A __________ is an organ that allows exchange of nutrients between an embryo and its mother. Fill in the blank(s) with the appropriate word(s)
placenta
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In Chase and Hershey’s experiments on bacteriophages, why were radioactive sulfur and phosphorus chosen as tagging elements?
a. Both isotopes have similar half-lives, so measurements would not be confounded by radioactive decay. b. Both sulfur and phosphorus are vital to viral metabolism and are readily absorbed into bacteriophages. c. Sulfur doesn’t occur in DNA, nor phosphorus in protein, so these molecules could be easily distinguished. d. The radiation emitted by these isotopes is strong enough to be detected without being lethal to the cells.
If human white blood cells were extracted from the circulatory system and then placed into an isotonic solution, which one of the following is most likely to occur?
A) Water will rush into the cells, and the cells will swell and eventually burst. B) Because there is more water outside the cell than inside the cell, an equal amount of water will enter the cell and leave the cell. C) There will be no change in the cells because the isotonic environment is in equilibrium with the cells. D) Because a hypertonic environment is highly acidic, these cells will become acidic as well. E) Water will diffuse out of the cells, and they will decrease in cell volume.
Why are epithelial membranes not very thick?
A. Epithelial tissues can only reach a certain thickness because their growth is constrained by microtubules inside the cell membrane. B. Thick epithelial tissues would collapse due to the drying effect of the environment. C. Epithelial tissues are required to support other cells growing on top of the tissue. D. Epithelial tissues are programmed to stop dividing after only a few cell cycles. E. Epithelial tissues play a critical role in transport, and must be thin to allow diffusion to occur.
An important function of nomenclature is to
A) facilitate unambiguous communication. B) clarify relationships among organisms. C) provide an understanding of evolutionary relationships. D) define the characteristics used for classification. E) provide a detailed description of an organism.