Prokaryotes vs. Eukaryotes

Prokaryotes are single-celled organisms that lack any nucleus or organelles. They include bacteria, archaea, and some unicellular eukaryotes. Bacteria are the most abundant type of prokaryote.

There are many different types of bacteria, each with its own unique characteristics. Some bacteria can cause disease while others can help decompose waste products.

Main Difference

Prokaryotes are bacteria that have no nucleus, while eukaryotes have a nucleus. They can be classified into two groups: Gram-positive and Gram-negative. Bacteria are prokaryotic organisms, meaning they do not contain a nucleus.

This means that their genetic material is located outside of the cell. In contrast, eukaryotic cells have a nucleus containing DNA. These cells are called eukaryotes.

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What are Prokaryotes?

Prokaryotes are single-celled organisms that lack a nucleus and other organelles. They include bacteria, archaea, and some protists. Bacteria are the most abundant type of prokaryote, and they can be found everywhere on Earth.

There are many different types of bacteria, but only two groups have been identified as being pathogenic (disease-causing). These are the Gram-positive and Gram-negative bacteria. Bacteria are classified into two groups based on their size: Gram-positive and Gram-negative. Most bacteria are Gram-positive. A few species of bacteria are Gram-negative.

Gram-Positive Bacteria

Gram-positive bacteria contain their cytoplasmic membrane inside out. This means that the inner side of the membrane is exposed to the outside environment while the outer side is protected from the environment.

This protects the cell from contamination by harmful substances in the surrounding environment. Gram-positive bacteria are further classified into three categories based on how their cell wall is constructed.

However, Gram-positive bacteria have a thick peptidoglycan layer around their cytoplasmic membrane. This layer contains long chains of polysaccharides called teichoic acid. These chains contain phosphate groups.

Gram-positive bacteria do not have lipopolysaccharide (LPS) in their outer membranes. LPS is a major constituent of the outer membrane of Gram-negative bacteria.

  • Lipid Bilayer Cell Wall: Lipid bilayer cell walls are composed of a thin layer of phospholipids embedded in a thicker peptidoglycan layer.
  • Murein Layer: Murein layers are thick, multilayered structures that consist of long chains of polysaccharides.
  • Peptidoglycan Layer: Peptidoglycan layers are similar to murein layers but do not contain any polysaccharide chains.

Gram-negative Bacteria

Gram-negative bacteria have a thin peptidoglycan layer surrounding their cytoplasmatic membrane. Their outer membrane has LPS. Lipoproteins are present in the outer membrane. Lipoproteins consist of lipid and protein components. Lipoprotein molecules are attached to the inner leaflet of the outer membrane via phospholipids.

What are Eukaryotes?

The eukaryotic cells are those that have a nucleus and organelles inside them. They include animals, fungi, algae, protists, and plants. Eukaryotic cells are characterized by their membrane-bound organelles.

These organelles contain the genetic material necessary for cellular functions. In addition, they contain many enzymes that enable these cells to carry out metabolic processes.

Besides, the eukaryotic cells are classified into two groups based on their shape and structure. They are unicellular (single-celled) and multicellular (many-celled). Unicellular organisms have only one nucleus while multicellular organisms contain many nuclei.

Eukaryotic cells are characterized by having a membrane-bound organelle called mitochondria that contains its own DNA. This DNA encodes for the production of 13 enzymes that synthesize ATP through oxidative phosphorylation.

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Moreover, these enzymes include the following:

  • NADH dehydrogenase
  • Cytochrome C reductase
  • Succinate dehydrogenase
  • Fumarate hydratase
  • Malate dehydrogenase
  • Pyruvate dehydrogenase
  • Alpha-ketoglutarate dehydrogenase
  • Branched-chain oxoacid dehydrogenase
  • Citrate synthase
  • Aconitase
  • Isocitrate dehydrogenase
  • 2-oxoglutarate dehydrogenases

These enzymes are responsible for producing energy from food molecules. Furthermore, Unicellular organisms are classified into prokaryotes and eukaryotes. Prokaryotes are single-celled organisms that lack a true nucleus and instead have a plasma membrane bounded by a peptidoglycan layer.

Their genetic material is located in the cell wall. In contrast, eukaryotes have a true nucleus and a double lipid bilayer membrane. Their genetic material is contained in chromosomes.

Types of Eukaryotes

Eukaryotes are organisms that have cells containing nuclei surrounded by membranes. They can be single-celled or multi-cellular. The major types of eukaryotes:


Algae are single-celled organisms that have no roots, stems, leaves, flowers, seeds, or fruit. They can live in both freshwater and saltwater environments. There are two types of algae: autotrophic (or photoautotrophs) and heterotrophic (or chemoheterotrophs).

Autotrophic algae use light energy from the sun to convert carbon dioxide into organic compounds using water and minerals. Heterotrophic algae obtain their nutrition through consuming other organisms.


Fungi are eukaryotic microorganisms that reproduce sexually and asexually. They lack true roots, stems, leaves and flowers but do have spores and fruiting bodies. Most fungi are saprophytes, meaning they eat dead or decaying matter. Some species are parasites, while others are symbiotic. Parasitic fungi infect animals, plants, and bacteria. Symbiotic fungi live in association with plants, animals, and humans.


Protozoa are unicellular eukaryotic organisms. They are similar to fungi in many ways, but they lack a true nucleus and instead contain a large number of small nuclei called karyosomes. Protozoa include amoebas, paramecia, ciliates, flagellates, and dinoflagellates. Amoebas are simple protozoa that move by means of muscular contractions.

Paramecia are tiny roundworms that swim freely in liquid media. Ciliates are microscopic aquatic organisms that form chains. Flagellates are motile cells that propel themselves forward by means of whip-like appendages. Dinoflagellates are marine planktonic organisms that possess two flagella.


Alveolates are unicellular organisms that lack flagella. Some examples include Amoebae, Diatoms, and Ciliates.


Apicomplexans are parasites that infect animals and humans. This group includes Plasmodium, Toxoplasma, Cryptosporidium, and Babesia.


The eukaryotic cells are much larger than prokaryotic cells. They have organelles like mitochondria, vacuoles, ribosomes, centrioles, etc. These organelles help them perform their functions. Prokaryotes are single-celled organisms that lack true nuclei and organelles. They have no membrane-bound structures and do not contain DNA. Eukaryotes are multi-cellular organisms that have true nuclei and organelle systems. They contain DNA and RNA.

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