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NEET Questions / Botany / Mineral Nutrition / Root Nodule Formation
A mutation in a legume plant prevents the formation of infection threads during rhizobial symbiosis. Which of the following processes would be MOST directly affected?
Recognition of the rhizobia by the root hairs
Curling of root hairs
Formation of the nodule meristem
Release of bacteria into the host cell cytoplasm
Which specific flavonoid is known to induce nod gene expression in Rhizobium leguminosarum when establishing symbiosis with pea plants?
Naringenin
Apigenin
Kaempferol
Luteolin
A researcher observes that a particular legume mutant forms nodules, but these nodules fail to fix nitrogen. Which of the following gene mutations is MOST likely responsible?
Mutation in nod genes
Mutation in genes encoding flavonoid biosynthesis
Mutation in nif genes
Mutation in genes encoding leghemoglobin
The enzyme nitrogenase is highly sensitive to oxygen. How do root nodules maintain a low oxygen environment necessary for nitrogen fixation?
Active transport of oxygen out of the nodule
Anaerobic respiration within the bacteroids
Leghemoglobin binds oxygen, buffering its concentration
Thick cell walls of the nodule prevent oxygen diffusion
Which of the following is NOT a direct consequence of Nod factor signaling in the host plant during root nodule formation?
Root hair curling
Formation of infection threads
Cortical cell division leading to nodule primordia formation
Expression of nif genes in bacteroids
Certain mutant legumes exhibit excessive root hair curling in the presence of rhizobia, but infection threads fail to penetrate the cortex. This phenotype is MOST likely due to a defect in:
Flavonoid production by the root
Rhizobial nod gene expression
Nod factor receptor function
Signaling pathway downstream of Nod factor perception, affecting infection thread growth
During the process of root nodule formation, which of the following is the initial signal molecule released by the plant roots that attracts rhizobia?
Flavonoids
Nod factors
Lectins
Cytokinins
The infection thread, crucial for rhizobial entry into the root hair, is primarily composed of which plant cell wall component?
Cellulose
Pectin
Lignin
Suberin
Which enzyme complex is responsible for the conversion of atmospheric nitrogen to ammonia within the root nodules?
Nitrogenase
Nitrate reductase
Nitrite reductase
Glutamine synthetase
Leghemoglobin, present in root nodules, plays a crucial role in nitrogen fixation by:
Protecting nitrogenase from oxygen
Providing oxygen to nitrogenase
Converting nitrogen to ammonia
Transporting nitrogen to bacteroids
