.

• It remains in the soil and enriches it.

What is the final form of nitrogen that plants utilize?

• Nitric oxide

• Nitrite

• Nitrate

• Ammonium ion