Plant Physiology

Step 1: Understanding the Concept:
This question requires matching terms from plant biology and tissue culture with their correct definition, example, or associated enzyme.
Step 2: Detailed Explanation:
A. Auxin: This is a class of plant hormones. The principal and most abundant natural auxin is III. Indole-3-Acetic Acid (IAA).
B. Protoplast: To create a protoplast (a plant cell without a wall), enzymes are used to digest the wall components. IV. Pectinase is an enzyme that digests pectin, the substance that glues cells together, and is a key component of the enzyme mixture used for protoplast isolation.
C. Callus: This is, by definition, an I. undifferentiated mass of cell that grows in tissue culture.
D. Cytokinin: This is another class of plant hormones. A well-known synthetic cytokinin is Kinetin, whose chemical name is II. 6-Furfuryl amino purine.
Step 3: Final Answer:
The correct matches are A-III, B-IV, C-I, and D-II.

Step 1: Understanding the Concept:
The question asks for the chemical reason why plants are unable to use the abundant nitrogen gas ( ) directly from the atmosphere. Nitrogen is an essential nutrient for plant growth.
Step 2: Detailed Explanation:
Atmospheric nitrogen exists as a diatomic molecule, .
The two nitrogen atoms in the molecule are linked by a very strong triple covalent bond ( ).
This triple bond has very high bond dissociation energy ( kJ/mol), which makes the molecule chemically inert and extremely stable.
Plants, and indeed almost all eukaryotes, lack the necessary enzymes to break this strong triple bond.
The process of converting atmospheric into a usable form like ammonia ( ) is called nitrogen fixation. This process is primarily carried out by certain prokaryotic microorganisms (like Rhizobium) that possess the enzyme complex called nitrogenase, which can break the triple bond.
Step 3: Final Answer:
The presence of a highly stable triple bond in molecular nitrogen makes it unavailable for direct absorption by plants.

Step 1: Understanding the Concept:
The question asks for the specific role of leghemoglobin, a protein found in the root nodules of nitrogen-fixing leguminous plants.
Step 2: Detailed Explanation:
Symbiotic nitrogen fixation presents a paradox: the nitrogen-fixing bacteria (Rhizobium) are aerobic and require oxygen for cellular respiration to produce the large amounts of ATP needed for nitrogen fixation. However, the key enzyme for this process, nitrogenase, is extremely sensitive to oxygen and is irreversibly inactivated by it.
Leghemoglobin solves this problem. It is an oxygen-binding protein, similar to hemoglobin in animal blood, that gives the active nodules their characteristic pink/red color. Its function is to act as an "oxygen buffer" or "oxygen scavenger". It binds strongly to free oxygen in the nodule, maintaining a very low concentration of free O . This protects the nitrogenase enzyme from damage while still delivering a steady supply of oxygen to the bacterial electron transport chain for respiration.
Therefore, its function is the effective removal or sequestration of free oxygen from the immediate environment of the nitrogenase enzyme.
Step 3: Final Answer:
The function of leghemoglobin is the removal of free oxygen to protect the nitrogenase enzyme.