Histones that are tightly wound by DNA and are the basic unit of chromatin are called
A. operons.
B. nucleosomes.
C. protein clusters.
D. repressor genes.
E. facilitators sites.
B. nucleosomes.
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When 10,000 molecules of ATP are hydrolyzed to ADP and i in a test tube, about half as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation?
A) Cells are open systems, but a test tube is an isolated system. B) Cells are less efficient at heat production than nonliving systems. C) The hydrolysis of ATP in a cell produces different chemical products than does the reaction in a test tube. D) The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes. E) Reactant and product concentrations in the test tube are different from those in the cell.
In a lichen, the mycobiont receives
a. nutrients. b. protection from herbivory. c. aid in sexual reproduction. d. enhanced dispersal of offspring. e. shelter from radiation and desiccation.
Individuals with a vitamin ____ deficiency may develop ____
a. A; bone softening b. D; night blindness c. C; increased blood clotting time d. E; nerve damage e. K; fatigue
Which organelle or structure is absent in plant cells?
A) mitochondria B) microtubules C) centrosomes D) peroxisomes