millions of animal and plant species of varying sizes and shapes inhabit the earth and they all have one thing in common they are all made up of cells the fundamental unit of life in living organisms scientists didn't know about the existence of cells until the invention of the microscope one Leeuwenhoek an amateur Dutch scientist is credited as the first person to see and describe living cells later Robert Brown expanded on Leeuwenhoek's studies and pointed to the presence of a cell nucleus 18:38 not earnest matthias schleiden examined numerous plant species and concluded that plants have different types of cells which form plant tissues a year later Theodor Schwann British zoologist different animal cells and discovered that the cells have a thin outer layer which we now know as the cell or plasma membrane also studied plant cells and concluded that in addition to a cell membrane plant cells also have a cell wall a characteristic unique to plants slidin and fun together formulated the cell theory which stated that both plants and animals are made up of cells and their products such as proteins and lipids cell theory did not explain the formation of new cells which was clarified by Rudolf theory Hall in 1855 he coined the latin phrase omnis cellula acellular which meant that new cells arise from pre-existing cells and accordingly modified the cell theory which now states that all living organisms are composed of cells and products of cells and these cells arise from pre-existing cells cell research received a further boost with the invention of the electron microscope as it enabled scientists to observe the structure of the cell they observed that the structure of a cell varies in plants and animals a plant cell for instance by a distinct cell wall on the outside and a plasma membrane on the inside whereas an animal cell lacks a cell wall and has a plasma membrane instead that forms the outer cell boundary both animal and plant cells have and spherical structure called the nucleus which contains thread-like structures called chromosomes each chromosome is made of deoxyribonucleic acid or DNA which stores the genetic information of the organism if the nucleus is membrane-bound then the cell is called a new carry at Excel they are founding members of kingdom Protista kingdom fungi kingdom Plantae and kingdom Animalia on the other hand cells without a membrane-bound nucleus are called prokaryotic cells and members of kingdom monera possessed such cells both eukaryotic and prokaryotic cells are filled with cytoplasm Semmy fluid matrix present in ER to the cell membrane however in a new curiata Excel not include the nucleoplasm the nucleus matrix filled with the contents of the nucleus cytoplasm is a hub of activities and chemical reactions such as protein synthesis so remain alive suspended inside the cytoplasm are distinct structures called organelles in eukaryotic cells we find membrane-bound organelles such as the endoplasmic reticulum the Golgi complex lysosomes mitochondria micro bodies and vacuoles as well as non membrane-bound organelles such as ribosomes interestingly ribosomes are also found in chloroplasts of plant cells as well as the mitochondria and rough endoplasmic reticulum of both plants and animals animal cells possess another non membrane-bound organelle called the centriole which aids in cell division the cytoplasm of prokaryotic cells on the other hand membrane-bound organelles but contains ribosomes and fragments of extra chromosomal DNA called plasmids cells usually differ in size and shape for instance mycoplasma measured only 0.3 microns in length whereas human red blood cells are about 7 microns in diameter and nerve cells measure around for 200 microns amazingly the ostrich egg is the largest isolated single cell and it measures 17 to 19 centimeters in length and 14 to 15 centimeters in width moreover the shapes of cells range from disk-like to thread-like and from polygonal to columnar and cuboid today though we have gained a lot of information about cells scientists are still engaged in unlocking the secrets of the cell and its organelles millions of microorganisms are present in every nook and corner of our surroundings of these certain microorganisms such as bacteria nucleoid but no membrane-bound organelles in their cytoplasm such organisms are called prokaryotes prokaryotes are smaller and multiply more rapidly than eukaryotes all members of kingdom monera bacteria blue-green algae and gluten ammonia like organisms or mycoplasma are prokaryotes and they can be rod-shaped spiral-shaped shaped microscopic studies revealed that most prokaryotes except for a few such as mycoplasma and thermo plasma CEL envelope complex tightly-bound three layered chemical structure consisting of the outermost glycocalyx wall and then the plasma membrane the layers together act as a