Overspecialized adaptations
A) promote survival in a wide range of habitats.
B) are the result of natural selection.
C) are found only in species with very wide geographic ranges.
D) enable a species to be more adaptable to environmental changes.
E) enable a species to be more independent of other species.
B
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Biological nitrogen fixation is carried out ________.
A. only by a limited number of prokaryotes B. only in totally anaerobic environments C. only by prokaryotes in symbiotic relationships with plants D. by prokaryotes and some protists
In Drosophila, germ cells develop from pole nuclei isolated from the rest of the embryo at the posterior end. How are they "protected" from the effects of posterior concentrations of zygote-produced mRNAs and proteins?
A) Their genes have unresponsive promoters. B) The cytoplasm at the pole is separated by a compartmentalizing membrane. C) The pair-rule, gap, and segmentation genes are not expressed in these cells. D) Homeotic genes in these cells are inhibited by zygotic genes from the mother. E) Paternal effects operate on the embryo only in the pole cells.
Low LET radiation is used to irradiate a cell culture. Suppose the cell culture is subjected to a high oxygen environment during the irradiation. This means a higher percentage of cells will:
a) be more resistant to the radiation. b) be more likely to survive the irradiation. c) be more likely to die as a result of the irradiation. d) not be affected by the presence of oxygen.
Why must water that has moved to the interstitial fluid in the medulla be quickly removed from the interstitial fluid?
A) to prevent dilution of urine B) to prevent destruction of the concentration gradient necessary for water reabsorption C) to equilibrate the concentration of solutes in the cortex and medulla D) to maintain an environment for transport of nutrients