The external covering of the body is produced by
a. the ectoderm only.
b. the endoderm only.
c. the mesoderm only.
d. the ectoderm and endoderm.
e. all of the germ layers.
Answer: a
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A hydrogen bond is a(n)
a. sharing of a pair of electrons between a hydrogen and an oxygen nucleus. b. sharing of a pair of electrons between a hydrogen nucleus and either an oxygen or a nitrogen nucleus. c. attractive force between a hydrogen atom and either an oxygen or a nitrogen atom that are in other molecules or within the same molecule. d. covalent bond between two hydrogen atoms. e. covalent bond between a hydrogen atom and either an oxygen atom or a nitrogen atom.
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Indicate whether the statement is true or false
Molecular lesions of DNA are called _____.
a) point mutations b) broken side rails c) cross-linking d) rung breaks