Prokaryotes are single-celled organisms that lack a distinct nucleus and other membrane-bound organelles. The term "prokaryote" is derived from two Greek words, "pro," meaning "before," and "karyon," meaning "nucleus." Prokaryotes are considered the first living organisms on Earth as they are the simplest life form.

Prokaryotes are classified into two domains: Bacteria and Archaea. Bacteria are ubiquitous microorganisms on Earth and can cause diseases or perform beneficial functions for other living things. Archaea are microorganisms mostly found in extreme environments and have some characteristics more closely related to eukaryotes, such as certain genes and metabolic pathways.

Prokaryotes have a simple cellular organization with a single circular chromosome and small rings of extrachromosomal DNA called plasmids. Their DNA is not organized into chromosomes, and they do not have a mitotic mechanism for cell division, microtubules, and mitochondria. Their cell wall is made up of peptidoglycan or pseudo peptidoglycan, depending on the domain. Some prokaryotes have cell appendages such as flagella, pili, and fimbriae that help them move, attach, or exchange genetic material.

Prokaryotes can vary in size, shape, oxygen requirement, and nutritional mode. They can be cocci (spherical), bacilli (rod-shaped), spirilla (spiral-shaped), or vibrio (comma-shaped). They can be aerobic (requiring oxygen), anaerobic (not requiring oxygen), or facultative (able to switch between oxygen conditions). They can be photoautotrophic (using light and carbon dioxide to make food), chemoautotrophic (using chemical sources to make food), or heterotrophic (obtaining food from other living things).

Prokaryotes reproduce asexually by binary fission, where a single cell divides into two identical daughter cells. They can also exchange genetic material through recombination processes such as conjugation, transformation, and transduction.

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote Definition & Meaning |http://dictionary.com/

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote - Definition and Examples | Biology Dictionary

: Prokaryote - Definition and Examples | Biology Dictionary

Characteristics of Prokaryotes

Prokaryotes are single-celled organisms that belong to the domains of Bacteria and Archaea. They are the simplest and most ancient forms of life on Earth. Prokaryotes have some common characteristics that distinguish them from eukaryotic cells. Some of these characteristics are:

• Size and shape: Prokaryotes are much smaller than eukaryotic cells, ranging from 0.1 to 5.0 µm in diameter. The shape of prokaryotes varies from spherical (cocci), rod-shaped (bacilli), spiral (spirilla), and comma-shaped (vibrio) to more complex forms. The shape of prokaryotes is influenced by environmental factors and functional adaptations.

• Cellular organization: Prokaryotes lack a membrane-bound nucleus and other membrane-bound organelles, such as mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, etc. The genetic material of prokaryotes is a single circular chromosome that is located in a region of the cytoplasm called the nucleoid. Prokaryotes also have small circular pieces of DNA called plasmids that can replicate independently and carry genes for antibiotic resistance, virulence factors, or metabolic pathways. Prokaryotes do not have histone proteins that associate with DNA in eukaryotes.

• Cell wall and Capsule: All prokaryotes have a cell wall that surrounds the plasma membrane and provides shape and protection, and prevents dehydration. The cell wall of most bacteria is composed of a polymer of carbohydrates and proteins called peptidoglycan, while the cell wall of archaea is made of pseudo peptidoglycan or other polymers. Some prokaryotes also have a capsule or slime layer outside the cell wall, which is made of polysaccharides or polypeptides and helps the cell adhere to surfaces, evade the immune system, or resist desiccation.

• Appendages: Many prokaryotes have structures that protrude from the cell surface, such as flagella, pili, and fimbriae. Flagella are long, whip-like structures that enable the cell to move by rotating. Pili are shorter and thinner than flagella and are used for exchanging genetic material between cells during a process called conjugation. Fimbriae are hair-like structures that help the cell attach to other cells or surfaces.

• Ribosomes: Prokaryotes have 70S ribosomes that are smaller and simpler than the 80S ribosomes found in eukaryotes. The 70S ribosomes consist of two subunits: 30S and 50S. The 30S subunit contains 16S rRNA and 21 proteins, while the 50S subunit contains 23S rRNA, 5S rRNA, and 31 proteins. Ribosomes are responsible for protein synthesis in prokaryotes.

• Reproduction: Prokaryotes reproduce asexually by binary fission, which is a process of dividing the cell into two identical daughter cells. Prokaryotes do not undergo sexual Reproduction involving the fusion of gametes, but they can exchange genetic material by horizontal gene transfer through mechanisms such as transformation, transduction, or conjugation. Horizontal gene transfer can introduce variation and new traits into prokaryotic populations.

Prokaryotes are single-celled organisms that lack a membrane-bound nucleus and other organelles. They are much smaller and simpler than eukaryotic cells, but they have some common features with them, such as a plasma membrane, cytoplasm, and ribosomes. However, prokaryotic cells also have some unique structures that distinguish them from eukaryotes. These include:

• Capsule: A capsule is a sticky layer of polysaccharides or proteins that surrounds some prokaryotic cells. It helps the cell adhere to surfaces, protect against dehydration, and evade the immune system of the host. Not all prokaryotes have a capsule, and its composition varies among different species.

• Cell wall: A cell wall is a rigid layer that lies outside the plasma membrane of most prokaryotes. It provides shape, support, and protection to the cell. The cell wall of most bacteria is made of peptidoglycan, a polymer of sugars and amino acids. The cell wall of archaea does not contain peptidoglycan but instead has pseudo peptidoglycan or other proteins and polysaccharides.

