The Precambrian supereon, in which life first appeared and diversified to multicellular eukaryotes, lasted approximately ___ of the geologic timescale.
A. 50%
B. 30%
C. 15%
D. 85%
E. None of the answer choices is correct.
D. 85%
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In humans and other mammals, dosage compensation is achieved by:
A. males transcribing double the normal amount of copies of X-chromosome genes. B. females decreasing transcription of both X chromosomes by ½. C. females eliminating one X chromosome in each cell. D. females inactivating the paternal X chromosome in each cell. E. females randomly inactivating one X chromosome in each cell.
Asexual reproduction can involve all of the following processes EXCEPT
a. fission. b. fertilization. c. fragmentation. d. budding. e. parthenogenesis.
The carbon dioxide needed for photosynthesis enters the plant through the:
a) roots. b) thylakoid. c) stroma. d) root hairs. e) stomata.
Which hormone affects the greatest variety of cell types?
A) parathyroid hormone B) melatonin C) growth hormone D) calcitonin