The cytoplasm is the cytosol of the human cell – the cell substance in the interior of the cell. Humans are eukaryotes, meaning that their cells have an outer plasma membrane and organelles and nucleus inside. The cytoplasm is sometimes described as being “jelly-like” as it is fluid with a gel consistency, and it contains approximately 80 percent water with other molecules, such as proteins, in the mix.
The outer plasma membrane is semi-permeable, letting through certain substances depending on the cell’s specific needs or current state. Fatty acids, amino acids, and sugars are all potentially needed by the cellular machinery and are found in the cytoplasm. Wastes and metabolites are also dissolved in the cytosol before being enveloped and disposed of by specialized structures within the cytosol, namely lysosomes. The cytosol also contains ions and salts that facilitate electrical conduction in cells that have mechanical function.
In addition to being the waiting room for molecules used by the cell, another function of the cytoplasm is to hold the organelles in suspension so that nucleic acids and proteins can communicate between them. Organelles in the human cell include mitochondria, Golgi complex, endoplasmic reticulum, and the nucleus. The nucleus contains its own cytosol, the nucleoplasm. Within the nuclear membrane, in the nucleolus (the inner nucleus) is where the DNA is stored, the genome present in every human cell except red blood cells. DNA encodes proteins that are transported through the cytosol to the endoplasmic reticulum and Golgi for processing, packaging, and transport to where they are needed. The cytoplasm contains specialized structures that aid in this process. Similarly, the cytoplasm contains enzymes necessary for the mitochondria to produce energy, which is needed for the cell to function.
The cytoplasm also functions to retain the cell’s shape. The cytoskeleton is a structure made of various fibers, tubules, and proteins that create the shape of the cell, allows binding and interactions with neighbor cells, aids in transport within the cell, and facilitates cellular movement. The lattices formed within the cytosol by the cytoskeletal fibers hold the organelles in place (Franklin Institute).
In summary, the main structure of the cytoplasm is as a molecular soup with a cytoskeletal lattice holding the cell’s shape and its organelles in place. The main function of the cytoplasm is to facilitate cellular function by assisting the organelles and intracellular transport, as well as maintain order within the cell.
For more information, see Biology4Kids.