• Flagella: Flagella are long, whip-like appendages that protrude from the cell surface and enable movement. Some prokaryotes have one or more flagella, while others lack them. The flagella of prokaryotes are composed of a protein called flagellin, which forms a helical filament that rotates by a motor at the base.

• Pili: Pili are short, hair-like projections that extend from the cell surface and help the cell attach to other cells or surfaces. Some pili are specialized for DNA transfer between cells, such as the sex pili that mediate bacterial conjugation.

• Fimbriae: Fimbriae are similar to pili but shorter and more numerous. They help the cell adhere to surfaces and form biofilms.

• Nucleoid: The nucleoid is the region of the cytoplasm where the genetic material of the prokaryotic cell is located. Unlike eukaryotes, prokaryotes do not have a membrane-bound nucleus. Instead, they have a single circular chromosome that is supercoiled and attached to the plasma membrane or other proteins. The chromosome contains all the essential genes for the cell`s survival and function.

• Plasmids: Plasmids are small, circular pieces of DNA that are separate from the chromosome and can replicate independently. They are not essential for the cell`s survival, but they may carry genes that confer advantages such as antibiotic resistance, toxin production, or metabolic capabilities. Plasmids can be transferred between cells by horizontal gene transfer mechanisms such as conjugation, transformation, or transduction.

• Ribosomes: Ribosomes are the structures where protein synthesis takes place. They are composed of two subunits: a large subunit (50S) and a small subunit (30S). The subunits are made of ribosomal RNA (rRNA) and proteins. The ribosomes of prokaryotes are smaller and simpler than those of eukaryotes (70S vs 80S). They are found either free in the cytoplasm or attached to the plasma membrane.

• Cytoplasmic inclusions: Cytoplasmic inclusions are granules or vesicles that store various substances in the cytoplasm. They may contain nutrients, waste products, pigments, gas vacuoles, or crystals. Some examples of cytoplasmic inclusions are glycogen granules in bacteria, sulfur globules in sulfur bacteria, carboxysomes in cyanobacteria, and magnetosomes in magnetotactic bacteria.

Division and Reproduction of Prokaryotes

Prokaryotes, such as bacteria and archaea, are single-celled organisms that reproduce asexually by a process called binary fission. Binary fission is a simple form of cell division that does not involve the formation of gametes or the mixing of genetic material from two individuals. Binary fission produces daughter cells that are genetically identical to the parent cell, except for rare mutations that may occur during DNA replication.

The steps of binary fission in prokaryotes are as follows:

1. The DNA of the cell is replicated, resulting in two identical copies of the circular chromosome attached to the cell membrane.

1. The cell grows and elongates, pushing the two copies of DNA apart towards the opposite poles of the cell.

1. The cell membrane and the cell wall begin to pinch inward at the center of the cell, forming a constriction called a septum.

1. The septum eventually divides the cell into two daughter cells, each with its own copy of DNA and other cellular components.

The following table summarizes the main differences between binary fission in prokaryotes and mitosis in eukaryotes:

| Binary fission | Mitosis |

| -------------- | ------- |

| Occurs in prokaryotes (bacteria and archaea) | Occurs in eukaryotes (animals, plants, fungi, protists) |

| Involves one circular chromosome | Involves multiple linear chromosomes |

| Does not require spindle fibers or centrioles | Requires spindle fibers and centrioles |

| Does not involve nuclear envelope breakdown or reformation | Involves nuclear envelope breakdown and reformation |

| Produces two identical daughter cells | Produces two identical daughter cells |

Some prokaryotes can undergo variations of binary fission that result in different arrangements or numbers of daughter cells. For example:

• Some bacteria, such as Streptococcus pneumonia, divide along a single plane and remain attached after division, forming chains of cells.

• Some bacteria, such as Staphylococcus aureus, divide along multiple planes and form clusters of cells.

• Some bacteria, such as Corynebacterium diphtheriae, divide asymmetrically and produce one large and one small daughter cell.

• Some bacteria, such as Bacillus anthracis, form endospores inside their cells before dividing. Endospores are dormant and resistant structures that can survive harsh environmental conditions.

• Some archaea, such as Sulfolobus acidocaldarius, form multiple buds on their cell surface that detach as daughter cells.

Although prokaryotes reproduce asexually by binary fission, they can exchange genetic material with other prokaryotes by three main mechanisms: transformation, transduction, and conjugation. These mechanisms are collectively called recombination and increase the genetic diversity of prokaryotic populations.

• Transformation is the uptake of free DNA fragments from the environment by a prokaryotic cell. The DNA fragments may come from dead or lysed cells of the same or different species. The DNA fragments may integrate into the chromosome or remain as plasmids (small circular DNA molecules) in the cytoplasm.

• Transduction is the transfer of DNA from one prokaryotic cell to another by a virus (called a bacteriophage or phage). The phage infects a donor cell and incorporates some of its DNA into its own genome. The phage then infects a recipient cell and injects its modified genome along with the donor DNA. The donor DNA may integrate into the chromosome or remain as plasmids in the cytoplasm.

