Embryonic stem cells reach an intermediary level of determination at which they are committed to becoming a particular ______ type, but not necessarily a particular ____ type.
A. cell/tissue
B. tissue/organ
C. tissue/cell
D. organ/tissue
C. tissue/cell
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The extent and duration of cellular response to a signal depend on:
A. the binding affinity of the receptor to the signaling molecule. B. the concentration of the signaling molecule in the vicinity of the receptor. C. the level of expression of the signaltransduction proteins. D. the level of expression of the terminating proteins. E. All of these choices are correct.
Which statement is NOT true?
a. Carbon dioxide is more soluble in fluid than in oxygen. b. Carbon dioxide diffuses more rapidly across the respiratory surface than oxygen does. c. The major muscle involved in breathing is the diaphragm. d. Oxygen is carried primarily by blood plasma. e. Carbon dioxide is carried by the blood plasma.
Which of the following statements is not true concerning olfactory cells?
A. Olfactory cells are modified neurons. B. Olfactory cells end in a tuft of about five cilia. C. Olfactory cells are located in the roof of the nasal cavity. D. Each olfactory cell has its own individual neuron leading to the olfactory bulb. E. Each olfactory cell has only one out of several hundred different types of receptor proteins.
A pregnant mouse is exposed to high levels of a chemical. Many of the mice in her litter are deformed, but when they are interbred with each other, all their offspring are normal. Which two of the following statements could explain these results?
(a) In the deformed mice, somatic cells but not germ cells were mutated. (b) The original mouse's germ cells were mutated. (c) In the deformed mice, germ cells but not somatic cells were mutated. (d) The toxic chemical affects development but is not mutagenic.