The cell is considered to be the basic functional or structural unit of all the living organisms that has its own metabolism and is capable of independent living, self-reproduction and development. Cells are “small and in almost all situations a microscope is needed to observe them and their subcellular components”ť (Wiser 9).
All the cellular forms can be divided into two major types: eukaryotic and prokaryotic. Prokaryotes are simpler in their structure, and therefore smaller. In turn, eukaryotes are more complex and wider, and therefore greater in their volume.
Thus, prokaryotes are organisms that have no, in contrast to eukaryotes, the formed cell nucleus and other internal membrane organelles (except for the flat tanks in photosynthetic species, such as cyanobacteria). Eukaryotes are organisms that have, in contrast to prokaryotes, the formed cell nucleus, delimited from the cytoplasm by the nuclear envelope.
The main parts of a living cell include as follows:
- cell membrane ”“ separates the contents of any cell from the external environment, ensures its integrity and regulates the exchange between the cell and its environment;
- nucleus ”“ one of the structural components of the eukaryotic cell that contains genetic information (the DNA molecule), which carries the main functions: storage, transfer and implementation of genetic information with providing protein synthesis;
- cytoskeleton ”“Â a cellular skeleton, located in the cytoplasm of the living cells;
- ribosomes ”“Â a major complex of RNA and protein of the living cells;
- endoplasmic reticulum ”“ an intracellular organelle of the eukaryotic cell, which is surrounded by an extensive system of flattened membrane cavities, vesicles and tubules;
- golgi apparatus ”“ a membrane structure of eukaryotic cells, mainly designed to remove the substances synthesized in the endoplasmic reticulum;
- mitochondrion ”“ a membrane-enclosed organelle that can be located in the eukaryotic cells.