Introduction: Prokaryotes And Eukaryotes
Biotic components of the environment include all forms of life from minute bacteria to towering giant sequoias. But at the microscopic level, all living organisms are made up of the same basic unit – the cell.
As a result, the cell is referred to as the structural and functional unit of all living organisms. The word cell has its origins from Latin, and when translated, it means “small room” and was first observed by Robert Hooke – an English natural philosopher in the year 1665.
He also compared his discovery to the cells in a honeycomb, as they showcase a similar structure.
Eventual advancements in science and technology shed more light into the cell, with new findings and discoveries about its structure and cellular components. During the 1950s, scientists postulated the concept of prokaryotic cell and eukaryotic cell, with earlier groundwork being laid by Edouard Chatton, a French Biologist in 1925.
Anatomically, cells vary with respect to their classification, therefore, prokaryotic cells and eukaryotic cells differ from each other quite drastically. Read on to explore how they differ from each other.
The term “prokaryote” is derived from the Greek word “pro“, (meaning: before) and “karyon” (meaning: kernel). It translates to “before nuclei.“
Prokaryotes are one of the most ancient groups of living organisms on earth, with fossil records dating back to almost 3.5 billion years ago.
These prokaryotes thrived in the earth’s ancient environment, some using up chemical energy and others using the sun’s energy. These extremophiles thrived for millions of years, evolving and adapting. Scientists speculate that these organisms gave rise to the eukaryotes.
Prokaryotic cells are comparatively smaller and much simpler than eukaryotic cells. The other defining characteristic of prokaryotic cells is that it does not possess membrane-bound cell organelles such as a nucleus. Reproduction happens through the process of binary fission.
Structurally, prokaryotes have a capsule enveloping its entire body, and it functions as a protective coat. This is crucial for preventing the process of phagocytosis (where the bacteria gets engulfed by other eukaryotic cells such as macrophages.) The pilus is a hair-like appendage found on the external surface of most prokaryotes and it helps the organism to attach itself to various environments. The pilus essentially resists being flushed, hence, it is also called attachment pili. It is commonly observed in bacteria.
Right below the protective coating lies the cell wall, which provides strength and rigidity to the cell. Further down lies the cytoplasm that helps in cellular growth, and this is contained within the plasma membrane, which separates the interior contents of the cell from the outside environment. Within the cytoplasm, ribosomes exist and it plays an important role in protein synthesis. It is also one of the smallest components within the cell.
Some prokaryotic cells contain special structures called mesosomes which assist in cellular respiration. Most prokaryotes also contain plasmids, which contains small, circular pieces of DNA. And to help with locomotion, flagella are present, though, pilus can also serve as an aid for locomotion. Common examples of Prokaryotic organisms are bacteria and archaea. Also, all members of Kingdom Monera are prokaryotes.
Main Article: Prokaryotic Cells
The term “Eukaryotes” is derived from the Greek word “eu“, (meaning: good) and “karyon” (meaning: kernel), therefore, translating to “good or true nuclei.” Eukaryotes are more complex and much larger than the prokaryotes. They include almost all the major kingdoms except kingdom monera.
Structurally, eukaryotes possess a cell wall, which supports and protects the plasma membrane. The cell is surrounded by the plasma membrane and it controls the entry and exit of certain substances.
The nucleus contains DNA, which is responsible for storing all genetic information. The nucleus is surrounded by the nuclear membrane. Within the nucleus exists the nucleolus, and it plays a crucial role in synthesising proteins. Eukaryotic cells also contain mitochondria, which are responsible for the creation of energy, which is then utilized by the cell.
Present in only plant cells, chloroplasts are the subcellular sites of photosynthesis. Endoplasmic reticulum helps in the transportation of materials. Besides these, there are also other cell organelles that perform various other functions and these include ribosomes, lysosomes, Golgi bodies, cytoplasm, chromosomes, vacuoles, and centrosomes.
Examples of eukaryotes include almost every unicellular organism with a nucleus and all multicellular organisms.
Main Article: Eukaryotic Cells
Difference between Prokaryotic and Eukaryotic Cells
Though these two classes of cells are quite different, they do possess some common characteristics. For instance, both posses cell membrane and ribosomes, but the similarities end there. The complete list of difference between prokaryotic and eukaryotic cells are summarized as follows:
|Type of Cell||Always unicellular||Unicellular and multi-cellular|
|Cell size||Ranges in size from 0.2 μm – 2.0 μm in diameter||Size ranges from 10 μm – 100 μm in diameter|
|Cell wall||Usually present; chemically complex in nature||When present, chemically simple in nature|
|Ribosomes||Present. Smaller in size and spherical in shape||Present. Comparatively larger in size and linear in shape|
|Cytoplasm||Present, but cell organelles absent||Present, cell organelles present|
|Plasmids||Present||Very rarely found in eukaryotes|
|Ribosome||Small ribosomes||Large ribosomes|
|Lysosome||In this, the lysosome, mesosome, and centrosome is absent||Mesosome, Lysosomes, and centrosomes are present|
|Cell division||Through binary fission||Through mitosis|
|Flagella||The flagella are smaller in size||The flagella are larger in size|
|Reproduction||Asexual||Both asexual and sexual|
|Example||Bacteria and Archaea||Plant and Animal cell|
Questions about Prokaryotic and Eukaryotic cells
1. What is a prokaryotic cell?
A prokaryotic cell is a primitive type of cell that is characterized by the absence of a nucleus. Furthermore, prokaryotes do not possess membrane-bound cellular organelles. Prokaryotes are exclusively unicellular.
2. What is a eukaryotic cell?
Eukaryotic cells are cells that possess a true nucleus along with membrane-bound organelles. Eukaryotes are can either be unicellular or multicellular.
3. What is the difference between prokaryotic and eukaryotic cell?
The defining characteristic feature that distinguishes between prokaryotic and eukaryotic cell is the nucleus. In prokaryotic cells, the true nucleus is absent, moreover, membrane-bound organelles are present only in eukaryotic cells.
Other major differences between prokaryotic and eukaryotic cells are that prokaryotic cells are exclusively unicellular, while the same does not apply for eukaryotic cells.
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