Kingdom of life: prokaryotes and eukaryotes
There are different living organisms in this world. Most of these organisms are completely different from one another in one or the other respect. So, it is not very difficult to identify and differentiate one from the other. But this does not mean that, all the organisms have large differences in their physical or morphological characters that can be easily noticed. Yes, they do have the differences, but seemingly very small that can be hard enough to be caught by our naked eyes. So, for this a separate branch of science has conducted the study on animals which is called taxonomy.
Taxonomy definition: Taxonomy is the branch of science that differentiate animals according to their morphology or the character they possess. As per the concept of taxonomy, those living organisms that have large differences are kept under different phylum and beside this; even the animals that comes under same phylum are divided into different groups, class and orders, in order to mark even the slightest variation between them. Hence, taxonomist is a person who studies these differences performing a detailed analysis on animals and keeping them under those groups where they fit perfectly.
There are mainly three groups of animal kingdom: bacteria, archaea and eukaryotes in which the living organisms are basically divided. Bacteria and archaea comes under the same domain i.e. prokaryotes whereas eukarya constitute the separate domain in the biology kingdom of life. So going detailed on the two most studied groups:
Prokaryotic definition: These are the single celled organisms that lack any kind of membrane bound organelles like that of mitochondria, chloroplast or membrane bound nucleus.
The first structure of the prokaryotic cell is the cell wall. Though cell wall is not present in all the groups, but most of the prokaryotes have cell wall that protects the interior of the cell. Then is the cell membrane that makes the outer covering of the cell. Cell membrane in the prokaryotes regulates the entry and exit of substances in and out of the cell. Inside the cell membrane is the cytoplasm. It is a gel like fluid that has all the content of the cell including different salts and ions.
Locomotion in prokaryotes takes place with the help of flagellum present in the outer margin of the cell. The shape, size and number of flagellum vary in different prokaryotes according to their body plan and function. Prokaryotes are mostly of four types: rod shaped, comma shaped, spiral shaped and spherical shaped. Apart from these basic structures, there are lots of variation in two domain of prokaryotes i.e. bacteria and archaea. Bacteria have peptidoglycan that protects its membrane from any kind of attack and destruction form external agents or antibiotics, whereas archaea lack peptidoglycan in its cell wall. Most importantly, archaea have lots of characteristics like that of eukaryotes rather than bacteria.
Do prokaryotes have nucleus?
No prokaryotes lack well- organized nucleus because the nucleus in prokaryotes is not properly shaped or defined. It lies in cytoplasm of the cell and has no membrane bound covering, hence called as nucleoid that consists of only double strand of DNA.
Examples of prokaryotes: There are lots of examples for prokaryotes like that of lactobacillus acidophilus, cynobacteria, streptococcus pyogenes, E.coli and many more.
Eukaryote definition: These are the multicellular organisms that have different types of membrane bound organelles.
The first structure that can be noticed in eukaryotic cell is the cell wall. Eukaryotic cell wall is made of three different types of polysaccharides called cellulose, hemicelluloses and pectin which provide protection against any kind of external agents. Then is the cell membrane that helps in exchange of substances in and out of the cell. The main feature of eukaryotic cell is the presence of membrane bound organelles like that of mitochondria, chloroplast and nucleus. These are the three essential organelles present in the inner of the cell that conducts the cell activities and development. Mitochondria is also called power house of the cell because it supplies energy to the cell in the form of ATP i.e. Adenosine Triphosphate. Beside this, there is the presence of ER that helps in regulation of protein, Golgi apparatus that helps in transfer of protein, lysosomes that discards and degrades any unwanted substances in the cell, chloroplast that helps to conduct the process of photosynthesis (in plants and algae). The presence of these organelles also depends on the type of eukaryotic cell and the function it have to perform in the living system. The major organelle that is present in a eukaryotic cell is nucleus. Nucleus consist of nuclear envelop which is the double membrane structure. This nuclear envelope consists of small pores for the exchange of materials in and out of the cell, which is called nuclear pores. In case of prokaryotes, it have been noticed that DNA is loosely scattered in the cytoplasm of the cell but in case of eukaryotes, DNA is present inside the nucleolus, which is the inner part of eukaryotic nucleus. Beside DNA; nucleolus also contains RNA and protein necessary for cell functioning. Colored substance called chromatin is also present in the nucleus of the cell. It lies in between the nuclear envelope and the nucleolus. Hence, all these organelles perform their function and reserve a separate compartment within the cell.
Eukaryotic cell examples: Thousands of examples can be listed for eukaryotic cells that include plants, animals, algae, fungi etc. In fact anything that can be easily noticed and seen by our naked eyes are the good example of eukaryotic cell.
Difference between eukaryotic and prokaryotic cell:
When we compare eukaryotic and prokaryotic cell, lots of differences in structure can be figured out. Some of them are listed below:
|Have single cell
|Presence of nucleoid instead of nucleus
|Presence of well organised nucleus
|No membrane bound organelles
|Presence of membrane bound organelles like chloroplast, ribosome, ER, etc
|example includes: E.coli
|Example includes: different plants and animals that can be seen with naked eyes
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