According to current thinking, the minimum requirement for life to have originated on Earth was the formation of a _______________
(a) molecule that could provide a template for the production of a complementary molecule.
(b) double-stranded DNA helix.
(c) molecule that could direct protein synthesis.
(d) molecule that could catalyze its own replication.
Choice (d) is correct. Choice (a) is incorrect in that, although this may have been a step in self-replication, it would not by itself be sufficient. Choices (b) and (c) are incorrect, as these stages in the evolution of the cell must have succeeded the formation of the first self-replicating molecules.
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Organisms that demonstrate a type I survivorship curve are characterized by:
a. death rate of the population does not vary with age b. low death rate until mid-life c. low death rate until late in life d. high death rate in early life e. high death rate in mid-life
During apoptosis
a. digestive enzymes are unleashed. b. proteases break down structural proteins. c. nucleases break down nucleic acids. d. the nucleus breaks apart. e. all of these occur.
The most ancient group of plants alive today are:a
horsetail. b. club moss. c. hornworts. d. liverworts. e. gymnosperms.
Special bone cells, called ________, are responsible for laying down new bone.
A. osteoclasts B. Haversian canals C. osteocytes D. osteoblasts