c. d. Type strain is used for referring to? a) species Microbiology MCQs 9. Which of the following is diagnosed by serologic means? a. b. c. d. 1. Which of these bacterial components is least likely to contain useful antigens? a. b. c. d. Cell wall Flagella Ribosomes Capsule Mycoplasmas Amoeba E.coli Spheroplast 10. Diarrhoea is not caused by a. b. c. d. a. b. c. d. 3. The association of endotoxin in gram-negative bacteria is due to the presence of Steroids Peptidoglycan Lipopolysaccharides Polypeptide Contains metabolic enzymes Is selectively permeable Regulates the entry and exit of materials Contains proteins and phospholipids a. b. c. d. b. c. d. Mycobacterium tuberculosis stains blue because of the thick lipid layer Streptococcus pyogenes stains blue because of a thick peptidoglycan layer Escherichia coli stains pink because of a thin peptidoglycan layer Mycoplasma pneumoniae is not visible in the Gram’s stain because it has no cell wall 13. The bacterial genus where sterols are present in the cell membrane is a. b. c. d. a. b. c. d. Vibrio Mycoplasma Escherichia Chlamydia 14. The bacterium that infects other gram-negative bacteria is a. b. c. d. Also Read: Gram positive and gram negative bacteria 6. Which of the following is not a recognised cause of diarrhoea? Their cell wall is composed of peptidoglycan They are selectively permeable They contain osmoregulating porins They block water molecules from entering the cell Also Read: Prokaryotic cells 5. Which of the statements regarding gram staining is wrong? a. Staphylococcus aureus from Staphylococcus epidermidis Staphylococcus epidermidis from Neisseria meningitidis Streptococcus pyogenes from Enterococcus faecalis Streptococcus pyogenes from Staphylococcus aureus 12. Prokaryotic cells are more resistant to osmotic shock than eukaryotic cells because 4. The prokaryotic cell membrane a. b. c. d. Shigella dysenteriae Streptococcus pyogenes Clostridium difficile Salmonella enteriditis 11. The coagulase is done to differentiate Also Read: Microbiology a. b. c. d. Actinomycosis Q-fever Pulmonary tuberculosis Gonorrhea Also Read: Bacteria 2. Which of the following contains structures composed of Nacetylmuramic acid and N- acetylglucosamine? a. b. c. d. Klebsiella pneumoniae Bacteroides fragilis Proteus mirabilis Haemophilus influenza Bdellovibrio Pseudomonas putida 15. Which phage is used for phage display technique? a. b. c. d. Vibrio cholerae Escherichia coli Clostridium perfringens Enterococcus faecalis T7 M13 ƛ-phage ɸ6 Also Read: Eukaryotic cells 7. Which of the following is a gram-positive eubacterium? a. b. c. d. Actinomyces Clostridium Rhizobium Clostridium, Actinomyces 8. Which of the following microorganisms is not responsible for urinary tract infection? a. b. Proteus mirabilis Escherichia coli Answer Key 1- c 2- c 3- c 4- d 5- a 6- d 7- d 8- d 9- b 10- b 11- a 12- a 13- b 14- c 15- b Microbiology is the study of a variety of living organisms which are invisible to the naked eye like bacteria and fungi and many other microscopic organisms. Although tiny in size these organisms form the basis for all life on earth. These microbes as they are also known to produce the soil in which plants grow and the fix atmospheric gases that both plants animals use. About 3 billion years ago at the time of formation of the earth, microbes were the only lives on earth. Microorganisms have played a key role in the evolution of the planet earth. The lineage of life on Earth originated from these microbes: Microorganisms affect animals, the environment, the food supply and also the healthcare industry. There are many different areas of microbiology including environmental, veterinary, food, pharmaceutical and medical microbiology, which is the most prominent. Branches of microbiology Microorganisms are very important to the environment, human health and the economy. Few have immense beneficial effects without which we could not exist. Others are really harmful, and our effort to overcome their effects tests our understanding and skills. Certain microorganisms can be beneficial or harmful depending on what we require from them. 2.Mycology –The study of fungi Harmful Microorganisms Disease and decay are neither inherent properties of organic objects, nor are caused by physical damage, it is microorganisms that bring about these changes. We are surrounded by bacteria, virus, and fungi. Many microorganisms cause diseases in cattle, crops and others are known for entering human bodies and causing various diseases. Examples of familiar human diseases are: Bacteria: pneumonia, bacterial dysentery, diphtheria, bubonic plague, meningitis, typhoid, cholera, salmonella, meningococcal Virus: Chickenpox, measles, mumps, German measles, colds, warts, cold sores, influenza Protozoa: amoebic dysentery, malaria, Fungi: ringworm, athlete’s foot Useful-Microorganisms As decomposers, bacteria and fungi play an important role in an ecosystem. They break down dead or waste organic matter and release inorganic molecules. Green plants take these nutrients which are in turn consumed by animals, and the products