The net movement of molecules or ions from a low concentration to a higher concentration is called ____
a. active transport
b. facilitated diffusion
c. exocytosis
d. osmosis
e. diffusion
ANSWER: a
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Indicate whether the statement is true or false.
All multicellular organisms have:
A. organs and organ systems. B. specialized and differentiated cells. C. predators. D. mechanisms for cell-cell adhesion.
In recombinant DNA technology, enzymes used to precisely cut DNA are called
a. DNA ligases. b. restriction enzymes. c. DNA polymerases. d. RNA polymerases. e. vectors.
The concentration of a particular protein, X, in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply
The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal. Which of the following mutations in the gene for X could explain these results? (a) the introduction of a stop codon that truncates protein X at the fourth amino acid (b) a change of the first ATG codon to CCA (c) the deletion of a sequence that encodes sites at which ubiquitin can be attached to the protein (d) a change at a splice site that prevents splicing of the RNA