Scientists hypothesize that the massive Permian extinction was triggered by ____
a. asteroid impacts that caused atmospheric dust clouds
b. a series of ongoing volcanic eruptions
c. degradation of the environment by humans
d. rising sea levels that covered most landmasses
e. extreme global cooling that made Earth uninhabitable
ANSWER: b
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Biochemicals, known as __________, are produced by glands, travel through the bloodstream, and alter the metabolism of specific target cells.
A. enzymes B. pheromones C. neurotransmitters D. hormones E. pectines
In homeostatic control, the ________ compensates for any deviation between the actual value and the set point. In body temperature regulation in mammals, this function is carried out by ________.
A. effector; brain B. effector; skeletal muscle C. sensor; neurons D. integrator; skeletal muscle E. integrator; brain
Everyone is exposed regularly to ionizing radiation found in the soil, water, and air and from cosmic rays. In fact, 80% of the ionizing radiation people are exposed to comes from naturally occurring sources. Ionizing radiation can cause double-strand breaks in the DNA. Often, the DNA breaks have missing nucleotides at the broken ends. What type of repair would likely be used, and what would be the result of repairing this type of damage?
A. Direct repair would be used and would lead to properly repaired DNA. B. Direct repair would be used to join the DNA, but errors would still remain. C. Nonhomologous end joining would be used and would lead to properly repaired DNA. D. Nonhomologous end joining would be used to join the DNA, but errors would still remain.
Plants prevent erosion by
A) supporting animals that consume excess water. B) promoting flooding. C) holding water. D) blocking winds and stabilizing soil with extensive root systems. E) recycling nutrients.