Mic 205 Exam Questions With Correct Answers Latest Update 2026

MIC 205 EXAM QUESTIONS WITH CORRECT ANSWERS LATEST UPDATE 2026 Know what the Spontaneous Generation Debate was, which scientists played a part, and how each contributed to settling the debate. Who finally disproved it? How? Why didn't the other experiments prove/disprove spontaneous generation? - Answers penned by Aristotle, held its own for over 2000 years. Francesco Redi did not believe in spontaneous generation. 1668, set up an experiment to disprove it. (Meat in the flask experiment. One uncovered, one with a film, and one with a cork. Flies/maggots only appeared on the uncovered one.) Robert Hooke, in 1665, discovered the "cell". 1683, Anton van Leeuwenhoek observed plaque from his teeth. Rekindled spontaneous generation debate when he discovered microbes randomly appearing in rainwater after a few days. John Needham conducted an experiment to prove Spontaneous Generation. Took water, boiled it, corked it, and then observed the growth after a few days had passed. Lazzarro Spallanzani disproved the Theory of Spontaneous Generation. He disproved it by recreating John Needham's experiment by making sure the example was not exposed to the air before being boiled. Understand the Germ Theory of Disease, what steps were taken (or proposed) early on to prevent infections? - Answers Germ Theory was coined by Louis Pasteur in 1861. Said that infection could be prevented by pasteurizing products such as beer, wine, and milk. Germ Theory states that, "many diseases are caused by microorganisms. These small organisms, too small to see without magnification, invade humans, animals, and other living hosts. Their growth and reproduction within their hosts can cause a disease" Be able to explain how Koch's Postulates are used to determine etiology of a disease. Be able to determine how each postulate can be invalidated (like the slide in class). - Answers Specific microbe is always associated with a given disease (not always true, multiple organisms can cause same disease/symptoms. not always caused by microbe: prion, fungus, plaque, virus etc.) microorganism can be isolated from the diseased animal and grown in pure culture (not all cultures can be grown in pure culture, may not be cultured at all if it's not caused by microbe) cultured microbe will cause disease when transferred to a healthy animal (some are opportunistic pathogens and only affect those with weak immune systems, some are not directly the cause of disease) same microorganism can be isolated from newly infected animal What kind of evidence do scientists use to categorize and classify living things? - Answers 16s rRNA, metabolic, morphology, or surface proteins What did the Hershey and Chase Experiment prove and disprove? Be able to describe the method used to determine if DNA or protein was injected into a bacteria from a bacteriophage - Answers The experiment proved that DNA was the genetic material of bacteriophages. Proved bacteriophages were injecting DNA, not protein. Using phage radioactively labeled with P32 (DNA) or S35 (Protein) they infected bacteria cells. Hershey & Chase wanted to know if the bacteriophages injected DNA or protein into the bacterial cell so they labeled the DNA (P32) and Proteins (S35). The bacteriophages injected DNA. That means that P32 should be inside the cell. Blended the bacteria, radioactive sulfur escaped the DNA pellet at the bottom and thus, the liquid was radioactive. Blended the bacteria, radioactive phosphorus was retained in the DNA pellet at the bottom and thus, the pellet was radioactive. What are the lytic and lysogenic cycles of a bacteriophage as described in class on the board. - Answers Feet of bacteriophage act as lock/key with external liposaccharides on bacteria surface. Lysogenic: bacterial genome has an insert of viral DNA, just inserted, nothing happens at the moment (has to become activated?) This can possibly last forever, but can turn into lytic cycle if activated (and the lytic cycle will start) Lytic cycle: Viral DNA takes over machinery of bacterial cell, takes control of everything in order to produce DNAases, proteases, lipases, to break down protein, lipids, and DNA. Attacks bacterial genome and cuts it randomly into smaller pieces. Bacterial genome is destroyed. Bacteria cannot do anything or defend itself. Viral DNA used ribosomes to produce new bacteriophages (tens of thousands) keeps producing. DNA parts self assembles into new bacteriophages. Viral DNA gets replicated, again, and put into heads of new bacteriophages. Once they are all assembled, they explode out and lyse the bacterial cell. What is the difference between a simple and differential stain? - Answers Simple stain stains all bacterial cells, allows for you to look at cell morphology. Differential stain stains certain bacterial cells allowing you to differentiate between those and others (usually targeted towards specific genuses/strains) What does a Gram stain detect? How does it differentiate bacterial cells? What color is a Gram-positive organism? What color is a Gram-negative organism? - Answers The gram