• Conjugation is the direct transfer of DNA from one prokaryotic cell to another through a physical connection called a sex pilus. The sex pilus is a thin filament that extends from the donor cell to the recipient cell. The DNA that is transferred is usually a plasmid that contains genes for antibiotic resistance or other traits. The plasmid may integrate into the chromosome or remain as a plasmid in the cytoplasm.

The following table summarizes the main differences between transformation, transduction, and conjugation:

| Transformation | Transduction | Conjugation |

| -------------- | ------------ | ----------- |

| Involves free DNA fragments from the environment | Involves DNA transfer by a virus | Involves direct contact between cells |

| Does not require special genes or structures | Requires phage infection | Requires sex pilus formation |

| Can occur between different species | Can occur between different species | Usually occurs between same species |

| Can transfer any part of the chromosome or plasmids | Can transfer any part of the chromosome or plasmids | Usually transfers plasmids only |

1. Examples of Prokaryotes

Prokaryotes are the most abundant and diverse group of organisms on Earth. They can be found in almost every habitat and environment, from the deep sea to the human gut. Prokaryotes include two major domains of life: Bacteria and Archaea. Here are some examples of prokaryotes from each domain:

Bacteria are the most common and well-known prokaryotes. They have a cell wall made of peptidoglycan, a polymer of carbohydrates and proteins. They can have various shapes, such as cocci (spherical), bacilli (rod-shaped), spirilla (spiral), and vibrio (comma-shaped). Some bacteria have additional structures, such as capsules, flagella, pili, and fimbriae, that help them survive and interact with their environment. Bacteria can be classified by their metabolic diversity, such as whether they are aerobic or anaerobic, autotrophic or heterotrophic, and chemotrophic or phototrophic. Some examples of bacteria are:

• Escherichia coli (E. coli): a common inhabitant of the human intestine that can cause food poisoning or urinary tract infections in some strains.

• Streptomyces spp.: soil bacteria that produce many antibiotics, such as streptomycin and tetracycline.

• Pseudomonas spp.: versatile bacteria that can degrade various organic compounds and cause infections in plants and animals.

• Cyanobacteria (blue-green algae): photosynthetic bacteria that can form blooms in water bodies and produce oxygen and nitrogen compounds.

Archaea are prokaryotes that are more closely related to eukaryotes than to bacteria. They have a cell wall made of pseudo peptidoglycan, a similar but distinct polymer from peptidoglycan. They also have a unique cell membrane composed of a monolayer of phospholipids with branched hydrocarbon chains. Archaea are often found in extreme environments, such as hot springs, oceans, and marshlands, where they can withstand high temperatures, salinity, acidity, or alkalinity. Archaea can also have diverse metabolic pathways, such as methanogenesis, sulfate reduction, and halt respiration. Some examples of archaea are:

• Halobacterium spp.: salt-loving archaea that can grow in saturated salt solutions and use light to generate energy through bacteriorhodopsin, a purple pigment.

• Thermoplasma spp.: acidophilic and thermophilic archaea that lack a cell wall and can grow at pH 2 and 55°C.

• Sulfolobus spp.: acidophilic and thermophilic archaea that oxidize sulfur to produce sulfuric acid and can grow at pH 3 and 80°C.

FAQs on Prokaryotes

In this section, we will answer some of the frequently asked questions about prokaryotes. These questions will help you understand the basic features and functions of prokaryotic cells.

What are three examples of prokaryotes?

Prokaryotes are single-celled organisms that belong to the domains of Bacteria and Archaea. There are millions of species of prokaryotes, but some of the common examples are:

• Escherichia coli, a bacterium that lives in the human gut and can cause infections.

• Streptococcus pyogenes, a bacterium that causes strep throat and other diseases.

• Methanobacterium thermoautotrophicum, an archaeon that produces methane gas in hot springs.

Do prokaryotes have ribosomes?

Yes, prokaryotes have ribosomes. Ribosomes are the structures that synthesize proteins from amino acids. Prokaryotic ribosomes are smaller and simpler than eukaryotic ribosomes. They have a size of 70S, which is composed of two subunits: 50S and 30S. The 50S subunit contains 23S and 5S rRNA, while the 30S subunit contains 16S rRNA.

Do prokaryotes have a nucleus?

No, prokaryotes do not have a nucleus. A nucleus is a membrane-bound organelle that contains the genetic material (DNA) of a cell. Prokaryotes lack membrane-bound organelles, so their DNA is not enclosed by a membrane. Instead, their DNA is found in a region of the cytoplasm called the nucleoid, where it forms a circular chromosome. Some prokaryotes also have extra pieces of DNA called plasmids, which can be transferred between cells.

Do prokaryotes have mitochondria?

No, prokaryotes do not have mitochondria. Mitochondria are membrane-bound organelles that produce energy (ATP) from oxygen and glucose. Prokaryotes lack membrane-bound organelles, so they do not have mitochondria. Instead, they produce energy by using enzymes on their cell membrane or in their cytoplasm.

Is DNA found in prokaryotes?

Yes, DNA is found in prokaryotes. DNA is the molecule that stores and transmits genetic information in all living cells. Prokaryotic DNA is usually circular and consists of a single chromosome. It is located in the nucleoid region of the cytoplasm. Some prokaryotes also have plasmids, which are small circular pieces of DNA that can carry extra genes.

How do prokaryotes divide?

Prokaryotes divide by asexual methods, which do not involve the formation of gametes (sex cells). The most common method of prokaryotic division is binary fission, where a cell grows and splits into two identical daughter cells. Some prokaryotes can also exchange genetic material through processes such as conjugation, transformation, and transduction. These processes increase the genetic diversity of prokaryotic populations.

