An element's mass number is equal to the sum of its
a. protons and electrons.
b. protons and neutrons.
c. electrons and neutrons.
d. protons only.
e. electrons only.
B
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Most eukaryotic genes contain noncoding sequences called ________ that are interspersed with the coding sequences.
A. introns B. exons C. codons D. spacers E. spliceosomes
The hard mineral defense of silica plates found in some grasses is effective because:
A. silica does not taste good, so herbivores don't feed on the grass that contains it. B. silica is abrasive and it wears down insect mouth parts, so insects feed less efficiently and more slowly. C. silica is a chemical defense that is toxic to most herbivores. D. silica is able to be consumed by herbivores and used to deter their predators. E. silica binds to proteins and prevents their uptake from the guts of herbivores.
Nucleophilic attack:
A. is carried out by a strongly electronegative atom such as carbon or hydrogen. B. can result in the formation of the transition state of the reaction. C. by an OH (hydroxyl) group on an inorganic phosphate molecule can cause hydrolysis of a chemical bond. D. occurs when a weakly electronegative atom attacks a strongly electronegative atom. E. never forms bonds between reactants and the enzyme active site.
Which of the following options lists major events in the history of life on Earth in the proper order, from earliest to most recent?
A) first prokaryotes, photosynthesis, colonization of land by plants and fungi, first eukaryotes B) first eukaryotes, photosynthesis, colonization of land by plants and fungi, first prokaryotes C) first prokaryotes, first eukaryotes, photosynthesis, colonization of land by plants and fungi D) first prokaryotes, photosynthesis, first eukaryotes, colonization of land by plants and fungi