Which of the following statements is not true of the two alternative hypotheses for how the force is generated to pull water up the xylem?
A. The pectin gel in which cellulose
microfibrils are embedded in the cell wall
causes water to flow into a partially
dehydrated cell wall by osmosis.
B. Water is drawn by capillary action into the
spaces between cellulose microfibrils in
partially dehydrated cell walls.
C. Evaporation out of the stomata causes the
cell walls of those cells lining the intercellular
air spaces to become partially dehydrated.
D. The pectin gel in which cellulose
microfibrils are embedded in the cell wall is
slightly positive in charge, restricting the
diffusion of positively charged ions.
E. Water loss to the air causes a decrease in
water vapor in the air spaces in the leaf.
D
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Many receptor tyrosine kinase pathways have MAPK as a downstream signaling component. MAPK can phosphorylate target proteins. What type of signaling molecule is MAPK?
A. Scaffold B. Adapter protein C. Second messenger D. Enzyme
The cell-mediated response targets intracellular
a. bacteria. b. histamine. c. TCRs. d. MHC markers. e. all of these.
A triploid nucleus cannot undergo meiosis because
a. the DNA cannot replicate. b. not all of the chromosomes can form homologous pairs. c. the sister chromatids cannot separate. d. cytokinesis cannot occur. e. a cell plate cannot form.
Consider a living plant cell in a living leaf that has higher water potential than the fluids surrounding the cell. What would happen to the water?
a. There would be no net flow of water into or out of the cell. b. There would be a gain of water by the cell only if the cell's pressure potential is low enough. c. There would be a net flow of water out of the cell. d. There would be a gain of water by the cell only if the cell's pressure potential is high enough.