All living cells that include microbial, animal as well as plant cells contain cytoplasm. This is a cell matrix that is present between the plasma membrane and nucleus of the cell. Different cellular organelles and inclusions are present in the cell matrix. If you have a look at its structure, it is semi-viscous in nature. It is a jelly-like substance that contains an aqueous, transparent substance called the hyaloplasm or cytosol. About 90% of the cytosol is made up of water. The other 10% consists of various micro as well as macro biomolecules. They appear in state of a solution within the cytoplasm. This substance is able to move within the cell and this movement is nothing but the flow of the cytosol (liquid component). It is also known as cyclosis.
The mechanism involves a continuous network of tubes and fibers of the rough endoplasmic reticulum which spread through the cytoplasm. Parts of the endoplasmic reticulum come in contact the parallel bundles of actin filaments called the microfilaments. These microfilaments are able to contract and lead to directed flow of the cytosol. So, in order to move the mitochondria, glycosomes, and other small organelles, the cell attaches them to the microfilaments. When these microfilaments contract, they push the organelles to move within the cytoplasm. These microfilaments are made of proteins like kinesin and dynamin. They store energy in form of ATP and help in pulling of the microfilaments, thus leading to organelle movement.
The function of cyclosis includes transportation of nutrients, enzymes and other particles within the cell. Cyclosis occurs along the actin filaments of the cytoskeleton of the cell.
Examples in Different Living Cells
There are different types of living cells where this process helps carry out various functions. Let us have a look at these cells to understand this phenomenon better.
Amoeba is a unicellular organism that moves around with the help of pseudopods. These pseudopods are flowing projections of the cytoplasm. They extend and pull the cell forward during a movement and even help in engulfing of food particles. This flow in an amoeba cell is a good example of streaming.
Paramecium is a protists that pulls in its food through the gullet. Once the food particle in within the cell, it is engulfed by phagocytosis. These food vacuoles created then get fused with lysosomes that contain enzymes for digestion. This vacuole is then passed around the cell as the food gets digested. The low-molecular weight nutrients are then passed through the vacuole membrane into the gel-like substance. The nutrients reach all the parts of the cell with the help of directed flow of cytosol that carries the vacuole around.
As you can see, cytoplasmic streaming helps in transport of cellular material within the cell without damaging or changing the cellular wall or structure. It also helps in speeding up the slow process of diffusion in a cell. It also helps in maintaining the concentration gradient between internal and external area of the cell.