A cell is the most primary unit of a living organism. All living things are made up of cells. But have you wondered what cells actually are? Or how many types of cells are actually there? Though all of you must have studied the same in the science lesson in middle school, very few of you can actually retain the complete information. Cells, which are made up of atom, are the smallest biologically functioning element of life. Bacteria is an organism with a single cell and thus called unicellular, while we humans are multi-cellular consisting of many cells. Life on earth has been divided into five kingdoms, each of which has its own attribute of cells. Cells in all the five kingdoms have been categorized into two broad kinds - prokaryotic cells and eukaryotic cells. The prokaryotic cells include only the Monera, while eukaryotic cells includes the other four kingdoms namely Animals, Plants, Fungi and Protista. Let’s have a look at the summarized detail of this basic classification.
Different Kinds Of Cells
Prokaryotic cells are the single-celled, without a nuclear membrane. Prokaryotic cells were the first cells to evolve when life came into existence on earth about 4 billion years ago. Bacteria are the most common example of prokaryotic cell, with the exception of Archaea, discovered lately, as the only other form of organism with prokaryotic cell. In a prokaryotic cell, instead of the membrane bound nucleus, they have chromosomal DNA. The DNA is in small loops known as plasmid. The reproduction process in prokaryotes like bacteria and archaea is asexual, and carried out through binary fission and budding.
Prokaryotic cells have three structural sections - flagella and pili, cell envelope and cytoplasmic region. Flagella and pili are proteins attached to the cells surface, which helps in movement of the cells. Cell envelope, on the other hand, consists of a capsule, cell wall and a plasma membrane. Conversely, a cytoplasmic region is one that holds the cell genome (DNA). Prokaryotes are unicellular and do not grow into multicellular organism. Some bacteria do grow into colonies, but each cell is alike and can survive independently. Prokaryotes can survive anywhere, on any surface, on the face of the earth. Prokaryotes like bacteria are very useful to us, as they work as decomposers, as means of fermentation and also in our own digestion process.
The eukaryotic cells include all the life kingdoms except Monera. The eukaryotic cells are membrane bound, that is, they contain sections where definite metabolic activities take place. There is also a framework of proteins known as cytoskeleton, which holds the cell together. The internal membrane-bound structures, known as organelles, also comprise of the nucleus which houses the DNA of the eukaryotic cells. Eukaryotic cells are ten times the size of the prokaryotic cell, and with a volume that is about 1000 times greater. Most organisms with eukaryotic cells are large organisms like plants, animals and fungi, with the only exception of protista which is a microorganism.
Mitochondria, a type of organelles, which is also known as the power station of the cell, is believed to be once a prokaryotic cell that developed into a eukaryotic cell through the process of endosymbiotic attachment. During reproduction, the eukaryotic cells go through a process called mitosis, where the chromosomes of eukaryotic cells are duplicated. While prokaryotic life came into existence about 4 billion years ago, eukaryotes have a relatively recent development of about 2 million years ago. Red algae are considered to be one of the first eukaryotes. Eukaryotic cells have a diverse constitution than prokaryotic cells; because of the variety that exists with the classification of eukaryotic plant and eukaryotic animal cell and eukaryotic fungi cells.