The water pressure gradient in phloem tubes is formed by the
A) leaves being higher than the roots, which means that gravity creates pressure.
B) diffusion of water from one sieve-tube cell to the next.
C) loading of sugars into phloem at sources and removal of sugars at sinks.
D) active transport of water from sugar sources to sugar sinks.
Answer: C
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Which of the following is not true of the reactions that methylate the 5' end of the primary mRNA transcripts?
A. The reaction occurs after the entire transcript is synthesized. B. The methyl groups are derived from S-adenosylmethionine. C. The enzymes that catalyze the reactions are guanylyltransferases. D. The enzymes that catalyze the reactions are associated with the C-terminal domain of RNA polymerase II.
During digestion ____
a. carbohydrates are split into proteins b. proteins are broken down into fatty acids c. fatty acids are split into non-fatty acids d. carbohydrates, proteins, lipids, and nucleic acids are split into smaller chemical subunits e. carbohydrates, proteins, lipids, and nucleic acids are split into larger chemical subunits
The site of gravity reception in roots is the:a
root apical meristem. b. periderm. c. root epidermis. d. root cap. e. root hair
When a certain allele at a particular gene loci has a frequency of 1.0 in a population, it is considered _____ for that population.
a) dominant b) lost c) recessive d) fixed e) balanced.