stain detects peptidoglycan/ Gram-Positive stain: with crystal violet (appears blue/purple) Gram-Negative stain: with safranin (appears red/pink) What are the principal differences between a gram - and gram + bacterial cell? (this is also covered in more detail in the external structures section)? - Answers Gram + cells have teichoic acids (t looks like a +) which are antigenic determinants/used for species identification. Also called lipoteichoic acid. Have very thick peptidoglycan layer and only one plasma membrane. These cells can also have mycolic acid (mycobacterium) Gram - cells have an outer and inner bilayer membrane. Outer portion has lipopolysaccharide (LPS), outer membrane also allows for survival in harsh conditions. Outer sugar portion is called O-antigen, an antigenic determinant. Lipid portion of LPS is lipid A (endotoxin), which causes fever, inflammation, shock, and blood clotting (only when cell dies). Gram - have a very thin layer of peptidoglycan and are harder to treat with antibiotics because their peptidoglycan layer is protected by outer membrane. What do penicillins and cephalosporin antibiotics act on with the bacterial cell? Are gram + or gram - bacteria more susceptible to these antibiotics? Why don't they harm eukaryotes? - Answers Classified as beta lactam antibiotics. Work better on gram+ bacteria because they have that huge, outer wall of peptidoglycan. Gram - has an outer cell membrane that antibiotic needs to get through. Do not work on eukaryotes because they do not have peptidoglycan. (don't work on archaea either) What does an acid-fast stain detect? How does it differentiate bacterial cells? What color are acid-fast organisms after staining with an acid-fast stain? Name an acid-fast organism. - Answers Presence of mycolic acid. Bacteria with mycolic acid can withstand acid staining, non mycolic acid containing bacteria are dissolved by it. Red/pink. The acid fast stain is used to differentiate cells with waxy cell walls that contain high amounts of mycolic acid like those of Mycobacterium and Nocardia. Bacillus (blue) and Mycobacterium (red). Nicardia (red filaments) Is a Schaeffer-Fulton (differential endospores green other bacterial cells red) stain a differential stain or a simple stain? What has to be done to the proteins in the cell membrane in order to drive the primary stain into the endospore? - Answers Differential. The dye, malachite green, must be driven into the cell walls using heat since they are impermeable to almost all chemicals What is an endospore? Why do bacteria make endospores? What are their characteristics? - Answers Dormant, non-reproductive resting structure. A way for bacteria to survive "tough times", a stripped down version of the bacteria Can be revived after millions of years. No nutrients needed to survive. Hardened to radiation, dessication Allow bacteria to resist phagocytosis (being eaten), which is the way bodies eliminate threatening cells (engulfed by white blood cells) Resist malnutrition, desiccation, identification Also allows bacteria to "stick" to surfaces, a key part of infections. Hides PAMPS from being seen by immune system (PAMPS are what the immune system uses to identify foreign invaders, so the capsule covers these and the immune system cannot identify what the cell is) What bacterial group discussed in class is medically important and form endospores? - Answers Bacillus (food poisoning?) What does it mean for a bacterial growth medium to be selective? Differential? - Answers Selective: excludes growth of EVERY BACTERIA except for the bacteria that will grow on it, most bacteria cannot grow on this type of medium. It's select. Differential: Allows for different bacteria to be differentiated. If a bacteria can use the nutrients in the substrate, an indicator will change the color and allow you to tell what specific strain of bacteria it is. Blood agar is not selective. Understand the selective and differential aspects of MacConkey's agar (MAC). What information does MAC provide about bacteria growing on this medium? - Answers Bile salts and crystal violet inhibit gram + bacteria (selective) so only gram - can grow. Also contains lactose which can be fermented into lactic acid. Used to differentiate those that can or cannot ferment lactose. (white if no lactic acid, pink if lactic acid) Understand the selective and differential aspects of Mannitol Salt agar (MSA). What information does MSA provide about bacteria growing on this medium? - Answers High salt (7.5%) which makes it selective, as only high salt-tolerant bacteria can grow (staphylococcus) Mannitol makes it differential, if the bacteria cannot ferment mannitol (red color) it can be any strain of staphylococcus. If it can ferment mannitol (yellow color) it is staphylococcus aureus. Very specific. What type of clinical samples is plated on Blood agar (BAP)? What broad type of bacteria are we looking for from a sample plated on BAP? - Answers Looking for bacteria that can perform hemolysis, the lysis of red blood cells. BAG beta- complete. alpha-incomplete. gamma-none. Used to differentiate between strep, commonly. What