Definition of Eukaryotes

Eukaryotes are organisms or cells that have a membrane-bound nucleus and other specialized structures called organelles in the cytoplasm. Eukaryotes are distinct from bacteria and other primitive microorganisms that lack a nucleus and organelles. Eukaryotes include protoctists, fungi, plants, and animals. The term "eukaryote" is derived from the Greek words "EU," meaningtrueand "karyonmeaningnucleus.`

Eukaryotic cells have a more advanced structural composition when compared to prokaryotes. By virtue of these advancements, eukaryotic cells are capable of performing more complex functions than prokaryotic cells. Eukaryotic cells are generally large and divide by mitosis or meiosis using microtubules. Some eukaryotes have cilia or flagella for movement, which are composed of a complex arrangement of microtubules and proteins.

Eukaryotes are thought to have evolved from prokaryotes about 1.5 to 2 billion years ago through a process of endosymbiosis, where some prokaryotic cells engulfed other prokaryotic cells and formed a symbiotic relationship. The earliest known fossils of eukaryotic cells date back to about 1.8 billion years ago.

Eukaryotes are a diverse group of living things, ranging from single microscopic cells, such as placozoans under 3 micrometers across, to animals like the blue whale, weighing up to 190 tonnes and measuring up to 33.6 meters (110 ft) long, or plants like the coast redwood, up to 120 meters (390 ft) tall.

: Endosymbiosis - Wikipedia

: Oldest Fossils of Eukaryotic Cells Found in China | Live Science

: List of largest organisms - Wikipedia

9. Characteristics of Eukaryotes

Eukaryotes are cells that have a more complex structure and function than prokaryotes. The term "eukaryote" means "true nucleus" in Greek, which reflects the presence of a membrane-bound nucleus that contains the genetic material of the cell. Eukaryotic cells also have other membrane-bound organelles that perform specific functions, such as mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes. Eukaryotic cells can be unicellular or multicellular, and they belong to four major groups: animals, plants, fungi, and protists.

Some of the general characteristics of eukaryotic cells are :

• The size of eukaryotic cells ranges from 10 to 100 micrometers in diameter, which is much larger than prokaryotic cells, ranging from 0.1 to 5 micrometers.

• The shape of eukaryotic cells varies depending on the type and function of the cell. Some cells are spherical, some are elongated, some are flat, and some are irregular. Some cells have cytoplasmic extensions, such as flagella, cilia, or pseudopodia, that help with movement or feeding.

• The cellular organization of eukaryotic cells is more advanced than prokaryotic cells, as they have a well-defined nucleus and other organelles that are surrounded by membranes. These membranes create compartments within the cell that allow different biochemical reactions to occur in different locations.

• The genetic material of eukaryotic cells is DNA, which is linear and has multiple origins of replication. The DNA is organized into chromosomes, which are composed of DNA wrapped around histone proteins. The chromosomes are located inside the nucleus, where they are protected and regulated by the nuclear envelope and the nucleolus.

• The cell wall is present in some eukaryotic cells, such as plant cells, fungal cells, and some protist cells. The cell wall provides support and protection to the cell and is made up of different materials depending on the type of cell. For example, plant cell walls are made of cellulose, fungal cell walls are made of chitin, and protist cell walls are made of various polysaccharides or silica.

• The plasma membrane is present in all eukaryotic cells and is made up of a phospholipid bilayer with embedded proteins. The plasma membrane regulates the transport of molecules in and out of the cell and also participates in cell signaling and recognition.

• The cytoplasm is the fluid-filled space inside the cell that contains the cytosol and various organelles and molecules. The cytosol is a gel-like substance that consists of water, salts, organic molecules, and enzymes. The cytoplasm also contains a cytoskeleton, which is a network of protein filaments that provide shape, support, and movement to the cell.

• The organelles are specialized structures within the cell that perform specific functions. Some of the common organelles in eukaryotic cells are:

• Nucleus: The nucleus is the control center of the cell that stores and transmits genetic information. It is surrounded by a double membrane called the nuclear envelope that has pores for communication with the cytoplasm. Inside the nucleus, there is a dense region called the nucleolus that produces ribosomes.

• Mitochondria: Mitochondria are oval-shaped organelles that produce energy for the cell by breaking down glucose and oxygen into carbon dioxide and water. This process is called cellular Respiration, and it generates ATP, the main energy currency of the cell. Mitochondria have their own DNA and ribosomes and can divide independently of the cell cycle.

• Chloroplasts: Chloroplasts are green-colored organelles that are found only in plant cells and some protist cells. They convert light energy into chemical energy by using water and carbon dioxide to produce glucose and oxygen. This process is called Photosynthesis, and it also generates ATP for the cell. Chloroplasts have their own DNA and ribosomes and can divide independently of the cell cycle.

• Endoplasmic reticulum: Endoplasmic reticulum (ER) is a network of membranous tubules and sacs that extends throughout the cytoplasm. There are two types of ER: rough ER and smooth ER. Rough ER has ribosomes attached to its surface and is involved in protein synthesis and modification. Smooth ER lacks ribosomes and is involved in lipid synthesis and detoxification.

