The ultimate source of energy flowing into nearly all ecosystems is
A. wind.
B. sunlight.
C. electricity.
D. radioactivity.
Ans: B. sunlight.
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The fate of the embryonic germ layers is:
A. The endoderm forms the gut, the ectoderm forms the epidermis and parts of the nervous system, and the mesoderm forms muscles and most internal organs. B. The endoderm forms the gut, the ectoderm forms the reproductive tract and endocrine system, and the mesoderm forms muscles and most internal organs. C. The endoderm forms the inner part of all internal organs, the mesoderm forms the middle parts, and the ectoderm forms the outer coverings. D. The layers are sequential structures that all disappear during development, with the endoderm appearing first and then is replaced by the mesoderm, which in turn is supplanted by the ectoderm. E. The endoderm is an embryonic structure that disappears early, whereas the ectoderm persists as the skin and the mesoderm as the internal organs.
Ctenophores and Cnidaria both have nerve and muscle cells, but Ctenophores lack Hox genes that occur in both Cnidaria and Porifera. What is the most likely explanation?
a. Porifera diverge from a common ancestor before nerve and muscle cells evolved, then Cnidaria and Ctenophores absorbed viral genomes containing Hox genes from plasmids contained within their environment. b. Hox genes were deleted from the Ctenophore genome after Ctenophores diverged from a common ancestor with Cnidaria, and Porifera developed nerve and muscle cells. c. Hox genes developed in a common ancestor of Cnidaria and Porifera after it diverged from an ancestor in common with Ctenophores, then nerve and muscle cells developed via parallel evolution. d. Hox genes are produced by mitochondria; Porifera lack mitochondria, and therefore cannot contain Hox genes. The presence of nerve and muscle cells is entirely unrelated and irrelevant.
For the polymerase chain reaction to occur,
a. isolated DNA molecules must be primed. b. all DNA fragments must be identical. c. the DNA must remain double stranded. d. a sticky end must be available for the ligase enzyme to function. e. all of these must occur
The stem apical meristem gives rise to:
a. leaf primordia. b. lateral meristems. c. root caps. d. root hairs. e. cork cells.