Mutation in master regulators, such as those governing the formation of body segments called _____________ that later develop into bones and skeletal muscles, are usually lethal to the embryo.
A. blastocysts
B. somites
C. embryonic disks
D. amnion
E. pharyngeal arches
Answer: B
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Most of the water that evaporates from leaves passes out through the
A. cuticle. B. ends of xylem vessels. C. epidermis. D. spaces between epidermal cells. E. stomata.
Regions of a specimen with higher electron density scatter ________ electrons and, therefore, appear ________ in the image projected onto the screen of a transmission electron microscope.
A. fewer; lighter B. more; lighter C. fewer; darker D. more; darker
Which of the following contradicts the one-gene, one-enzyme hypothesis?
A) A mutation in a single gene can result in a defective protein. B) Alkaptonuria results when individuals lack a single enzyme involved in the catalysis of homogentisic acid. C) Sickle-cell anemia results in defective hemoglobin. D) A single antibody gene can code for different related proteins, depending on the splicing that takes place post-transcriptionally.
When bar-headed geese fly at very high altitudes (possibly over Mount Everest!), they breathe very thin air where the partial pressure of oxygen is very low compared to that at sea level. They are able to do this because they have a modified version of
the hemoglobin protein. To which of the following is their hemoglobin protein most likely similar in terms of its ability to bind oxygen? A) an adult human B) a human fetus C) a bird that lives at sea level D) an earthworm