Viroids characteristically are composed of
A. ssRNA.
B. dsRNA.
C. ssDNA.
D. dsDNA.
A
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Human triploid and tetraploid fetuses occur, but they are inviable and undergo spontaneous abortion. Any of the following events could produce a polyploid fetus EXCEPT:
A. defective spindle apparatus during early mitosis. B. failure of homologous chromosome separation. C. fertilization of an egg by more than one sperm. D. chromosome duplication without cell division. E. development of an unfertilized ovum.
Paralytic shellfish poisoning occurs when humans eat shellfish that have fed on
A. Gonyaulax spp. B. Salmonella spp. C. Vibrio cholerae. D. E. coli.
What would be the best approach to curbing excessive human population growth?
A. lowering birth rates through education and family planning B. a return to historical health care practices C. encouraging women to postpone children till after age 35 D. embracing traditional agricultural practices
The water absorption rate of a plant's roots is greatly increased by
A. presence of many stomata only. B. presence of root hairs only. C. both association with mycorrhizal fungi and presence of root hairs. D. association with mycorrhizal fungi only. E. both presence of many stomata and root hairs.