single protective unit though each has its distinct function the glycocalyx for instance helps prokaryotes such as bacteria to resist antibiotics when they invade host cells did you know that the glycocalyx differs in thickness and composition among different prokaryotes it occurs as a thick and tough sheath called a capsule while in others it may be a loose sheath called a slime layer the glycocalyx is followed by a cell wall which determines the shape of the cell and provides structural support thereby preventing the cell from collapsing or bursting interestingly the cell wall structure differs in different prokaryotes in certain prokaryotes such as Pseudomonas the cell wall is composed of a thin inner layer of peptidoglycan and an outer membrane of lipopolysaccharide and lipoprotein when such prokaryotes are subjected to the gram staining procedure they do not take a Gram stain but appear red or pink when counter stains such as safranin are added they are called gram-negative bacteria you on the other hand the cell wall of prokaryotes such as bacillus anthracis composed of a dense layer of peptidoglycan and tqeq acids turns violet when subject gram staining procedure such prokaryotes are called gram-positive the cell wall is followed by the semi permeable plasma membrane which controls the entry and exit of small molecules like food particles and ions like chloride sodium by cabinets the plasma membrane extends into the cell forming the messes own a membranous structure seen in the form of vesicles tubules incidentally the presence of the Mesozoic mystic feature of prokaryotes Mesa's ohms help in cell wall formation secretion processors expansion of the surface area of the plasma membrane and enzymatic content DNA replication and distribution to daughter cells some prokaryotes such as blue-green algae also have membranous extensions called photosynthetic lamellae that contain photosynthetic pigments such as chlorophyll prokaryotes also have extensions from their cell walls instance cells have a thin filamentous extension from their cell wall called a flagellum which consists of a filament okay and a basal body with the filament being the longest portion as well as non-motile prokaryotes also possess pili and fimbria surface structures that attach the prokaryotes to rocks in streams and also to host tissues while Billy are elongated tubular structures made up of a special protein called B Lin fimbria are tiny bristle like fibers sprouting out of the cell however these structures don't play any Roden motility while Billy and fimbria are present outside the cell envelope the inside is filled with cytoplasm that hosts the genomic DNA a single chromosome made up of circular DNA many prokaryotes also have small circular DNA called plasmids outside their genomic DNA which confer unique inner typic characteristics such as resistance to antibiotics the cytoplasm also contains ribosomes measuring about 15 microns by 20 microns in size and consisting of two subunits 50s and 30s which together form the 70s ribosome here s or sweat bugs unit stands for the sedimentation coefficient it indirectly is a measure of the density and size of ribosomes these ribosomes a single messenger RNA a that aids in protein synthesis chain called a poly ribosome or polysome and ultimately translate messenger RNA into proteins apart from the ribosomes cytoplasm also contains inclusion bodies such as phosphate granules sign of ICN granules and glycogen granules used for storing reserved materials these bodies are not bounded by any membrane system and live free in the cytoplasm certain prokaryotes such as Bluegreen purple synthetic bacteria also have other inclusion bodies such as gas vacuoles which held them to float in water prokaryotes thus are primitive organisms that possess a simple cell structure yet they are the only organisms to thrive in almost all habitats including underground caves and deep oceans earth is home to diverse species of plants and animals yet they all have a common structural unit the eukaryotic cell or a cell which possesses an organized nucleus surrounded by a nuclear envelope this nucleus containing chromosomes that carry the genetic code of the organism is surrounded by cytoplasm a semi fluid matrix which makes up the volume of the cell present in the cytoplasm is the cytoskeleton network of filamentous proteinaceous structures that gives the cell its characteristic shape aids in intracellular transport gives mechanical strength to the cell and also helps in motility in case of motile cells the cytoplasm also contains numerous single membrane-bound my new two vesicles called micro bodies which are filled with enzymes that aid in the synthesis of amino acids also embedded in the cytoplasm are several organelles or membrane-bound structures which lead to its extensive compartmentalization