of these plants and animals are again broken down by decomposers. Yeast is a single-celled fungus that lives naturally on the surface of the fruit. It is economically important in bread-making and brewing beer and also in the making of yoghurt. Most microorganisms are unicellular; if they are multicellular, they lack highly differentiated tissues. There fundamentally two different types of cells, One being Prokaryotic and the other Eukaryotic 1.Bacteria 2.Archaea 3.Eucarya There are various different branches in microbiology and these include the following: 1.Bacteriology- The study of bacteria 3.Phycology- The study of photosynthetic eukaryotes. (AlgaeSeaweed) 4.Protozoology – The study of protozoa (Single-celled eukaryotes) 5.Virology- The study of viruses, non-cellular particles which parasitize cells. 6.Parasitology- The study of parasites which include pathogenic protozoa certain insects and helminth worms. 7.Nematology- The study of nematodes. Eukaryotic Cell Definition “Eukaryotic cells are the cells that contain a membrane bound nucleus and organelles.” Table of Contents Explanation Characteristics Structure Diagram Cell Cycle Examples What is a Eukaryotic Cell? Eukaryotic cells have a nucleus enclosed within the nuclear membrane and form large and complex organisms. Protozoa, fungi, plants, and animals all have eukaryotic cells. They are classified under the kingdom Eukaryota. They can maintain different environments in a single cell that allows them to carry out various metabolic reactions. This helps them grow many times larger than the prokaryotic cells. Also refer: Difference between Prokaryotic and Eukaryotic Cells Characteristics of Eukaryotic Cells The features of eukaryotic cells are as follows: 1. Eukaryotic cells have the nucleus enclosed within the nuclear membrane. 2. The cell has mitochondria. 3. Flagella and cilia are the locomotory organs in a eukaryotic cell. 4. A cell wall is the outermost layer of the eukaryotic cells. 5. The cells divide by a process called mitosis. Microbes especially prokaryotes are numerous in number in comparison to eukaryotes. 6. The eukaryotic cells contain a cytoskeletal structure. 7. The nucleus contains a single, linear DNA, which carries all These are the main site for protein synthesis and are composed of the genetic information. proteins and ribonucleic acids. Structure Of Eukaryotic Cell The eukaryotic cell structure comprises the following: Plasma Membrane The plasma membrane separates the cell from the outside environment. It comprises specific embedded proteins, which help in the exchange of substances in and out of the cell. Cell Wall A cell wall is a rigid structure present outside the plant cell. It is, however, absent in animal cells. It provides shape to the cell and helps in cell-to-cell interaction. It is a protective layer that protects the cell from any injury or pathogen attacks. It is composed of cellulose, hemicellulose, pectins, proteins, etc. Also refer: Cell Wall Mitochondria These are also known as “powerhouse of cells” because they produce energy. It consists of an outer membrane and an inner membrane. The inner membrane is divided into folds called cristae. They help in the regulation of cell metabolism. Lysosomes They are known as “suicidal bags” because they possess hydrolytic enzymes to digest protein, lipids, carbohydrates, and nucleic acids. Plastids These are double-membraned structures and are found only in plant cells. These are of three types: Chloroplast that contains chlorophyll and is involved in photosynthesis. Chromoplast that contains a pigment called carotene that provides the plants yellow, red, or orange colours. Leucoplasts that are colourless and store oil, fats, carbohydrates, or proteins. Cytoskeleton The cytoskeleton is present inside the cytoplasm, which consists of microfilaments, microtubules, and fibres to provide perfect shape to the cell, anchor the organelles, and stimulate the cell movement. Endoplasmic Reticulum It is a network of small, tubular structures that divides the cell surface into two parts: luminal and extraluminal. Endoplasmic Reticulum is of two types: Rough Endoplasmic Reticulum contains ribosomes. Smooth Endoplasmic Reticulum that lacks ribosomes and is therefore smooth. Nucleus Eukaryotic Cell Diagram Eukaryotic cell diagram mentioned below depicts different cell organelles present in eukaryotic cells. The nucleus, endoplasmic reticulum, cytoplasm, mitochondria, ribosomes, lysosomes are clearly mentioned in the diagram. Explore more about Cell organelles Eukaryotic Cell Diagram illustrated above shows the presence of a true nucleus. Eukaryotic Cell Cycle The eukaryotic cells divide during the cell cycle. The cell passes through different stages during the cycle. There are various checkpoints between each stage. The nucleoplasm enclosed within the nucleus contains DNA and proteins. Quiescence (G0) The nuclear envelop consists of two layers- the outer membrane and the inner membrane. Both the membranes are permeable to ions, molecules, and RNA material. Ribosome production also takes place inside the nucleus. This