In a frog embryo, gastrulation
A. is impossible because of the large amount of yolk in the egg.
B. proceeds by invagination and involution as cells roll over the dorsal lip of the blastopore.
C. occurs within the inner cell mass that is embedded in the large amount of yolk.
D. produces a blastocoel displaced into the animal hemisphere.
E. occurs along the primitive streak in the animal hemisphere.
Answer: B
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Heterosis is _______
A. the combination of lethal alleles due to inbreeding B. an increased vigor of hybrids resulting from the crossing of inbred strains C. a measurement of the variance due to environmental factors D. the result of homozygosity of multiple, dominant, detrimental alleles.
Why did local residents in the Pacific Northwest remain hostile to conservation efforts?
a. When the northern spotted owl was listed as endangered, logging workers lost jobs. b. The northern spotted owl has not been listed as endangered. c. When the northern spotted owl was listed as endangered, the logging industry experienced a boom. d. Conservation efforts to protect trees from logging have been unsuccessful. e. Conservation efforts focus on the local population and take their jobs into consideration.
Why does sexual reproduction produce more genetic variability in a population than asexual reproduction?
A. Sexually reproducing organisms mutate more rapidly during DNA replication than asexually reproducing organisms. B. Sexually reproducing organisms mix parental genetics in addition to crossing-over and random alignment. C. Organisms arising from sexual reproduction can change their genetic material in response to environmental changes. D. In sexual reproduction, the parents exchange genetic material of the nuclei, thus increasing their variability. E. Offspring are identical to one parent, when produced through sexual reproduction.
The driving force for the movement of materials in the phloem of plants it
A. gravity B. a difference in osmotic potential between the source and the sink C. root pressure D. transpiration of water through the stomates E. adhesion of water to vessel elements