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Cellular and Molecular Biology

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Legumes, Nitrogen Fixation and Special Genetic Expression

CELLS-QU1LEH

Nitrogen is a vital element for plant growth. It is a major component of chlorophyll, amino acids, ATP and nucleic acids. While the atmosphere contains great quantities of nitrogen, plants can only utilize the reduced form of this element. One method that plants acquire usable nitrogen is through bacterial nitrogen fixation. Bacteria that fix nitrogen in legume roots are called rhizobia.

Biological nitrogen fixation conducted by rhizobia occurs through their use of the enzyme nitrogenase to catalyze the conversion of atmospheric nitrogen to ammonia. Plants can readily utilize ammonia to produce important biological molecules. Legumes are unique in that they form symbiotic relationships with the rhizobia. In return for receiving fixed nitrogen from the rhizobia, the legumes provides them with sugars needed for energy in the nitrogen fixation.

The symbiotic relationship between legumes and rhizobia entails the entrance of the rhizobia into the roots of the legume and the formation of nodules. Interestingly, legume genes are required for this relationship to develop. Genes that are specifically expressed during nodulation are termed nodulins. Specific transcription factors are involved in the rhizobial infection process. Mutations of the nodulin genes or the transcription factors prevents nodule formation.

From the information in this passage, which ONE of the following statements is FALSE in regard to legumes and nitrogen fixation?

A

Legumes express genes that allow nitrogen-fixing bacteria to enter their root hairs.

B

Nitrogen-fixing bacteria use nitrogenase to produce ammonia.

C

Nodulin genes are expressed by bacteria to allow them entrance into root hairs.

D

Transcription factors are required for nodule formation.

E

The symbiotic relationship between legumes and bacteria results in ammonia being traded for sugar.