The significance of Fred Griffith's experiment in which he used two strains of Streptococcus pneumoniae is that
a. the semiconservative nature of DNA replication was finally demonstrated.
b. it demonstrated that harmless bacterial cells had become permanently transformed through a change in the bacterial hereditary system.
c. it confirmed that each cell of a given species contains the same amount of DNA.
d. it demonstrated that radioactively labeled bacteriophages transfer their DNA but not their protein coats to their host bacteria.
e. it demonstrated that mice can change the hereditary content of bacteria.
Answer: b. it demonstrated that harmless bacterial cells had become permanently transformed through a change in the bacterial hereditary system.
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Which structure selectively regulates the transport of substances into and out of a plant cell?
A. The chloroplast B. The nucleus C. The cell wall D. The plasma membrane
In suggesting alternative hypotheses to explain the figure above, your lab partner states that perhaps mosses didn't evolve until recently, which is why they increase after herbs and shrubs. Which of the following would be the best response to your lab partner?
A. If you look carefully at the graph, there were a few mosses present 300,000 years ago, so they probably arose then. B. The percent of moss species has actually been steadily increasing since 300,000 years ago as climates became drier. C. Mosses are bryophytes and resemble early plants, so increases in more recent years more likely indicate a shift in climate. D. Mosses are angiosperms, so they didn't become widespread until the climate was dry enough for pollen transfer. E. Mammoths probably ate the mosses, so they did not appear until after the mammoths went extinct.
When the chromosomes line up at the equatorial plane, you can conclude the cell is in
A. anaphase. B. metaphase. C. interphase. D. telophase. E. prophase.
Every protein has a unique shape and function because:
A) each protein has a unique sequence of amino acids. B) the bonds between the amino acids vary from protein to protein. C) the number of nitrogen atoms in each amino acid differs. D) each protein has a unique sequence of nucleotides.