Cytoplasm

Cytoplasm is a gelatinous fluid that fills most cells in biological lifeforms.

The Earth medical reference cites that "in the higher organisms a cell may be defined as a nucleated mass of protoplasm of microscopic size. Its two essentials, therefore, are: a soft jelly-like material, similar to that found in the ovum, and usually styled cytoplasm, and a small spherical body embedded in it, and termed a nucleus. Some of the unicellular protozoa contain no nuclei..."

In 2373, Doctor Bashir speculated that exposure to tetryon radiation damaged the cytoplasm of the infant Changeling, resulting in its failing life signs. 

The biochemical analysis symbiogenetic orchid discovered in the Delta Quadrant by Tuvok and Neelix, which was later a contributing factor in the creation of Tuvix, was found to contain the same elements as many plants including chloroplasts, lysosomal enzymes, and cytoplasmic proteins. 

The Klingon retrovirus known as nehret destroyed the cells of its host by attacking their cytoplasmic membranes.