however the cytoplasm of all eukaryotic cells does not contain the same set of organelles plant cells for instance have a large central vacuole and plastids whereas centrosomes are only found in animal cells the centrosome surrounded by office berry centriole a material is made up of two cylindrical structures called centrioles that lie perpendicular to each other each central is made up of nine evenly spaced peripheral fibrils of tubulin protein with each peripheral fybel being a triplet all adjacent triplets are linked to each other forming a cut wheel like structure the central part of the central all of the hub is progenation and is linked to the tubules of the peripheral triplets by radial spokes made of protein centrioles form the basal body of cilia or flagella and spindle fibers that give rise to a spindle like apparatus during cell division eukaryotic cells defer not only in their cytoplasmic organelles but also in their structure take for instance animal cells in which the plasma membrane forms the outer boundary of the cell but in fungi and plant cells the plasma membrane is covered by a cell wall which forms the outer boundary interestingly the composition of the cell wall is different in different eukaryotic cells in algae the cell wall is made up of cellulose Manon's Galacta pnes and calcium carbonate whereas in fungi made up of chitin and blackens on the other hand the plant cell wall is made up of cellulose Hemi cellulose pectins and proteins consists of three layers the middle lamella primary wall and secondary wall the middle lamella mainly made of calcium pecked 8 lies between neighboring cells and blues the cells together the primary wall is the first formed wall that develops when the cell is growing it is thin elastic and extensible however its growth capability diminishes as the cell matures the secondary cell wall develops after the cell has matured it is formed on the inner side of the cell and faces the plasma membrane interestingly the secondary cell wall and lamellae do not occur as continuous layers as they are interrupted by plasmodesmata fine strands of cytoplasm that facilitate the transportation of materials between different cells in a plant cell wall is an important part of the cell as it lends shape to the cell takes it from mechanical damage and infection prevents the entry of undesirable macromolecules such as nucleic acids and also aids in cell to cell interaction though a cell wall may be present or absent in different types of eukaryotic cells these cells are the basic unit of life in many organisms including plants and animals the cell the basic unit of life in all organisms has several organelles embedded in its cytoplasm these organelles are surrounded by a thin membrane called the plasma membrane which not only separates the extracellular environment from the cytoplasm but also gives shape to the cell before the advent of the electron microscope scientists conducted chemical studies on the cell membrane and deduced that it is composed of lipids that mainly consists of phosphoglycerates these lipids are arranged in a bilayer with a polar hydrophilic head of both layers pointing outward towards the equus environment and the nonpolar hydrophobic tail made of saturated hydrocarbons pointing inward arrangement not only protects the tale from the aqueous environment it also prevents polar molecules such as nucleic acids proteins and ions from diffusing through it later biochemical investigations revealed that apart from lipids proteins and carbohydrates too are a part of the cell membrane moreover the proteins are arranged in two forms peripheral and intrinsic peripheral proteins lie on the surface of the membrane and can be easily removed by physical methods on the other hand trinsic proteins are totally or partially embedded in the bilayer and can be removed only after disrupting the entire membrane scientists also deduced that the ratio of proteins to lipids varies greatly between different types of cells for instance the cell membrane of red blood cells is 52% proteins and 40% lipids the advent of the electron microscope helped scientists better understand the structure of the cell membrane and finally in 1972 singer and Nicholson put forth the fluid mosaic model which was widely accepted by the scientific community this model stated that lipids are found in the form of a fluid bilayer this quasi fluid of almost fluid like nature allows proteins to move laterally within the bilayer and this ability of the membrane to allow the movement of molecules within it is referred to as membrane fluidity the fluid nature of the membrane also allows the cell to perform important functions such as cell growth the formation of intercellular junctions secretion and cell division all these functions require flexibility in the membrane during cell growth and cell division