Cytoplasm sounds like some sort of goop that aliens spray out, but it is actually something more commonplace and important. It is all the material within a cell besides the cell nucleus and plays crucial roles in the cell.

Composition of cytoplasm

It is composed of three key parts: the cytosol, organelles, and cytoplasmic inclusions.

The cytosol makes up the vast majority of a cell, about 70% of its total volume. It comprises everything that is inside the cell except what can be found within the organelles. Think of it like a tiny soup with noodles (cytosketelon filaments that give the cell structure), broth (dissolved molecules), and water (actually water). There are also some bonuses in the mix including ribosomes (that create proteins) and proteasomes (that degrade unneeded or damaged proteins).

Organelles, as the name suggests, are like little organs found within a cell, each with their own function to carry out that allows the cell to function as a whole. The major organelles in cells are the ones that we all learn about in high school biology: mitochondria, the endoplasmic reticulum, the Golgi apparatus, vacuoles, lysosomes, and chloroplasts in plant cells.

Cytoplasmic inclusions are substances that do not dissolve in cytoplasm. For example, starch and glycogen granules store energy within the cell. Lipid droplets are storage spheres for fatty acids and sterols.

Functions

1. The cytoplasm is crucial for keeping the cell in shape, without it, the cell would be like a deflated balloon and the organelles wouldn’t stay suspended. The cytoskeleton filaments give the cells shape, while the semi-liquid quality of the cytoplasm keeps everything in place, but also allows the various parts of the cell to move around and perform their functions.
2. It also performs essential processes such as cell respiration and cell division.
3. The ribosomes and proteasomes take care of all of the protein synthesis and destruction.
4. Enzymes making up the cytoplasm break down waste and help with metabolic activity.
5. The cytoplasm plays an active role in moving nutrients in and out of the cell.

Disagreement

One aspect of the cytoplasm that is still unknown is what the physical nature of the cytoplasm is. It is often jelly-like and smaller particles travel faster through it than larger particles. A researcher in 1923 postulated that the cytoplasm acts like a sol-gel, meaning that it goes through some phases of being a more liquid solution and a some of being a solid gel. Through tracking single cytoplasm components, researchers have recently proposed that cytoplasm acts like a glass-forming liquid approaching the glass transition. The higher the concentration of elements in the cytoplasm, the more it behaves like a solid. Further, researchers measuring cytoplasm with force spectrum microscopy found that it acts like an elastic solid.

Regardless of the disagreement, we know that cytoplasm provides the backbone for all the functions in the cell.