Which of these events occurred during the Paleozoic?
a. origin of Earth
b. colonization of land by plants
c. origin of eukaryotes
d. origin of multicellularity
e. first humans
Answer: b. colonization of land by plants
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The slender stalk that connects the flattened leaf blade to the stem in most dicots is the
A. meristem. B. petiole. C. stele. D. receptacle. E. vein.
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.
High-energy radiation is often used to treat cancer. The radiation kills the cancerous cells, and the cell cycle checkpoint for DNA repair is overwhelmed. Radiation
a. causes apoptosis at the S and G2 checkpoints. b. inhibits the growth factor at the restriction point. c. blocks DNA replication. d. only causes apoptosis at the tumor site. e. kills all tumor cells without harm to healthy cells.
Which type of cell has the fewest number of chromosomes?
a. somatic b. gametes c. archaea d. diploid