in has to extend the cell membrane also guards the entry and exit of different molecules and ions in and out of the cell however the cell membrane is selectively permeable which means the lipid bilayer allows only certain small nonpolar substances such as oxygen and carbon dioxide molecules to pass freely through it while selectively permitting ions and other polar molecules including water to pass through it with the aid of membrane proteins the transport of these ions and molecules takes place either through passive transport or through active transport in passive transport metabolic energy to move across the membrane passive transport occurs either through diffusion or rasmus's in a cell membrane we observe simple diffusion and facilitated diffusion in simple diffusion oxygen and carbon dioxide molecules freely move across the membrane from higher to lower concentration whereas larger molecules such as glucose are transported by facilitated diffusion in which carrier proteins in the membrane change their shape and accelerate the diffusion process on the other hand osmosis refers to the movement of water molecules across the cell membrane through diffusion in active transport transmembrane proteins act as pumps and utilize the energy from ATP to move substances against their concentration gradient that is from lower concentration to higher concentration an example for this is the sodium potassium pump sometimes glucose is also transported against the concentration gradient by a active transport the cell membrane which helps in the transport of substances is also a part of the cilia and flagella structures that project from the cells surface these structures emerge from Centurion like structures called basal bodies and share a similar structure the cilia are smaller than flagella their core called the action een is covered by the cell membrane and has numerous microtubules running parallel to its axis to microtubules join to form a doublet if we observe a cross-section of the axon eeem we will see nine pairs of radially arranged peripheral doublets of centrally-located microtubules which are interconnected by a bridge such an arrangement of eggs animal microtubules is known as the 9+2 array the central microtubules are enclosed by a central sheath connected to one of the microtubules of each peripheral doublet by a radial spoke the peripheral doublet stew are interconnected by linkers called an inter doublet bridge the cilia and flagella help the cell propel or move the fluid surrounding the cell thus helps and motility thus cilia and flagella helped cells and motility while the cell membrane gives shape to the cell separates the intracellular components from the extracellular matrix and also plays an important role in the transport of substances across the cell the cytoplasm of a eukaryotic cell is embedded with several membranous organelles of which the endoplasmic reticulum Golgi apparatus lysosomes and vacuoles are referred to as an endomembrane system because their functions are coordinated the endoplasmic reticulum or er for instance emphasizes processes sports proteins and lipids to the other organelles as well as metabolizes carbohydrates in liver cells and detoxifies drugs present in the body microscopic studies reveal that the endoplasmic reticulum occurs as a network or reticulum of tiny tubular structures dividing the intracellular space into two distinct compartments the luminol compartment which consists of the space within the folds of the endoplasmic reticulum and the extra luminal compartment which consists of the cytoplasm that lies outside the fold there are two types of endoplasmic reticulum endoplasmic reticulum or RER and smooth endoplasmic reticulum or ser endoplasmic reticulum has ribosomes attached to its surface and is mainly found in cells actively involved in protein synthesis and secretion they are continuous with the outer membrane of the nucleus the smooth endoplasmic reticulum on the other hand is devoid of ribosomes and hence appears smooth the sizes lipids and lipid like steroidal hormones such as estrogen x' in the case of animal cells did you know that the smooth endoplasmic reticulum present in muscle cells is called the sarcoplasmic reticulum that it stores and pumps calcium ions apart from the endoplasmic reticulum brain system also consists of the Golgi apparatus named after Camillo Golgi of a series of flat disc-shaped sex or sister knee stacked one above the other each cisterna measures 0.5 to 1 micron in diameter and their number may vary in each Golgi apparatus sister nee centrally arranged near the nucleus have two distinct phases the convex shaped sis forming face that faces the nuclear envelope and the concave shaped trans or the maturing face that lies opposite the nuclear envelope though both the sis face and the trans face are interconnected