Antiseptics are chemical substances that inhibit microbial growth in or on living tissues (e.g., skin). Disinfectants are used on non-living surfaces. Antiseptics must be safe enough for use on the body.

Antibiotics can have side effects: some cause allergic reactions (penicillin), some affect the auditory nerve causing hearing loss (aminoglycosides), and some interfere with normal human metabolism.

Cyanobacteria have three specialised structures: heterocysts (nitrogen fixation), akinetes (resting spores for survival), and hormogonia (short motile fragments for asexual reproduction).

Photosynthetic bacteria lack chloroplasts. Their photosynthetic pigments (bacteriochlorophyll) are dispersed throughout the cytoplasm on internal membrane systems called chromatophores.

Microaerophilic bacteria require small amounts of oxygen (2-10%) for growth — more than anaerobes but less than aerobes. Helicobacter pylori (causes stomach ulcers) is a classic microaerophile.

Mesosomes are infoldings of the bacterial cell membrane that increase surface area. They are believed to be involved in DNA replication, cell wall synthesis, and possibly respiration.

Bacteria are used in food industry (yogurt, cheese, vinegar), pharmaceutical industry (antibiotics, insulin, vitamins), and biotechnology (genetic engineering, wastewater treatment, biofuels).

Peptidoglycan (murein) is a unique macromolecule found in bacterial cell walls. It forms a mesh-like layer providing structural strength. It is absent in eukaryotes, making it a key target for antibiotics.

Plasmids are small, circular, self-replicating DNA molecules in bacteria separate from the main chromosome. They are widely used in genetic engineering as vectors to clone and express foreign genes.

The bacterial cell wall, made of peptidoglycan, gives rigidity and shape to the cell. It prevents the cell from bursting due to osmotic pressure and protects against mechanical damage.

Prokaryotic ribosomes are 70S — smaller than eukaryotic 80S ribosomes. This size difference is exploited by antibiotics (e.g., streptomycin, erythromycin) that target 70S ribosomes without harming human cells.

The bacterial cell membrane is selectively permeable and regulates transport of all substances in and out of the cell — proteins, nutrients, sugars, ions, and metabolic waste products.

Bacteria are found in all three main shapes: cocci (spherical), bacilli (rod-shaped), and spiral forms (spirilla and vibrios). Some also form filaments or other arrangements.

Robert Koch formulated the germ theory of disease and developed Koch's Postulates (1876-1884), proving that specific microorganisms cause specific diseases using anthrax and tuberculosis as models.

Cocci (singular: coccus) are bacteria with a spherical or oval shape. They are one of the main bacterial morphologies, the others being bacilli (rods) and spirilla (spirals).

Ribosomes are the only organelle universally present in all bacteria. They are essential for protein synthesis. Not all bacteria have flagella, slime capsules, or storage granules.

Diplococci are cocci bacteria that divide and remain in pairs. Classic examples include Streptococcus pneumoniae (causes pneumonia) and Neisseria gonorrhoeae (causes gonorrhoea).

The Greek word 'karyon' means nut or kernel, referring to the nucleus. This is the root of terms like prokaryote (before nucleus), eukaryote (true nucleus), and karyotype (chromosome set).

Nostoc is a cyanobacterium that forms jelly-like colonies on soil and rocks. It contains heterocysts for nitrogen fixation. E. coli and Pseudomonas are true bacteria; Spirochete is a spiral bacterium.

Nostoc reproduces asexually by hormogonia (short motile filament fragments) and akinetes (thick-walled spore-like resting cells). Heterocysts are not reproductive but fix nitrogen.

Blue-green algae (cyanobacteria) form harmful algal blooms in nutrient-rich water bodies. These blooms produce toxins (cyanotoxins), deplete oxygen, and create 'dead zones' in water.

Cyanobacteria form symbiotic associations with fungi to form lichens. They also associate with plants (Azolla) and animals, providing photosynthate and fixed nitrogen to their partners.

Cyanobacteria store reserve food as cyanophycean starch (a form similar to glycogen). This is different from true plants which store amylose and amylopectin starch.

Cyanobacteria have gram-negative type cell walls with an outer membrane, thin peptidoglycan layer, and an inner membrane. They do not retain crystal violet stain in Gram staining.

