After a decline to an historic low about 300 million years ago, carbon dioxide levels in the Earth's atmosphere rose again for a while. Hypothesize a reason why this occurred.
A. All the vegetation that had been produced in warmer times decayed and released carbon dioxide.
B. There was an increase in aerobic bacteria that released large amounts of carbon dioxide.
C. There was an increase in oxygen that stimulated respiration and hence greater production of carbon dioxide.
D. The low carbon dioxide levels caused cooling of the Earth, resulting in the decline of ancient vegetation; with less vegetation to absorb carbon dioxide, the carbon dioxide levels rose.
E. All of the other choices provided are incorrect.
D. The low carbon dioxide levels caused cooling of the Earth, resulting in the decline of ancient vegetation; with less vegetation to absorb carbon dioxide, the carbon dioxide levels rose.
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Why is calcium necessary for muscle contraction?
A. Calcium is needed to activate troponin so that tropomyosin can be moved to expose the myosin-binding sites on the actin filament. B. Calcium is needed to allow the muscle fiber to become depolarized. C. Calcium functions as a neurotransmitter and is released from the motor neuron. D. Calcium is needed to cock the myosin head so that it can form a cross-bridge with actin. E. Calcium is needed to detach the myosin from the actin.
The surface receptors that recognize and bind signal molecules are ____
a. glycoproteins b. glycolipids c. phospholipids d. promoters e. cadherins
Genetic studies of an animal show that eye color is controlled by an autosomal gene with the dominant
allele (R) for red eye color and the recessive allele (r) for yellow eye color. A second autosomal gene has the dominant allele (T) leading to paws with thumbs while the recessive allele (t) codes for paws without thumbs. The genetic cross RRTT ? rrtt creates offspring with genotype RrTt. One of those dihybrids is mated in a testcross (RrTt ? rrtt). If the two genes are completely linked (no recombination occurs between them), then the testcross should produce offspring with the phenotype ratio
a. 3 red-eyed with thumbs: 1 yellow-eyed without thumbs. b. 1 red-eyed with thumbs: 1 yellow-eyed with thumbs: 1 red-eyed without thumbs: 1 yellow-eyed without thumbs. c. 1 red-eyed with thumbs: 1 yellow-eyed without thumbs. d. 9 red-eyed with thumbs: 3 yellow-eyed with thumbs: 3 red-eyed without thumbs: 1 yellow-eyed without thumbs. e. 1 yellow-eyed with thumbs: 1 red-eyed without thumbs.
Archibald Garrod was the first to advance the idea that there is a direct link between ____________________ and
__________________ Fill in the blank(s) with the appropriate word(s).