The rise of methicillin-resistant staphylococcus aureus (mrsa) can be considered to be an example of artificial selection because a) humans purposefully raise mrsa in large fermenters in an attempt to make the bacteria ever-more resistant. b) s. aureus is cultivated by humans to replenish the soil with nutrients. c) humans synthesize methicillin and create environments in which bacteria frequently come into contact with methicillin. d) humans are becoming resistant to bacteria by taking methicillin.

C

Explanation:

Frequent exposure of Staphylococcus aureus methicillin by humans – such as through excessive use of non-prescribed antibiotics-, the rate of mutations in the bacteria population increases. This results to increases chances that a mutant will develop that is resistant to methicilin. Once a mutant develops, its population increases even when exposed to the antibiotic because it is resistant to methicilin.  Bacteria also exchange genetic material horizontally so the gene for resistance will quickly spread in a population. This results in MRSA that is hard to eradicate.

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many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.