Question

read the passage and then answer the question
the tardigrade, or water bear, is less than two millimeters long—tiny enough to be preyed upon by other microscopic creatures. however, these minuscule invertebrates are extraordinarily widespread and resilient. tardigrades have been found on all seven continents and in an incredible variety of environments, from hot springs to arid deserts to icy mountaintops. they can even survive in the vacuum of space, as a 2007 study revealed. how do these creatures survive without water, warmth, or even air? when resources are scarce, a tardigrade undergoes cryptobiosis, a temporary reduction of its metabolism to nearly undetectable levels. with its life-sustaining chemical processes decreased to 0.01% of their normal levels, the tardigrade can survive under even the harshest circumstances, reviving when conditions improve.
what is the meaning of metabolism as used in the passage?
the set of chemical reactions occurring within a living organism
the energy expenditure of an organism under stress
the set of chemical reactions occurring within a cryptobiotic organism

Explanation:

The passage mentions "life - sustaining chemical processes" in relation to metabolism. Metabolism in general refers to the set of chemical reactions in a living organism. The option "the set of chemical reactions occurring within a living organism" aligns with this general and the passage - implied meaning. The second option is too narrow as it focuses only on energy expenditure under stress (the passage shows metabolism in a general context of life - sustaining, not just stress). The third option limits it to cryptobiotic organisms, but metabolism is a general term for living organisms, not just those in cryptobiosis (though the passage uses it in the context of cryptobiosis, the fundamental meaning is broader).

Answer:

the set of chemical reactions occurring within a living organism