is known as the resting phase, and the cell does not divide during this stage. The cell cycle starts at this stage. The cells of the liver, kidney, neurons, and stomach all reach this stage and can remain there for longer periods. Many cells do not enter this stage and divide indefinitely throughout their lives. Golgi Apparatus Interphase In this stage, the cells grow and take in nutrients to prepare them for the division. It consists of three It is made up of flat disc-shaped structures called cisternae. It is absent in red blood cells of humans and sieve cells of plants. checkpoints: They are arranged parallel and concentrically near the nucleus. Synthesis (S) – DNA replication takes place in this phase. It is an important site for the formation of glycoproteins and glycolipids. Also read: Golgi Apparatus Gap 1 (G1) – Here the cell enlarges. The proteins also increase. Gap 2 (G2) – Ther cells enlarge further to undergo mitotic division. Mitosis Mitosis involves the following stages: Ribosomes Prophase Are viruses eukaryotes? Prometaphase Metaphase Viruses are neither eukaryotes nor prokaryotes. Since viruses are a link between living and non-living they are not considered in either category. Anaphase Telophase Cytokinesis On division, each daughter cell is an exact replica of the original cell. Examples of Eukaryotic Cells Eukaryotic cells are exclusively found in plants, animals, fungi, protozoa, and other complex organisms. The examples of eukaryotic cells are mentioned below: Plant Cells The cell wall is made up of cellulose, which provides support to the plant. It has a large vacuole which maintains the turgor pressure. The plant cell contains chloroplast, which aids in the process of photosynthesis. Fungal Cells The cell wall is made of chitin. Some fungi have holes known as septa which allow the organelles and cytoplasm to pass through them. Animal Cells What are the salient features of a eukaryotic cell? A eukaryotic cell has the following important features: A eukaryotic cell has a nuclear membrane. It has mitochondria, Golgi bodies, cell wall. It also contains locomotory organs such as cilia and flagella. The nucleus has a DNA that carries all the genetic information. How does a eukaryotic cell divide? A eukaryotic cell divides by the process of mitosis. It undergoes the following stages during cell division: Prophase Metaphase Anaphase Telophase Cytokinesis When did the first eukaryotic cell evolve? These do not have cell walls. Instead, they have a cell membrane. That is why animals have varied shapes. They have the ability to perform phagocytosis and pinocytosis. The first eukaryotic cells evolved about 2 billion years ago. This is explained by the endosymbiotic theory that explains the origin of eukaryotic cells by the prokaryotic organisms. Mitochondria and chloroplasts are believed to have evolved from symbiotic bacteria. Protozoa What is the evidence for endosymbiotic theory? Protozoans are unicellular organisms. Some protozoa have cilia for locomotion. A thin layer called pellicle provides supports to the cell. The first evidence in support of the endosymbiotic theory is that mitochondria and chloroplast have their own DNA and this DNA is similar to the bacterial DNA. The organelles use their DNA to produce several proteins and enzymes to carry out certain activities. For more information on Eukaryotic Cells, its definition, characteristics, structure, and examples, keep visiting BYJU’S website or download BYJU’S app for further reference. Related Links Prokaryotic and Eukaryotic Cells Difference between the Plant cell and Animal cell Frequently Asked Questions Are eukaryotic cells unicellular or multicellular? Eukaryotic cells may be unicellular or multicellular. Paramecium, Euglena, Trypanosoma, Dinoflagellates are unicellular eukaryotes. Plants and animals are multicellular eukaryotes. What is the most important characteristic of eukaryotic cells that distinguishes it from prokaryotic cells? Eukaryotic cells have a membrane-bound nucleus. On the contrary, prokaryotic cells lack a true nucleus, i.e., they have no nuclear membrane. Unlike eukaryotic cells, the prokaryotic cells do not have mitochondria, chloroplast and endoplasmic reticulum. Prokaryotic Cell Definition “Prokaryotic cells are the cells that do not have a true nucleus and membrane-bound organelles.” Table of Contents Explanation Characteristics Structure Diagram Components Reproduction Examples Prokaryotic Cell Diagram The prokaryotic cell diagram given below represents a bacterial cell. It depicts the absence of a true nucleus and the presence of a flagellum that differentiates it from a eukaryotic cell. Prokaryotic Cell Diagram illustrates the absence of a true nucleus What is a Prokaryotic Cell? Components of Prokaryotic Cells Prokaryotic cells are single-celled microorganisms known to be the earliest on earth. Prokaryotes include Bacteria and Archaea. The photosynthetic prokaryotes include cyanobacteria that perform photosynthesis. The prokaryotic cells have four main components: Plasma Membrane- It is an outer protective covering of phospholipid molecules which separates the cell from the surrounding environment. A prokaryotic cell consists of a single membrane and therefore, all the reactions occur within the cytoplasm. They can be free-living or parasites. Cytoplasm- It is a jelly-like substance present inside the cell. All the cell organelles are suspended in it. Characteristics of Prokaryotic Cell DNA- It is the genetic material of the cell. All the prokaryotes possess a circular DNA. It directs what proteins the cell creates. It also regulates the actions of the cell. Prokaryotic cells have different characteristic features. The characteristics of the prokaryotic cells are mentioned below. Ribosomes- Protein synthesis occurs here. 1. They lack a nuclear membrane. 