are beta, alpha and gamma hemolytic bacteria? How would they appear on blood agar? What are some examples that were discussed in class? - Answers Beta hemolysis: Enzymes lyse the blood cells completely, producing a clear area around the colony. GROUP A STREP!!! Example: Streptococcus haemolyticus, found on biofilms on medical instruments, genitals, armpits. Example 2: Streptococcus pyogenes, common strep throat. Alpha hemolysis: Incomplete hemolysis produces a greenish discoloration around the colony. Example: Viridans Group Strep: Plaque on gums and teeth, can travel through bloodstream into heart, causing endocarditis. Gamma hemolysis: No effect on the red cells. No example for gamma? What is the difference between colony morphology and cell morphology? - Answers Not the same thing. Cell morphology is the morphological features of the cell, these do not usually change. Colony morphology is the morphology of a single, isolated colony of cells. Colony morphology can change depending on temperature, nutrients, space, time, and waste buildup. Know the two basic types of cells. - Answers Eukaryotic and prokaryotic What is the 16S rRNA gene used for? What does it encode for? Why is the 16S rRNA gene chosen as an 'identifying characteristic'? - Answers Barcode of life: 16s rRNA gene, "bar-code" of life. Encodes ribosomes that make proteins, reads RNA. Ribosome is essential for life because it makes proteins, building blocks, for the bacteria. Use this to find taxonomy name and classify bacteria. Part of this genetic sequence cannot change or else it changes the shape of the ribosome (for active sites) but there are other parts that are variable. So we use the variable regions to identify who the bacteria is since they're unique. How do the archaea differ from eukaryotes and prokaryotes? - Answers Do not have peptidoglycan, are still classified as prokaryotes, binary fission (asexual), are usually found in extreme environments, not known to ever be pathogenic. Examples include methanogens, halophiles, and thermophiles. (love salts, love high temperatures, love environments with little to no oxygen, etc.) What is phage typing? What characteristic of a bacteriophage make this possible? - Answers Phages are specific to certain bacteria, even down to a specific strain. Infecting an agar plate with these phages allows for you to determine if the bacteria on the plate is your target bacteria, causes "plaques" which look like "holes" in the agar. The phage is able to bind with the surface of the bacteria cell. It has a tail that bonds with the surface like a "lock and key". It then compresses and attaches to the cell, allowing it to inject the bacteria with its own DNA alongside proteases, DNAeases, and lipases, to break down the bacterial DNA, proteins, and lipids. It then takes control of the bacterial ribosomes and replicates itself many times over, creating small pieces of DNA that it then assembles into more bacteriophages. After the DNA has been copied a second time (to be inserted into the new bacteriophages heads), the phages burst out, exploding the cell and lysing it. What is a biolog plate used for? - Answers 96 well plate, different salt concentration/different nutrients in each one. Place sample into all wells in biolog plate. If bacteria can grow it changes to blue. IDs metabolism of bacteria. Understand diffusion, osmosis, and different types of transport. What are the different ways that molecule can move across the plasma membrane? - Answers Osmosis is the diffusion of water across a concentration gradient (high to low) Passive diffusion is the movement of substance across a concentration gradient (high to low), this is used for small, lipid (hydrophobic) molecules. They can diffuse across the membrane because the inside is also hydrophobic. Facilitated diffusion is the diffusion of large or hydrophilic molecules across a membrane through the use of integral proteins (high to low). Permeases are special integral proteins that only allow a certain substance across the membrane. Active transport also uses these permease proteins, however, requires ATP for transport against their gradient. (So this would be low to high) What are the different transport proteins? How do they operate? - Answers Permeases is a special protein that only allows certain substances through. Specialized versions of these permeases include symports, antiports, and uniports. Understand the importance of the plasma membrane in regulating the movement of substances into and out of the cell. - Answers Semipermeable, allows for small lipids to be diffused across but inhibits other molecules, allowing it to decide what and what not to let in (Membrane has integral proteins in it that are coded to specifically let in certain molecules) How do bacteria reproduce? How is the cytoskeleton involved in this process? - Answers They reproduce by binary fission, or asexually reproducing. HOW IS THE CYTOSKELETON INVOLVED? Cytoskeleton is involved because it enables cell movement and has scaffolds that allows nutrients out and in of cell for ribosomes to gather and helps binary fission occur.