• Golgi apparatus: Golgi apparatus is a stack of flattened membranous sacs that receives proteins and lipids from the ER and modifies them further by adding sugars or other groups. It also sorts, packages, and distributes them to different destinations within or outside the cell.

• Lysosomes: Lysosomes are spherical organelles that contain digestive enzymes that break down various macromolecules, pathogens, or damaged organelles within the cell. They also participate in programmed cell death or apoptosis.

• Peroxisomes: Peroxisomes are small organelles that contain enzymes that catalyze various oxidative reactions, such as breaking down fatty acids or detoxifying harmful substances. They also produce hydrogen peroxide as a by-product, which they convert into water using another enzyme called catalase.

• The ribosomes are small structures composed of RNA and protein that synthesize proteins according to the instructions from DNA. In eukaryotic cells, there are two types of ribosomes: 80S ribosomes that are found in the cytoplasm or attached to the rough ER, and 70S ribosomes that are found inside mitochondria or chloroplasts.

1. Structure of Eukaryotes

The structure of a eukaryotic cell consists of a plasma membrane that separates the cell from the outside environment and contains embedded proteins. The plasma membrane may be surrounded by a rigid cell wall in some eukaryotic cells, such as plants, fungi, and some protists, but not in animals. The eukaryotic cell also has a membrane-bound nucleus that contains the genetic material of the cell in the form of chromosomes. Additionally, the eukaryotic cell has various membrane-bound organelles that perform different functions, such as the endoplasmic reticulum, Golgi apparatus, mitochondria, and chloroplasts (in plant cells).

The following table summarizes the main components of a eukaryotic cell and their functions:

| Component | Function |

| --- | --- |

| Plasma membrane | Regulates the transport of molecules in and out of the cell; maintains cell integrity and communication |

| Cell wall | Provides support and shape to the cell; protects the cell from mechanical stress and dehydration |

| Nucleus | Stores and protects the DNA; controls gene expression and cell division |

| Endoplasmic reticulum | Synthesizes and transports proteins and lipids; detoxifies drugs and toxins |

| Golgi apparatus | Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles |

| Mitochondria | Produces ATP (energy) by cellular respiration; regulates apoptosis (cell death) |

| Chloroplasts | Converts light energy into chemical energy (glucose) by Photosynthesis; contains chlorophyll (green pigment) |

| Cytoskeleton | Provides structural support and shape to the cell; enables cell movement and division; anchors organelles |

| Lysosomes | Digests macromolecules, pathogens, and damaged organelles; recycles cellular components |

| Peroxisomes | Breaks down fatty acids, amino acids, and toxins; produces hydrogen peroxide as a by-product |

| Vacuoles | Stores water, ions, nutrients, and waste products; maintains turgor pressure and pH balance |

Eukaryotic cells are typically much larger than prokaryotic cells, having a volume of around 10,000 times greater than prokaryotic cells. Eukaryotic cells are also more diverse in shape and function than prokaryotic cells. Some eukaryotic cells have specialized structures or appendages, such as cilia, flagella, pseudopodia, or microvilli, that enable them to move, feed, or sense their environment. Eukaryotic cells can be either unicellular or multicellular. Unicellular eukaryotes are sometimes called protists. Multicellular eukaryotes include animals, plants, fungi, and algae.

1. Division and Reproduction of Eukaryotes

Eukaryotes are cells that have a membrane-bound nucleus and other organelles. Unlike prokaryotes, which divide by binary fission or recombination, eukaryotes have two distinct types of cell division: mitosis and meiosis.

Mitosis is a process of asexual Reproduction that produces two daughter cells that are genetically identical to the parent cell. Mitosis occurs in four main phases: prophase, metaphase, anaphase, and telophase. During prophase, the chromosomes condense, and the nuclear envelope breaks down. During metaphase, the chromosomes align at the equator of the cell. During anaphase, the sister chromatids separate and move to opposite poles of the cell. During telophase, the chromosomes decondensed, and the nuclear envelope reforms. Cytokinesis, the division of the cytoplasm, usually occurs simultaneously with telophase. Mitosis is important for the growth, development, and repair of eukaryotic cells.

Meiosis is a process of sexual Reproduction that produces four daughter cells that are genetically different from the parent cell. Meiosis occurs in two consecutive rounds: meiosis I and meiosis II. During meiosis, the homologous chromosomes pair up and exchange segments in a process called crossing over. Then, the homologous pairs separate and move to opposite poles of the cell. During meiosis II, the sister chromatids separate and move to opposite poles of the cell. Cytokinesis occurs at the end of each round of meiosis, resulting in four haploid cells. Meiosis is important for generating genetic diversity and producing gametes for sexual Reproduction.

Some eukaryotic cells can also reproduce by other methods, such as budding, fragmentation, or parthenogenesis. These methods are also asexual and produce offspring that are genetically similar to the parent cell. However, they do not involve mitosis or meiosis. For example, budding is a process where a small outgrowth of the parent cell develops into a new individual. Fragmentation is a process where a piece of the parent cell breaks off and regenerates into a new individual. Parthenogenesis is a process where an unfertilized egg develops into a new individual without fertilization.

Eukaryotic cells have different modes of division and Reproduction depending on their type and function. However, all eukaryotic cells share some common features: they have a complex structure with a nucleus and organelles, they have linear chromosomes with multiple origins of replication, and they use microtubules to separate their chromosomes during division.

