Explain the process by which leguminous plants obtain usable nitrogen from the atmosphere, mentioning the role of root nodules, bacteria, and the subsequent assimilation into plant proteins.
Answer
Atmospheric N₂ is fixed by rhizobial bacteria in root nodules to ammonia, which is assimilated into amino acids and transported throughout the plant.
Step-by-step solution
- State that leguminous plants form a symbiotic association with nitrogen‑fixing bacteria (Rhizobium) in specialised root structures called nodules.
- Explain that inside the nodules, the enzyme nitrogenase in Rhizobium converts atmospheric N₂ into ammonia (NH₃).
- Mention that ammonia is quickly protonated to form ammonium (NH₄⁺), which the plant can uptake.
- Describe how the plant incorporates NH₄⁺ into the amino acid glutamine via the enzyme glutamine synthetase.
- Show that glutamine transfers its amino group to other carbon skeletons, forming a variety of amino acids that are used for protein synthesis.
- Conclude that the newly formed proteins are transported via the phloem to other parts of the plant, completing the nitrogen assimilation cycle.
Common mistake: Omitting the involvement of rhizobium bacteria or the conversion of ammonia to amino acids.
Concept tested: Nitrogen fixation and assimilation in legumes
Published · How this solution was prepared and checked
Related questions
- 1 Explain how oxygen is transported from the alveoli of the lungs to the body cells.
- 2 What is the pigment present in chloroplasts that captures sunlight for photosynthesis?
- 3 Which tissue in a tall tree is primarily responsible for the upward movement of water from roots to leaves?
- 4 A plant loses 0.12 g of water in 30 minutes. Calculate the rate of transpiration in milligrams per minute.
- 5 Which enzyme present in human saliva initiates the digestion of carbohydrates?
- 6 A 10 g sample of starch (molar mass 162 g·mol⁻¹) is completely hydrolyzed by amylase to glucose (molar mass 180 g·mol⁻¹). Calculate the mass of glucose formed.