During initial transcription, the active center of RNA polymerase is translocated forward relative to the DNA template and synthesizes short transcripts before aborting, then repeats this cycle until it escapes the promoter. Three models have been proposed to account for this;

i. Polymerase moves along the DNA.

ii. The front part of the enzyme moves along the DNA, but because of a flexible region within the enzyme, the back part of the enzyme can remain stationary at the promoter.

iii. The enzyme remains stationary and pulls the DNA into itself.

#Question id: 4960

#Unit 11. Evolution and Behavior

Letʹs say that a hypothetical submersible robot was used to collect samples of sedimentary rock from the sea floor along the section illustrated. The robot moved back and forth along the transect, collecting first from site A, then site III, then site B, then site II, and lastly site D. Assuming that sedimentation has occurred at a constant rate along the transect over the past million years, rearrange the sites mentioned above on the basis of the thickness of the sediments overlying the igneous rock, from thickest to thinnest.

#Question id: 4961

#Unit 11. Evolution and Behavior

An early consequence of the release of oxygen gas by plant and bacterial photosynthesis was to

#Question id: 4963

#Unit 11. Evolution and Behavior

Which free-living cells were the earliest contributors to the formation of Earthʹs oxidizing atmosphere?

#Question id: 4964

#Unit 11. Evolution and Behavior

Which of the following statements provides the strongest evidence that prokaryotes evolved before eukaryotes?

#Question id: 4965

#Unit 11. Evolution and Behavior

What is thought to be the correct sequence of these events, from earliest to most recent, in the evolution of life on Earth?

1.  origin of mitochondria

2.  origin of multicellular eukaryotes

3.  origin of chloroplasts

4.  origin of cyanobacteria

5.  origin of fungal-plant symbioses

#Question id: 4966

#Unit 11. Evolution and Behavior

If it were possible to conduct sophisticated microscopic and chemical analyses of microfossils found in 3.2-billion-year-old stromatolites, then within such microfossils, one should be surprised to observe evidence of:

I. double-stranded DNA

II. a nuclear envelope

III. a nucleoid

IV. a nucleolus

V. nucleic acids