Multiple Choice
Nitrogen fixation is carried out primarily by which of the following?
25
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35. Soil
Nitrogen Fixation
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Which of these describes the initial interaction between Rhizobium and a soybean root?
A
Vesicles containing bacteria bud into cortical cells.
B
The nodule develops vascular tissue.
C
An infection thread is initiated in the root hair of the legume.
D
There is nodule growth in response to secretions from Rhizobium.
E
Soybeans secrete chemical signals that are detected by Rhizobium.
Verified step by step guidance1
Understand the symbiotic relationship between Rhizobium bacteria and leguminous plants like soybeans. This relationship is crucial for nitrogen fixation, which benefits the plant by converting atmospheric nitrogen into a form it can use.
Recognize that the initial interaction involves chemical signaling. Soybean roots secrete specific chemical compounds called flavonoids into the soil.
These flavonoids are detected by Rhizobium bacteria in the soil. In response, the bacteria produce signaling molecules called Nod factors.
The Nod factors are recognized by the soybean root hairs, which leads to changes in the root hair structure, such as curling, to facilitate the entry of the bacteria.
This interaction eventually leads to the formation of an infection thread, allowing the bacteria to enter the root and initiate the formation of root nodules where nitrogen fixation occurs.
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