The natural role of restriction enzymes in bacteria is to
A. make conjugation more efficient.
B. allow transposons to move to another place in the chromosome.
C. protect the cell from invading phages.
D. allow cells to accept foreign DNA.
E. provide the cell with new phenotypes, such as antibiotic resistance.
Answer: C
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Which of the following statements about double fertilization in angiosperms is correct?
A) One pollen grain combines with the egg to form the zygote, and one pollen grain combines with the polar nuclei to form endosperm. Two sperm combine with a polar nucleus to form endosperm. B) Two pollen grains combine with two ovules to form the zygote and endosperm. C) One sperm combines with the polar nuclei to form the zygote, and one sperm combines with the egg to form endosperm. D) One sperm combines with the egg to form the zygote, and one sperm combines with the polar nuclei to form endosperm.
The most common method used by clinical microbiology labs for identifying bacteria are ________.
A. biochemical B. DNA fingerprinting C. morphological D. PCR
Which of the following statements best describes the history of life on Earth?
A) The Earth had multicellular life-forms for most of its history. B) The Earth had single-celled life-forms for most of its history. C) The Earth was lifeless far longer than it had living things. D) The Earth had photosynthetic organisms about 100 million years after it formed.
Severe combined immunodeficiency occurs when
a. T cells are improperly formed. b. B cells are improperly formed. c. an individual has no adaptive immunity. d. all of the above occur.