1. Examples of Eukaryotes

Eukaryotes are a diverse group of organisms that include all animals, plants, fungi, and protists, as well as most algae. Eukaryotes have cells that are complex and organized, with a membrane-bound nucleus and other organelles. Here are some examples of eukaryotes from different kingdoms:

• Animals are multicellular eukaryotes that lack cell walls and chloroplasts. They obtain energy by consuming organic matter and have specialized tissues and organs for different functions. Animals can be classified into different phyla based on their body plans, such as chordates (vertebrates), arthropods (insects, spiders, crustaceans), mollusks (snails, clams, octopuses), echinoderms (starfish, sea urchins), and cnidarians (jellyfish, corals).

• Plants are multicellular eukaryotes that have cell walls made of cellulose and chloroplasts that enable them to perform Photosynthesis. They synthesize organic molecules from carbon dioxide and water using light energy and release oxygen as a by-product. Plants can be classified into different groups based on their reproductive structures, such as bryophytes (mosses, liverworts), pteridophytes (ferns, horsetails), gymnosperms (conifers, cycads), and angiosperms (flowering plants).

• Fungi are mostly multicellular eukaryotes that have cell walls made of chitin and lack chloroplasts. They obtain energy by decomposing organic matter and absorbing nutrients from their environment. Fungi can be classified into different phyla based on their reproductive structures, such as zygomycetes (bread molds), ascomycetes (yeasts, morels, truffles), basidiomycetes (mushrooms, puffballs), and Deuteromycetes (penicillium, aspergillus).

• Protists are mostly unicellular eukaryotes that have diverse forms and functions. They do not fit into any other kingdom and are often considered a paraphyletic group. Protists can be classified into different groups based on their modes of nutrition, such as autotrophs (algae, diatoms, dinoflagellates), heterotrophs (amoeba, paramecium, plasmodium), and mixotrophs (euglena). Protists can also be classified based on their motility, such as flagellates (Trypanosoma, giardia), ciliates (tetrahymena, stentor), and amoeboids (entamoeba, slime molds).

1. 47 Differences Between Prokaryotes and Eukaryotes

Prokaryotes and eukaryotes are the two major types of cells on Earth, but they have many differences in their structure, function, and evolution. Here are 47 differences between prokaryotes and eukaryotes:

| Prokaryotes | Eukaryotes |

| --- | --- |

| Always unicellular | Can be unicellular or multicellular |

| No nucleus | Have a nucleus |

| DNA is circular and free-floating in the nucleoid region | DNA is linear and stored in the nucleus |

| No membrane-bound organelles | Have membrane-bound organelles |

| Cell wall is made of peptidoglycan or pseudo peptidoglycan | Cell wall is made of cellulose, chitin, or absent |

| Ribosomes are 70S type | Ribosomes are 80S type |

| Cell size is 0.2-2.0 µm in diameter | Cell size is 10-100 µm in diameter |

| Cell division is by binary fission | Cell division is by mitosis or meiosis |

| Reproduction is asexual | Reproduction can be asexual or sexual |

| No sexual life cycle | Have a sexual life cycle |

| No mitotic apparatus | Have a mitotic apparatus |

| No cytoskeleton | Have a cytoskeleton |

| Flagella are simple and made of flagellin protein | Flagella are complex and made of microtubules |

| Pili and fimbriae are present for attachment and conjugation | Pili and fimbriae are absent |

| Capsule may be present for protection and adhesion | Capsule is absent |

| Plasmids are common and carry extra genes | Plasmids are rare and usually found in mitochondria and plastids |

| Histone proteins are absent or rare | Histone proteins are abundant and bind to DNA |

| Chromosomes are single and haploid | Chromosomes are multiple and diploid or polyploid |

| No introns in genes | Introns are present in most genes |

| Operons are common for gene regulation | Operons are rare or absent |

| Transcription and translation occur simultaneously in the cytoplasm | Transcription occurs in the nucleus, and translation occurs in the cytoplasm |

| No mRNA processing or splicing | mRNA undergoes processing and splicing before translation |

| No post-translational modifications of proteins | Proteins undergo post-translational modifications in the endoplasmic reticulum and Golgi apparatus |

| Horizontal gene transfer is common | Horizontal gene transfer is rare or limited to specific groups |

| Genetic recombination occurs by transformation, transduction, or conjugation | Genetic recombination occurs by crossing over during meiosis |

| No telomeres at the ends of DNA molecules | Telomeres are present at the ends of DNA molecules |

| No apoptosis or programmed cell death | Apoptosis is a common mechanism of cell death |

| Metabolic diversity is high, can use various sources of energy and carbon | Metabolic diversity is low, mostly use organic molecules as energy and carbon sources |

| Photosynthesis occurs in the cytoplasm or thylakoid membranes | Photosynthesis occurs in the chloroplasts |

| Respiration occurs in the cell membrane or cytoplasm | Respiration occurs in the mitochondria |

| Endospores may be formed under unfavorable conditions | Endospores are not formed |

| No endocytosis or exocytosis | Endocytosis and exocytosis are common processes for transport across the cell membrane |

| No cytoplasmic streaming or movement of cytoplasm | Cytoplasmic streaming occurs in some cells for transport and movement |

| No vacuoles or very small ones | Vacuoles are large and important for storage, digestion, and turgor pressure |

| No lysosomes or peroxisomes for intracellular digestion | Lysosomes and peroxisomes are present for intracellular digestion |

