What was the probable role of oxygen gas in the early stages of life's appearance on Earth?
A) Cellular respiration, which depends on oxygen availability, provided abundant energy to the first life-forms.
B) Oxygen promoted the formation of complex organic molecules through physical processes.
C) Oxygen gas tends to disrupt organic molecules, so its absence promoted the formation and stability of complex organic molecules on the early Earth.
D) Abundant atmospheric oxygen would have created an ozone layer, which would have blocked out ultraviolet light and thereby protected the earliest life-forms.
Answer: C
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Chromosomes can be condensed into compact structures, visible with the light microscope, but usually only:
A. while the nuclear pores are open. B. while the proteins are being assembled. C. after the cell is dead. D. while the DNA is being copied into RNA. E. during cell division.
Which of the following human diseases is linked to a class of Epsilonproteobacteria?
A. Guillian-Barre Syndrome B. Diarrhea C. Stomach ulcers D. Gastric cancer
Based on the Mayr definition of a biological species, bacteria cannot be classified as a species for which reason?
A. The DNA sequences of all bacteria are more than 97% identical. B. Bacteria are present everywhere and cannot be reproductively isolated from other bacteria. C. Bacteria cannot reproduce. D. Bacteria do not evolve. E. Bacteria are asexual.
Atoms are composed of a central nucleus which is surrounded by which orbiting particles?
a. Neutrons b. Electrons c. Protons d. Ions