Signaling by cadherins is an example of _______ signaling.
a. autocrine
b. endocrine
c. paracrine
d. direct cell-to-cell
Ans: d. direct cell-to-cell
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Which of the following isnot an additional role for nucleosides and nucleotides?
A. primary energy currency of the cell (ATP) B. electron carrier (NAD+) C. methyl group donor (S-adenosylmethionine) D. regulatory molecule (cAMP) E. catalyst for splicing reactions (dUTP)
Methanotrophs affect global temperature. This is because:
A. Methanotrophs use oxygen produced by plants to metabolize methane, thereby reducing the amount of methane in the atmosphere. Since methane is one of the greenhouse gases whose accumulation causes a rise in global temperature, its reduction by methanotrophs helps prevent global warming. B. Methanotrophs convert methane to carbon dioxide and increase the amount of carbon dioxide in the atmosphere. Since carbon dioxide is one of the greenhouse gases whose accumulation causes a rise in global temperature, its production by methanotrophs contributes to global warming. C. Methanotrophs convert carbon dioxide to methane and increase the amount of methane in the atmosphere. Since methane is one of the greenhouse gases whose accumulation causes a rise in global temperature, its production by methanotrophs contributes to global warming. D. Methanotrophs convert methane to carbon dioxide, thereby decreasing the amount of methane in the environment but increasing the amount of carbon dioxide there. Since both methane and carbon dioxide are greenhouse gases whose accumulation causes a rise in global temperature, the decrease in one cancels the increase in the other and methanotrophs have no net effect on global warming. E. Methanotrophs combine carbon dioxide and methane to form petroleum and in this way take both methane and carbon dioxide out of the atmosphere. Since both methane and carbon dioxide are greenhouse gases whose accumulation causes a rise in global temperature, the decrease in both helps prevent global warming.
Which structure prevents blood flowing back into the atria during ventricular contractions?
A. semilunar valves B. atrioventricular valves C. sinoatrial node D. carotid blood shunts E. foramen ovale
Pioneer plant species are usually characterized
by a. small size. b. high dispersal rates. c. slow maturation. d. high dispersal rates and high numbers of offspring e. small size, efficient dispersal mechanisms, and slow maturation.