| No centrioles or spindle fibers for cell division | Centrioles and spindle fibers are present for cell division |

| Cilia are rare or absent | Cilia are common in some cells for movement and sensation |

| No sterols in the cell membrane | Sterols are present in the cell membrane to regulate fluidity |

| No nuclear envelope or pores | Nuclear envelope and pores are present to regulate the passage of molecules between the nucleus and cytoplasm |

| No nucleolus in the nucleus | nucleolus is present in the nucleus to synthesize ribosomal RNA |

| No plastids for storage or photosynthesis | Plastids are present in plants and algae for storage or photosynthesis |

| Growth rate is fast due to simple structure and metabolism | Growth rate is slow due to complex structure and metabolism |

| Adaptation to extreme environments is high due to genetic flexibility and diversity | Adaptation to extreme environments is low due to genetic stability and uniformity |

| Examples: bacteria, archaea | Examples: plants, animals, fungi, protists |

1. 47 Differences Between Prokaryotes and Eukaryotes

Prokaryotes and eukaryotes are two major groups of living organisms that differ in many aspects of their cell structure and function. Prokaryotes include bacteria and archaea, while eukaryotes include animals, plants, fungi, and protists. Here are 47 differences between prokaryotes and eukaryotes:

| Prokaryotes | Eukaryotes |

| --- | --- |

| 1. Size: Usually 0.1-5 µm in diameter | 1. Size: Usually 10-100 µm in diameter |

| 2. Shape: Mostly cocci, bacilli, spirilla, or vibrio | 2. Shape: Highly variable, depending on the type of cell |

| 3. Cellular organization: Simple, with no membrane-bound organelles | 3. Cellular organization: Complex, with many membrane-bound organelles |

| 4. Nucleus: Absent; DNA is free in the cytoplasm | 4. Nucleus: At Present, DNA is enclosed by a nuclear envelope |

| 5. DNA: Single, circular chromosome; no histones; may have plasmids | 5. DNA: Multiple, linear chromosomes; associated with histones; no plasmids |

| 6. Gene structure: Compact, with no introns or repetitive sequences | 6. Gene structure: Less compact, with introns and repetitive sequences |

| 7. Ribosomes: Smaller (70S), composed of 30S and 50S subunits | 7. Ribosomes: Larger (80S), composed of 40S and 60S subunits |

| 8. Cell wall: Present in most prokaryotes, made of peptidoglycan or pseudo peptidoglycan | 8. Cell wall: Present in some eukaryotes (plants, fungi, some protists), made of cellulose, chitin, or other polysaccharides |

| 9. Capsule: Present in some prokaryotes, made of polysaccharides | 9. Capsule: Absent in eukaryotes |

| 10. Plasma membrane: Phospholipid bilayer with embedded proteins; no cholesterol or sterols | 10. Plasma membrane: Phospholipid bilayer with embedded proteins; contains cholesterol and sterols |

| 11. Cytoplasm: Gel-like fluid with dissolved minerals and ions; contains ribosomes and nucleoid region | 11. Cytoplasm: Gel-like fluid with dissolved minerals and ions; contains ribosomes and various organelles |

| 12. Cytoskeleton: Absent or rudimentary in most prokaryotes | 12. Cytoskeleton: Well-developed, composed of microfilaments, microtubules, and intermediate filaments |

| 13. Flagella: Simple, composed of a single protein (flagellin) | 13. Flagella: Complex, composed of multiple proteins (tubulin) arranged in a "9+2" pattern |

| 14. Pili: Present in some prokaryotes, used for attachment, movement, or DNA transfer | 14. Pili: Absent in eukaryotes |

| 15. Fimbriae: Present in some prokaryotes, used for adhesion to surfaces | 15. Fimbriae: Absent in eukaryotes |

| 16. Mitochondria: Absent in prokaryotes | 16. Mitochondria: Present in most eukaryotes, involved in cellular respiration |

| 17. Chloroplasts: Absent in prokaryotes (some cyanobacteria have thylakoids) | 17. Chloroplasts: Present in plants and some protists, involved in photosynthesis |

| 18. Endoplasmic reticulum: Absent in prokaryotes | 18. Endoplasmic reticulum: Present in eukaryotes, involved in protein synthesis and transport |

| 19. Golgi apparatus: Absent in prokaryotes | 19. Golgi apparatus: Present in eukaryotes, involved in protein modification and sorting |

| 20. Lysosomes: Absent in prokaryotes | 20. Lysosomes: Present in animal cells and some protists, involved in the digestion and recycling of cellular components |

| 21. Peroxisomes: Absent in prokaryotes | 21. Peroxisomes: Present in eukaryotes, involved in lipid metabolism and detoxification |

| 22. Vacuoles: Absent or small in prokaryotes | Vacuoles: Present or large in some eukaryotes (plants, fungi, some protists), involved in storage and osmoregulation |

|23.Centrioles/Centrosomes: Absentinprokaryotes|23.Centrioles/Centrosomes: Presentinanimalcellsandsomeprotists,involvedincelldivisionandmicrotubuleorganization|

24.Nucleolus :Absentinprokaryotes|24.Nucleolus :Presentineukaryoticnucleus ,involvedinribosomebiogenesis|

25.Spindleapparatus :Absentinprokaryotes|25.Spindleapparatus :Presentineukaryoticcells ,involvedinchromosomealignmentandseparation|

