Cytoplasm is the semi-fluid substance of a cell that is present within the cellular membrane and surrounds the nuclear membrane. It is sometimes described as the nonnuclear content of the protoplasm. All the cellular contents in a prokaryote organisms are contained within cell's cytoplasm. In eukaryote organisms, the nucleus of the cell is separated from the cytoplasm. Cytoplasm is a thick and semi-transparent fluid. The cytoplasm was discovered in the year 1835 by Robert Brown and other scientists.
The cytoplasm is made of 70% - 90% water and is colorless usually. Most of the cellular activities occurs in the cytoplasm. Metabolic pathways like glycolysis and cellular processes like cell division take place in the cytoplasm. The outer clear and glassy layer of the cytoplasm is called the ectoplasm or the cell cortex and the inner granular mass is called the endoplasm. In plants cells, a process known as cytoplasmic streaming takes place where there is movements of the cytoplasm around the vacuoles.General Characteristics of Cytoplasm:
- Cytoplasm is the fluid substance that fills the space between the cell membrane and the cellular organelles.
- Cytoplasm shows differential staining properties, the areas stained with the basic dyes are the basophilic areas of the cytoplasm and is termed as ergatoplasm for this material.
- It is heterogenous mixture of opaque granules and organic compounds which gives it its colloidal nature.
- The peripheral zone of cytoplasm is thick and jelly-like substance, known as the plasmogel. The surrounding area of the nuclear zone is thin and liquefied in nature and is known as the plasmosol.
- The physical nature of cytoplasm is colloidal. It has a high percentage of water and particles of various shapes and sizes are suspended in it.
- It also contains proteins, of which 20-25 percent are soluble proteins including enzymes.
- Also, certain amount of carbohydrates, inorganic salts, lipids and lipoidal substances are found.
- The plasmogel part of the cytoplasm is capable of absorbing water and removing it, according to the cells need.
- The stomatal guard cell present in the leaves exhibit this property.
- An organized system of fibrers can be observed by specific staining techniques.
- Chemically cytoplasm contains 90% water and 10% include a mixture of organic and inorganic compounds in various proportions.
The cell membrane or the cytoplasmic membrane or the plasma membrane is a biological membrane, it separates the cell interior from the external environment. The cytoplasmic membrane shows selective permeability to organic molecules and ions. It controls in and out movement of substances in the cells. The main function of the cell membrane is to protect the cell from its surrounding environment. The cell membrane is made of the phospholipid bilayer in which the proteins are embedded. The cell membrane performs various processes of the cells like ion conductivity, cell adhesion, and cell signaling. It also serves as attachment for certain cellular structures like the cell wall, glycocalyx and intracellular cytoskeleton.
Cytoplasm is the fluid where the cellular organelles are suspended. It fills up the spaces that are not occupied by the organelles. The constituents of cytoplasm are cytosol, organelles and cytoplasmic inclusions.
Cytosol makes up about 70% of the volume of the cell. It is composed of water, salts and organic molecules. Cytosol is composed of a mixture of cytoskeleton filaments, organic and inorganic molecules that are dissolved and water. It also contains protein filaments that make up the cytoskeleton, and also soluble proteins and structures like ribosomes, proteasomes are also present. The inner, more fluid and granular potion of the cytoplasm is known as the endoplasm. The network of fibers and high concentrations of the dissolved macromolecules like proteins causes macromolecular crowding. This effects how the components of the cytoplasm interact with each other.
Organelles mean "little organs", that are membrane bound. They are present inside the cell and perform specific functions that are necessary for the survival of the cell. Some of the constituents of the cell that are suspended in the cytosol are cellular organelles like mitochondria, endoplasmic reticulum, Golgi apparatus, vacuoles, lysosomes and chloroplasts in plant cells.
The cytoplasmic inclusions are tiny particles suspended in the cytosol. A vast range of inclusion are present in different cell types. The inclusions range from calcium oxalate crystals or silicon dioxide crystals in plants to storage granules of materials like starch, glycogen, etc. Lipid droplets are a widespread example of inclusions, these are spherical droplets, they are made of lipids and proteins and are present in both prokaryotes and eukaryotes as a medium to store lipids like fatty acids and sterols. These droplets take up much of the volume of adipocytes which are specialized storage cells, they are also found in other types of cells also.