Cyanobacteria are the largest and most diverse group of photosynthetic prokaryotes. They perform oxygenic photosynthesis using chlorophyll-a and were responsible for oxygenating Earth's early atmosphere.

Vaccination is the process of immunizing a person using attenuated (weakened) or killed cultures of pathogens to stimulate immune memory without causing disease.

Microbial diseases are controlled by immunization (vaccines), antisepsis (using antiseptics to prevent infection), and chemotherapy (using drugs like antibiotics to treat infection) — all three approaches.

Gamma rays are used for sterilization of medical equipment, food, and pharmaceuticals because they penetrate deeply and kill all microorganisms including endospores. UV radiation only sterilises surfaces.

Sterilization is the complete destruction or removal of all life forms including endospores from a material. Pasteurization only kills most pathogens but not all organisms.

Bacteria play crucial roles in biogeochemical cycles — they fix nitrogen (N₂), decompose organic matter releasing CO₂ (carbon cycle), and mineralise phosphorus compounds, completing these vital nutrient cycles.

The log (logarithmic) phase is when bacteria grow and divide exponentially at maximum rate. The lag phase is adaptation, stationary phase is when growth equals death, and decline is when cells die.

Conjugation is the direct transfer of DNA from a donor to a recipient bacterium through a physical connection (sex pilus). It is the main mechanism for spreading antibiotic resistance genes.

Facultative anaerobes can grow in both the presence and absence of oxygen. Examples include E. coli and Staphylococcus. They use aerobic respiration when oxygen is available and fermentation when it is not.

Parasitic bacteria obtain all their nutrition from a host organism, often causing disease. Examples include Mycobacterium tuberculosis (TB) and Salmonella typhi (typhoid fever).

Bacteria are haploid — they contain only one copy of their circular chromosome. This means mutations are immediately expressed, making them very adaptable and fast-evolving.

Endospores are highly resistant dormant structures formed inside some bacteria (e.g., Bacillus, Clostridium) during harsh conditions. They can survive boiling, UV radiation, and disinfectants for decades.

Ribosomes are the sites of protein synthesis in all cells, including bacteria. Bacterial ribosomes are 70S (smaller than eukaryotic 80S ribosomes), making them targets for many antibiotics.

The cell envelope is the collective term for all layers outside the bacterial cytoplasm, including the cell membrane, cell wall, and any capsule or slime layer present.

Plasmids are small, circular, double-stranded DNA molecules separate from the main chromosome. They carry non-essential but often advantageous genes (antibiotic resistance, toxin production).

Archaeobacteria lack peptidoglycan in their cell walls — a key difference from true bacteria. Instead they have pseudopeptidoglycan or other unique polymers, making them resistant to many antibiotics.

Pili (fimbriae) are hair-like appendages on bacteria made of the protein pilin. They help bacteria attach to host surfaces. Sex pili are used in conjugation to transfer DNA.

Flagellate bacteria can perform chemotaxis — moving toward favourable chemicals (attractants like nutrients) or away from harmful ones (repellents) using their flagella for motility.

Lophotrichous bacteria have a tuft (bundle) of flagella at one or both poles. Amphitrichous bacteria have a single flagellum at each pole. Monotrichous have one flagellum at one pole.

The basal body is a ring structure embedded in the cell membrane and wall from which the bacterial flagellum arises. It acts as the motor driving flagellar rotation for motility.

Spirilla are thick, rigid, spiral-shaped bacteria with a cell wall. They differ from spirochetes which are thin, flexible, and move by axial filaments. Spirillum minus causes rat-bite fever.

Streptococci are cocci that divide in one plane and remain attached in long chains. Streptococcus pyogenes causes strep throat and Streptococcus pneumoniae causes pneumonia.

Staphylococci are cocci bacteria arranged in irregular grape-like clusters. Staphylococcus aureus is a major pathogen causing skin infections, food poisoning, and toxic shock syndrome.

When cocci bacteria remain together in pairs after division, they are called diplococci (e.g., Streptococcus pneumoniae, Neisseria gonorrhoeae). 'Diplo' means two.

Archaeobacteria (Archaea) are ancient prokaryotes that live in extreme environments (hot springs, salt lakes, anaerobic conditions). They differ from true bacteria in membrane lipid structure and gene expression.