2. Mitochondria, Golgi bodies, chloroplast, and lysosomes are absent. 3. The genetic material is present on a single chromosome. 4. The histone proteins, the important constituents of eukaryotic chromosomes, are lacking in them. 5. The cell wall is made up of carbohydrates and amino acids. 6. The plasma membrane acts as the mitochondrial membrane carrying respiratory enzymes. 7. They divide asexually by binary fission. The sexual mode of reproduction involves conjugation. Some prokaryotic cells possess cilia and flagella which helps in Prokaryotic Cell Structure A prokaryotic cell does not have a nuclear membrane. However, the genetic material is present in a region in the cytoplasm known as the nucleoid. They may be spherical, rod-shaped, or spiral. A prokaryotic cell structure is as follows: 1. Capsule– It is an outer protective covering found in the bacterial cells, in addition to the cell wall. It helps in moisture retention, protects the cell when engulfed, and helps in the attachment of cells to nutrients and surfaces. 2. Cell Wall– It is the outermost layer of the cell which gives shape to the cell. 3. Cytoplasm– The cytoplasm is mainly composed of enzymes, salts, cell organelles and is a gel-like component. locomotion. Reproduction in Prokaryotes A prokaryote reproduces in two ways: Asexually by binary fission Sexually by conjugation Binary Fission 1. The DNA of an organism replicates and the new copies attach to the cell membrane. 4. Cell Membrane– This layer surrounds the cytoplasm and regulates the entry and exit of substances in the cells. 2. The cell wall starts increasing in size and starts moving inwards. 5. Pili– These are hair-like outgrowths that attach to the surface of other bacterial cells. 3. A cell wall is then formed between each DNA, dividing the cell into two daughter cells. 6. Flagella– These are long structures in the form of a whip, that help in the locomotion of a cell. 7. Ribosomes– These are involved in protein synthesis. 8. Plasmids– Plasmids are non-chromosomal DNA structures. These are not involved in reproduction. 9. Nucleoid Region– It is the region in the cytoplasm where the genetic material is present. A prokaryotic cell lacks certain organelles like mitochondria, endoplasmic reticulum, and Golgi bodies. Recombination In this process, genes from one bacteria are transferred to the genome of other bacteria. It takes place in three ways-conjugation, transformation, transduction. Conjugation is the process in which genes are transferred between two bacteria through a protein tube structure called a pilus. Transformation is the mode of sexual reproduction in which the DNA from the surroundings is taken by the bacterial cell and incorporated in its DNA. How is the prokaryotic cell structure different from that of the eukaryotic cell? Transduction is the process in which the genetic material is transferred into the bacterial cell with the help of viruses. Bacteriophages are the virus that initiates the process. Prokaryotic cells lack a true nucleus. The nucleus is devoid of the nuclear membrane. On the contrary, the nucleus of the eukaryotic cells is enclosed by a nuclear membrane. A prokaryotic cell also lacks mitochondria and chloroplast, unlike a eukaryotic cell. Examples of Prokaryotic Cells The examples of the prokaryotic cells are mentioned below: Bacterial Cells These are unicellular organisms found everywhere on earth from soil to the human body. They have different shapes and structures. How does a prokaryotic cell divide? Prokaryotic cells undergo asexual reproduction. Most prokaryotic cells divide by binary fission, where the cells divide into two daughter cells. Why is the process of cell division in prokaryotic cells different from that in eukaryotes? Prokaryotic cells are simpler than eukaryotic cells. They do not have The cell wall is composed of peptidoglycan that provides structure to a nuclear membrane surrounding their DNA, therefore, cell division the cell wall. is different than that in eukaryotes. Bacteria have some unique structures such as pili, flagella and capsule. When did the prokaryotic cells evolve? They also possess extrachromosomal DNA known as plasmids. They have the ability to form tough, dormant structures known as endospores that helps them to survive under unfavourable conditions. The endospores become active when the conditions