The early atmosphere of Earth consisted mainly of
A. oxygen, water vapor, and carbon monoxide.
B. water vapor, hydrogen, and carbon dioxide.
C. hydrogen, carbon monoxide, and nitrogen.
D. hydrogen, oxygen, and carbon dioxide.
E. water vapor, nitrogen, and carbon dioxide.
Answer: E
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The primary reason for hybrid sterility is
a. the inability of the hybrid to attract a mate. b. the difficulty in finding a suitable habitat in which to survive. c. that the hybrids are usually weak and have difficulty surviving to reproductive maturity. d. that hybrids cannot produce viable gametes. e. the inability of the hybrid to develop an appropriate courtship pattern.
The carbon dioxide acceptor in the Calvin-Benson cycle of photosynthesis is ____
a. phosphoglycerate (PGA) b. ribulose bisphosphate (RuBP) c. phosphoglyceraldehyde (PGAL) d. glucose e. Phosphoenolpyruvate
When an individual with an unknown genotype is crossed with an individual that is homozygous
recessive for the trait being studied, the procedure is called a a. backcross. b. dihybrid cross. c. testcross. d. linked cross. e. modified cross.
A scientist studying the oxygen concentration in sealed chambers containing cultured plant cells finds that when the chambers are illuminated, the concentration of oxygen increases. However, when the chambers are kept in the dark, the concentration of oxygen decreases. Why does the oxygen concentration decrease when the chamber is kept in the dark?
(A) Plant cell mitochondria consume oxygen by aerobic respiration. (B) Plant cell chloroplasts run the photosynthetic pathways backward to consume oxygen. (C) Plant cell chloroplasts switch their structure and function and become mitochondria. (D) The chambers must not be properly sealed, so that oxygen is leaking out.