<span>In the sentence "Biologists recognize the following levels of cell organization: _____, the choice that correctly completes the sentence is b. cellular, tissue, organ, system, and organism. A cell is the basic unit of living organisms. The group of similar cells that work together to perform a specific job is a tissue. The group of multiple tissues joined together in the functional structure is an organ. Functionally related organs form organ systems, which all together form one organism.</span>
Provided that there's no diagram, most molecules have particular areas on the molecules, called the "active area" that act as a lock to a particular substrate's molecular structure, providing the key.
An enzyme's active area is only able to be "unlocked" by a certain substrate's "key".
Answer:
Nucleus
Explanation:
Nucleus is the most common cell that a animal will have.
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