are favourable again. Archaeal Cells Archaebacteria are unicellular organisms similar to bacteria in shape and size. They are found in extreme environments such as hot springs and other places such as soil, marshes, and even inside humans. They have a cell wall and flagella. The cell wall of archaea does not contain peptidoglycan. The membranes of the archaea have different lipids with a completely different stereochemistry. Just like bacteria, archaea have one circular chromosome. They also possess plasmids. For more information on Prokaryotic Cells, its definition, structure, characteristics and examples, keep visiting BYJU’S Biology website or download BYJU’S app for further reference. Related Links Difference between a prokaryotic cell and eukaryotic cell Difference between an archaea and bacteria Frequently Asked Questions What are the structural features of prokaryotic cells? The prokaryotic cell structure is composed of: Cell wall Cell membrane Capsule Pili Flagella Ribosomes Plasmids The first prokaryotic cells evolved around 3.5 billion years ago. The eukaryotic cells were formed after the prokaryotic cells and are believed to have evolved from them. Bacteria One of the very first organisms to evolve on earth was probably a unicellular organism, similar to modern bacteria. Ever since then, life has evolved into a multitude of life forms over many millennia. However, we can still trace our ancestry back to this single-celled organism. Table of Contents Definition Diagram Structure Classification Reproduction Useful Bacteria Harmful Bacteria Today, bacteria are considered as one of the oldest forms of life on earth. Even though most bacteria make us ill, they have a long-term, mutual relationship with humans and are very much important for our survival. But before we elaborate on its uses, let us know the structure of bacteria, its classification, and the bacteria diagram in detail. Bacteria Definition “Bacteria are unicellular organisms belonging to the prokaryotic group where the organisms lack a few organelles and a true nucleus”. Also Read: Gram Negative Bacteria Bacteria Diagram The bacteria diagram given below represents the Bacteria can be classified into various categories based structure of bacteria with its different parts. The cell on their features and characteristics. The classification wall, plasmid, cytoplasm and flagella are clearly marked of bacteria is mainly based on the following: in the diagram. Shape Composition of the cell wall Mode of respiration Mode of nutrition Classification of bacteria based on Shape Bacteria Diagram representing the Structure of Bacteria Type of Classification Examples Bacillus (Rod-shaped) Escherichia coli (E. coli) Spirilla or spirochete (Spiral) Spirillum volutans Coccus (Sphere) Streptococcus pneumoniae Vibrio (Comma-shaped) Vibrio cholerae Structure of Bacteria The structure of bacteria is known for its simple body design. Bacteria are single-celled microorganisms with the absence of the nucleus and other cell organelles; hence, they are classified as prokaryotic organisms. They are also very versatile organisms, surviving in extremely inhospitable conditions. Such organisms are called extremophiles. Extremophiles are further categorized into various types based on the types of environments they inhabit: 1. 2. 3. 4. 5. 6. Thermophiles Acidophiles Alkaliphiles Osmophiles Barophiles Cryophiles Another fascinating feature of bacteria is their protective cell wall, which is made up of a special protein called peptidoglycan. This particular protein isn’t found anywhere else in nature except in the cell walls of bacteria. Classification of bacteria based on the Composition of the Cell Wall Type of Classification Examples Peptidoglycan cell wall Gram-positive bacteria Lipopolysaccharide cell wall Gram-negative bacteria Classification of bacteria based on the Mode of Nutrition Type of Classification But few of them are devoid of this cell wall, and others have a third protection layer called capsule. On the outer layer, one or more flagella or pili is attached, and it Autotrophic Bacteria functions as a locomotory organ. Pili can also help certain bacteria to attach themselves to the host’s cells. Heterotrophic Bacteria They do not contain any cell organelle as in animal or plant cell except for ribosomes. Examples Cyanobacteria All disease-causing bacteria Ribosomes are the sites of protein synthesis. In addition Classification of bacteria based on the Mode of to this DNA, they have an extra circular DNA called Respiration plasmid. These plasmids make some strains of bacteria resistant to antibiotics. Type of Classification Examples Also Read: Gram Positive Bacteria Classification of Bacteria Anaerobic Bacteria Actinomyces Aerobic Bacteria Mycobacterium Also Read: Difference between Bacteria and Virus Reproduction in Bacteria 4. Production of antibiotics, which is used in the treatment and prevention of bacterial infections – Soil bacteria Also Refer: Antibiotics Harmful Bacteria There are bacteria that can cause a multitude of illnesses. They are responsible for many of the