Which of the following best describes the nature of the cells of mature, functioning xylem?

A) dead, thick-walled tubes
B) living cells that have lost their nucleus
C) dead cells that retain some organelles and some maintenance functions
D) living, thick-walled tubes


Answer: A

Biology & Microbiology

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Chemical messengers produced by endocrine glands are called

a. agonists b. neurotransmitters c. hormones d. enzymes

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Which of the following is NOT a part of the MAP kinase pathway? (Select all correct choices.)

A. A receptor kinase is activated by binding to a growth factor and phosphorylates receptor cytoplasmic domains. B. The activated receptor kinase dimer activates the RAS protein to bind to a GTP. C. The activated RAS protein activates protein kinases in the signal-transduction pathway. D. A series of protein kinases amplify the signal to the nucleus where genes responsible for cell division are switched on. E. A pyrophosphatase enzyme terminates the cellular response.

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Genetic counselors are typically medical doctors who specialize in treating infertile couples

a. True b. False Indicate whether the statement is true or false

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The FBI currently determines an individual's DNA profile using:a

DNA sequencing. b. mitochondrial DNA variations. c. RFLPs. d. DNA ligation. e. 13 STR markers.

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