How do Rhizobia bacteria colonize root cells to conduct N fixation?
What will be an ideal response?
Rhizobia are attracted to the legume by chemotaxis toward plant flavonoids. Nod factors (protein molecules composed of chitin with lipid attachments) establish species-specificity for the plant to detect the Rhizobium species. The Nod factor induces an epidermal root hair to curl around the bacterium and take it up into the infection thread, a tube of plant cell wall material. The plant nucleus directs then tube growth inside the plant cell. The thread eventually penetrates the plant cortical cells, where the bacteria lose their cell walls and become nitrogen-fixing bacteroids. The bacteriods remain sequestered within a sac of plant-derived membrane called a symbiosome. The membrane of the symbiosome contains transporters that exchange nutrients between bacteriods and plant cell.
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Reciprocal translocations can affect gene dosage because:
A. the genes involved in the translocation are nonfunctional. B. the two chromosomes involved in the translocation may not assort together during meiosis. C. the two chromosomes involved in the translocation always assort together during meiosis. D. reciprocal translocation involves the duplication of one set of genes and the deletion of another set of genes. E. none of these
Variation that approximates a bell-shaped curve when plotted on a bar graph is
a. undergoing disruptive selection. b. undergoing stabilizing selection. c. quantitative variation. d. qualitative variation. e. in genetic equilibrium.
Darwin made which large set of observations on the Beagle during his four-year voyage?
A. An individual's chance of survival is random. B. Populations grow constantly. C. More individuals of a population are born than survive to reproduce. D. Species do not appear to change over time. E. Organisms are varied and some variations are inherited.
Mosses have stems, roots, and leaves
____________________ Indicate whether the statement is true or false.