infectious diseases like pneumonia, tuberculosis, diphtheria, syphilis, tooth decay. Their effects can be rectified by taking antibiotics and prescribed medication. However, precaution is much more effective. Most of these disease-causing bacteria can be eliminated by sterilizing or disinfecting exposed surfaces, instruments, tools and other utilities. These methods include- application of heat, disinfectants, UV radiations, pasteurization, boiling, etc. Bacteria follow an asexual mode of reproduction, called binary fission. A single bacterium divides into two daughter cells. These are identical to the parent cell as well as to each other. Replication of DNA within parent bacterium marks the beginning of the fission. Eventually, cell elongates to form two daughter cells. The rate and timing of reproduction depend upon the conditions like temperature and availability of nutrients. When there is a favourable condition, E.coli or Escherichia coli produces about 2 million bacteria every 7 hours. Bacterial reproduction is strictly asexual, but it can undergo sexual reproduction in very rare cases. Genetic recombination in bacteria has the potential to occur through conjugation, transformation, or transduction. In such cases, the bacteria may become resistant to antibiotics since there is variation in the genetic material (as opposed to asexual reproduction where the same genetic material is present in generations) Also Read: Cryptobiosis Microorganisms: Friend And Foe Biology Frequently Asked Questions 1. What are the different types of bacteria?? Bacteria can be divided into several types based on several characteristics such as shape, cell wall composition, mode of respiration, and mode of nutrition. 2. What is bacteria? How do you define bacteria? Bacteria are prokaryotic unicellular organisms. They have a relatively simple cell structure compared to eukaryotic cells. They also do not possess any membrane-bound organelles such as a nucleus. However, do they possess genetic material (DNA or RNA) in the intracellular space called the nucleoid Also Read: Binary fission 3. How do bacteria reproduce? Useful Bacteria Bacteria reproduce through a process called binary fission. In this process, a single bacterium divides into two daughter cells. These daughter cells are identical to the parent cell as well as to each other. Not all bacteria are harmful to humans. There are some bacteria which are beneficial in different ways. Listed below are few benefits of bacteria: 1. Convert milk into curd – Lactobacillus or lactic acid bacteria 2. Ferment food products – Streptococcus and Bacillus 3. Help in digestion and improving the body’s immunity system – Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria 4. State 4 examples of bacteria. Streptococcus Bacillus Actinobacteria Proteobacteria Classification of Microorganism Bacteria Fungi Protozoa Microbes are categorized into four major groups: Bacteria Fungi Algae Protozoa Viruses, on the other hand, are microscopic but differ from microbes. Differ in their reproduction aspects, as they reproduce only in the cells of their hosts. These host organisms can be of animals, bacteria or even plants for that matter. A virus is typically coated by protein and has a nucleic acid molecule. Useful Microorganisms Tuberculosis Ringworm Malaria Flu & Common cold Typhoid Athlete’s foot Dysentery Warts Cholera Candidiasis Chagas disease Polio Plague Tinea versicolor Sleeping sickness Herpes and cold sores Meningitis Onychomycosis Intestinal protozoan disease Chickenpox Following are a few examples of useful microorganisms: Extensively used in the baking industry to make cakes, bread, pastry etc. Used in the production of milk products. Example: Lactobacillus bacteria is used in the formation of curd from milk Since ages, microbes are being used in the production of alcohol It is also used to make organic acids. Acids such as citric acid, lactic acid, fumaric acid, gluconic acids are made using microbial activity Used in the production of steroids Antibiotics are produced using microorganisms Used in the production of vitamins: Vitamins such as Vitamin B complex, Riboflavin is produced by Ashbya gossypii, Eremothecium ashbyii and Clostridium bytyricum. Ascorbic acid, also known as Vitamin C is produced by species of Acetobacter Tetanus Smallpox Lyme disease Ebola Diseases Caused by Microorganisms in Animals Diseases Microorganism Anthrax diseases Bacillus anthracis Foot and Mouth disease Virus Diseases Caused by Microorganisms in Plants Diseases Microorganism Citrus canker Bacteria Rust of wheat Fungi Yellow vein mosaic of Okra Virus Microorganisms synthesize enzymes such as Lipase, Lactase, Amylase, Pectinase, Penicillinase. They increase the fertility of the soil and by fixing nitrogen Help in the treatment of sewage Extensively used to clean up our environment Used in pest control Food Spoilage by Microorganisms 1. Harmful Microorganisms The microorganisms that cause diseases in living beings are known as pathogens. The pathogens can enter our bodies through air, water and food. Some pathogens are transmitted directly from an infected person. The diseases which are transmitted by an infected person directly or indirectly are known as communicable diseases. For eg., common cold, tuberculosis, etc. Virus 2. 