Explain why stromatolites are believed to hold a clue to the origin of the first prokaryotic cells on Earth during the Precambrian Era.
What will be an ideal response?
Answers may vary but should indicate that the oldest fossils resemble today's cyanobacteria. The outer surface of stromatolites are alive with cyanobacteria. It is believed that these cyanobacteria released oxygen into the atmosphere which eventually contributed to the ozone shield.
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Which proteins in the plasma membrane identify a cell as part of the same individual or as foreign?
a. transport proteins b. recognition proteins c. receptor proteins d. cell adhesion proteins e. nuclear proteins
You decide to alter the rate of a reaction. Which of the following is not going to help you increase the rate of this reaction?
a. adding more reactants b. adding more enzyme c. adding heat d. mechanically stirring the contents of a beaker of reactants e. adding more product
A single, quick contraction of skeletal muscle is called a:
a. simple twitch. b. tetanus. c. brief contraction. d. red fiber contraction. e. white fiber contraction.
Obligate anaerobes may be cultured in the laboratory
A) in a reducing medium. B) in a standard incubator. C) in standard Petri plates. D) on blood agar plates. E) in standard complex media.