With the appearance of photosynthetic cyanobacteria and aerobic bacteria during the Precambrian era,

A. the amount of UV light reaching the Earth was reduced and chemical evolution slowed.
B. an oxidizing atmosphere developed on Earth.
C. the formation of the ozone shield occurred.
D. All of the choices are correct.


Answer: D

Biology & Microbiology

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A group of interacting serum proteins that provide a nonspecific defense mechanism is

A. complement. B. interferon. C. glycoprotein. D. lysozyme.

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What will be an ideal response?

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The tube feet of echinoderms that are used for locomotion, capturing prey, and gas exchange are "inflated" by the ________, which is unique to the echinoderms

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