3. 4. 5. Food spoilage refers to the damage in the quality of food that makes it unsuitable for human consumption. Bacteria, moulds, and yeast are the main causes of food spoilage. Moulds spoil food with reduced water activity. For eg., dry cereals, cereal products. These microbes produce certain enzymes that decompose the important constituents of food. Bacteria, on the other hand, cause the spoilage of food with increased water activity. For eg., milk products. Some Interesting Facts About Microbes Microbes can be fatal. Microbes in our gut cause change of mood. Dry hands have fewer bacteria than damp hands. The smallest known bacteria is the Mycoplasma. Diseases Caused By Microorganisms 50% of the oxygen we breathe come from microbes. Some diseases caused by microbes are: Your belly button alone has more than 1400 bacteria. Microorganisms also grow on food and spoil it. That is why preservatives are added in the food to prevent it from spoilage. There are more than a billion microbes in a person’s mouth. 1.82kgs of your body’s weight constitutes the collective weight of microbes in your body. This was just a brief about the microorganisms- its beneficial, harmful and few facts Stay tuned with BYJU’S Biology to learn more about microorganisms-friend and foe and other related topics. Diseases Caused By Microorganisms There are several diseases caused by microorganisms. Let us have a look at a few of them. Viral diseases are caused by viruses. These include both acute and infectious diseases like the common cold, to chronic disease like AIDS. Apart from these acute diseases, viruses are also responsible for mumps, polio, rabies etc. Diseases caused by bacteria include diphtheria, typhoid, cholera etc. Malaria and sleeping sickness are diseases caused by protozoa. Worms like roundworms, tapeworms could cause diseases like Ascariasis and Taeniasis respectively. German Measles Rubella Chickenpox Varicella zoster Whooping cough Bardotella pertussis Bubonic plague Yersinia pestis Ringworm Trichophyton rubrum Tuberculosis Mycobacterium tuberculosis Malaria Plasmodium falciparum Athlete’s foot Trichophyton mentagrophytes Who is the father of biology? Philosopher Aristotle Who is the mother of biology? Maria Sibylla Merian The microorganisms cause diseases in the following ways: Who first discovered biology? They reach their target site in the body. Multiply rapidly. Attach to the target site to be infected. Who is the Father of Zoology? Avoid and survive an attack by the immune system of the host. Aristotle Obtain nutrients from the host. Who is the Father of Virology? Microbes and Diseases Viruses Viruses can be seen only through an electron microscope. They are inactive outside a living cell. Once they are inside the host body, they take over the entire cellular activities of the organism. They cannot be destroyed by antibiotics. Common cold, measles, mumps, smallpox are some of the diseases caused by viruses. Bacteria Not all bacteria cause diseases. The bacteria that infects an organism produces toxins that can cause diseases. Cholera, tuberculosis, anthrax are caused by bacteria. These can be killed by antibiotics. Fungi Thomas Beddoes Martinus Beijerinck Difference Between Gram-positive and Gram-negative Bacteria Bacteria are a large group of minute, unicellular, microscopic organisms, which have been classified as prokaryotic cells, as they lack a true nucleus. These microscopic organisms comprise a simple physical structure, including cell wall, capsule, DNA, pili, flagellum, cytoplasm and ribosomes. Bacteria can be gram-positive or gram-negative depending upon the staining methods. Let us have a detailed look at the difference between the two types of bacteria. Fungi can grow in damp, moist areas on the body and lead to infections such as athlete’s foot, ringworm, etc. Difference between Gram-Positive and GramNegative Bacteria Protozoa Following are the important differences between grampositive and gram-negative bacteria: Protozoans such as amoeba cause diseases such as amoebic dysentery. Malaria and sleeping sickness is also caused by protozoans. Following is the list of microorganisms and infectious diseases caused by them: Diseases Microorganisms Cold Rhinovirus Mesosome Difference between Gram-Positive and Gram-Negative Bacteria It is more prominent. It is less prominent. Gram-Negative bacteria Gram-Positive bacteria Morphology Cell Wall Cocci or spore-forming rods A single-layered, smooth cell wall A double-layered, wavy cellwall Cell Wall thickness The thickness of the cell wall is 20 to 80 nanometres It is a thick layer/ also can be multilayered Flagella Structure Two rings in basal body The thickness of the cell wall is 8 to 10 nanometres Peptidoglycan Layer Non-spore forming rods. Four rings in basal body Lipid content Very low 20 to 30% Lipopolysaccharide It is a thin layer/ often singlelayered. Absent Present Teichoic