Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?
A) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.
B) The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism.
C) Cells of each domain evolved proton pumps independently when oceans became more acidic.
D) Proton pumps are necessary to all cell membranes.
A
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Kohler and Lipton first discovered a growth factor (PDGF) by:
A. observing that fibroblasts could not grow in cell culture without adding PDGF to the growth medium. B. observing that fibroblasts could not grow in cell culture without adding bovine blood serum to the growth medium. C. observing that fibroblasts grew better in cell culture when blood serum was added to the growth medium instead of blood plasma. D. observing that fibroblasts could not grow and repair wounding without the action of platelets. E. observing that fibroblasts could not grow in cell culture without the addition of purified red blood cells.
The meiosis that produces the megaspores is
indicated by a. A. b. B. c. C. d. D. e. E.
The portal of entry for the largest number of pathogens is the _____
Fill in the blank(s) with the appropriate word(s).
A biologist discovers an alga that is marine, multicellular, and lives at a depth reached only by blue light. This alga probably belongs to which group?
A) brown algae B) golden algae C) red algae D) green algae E) dinoflagellates