Oxygen built up in the atmosphere approximately 2 billion years ago and
a. occurred due to carbon dioxide being split by lightning strikes.
b. could not have occurred without the oxygen coming from outer space.
c. destroyed ozone forming more oxygen.
d. helped to form the ozone layer that is so important to life today.
e. occurred because aerobic organisms required the oxygen.
D
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With respect to RNA processing, which of the following is false?
A) It leads to the production of alternative gene products. B) Some introns are removed by spliceosomes. C) Some introns are self-splicing. D) Prokaryotic mRNAs are polyadenylated at the 3' end. E) Chemical modification occurs with tRNA transcripts.
Multistranded cords of primary xylem and phloem are
a. vascular bundles. b. found only in monocots. c. found only in dicots. d. formed by stele. e. formed by pith.
Each of the following statements accurately describes the Calvin cycle except
A) It is found in all oxygenic and most anoxygenic phototrophs. B) Carbon dioxide is fixed by reduction to form organic sugars. C) Its products enter a variety of metabolic pathways including sugar and starch biosynthesis. D) It involves ribulose-1,5-bisphosphate (RuBP). E) It is confined to the cytoplasm in plants and algae.
Photorespiration results in:
A) sometimes more and sometimes less sugar being produced during photosynthesis. B) no change in the sugar being produced during photosynthesis. C) more sugar being produced during photosynthesis. D) less sugar being produced during photosynthesis.