they are different for instance the sis phase has a thin membrane whereas the membrane of the trans phase is thick in a cell the Golgi apparatus acts as a packaging and forwarding Center for instance vesicles containing proteins synthesized by the ribosomes of the rough endoplasmic reticulum get pinched off the surface of the rough endoplasmic reticulum fused with the SIS phase of the Golgi apparatus they are modified in the Sistani before they are released from the trance face this explains why the Golgi apparatus remains closely associated with the endoplasmic reticulum in addition to being a packaging and forwarding Center the Golgi apparatus is an important site for the formation of glycoproteins and glycolipids that form a part of the plasma membrane lysosomes another member of the endomembrane system our single membrane vesicular structures formed during the packaging process in the Golgi apparatus contain hydrolytic enzymes such as lipases proteases and carbohydrate --is that digests lipids proteins and carbohydrates and also nucleic acids lysosomes the endomembrane system also comprises vacuoles on the latina membrane called toner blast vacuole contains water sap excretory products other materials not useful for the sale the turnip last of vacuoles in plant cells aids in the transportation of a number of ions and other materials against their concentration gradients into the vacuole which is one of the reasons for the higher concentration of ions in the vacuole in plant cells vacuoles can make up 90% of the volume of the cell these vacuoles also perform different functions for instance in amoeba vacuo helps the organism excrete waste products and also in osmoregulation on the other hand protists food vacuoles formed by engulfing food particles provide nutrition to the organism all the organelles of the endomembrane system work in a coordinated manner and play a vital role in biosynthesis processing packaging transport crucian of proteins and lipids as well as in storage and digestion of wastes fifty-three George pallid was observing a cell under an electron microscope when he noticed a few dense particles in the cytoplasm of the cell today we know these particles as ribosomes these granular and non membrane-bound structures composed of ribosomal RNA and proteins are found in both prokaryotic and eukaryotic cells they synthesize proteins by attaching to a single messenger RNA to form a chain called a poly ribosome or poly song and ultimately translate mRNA into proteins in both eukaryotes and prokaryotes while eukaryotic ribosomes are ATS and composed of 40s and 60s subunits prokaryotic ribosomes are 70's and composed of two subunits 30s and 50s apart from the to plasm ribosomes also occur on the rough endoplasmic reticulum in chloroplasts in plants as well as within the mitochondria the powerhouse of the cell mitochondria are sites of aerobic respiration and produce cellular energy in the form of ATP the number of mitochondria in a cell varies depending on the cells metabolism muscle cells for instance need a continuous supply of energy and hence they contain a large number of mitochondria microscopic studies have revealed that a typical mitochondrion which divides by fission a sausage shaped or cylindrical with a diameter of 0.221 microns and a length of 1/2 4.1 microns it is a double membrane bound structure consisting of an outer membrane and an inner membrane and each membrane has its own specific enzymes associated with the mitochondrial function the membranes divide the mitochondria lumen into two equus compartments the outer compartment and the inner compartment called the matrix that contains a single circular DNA molecule a few RNA molecules 70s ribosomes and the components required for the synthesis of proteins while the outer membrane forms a continuous limiting boundary the inner membrane Falls towards the matrix to form in foldings called cristae these Christy increased the surface area of the inner membrane of the mitochondria apart from ribosomes and mitochondria glass tubes are also one of the most important cytoplasmic organelles in plants they are bound by a double membrane and contain big ones that impart specific colors to plants based on the pigments they possess plastics can be classified as chloroplasts chroma blasts and Luca PLAs plus contain chlorophyll and carotenoid pigments that capture light energy needed for photosynthesis moreover chlorophyll also imparts a green color to the leaves found mostly in the mesophyll cells of the leaves chloroplasts have a length of 5 to 10 millimeters and a width of 2 to 4 millimeters a cell can contain a single chloroplast as seen in chlamydomonas or multiple chloroplasts as seen in a green alga cell morphological studies about chloroplast reveal that they possess an outer membrane and an inner membrane with the inner