A mordant that is applied after the primary stain to bond chemically the alkaline dye to the bacterial cell wall is:
a. safranin.
b. crystal violet.
c. Gram's iodine.
d. Gram's decolorizer.
C
Gram's iodine serves to stabilize the crystal violet in the cell wall of gram-positive bacteria.
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When yeast cells of opposite mating types are in close proximity, cell changes occur inside those cells that result in the polymerization of actin filaments, allowing the yeast cells to mate
Those changes in cell behavior are initially due to signaling molecules (pheromones) released by the yeast cells. Pheromones are A) a type of steroid hormone that diffuses through the plasma membrane causing cytoplasmic actin proteins to form filaments B) a type of hormone that binds cell surface receptors causing cytoplasmic actin proteins to form filaments C) signaling molecules that bind cell surface receptors causing yeast cells to become motile, insuring mating success D) signaling molecules that cause the extracellular matrix of yeast cells to thicken in preparation for cell fusion E) signaling molecules that cause intracellular G proteins to be inhibited
Which scenario is not an example of a prezygotic isolating mechanism?
a. An iris blooms at a different time of the year than a daffodil. b. A peacock puts on a different mating display than a sparrow. c. A snail with a shell coiling in one direction cannot mate with a snail whose shell curls in the other direction. d. A zebroid, a cross between a horse and zebra, is sterile. e. One type of roundworm would reject the sperm from another species of roundworm.
Which is the correct pairing of nucleotides in DNA?
1.guanine - adenine, cytosine - thymine
2.thymine - guanine, cytosine - adenine
3.cytosine - thymine, guanine - adenine
4.guanine - cytosine, adenine - thymine
Carbon dioxide crosses the plasma membrane by simple diffusion. The rate at which carbon dioxide enters the cell is determined by the
A) amount of energy being produced by the cell. B) amount of transport protein in the membrane. C) concentration of carbon dioxide on each side of the membrane. D) amount of oxygen being exported from the cell. E) amount of carbon dioxide outside of the cell.