Cytoplasm is the correct answer because it is the jelly-like substance that fills the interior of a cell, providing a medium where various chemical reactions occur. This includes vital processes like metabolism, where nutrients are converted into energy, and the synthesis of macromolecules such as proteins and nucleic acids.
The cytoplasm contains various organelles, such as mitochondria, ribosomes, and in plant cells, chloroplasts, all of which perform specific functions but rely on the cytoplasm to facilitate the transport of materials and the interaction of different chemical reactions. This central role makes the cytoplasm essential for maintaining cellular function and supporting life processes in both plant and animal cells.