membrane being less permeable than the outer membrane stroma the space enclosed by the inner membrane contains double-stranded circular DNA molecules 70s ribosomes and enzymes required for the synthesis of carbohydrates and proteins Stromer also contains thylakoids flattened membranous sacs containing chlorophyll pigment in their lumen the space enclosed by the thylakoid membranes around 2250 thylakoids are stacked like piles of coins forming grana or intergranular coins the thylakoids of different grana are connected to each other by flat membranous tubules called stroma lamellae did you know that chloroplasts as well as mitochondria are known as semi-autonomous organelles as they possess their own DNA chrome applause another type of plastids found in plant cells in fat-soluble carotenoid pigments such as carotene and xanthophylls that give red yellow and orange color to plant parts the third type of plastids Lukic lasts colorless plastids that store nutrients such as carbohydrates and fats based on the type of nutrient stored leuco PLAs can be classified as amyloplasts alejo class and a euro class while amyloplasts store carbohydrates such as starch in potato ilio blasts store oils and fats on the other hand a Europe lasts which are usually found in food grains store proteins the various plastids found in plants not only impart color to the plants but also store nutrients and play a role in photosynthesis thus we find that ribosomes mitochondria and plastids are important organelles taking part in vital functions of the cell such as protein synthesis respiration and photosynthesis of the various organelles found in a cell the nucleus occupies a place of prime importance as it is the control center that regulates metabolic activities which keep a cell alive most eukaryotic cells possess a single nucleus however we do find cells with multiple nuclei as well as cells without a nucleus described by Robert Brown in 1831 the nucleus was one of the earliest organelles that scientists became aware of the advent of the electron microscope enabled scientists to become aware of the various components of a nucleus for instance scientists observed that the nucleus is surrounded by a nuclear envelope or nuclear membrane that acts as a barrier between the contents of the nucleus and the other organelles present in the cytoplasm the nuclear envelope consists of the outer membrane and inner membrane which run parallel to each other and are separated by the perinuclear space the outer membrane of the nuclear envelope is connected with the endoplasmic reticulum and also bears ribosomes on it at a number of places the two membranes fuse and give rise to minut pores called nuclear pores these pores allow to a movement of RNA and protein molecules between the nucleus and the cytoplasm present inside the nuclear envelope is the nucleoplasm of the nuclear matrix that contains a spherical structure called the nucleolus the nucleolus lacks a membrane which makes its content continuous with the nucleoplasm the nucleolus is a major site for active ribosomal RNA synthesis and hence cells that are active in protein synthesis have larger and numerous nucleoli apart from the nucleolus the nucleoplasm also contains chromatin a network of highly extended and elaborate nuclear protein fibers that mainly consists of DNA and histone proteins though non-histone proteins are also associated with it you when a cell begins to divide condensers and coils to form rod like structures called chromosomes the DNA threads remain distributed in these chromosomes morphological studies of a chromosome have revealed that it consists of a primary constriction or centromere that has disc-shaped structures called time it's a cause attached to its side the parts present on either side of the centromere are called the arms of the chromosomes based on the position of the centromere chromosomes can be classified as metacentric sub metacentric acrocentric and telocentric in metacentric chromosome Mia is exactly in the middle forming two equal arms metacentric chromosome the ramier appears closer to one arm of the chromosome creating two arms of unequal length Centrica chromosome has its centromere located very close to one of its ends resulting in one extremely short and one very long arm century chromosomes centromere is located at one end of the single arm at times chromosomes have secondary constrictions at a fixed location lending the appearance of a small fragment called a satellite these areas of secondary constriction help in the formation of a nucleolus after cell division chromosomes are an important part of the nucleus as they contain the genetic code of an organism seen that the nucleus along with its components is an important organelle as it not only coordinates the functioning of the cell but also plays a vital role in cell division