Which of the following statements is false?
(a) Nucleotides and amino acids can act as extracellular signal molecules.
(b) Some signal molecules can bind directly to intracellular proteins that bind DNA and regulate gene transcription.
(c) Some signal molecules are transmembrane proteins.
(d) Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids.
Choice (d) is not true. NO can diffuse across the plasma membrane and directly activate intracellular proteins such as the enzyme guanylyl cyclase.
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What type of chemical reaction must occur for electrons to flow from one molecule to the next and supply the energy
for metabolism?
a. acid/base b. reduction/oxidation c. exothermic d. trimolecular e. phosphorylation
How long ago did the first gymnosperms evolved?
A. 360 million years ago B. 360 thousand years ago C. 36 million years ago D. 36 thousand years ago
What is meant by adaptation from standing genetic variation in natural populations?
A) A population adapts to an environmental change by the occurrence of a beneficial mutation in an individual that introduces genetic variation, which rises to high frequency in the population because it is favored by natural selection following the environmental change. B) A population adapts to an environmental change by the rise to high frequency of an existing genetic variant that was already present in the population at low frequency before the environmental change. C) Individuals with more variation present in their genomes are favored by natural selection following an environmental change, and the population adapts via an overall increase in genetic variation in the population because the most genetically variable individuals have highest fitness. D) Genetic variation becomes costly for individuals following an environmental change, and the result is that overall genetic variation in a population decreases as the population adapts to the environmental change.
In an experiment to test the effect of a new weight loss drug, half of the people in the study received the drug, and the other half received a placebo (a pill that has no physiological effect). In addition, only males from the ages of 20 to 25 were
selected to participate in the study. All participants received their treatments (drug or placebo) every day for 4 weeks. Which of the following components of the study design served as the control group? A) The 4-week length of the experiment. B) The restriction of study participants in age and gender. C) The participants who received a placebo. D) The participants who received the drug.