Final answer:
The word organism denotes any whole, living individual plant or animal. It is part of the biological hierarchy, where cells form tissues, which create organs, and ultimately, organisms.
Step-by-step explanation:
Within the hierarchy of biological organization, the correct answer to the question is C. Organism. An organism is any whole, living individual plant or animal. This is distinct from a cell, which is the smallest unit of a living thing, and from a tissue, which is a group of interconnected cells of the same kind. While a molecule is a chemical structure consisting of at least two atoms held together by a chemical bond, it is not a living entity. A zygote, though living, represents the earliest stage of development of an organism, but not the whole developed organism itself.
To clarify further, levels of biological organization range from the smallest, such as atoms and molecules, to larger structures like organelles and cells. Cells form tissues, which in turn create organs, then organ systems, and finally individual organisms. Organisms can live as single-cell entities like bacteria, or as complex multicellular entities like humans, which are made up of trillions of cells.