Antonie van Leeuwenhoek coined the term 'animalcules' (little animals) for the microorganisms he observed under his microscope, which included bacteria, though the term was used for various microbes.

Bacteria perform two types of respiration: aerobic respiration (using oxygen) and anaerobic respiration (without oxygen). Some bacteria can switch between both modes (facultative anaerobes).

Both Nostoc and Anabaena are cyanobacteria that perform nitrogen fixation using specialised cells called heterocysts, converting atmospheric N₂ into ammonia usable by plants.

Modern biologists place bacteria in their own kingdom (Monera or Prokaryotae), recognising them as a completely distinct group different from both plants and animals due to their prokaryotic nature.

Plasmids are small, circular, double-stranded DNA molecules that exist separately from the main bacterial chromosome. They often carry genes for antibiotic resistance and can be transferred between bacteria.

Gram-positive bacteria have a thick peptidoglycan wall that retains the crystal violet stain. They are generally more susceptible to antibiotics like penicillin than gram-negative bacteria.

Cyanobacteria form harmful algal blooms in water bodies when nutrients are excessive (eutrophication). These blooms deplete oxygen, produce toxins, and kill fish and other aquatic life.

Bacteriology is the specific branch of microbiology dedicated to the study of bacteria — their structure, genetics, ecology, physiology, and relationship to disease.

The primary mode of reproduction in bacteria is binary fission — the cell replicates its DNA, grows, and divides into two identical daughter cells without a true mitotic spindle.

Mycoplasma is the smallest living cell known, lacking a cell wall. Bacteria in general are among the smallest living cells, ranging from 0.2 to 10 micrometres.

Bacterial endospores are not reproductive structures but are survival structures. They form when conditions become unfavourable and can survive extreme heat, dryness, and radiation for years.

Bacteria are most beneficial to humans — they are used in food production (yogurt, cheese), antibiotic production, decomposition, nitrogen fixation, biotechnology, and as normal gut flora.

True sexual reproduction (involving meiosis and fusion of gametes) is totally absent in bacteria. They have parasexual processes like conjugation, transformation, and transduction for gene transfer.

Cyanobacteria increase soil fertility by adding organic matter through photosynthesis and by fixing atmospheric nitrogen, enriching the soil for other plants to grow.

Symbiotic nitrogen-fixing bacteria (Rhizobium) live in nodules on the roots of leguminous plants. The bacteria benefit from plant nutrients while providing fixed nitrogen to the plant.

Rhizobium is the nitrogen-fixing bacterium that lives in symbiotic root nodules of leguminous plants (peas, beans, clover). It converts atmospheric N₂ into ammonia usable by the plant.

Joshua Lederberg and Edward Tatum discovered bacterial conjugation in 1946 — the process of direct cell-to-cell transfer of genetic material through a pilus connecting two bacteria.

Heterocysts are specialised thick-walled cells in cyanobacteria (like Nostoc and Anabaena) that are the sites of nitrogen fixation, converting atmospheric N₂ into ammonia.

Nostoc consists of beaded cells arranged in unbranched filaments called trichomes. These trichomes are enclosed in a mucilaginous sheath and contain heterocysts.

Cyanobacteria are commonly called blue-green algae because of their blue-green colour from the pigments chlorophyll-a and phycocyanin. They are prokaryotes, not true algae.

Lederberg and Zinder discovered transduction in 1952 — the process by which bacteriophages transfer genetic material from one bacterium to another.

Rhizobium bacteria form root nodules in a symbiotic relationship with leguminous plants. The bacteria fix atmospheric nitrogen while the plant provides carbohydrates in return.

The main form of vegetative (asexual) reproduction in bacteria is binary fission, where one cell divides into two equal daughter cells. This can occur every 20-30 minutes under ideal conditions.

Antonie van Leeuwenhoek first discovered bacteria in 1676 using his hand-crafted microscopes, observing them in pond water and tooth scrapings. He called them 'animalcules'.

Fungi are the major decomposers of the world, breaking down dead organic matter (especially wood containing lignin) and recycling nutrients back into the ecosystem.

Bacteria occur in four main shapes: spherical (cocci), rod-shaped (bacilli), spiral (spirillum), and comma-shaped (vibrio). All these shapes are found in the kingdom Monera.