The main human activities that have raised atmospheric CO2 levels are
A) succession and adaptive radiation.
B) home development on grasslands and wetlands.
C) drainage of wetlands along rivers and oceans.
D) deforestation and burning fossil fuels.
E) negligible because CO2 levels have risen and fallen naturally regardless of human activity.
D
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DNA replication is bidirectional in prokaryotes with circular chromosomes
Indicate whether the statement is true or false.
Which of the following statements about microtubules is true?
(a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament. (b) The centromere nucleates the microtubules of the mitotic spindle. (c) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell. (d) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.
Phosphofructokinase is an important control enzyme in the regulation of cellular respiration. Which of the following statements concerning phosphofructokinase is not true?
A) It is activated by AMP (derived from ADP). B) It is inhibited by ATP. C) It is activated by citrate, an intermediate of the citric acid cycle. D) It specifically catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate, an early step of glycolysis. E) It is an allosteric enzyme.
Which of the following is derived from the ground tissue system?
A) root hair B) cuticle C) periderm D) pith E) phloem