Oxygen during the early development of the atmosphere was:

a. common.
b. rare.
c. important for photosynthesis.
d. about the same as now.
e. created from the cooling of hot lava.


B

Biology & Microbiology

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Answer the following statement true (T) or false (F)

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A collection of similarly specialized cells and any extracellular material they secrete and maintain describes

(a) an organ. (b) a system. (c) a tissue. (d) organelles.

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The markers that identify "self" are actually

A) genes. B) proteins. C) lipids. D) small surface bumps. E) triplet codons

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Chemical defenses are found in all of the following except 

A. marine animals. B. insects. C. plants. D. snakes, spiders, and fishes. E. Batesian mimics.

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