Used light and heavy nitrogen to prove the theory of semiconservative replication. Discovered that DNA is copied in a semiconservative model
Answer: Messelson and Stahl
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Hybridization between different species is rare because it ____
a. requires the breakdown of a barrier preventing interbreeding b. causes lethal mutations in hybrid offspring c. leads to the exchange of genes between closely related species
d. leads to gene flow between species e. contradicts the species concept
To avoid sinking the purple sea snail
a. uses jet propulsion from the mantle to move upward. b. has wings on its foot for swimming. c. has gas vacuoles in its shell. d. produces a bubble raft surrounded by mucus. e. fills its liver with low-density oil.
Neutrophils engulf microbes by phagocytosis to fight an infection. Normally, they perform this function for some time but then die off. These dead cells and other foreign materials form pus. Which cells then clean up all the dead neutrophils?
A) macrophages B) other neutrophils C) T lymphocytes D) eosinophils
Figure 33.17
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Use the accompanying figure to answer the following question.
The structure that protects the eyeball is indicated by the letter ____.
A. A B. B C. C D. D E. E