G protein-coupled receptors are important molecules involved in signal transduction. Which of the following statements about G protein-coupled receptors is true?
a. They are activated only by steroid hormones.
b. They bind only guanine nucleotides.
c. They bind both adenine and guanine nucleotides.
d. They generally contain seven membrane-spanning ? helices.
Ans: d. They generally contain seven membrane-spanning ? helices.
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Lichens are used by scientists as an indicator of pollution because they
a. require nonpolluted water to grow. b. are extremely sensitive to sulfur dioxide. c. react to small amounts of carbon monoxide. d. are very sensitive to ultraviolet radiation. e. respond to increased levels of chlorofluorocarbons.
Which of the following is an actively dividing tissue in plants?
A. Cambium B. Xylem C. Endodermis D. Phloem E. Pith
What do we mean when we use the terms monohybrid cross and dihybrid cross?
A) A monohybrid cross involves a single parent, whereas a dihybrid cross involves two parents. B) A dihybrid cross involves organisms that are heterozygous for two characters that are being studied, and a monohybrid cross involves organisms that are heterozygous for only one character being studied. C) A monohybrid cross is performed for one generation, whereas a dihybrid cross is performed for two generations. D) A monohybrid cross results in a 9:3:3:1 ratio whereas a dihybrid cross gives a 3:1 ratio.
All vertebrates have a(n) __________ system of secretory glands and cells.
Fill in the blank(s) with the appropriate word(s).