Final answer:
The cytosol is the fluid inside of cells, a part of the cytoplasm, that surrounds cellular organelles and is essential for numerous biochemical reactions.
Step-by-step explanation:
The fluid inside of cells is called the cytosol, which is a part of the cytoplasm. The cytosol is a jelly-like substance that consists mainly of water, but it also contains various dissolved nutrients and other molecules. Organelles such as ribosomes, endoplasmic reticulum, and the Golgi apparatus float in the cytosol and perform various functions necessary for the cell's survival. The phospholipid bilayer of the cell membrane encases the cytoplasm, providing structure and protecting the cellular contents from the extracellular environment. The role of cytosol is critically important as it hosts a multitude of biochemical reactions essential for cellular processes.