The main substance that makes up cytoplasm is cytosol, a gel-like fluid that contains various organelles and dissolved substances. Cytosol is primarily composed of water, salts, and organic molecules, providing an environment for chemical reactions to occur. Additionally, cytoplasm includes organelles like the mitochondria, endoplasmic reticulum, and golgi apparatus, which perform specific functions necessary for cell survival and maintenance. This fluid matrix supports cellular structures, helps in transporting materials, and plays a role in regulating metabolic processes.