1. Cilia: Absentorpresentinsomearchaea,composedofflagellinprotein|26.Cilia: Present in some eukaryotic cells,composedoftubulinprotein|

1. Transposons: Absentor presenting some prokaryotic plasmids,involvedingeneticvariationandantibioticresistance|27.Transposons: Present in eukaryotic DNA,involvedingeneticvariationandgeneexpression|

1. Inclusion bodies: Present in some prokaryotic cells, used for storage of nutrients or waste products |28.Inclusion bodies: Absent in eukaryotic cells|

1. Gas vesicles: Present in some prokaryotic cells used for buoyancy and movement in water |29.Gas vesicles: Absent in eukaryotic cells|

1. Carboxysomes: Present in some prokaryotic cells, used for enzymatic fixation of carbon dioxide|30.Carboxysomes: Absent in eukaryotic cells|

1. Magnetosomes: Present in some prokaryotic cells, used for navigation using magnetic fields|31.Magnetosomes: Absent in eukaryotic cells|

1. Endospores: Present in some prokaryotic cells, used for survival under harsh conditions |32.Endospores: Absent in eukaryotic cells|

1. Photosynthetic pigments: Present in some prokaryotic cells, located in thylakoid membranes of cyanophycin granules|33.Photosynthetic pigments: Present in plants and some protists, located in chloroplasts|

1. Respiratory enzymes: Present in some prokaryotic cells, located in the cell membrane or periplasmic space|34.Respiratory enzymes: Present in eukaryotic cells, located in the mitochondrial inner membrane|

1. Nitrogen fixation enzymes: Presenti some prokaryotic cells located inc cytoplasm or nitrogen-fixing organelles (cyanobacteria)|35.Nitrogenfixationenzymes :Absentineukaryoticcells(except some protists with endosymbiotic cyanobacteria)|

36.Sulfurreductionenzymes :Presentinsomeprokaryoticcells ,locatedinthecellmembraneorperiplasmicspace|36.Sulfurreductionenzymes :Absentineukaryoticcells(exceptsomeprotistswithendosymbioticbacteria)|

37.Methanogenesisenzymes :Presentinsomemethanogenicarchaea ,locatedinthecytoplasmormethanosomes(organelles)|37.Methanogenesisenzymes :Absentineukaryoticcells(exceptsomeprotistswithendosymbioticarchaea)|

38.Cellulosedigestionenzymes :Absentinmostprokaryoticcells(exceptsomecellulolyticbacteria)|38.Cellulosedigestionenzymes :Presentinsomeeukaroyticcellssuchasfungiandsomeprotists|

39.Proteasomes :Absentinmostprokayroticcells(exceptsomearchaea)|39.Proteasomes :Presentineukaroyticcellsinthecytoplasmornucleus ,involvedindegradationofmisfoldedorunwantedproteins|

40.Autophagyprocesses :Absentinmostprokaroyticcells(except some cyanobacteria)|40.Auto phagyprocesses: Present in eukaryotic cells in the cytoplasm, involved in the degradation of damaged or unneeded organelles|

41.Apoptosis processes :Absentinmostprokaroyticcells(exceptsomecyanobacteria)|41.Apoptosisprocesses :Presentineukaroyticcellsinthecytoplasmornucleus ,involvedinprogrammedcelldeath|

1. Cell communication mechanisms: Limitedinprokaroyticcellstoquorum-sensingandplasmidtransferbyconjugationpili|42.Cellcommunicationmechanisms: Diverseandeffectiveineukaroytic

1. DNA

DNA is the genetic material of both prokaryotic and eukaryotic cells, but it differs in structure, organization, and replication between the two groups. Some of the main differences between prokaryotic and eukaryotic DNA are:

• Prokaryotic DNA is circular, while eukaryotic DNA is linear. This means that prokaryotic DNA has no ends, while eukaryotic DNA has free ends that need to be protected by special structures called telomeres.

• Prokaryotic DNA is located in the cytoplasm, in a region called the nucleoid. Eukaryotic DNA is enclosed within a membrane-bound nucleus. This provides an extra level of protection and regulation for eukaryotic DNA.

• Prokaryotic DNA is usually present as a single chromosome, while eukaryotic DNA is organized into multiple chromosomes. Each chromosome consists of a long molecule of DNA wrapped around proteins called histones. Histones help compact and organize the DNA into a structure called chromatin.

• Prokaryotic DNA may also contain smaller circular pieces of DNA called plasmids. Plasmids are not essential for the survival of the cell, but they may carry genes that confer advantages such as antibiotic resistance or metabolic capabilities. Eukaryotic cells generally do not have plasmids, but some exceptions exist, such as mitochondria and chloroplasts.

• Prokaryotic DNA replication is simpler and faster than eukaryotic DNA replication. Prokaryotic DNA replication starts from a single origin of replication and proceeds in both directions around the circular chromosome. Eukaryotic DNA replication starts from multiple origins of replication and proceeds in both directions along the linear chromosomes. Eukaryotic DNA replication also involves more enzymes and factors than prokaryotic DNA replication.

These differences reflect the evolutionary history and complexity of prokaryotes and eukaryotes. Prokaryotes are considered to be the first living organisms on the Earth, and their DNA structure is simpler and more efficient for their small size and rapid growth. Eukaryotes evolved from prokaryotes, and their DNA structure is more complex and sophisticated for their larger size and diverse functions.

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