acids Toxin Produced Presence of teichoic acids Absence of teichoic acids Exotoxins Endotoxins or Exotoxins Outer membrane Resistance to Antibiotic The outer membrane is absent The outer membrane is present (mostly) Porins Absent More susceptible More resistant Examples Occurs in Outer Membrane Staphylococcus, Streptococcus, Escherichia, Salmonella, etc. etc. Gram Staining These bacteria retain the crystal violet colour even after they are washed with acetone or alcohol and appear as purple-coloured when examined under the microscope after gram staining. These bacteria do not retain the stain colour even after they are washed with acetone or alcohol and appear as pinkcoloured when examined under the microscope after gram staining. Gram-Positive and Gram-Negative Bacteria – Overview The gram-positive bacteria retain the crystal violet colour and stains purple whereas the gram-negative bacteria lose crystal violet and stain red. Thus, the two types of bacteria are distinguished by gram staining. Gram-negative bacteria are more resistant against antibodies because their cell wall is impenetrable. Gram-positive and gram-negative bacteria are classified based on their ability to hold the gram stain. The gramnegative bacteria are stained by a counterstain such as safranin, and they are de-stained because of the alcohol wash. Hence under a microscope, they are noticeably pink in colour. Gram-positive bacteria, on the other hand, retains the gram stain and show a visible violet colour upon the application of mordant (iodine) and ethanol (alcohol). This technique was proposed by Christian Gram to distinguish the two types of bacteria based on the difference in their cell wall structures. The grampositive bacteria retain the crystal violet dye, which is because of their thick layer of peptidoglycan in the cell wall. This process distinguishes bacteria by identifying peptidoglycan that is found in the cell wall of the grampositive bacteria. A very small layer of peptidoglycan is dissolved in gram-negative bacteria when alcohol is added. Difference between Gram-Positive and GramNegative Bacteria – Key Points The cell wall of gram-positive bacteria is composed of thick layers peptidoglycan. The cell wall of gram-negative bacteria is composed of thin layers of peptidoglycan. In the gram staining procedure, gram-positive cells retain the purple coloured stain. In the gram staining procedure, gram-negative cells do not retain the purple coloured stain. Gram-positive bacteria produce exotoxins. Gram-negative bacteria produce endotoxins. For more information on the differences between grampositive and gram-negative bacteria, keep visiting BYJU’S website or download the BYJU’S app for further reference. Further Reading: Gram-positive bacteria constitute a cell wall, which is Microorganisms – Useful Or Harmful mainly composed of multiple layers of peptidoglycan Gram-Positive Bacteria that forms a rigid and thick structure. Its cell wall additionally has teichoic acids and phosphate. The Frequently Asked Questions teichoic acids present in the gram-positive bacteria are of two types – the lipoteichoic acid and the teichoic wall Give a few examples of gram-positive bacteria. acid. The cell wall is known as murein. In gram-negative bacteria, the cell wall is made up of an Gram-positive bacteria include the bacteria of genre Staphylococcus, Streptococcus, Enterococcus. These outer membrane and several layers of peptidoglycan. bacteria are the most common cause of clinical The outer membrane is composed of lipoproteins, phospholipids, and LPS. The peptidoglycan stays intact infections. to lipoproteins of the outer membrane that is located in the fluid-like periplasm between the plasma membrane Which is more harmful- gram-positive bacteria or gram-negative bacteria? and the outer membrane. The periplasm is contained with proteins and degrading enzymes which assist in Gram-negative bacteria are more harmful and cause transporting molecules. certain diseases. Their outer membranes are hidden by a The cell walls of the gram-negative bacteria, unlike the slime layer that hides the antigens present in the cell. gram-positive, lacks the teichoic acid. Due to the presence of porins, the outer membrane is permeable to Is it easier to kill gram-positive bacteria? nutrition, water, food, iron, etc. The cell wall of the gram-positive bacteria absorbs antibiotics and cleaning products. Because of the outer Gram Staining peptidoglycan layer, they are easier to kill. Gramnegative bacteria cannot be killed easily. What infections are caused by gram-positive bacteria? Gram-positive bacteria usually cause Urinary Tract Infections. These are caused commonly in people who are more prone to urinary tract infections or are elderly or pregnant. Which infections are caused by gram-negative bacteria? The gram-negative bacteria cause various infections in humans such as indigestion, food poisoning, pneumonia, meningitis and other bacterial infections in the blood cells, bloodstream, wound infections, etc. The infections are caused by Acinetobacter, Pseudomonas aeruginosa and E.coli.