micro bio chap 1 and 2 study guide
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How did the evolution of cyanobacteria change the Earth forever?
Cyanobacteria were the first oxygenic phototrophs which produced O2
as a waste product, so their evolution allowed for increases in O2
in the atmosphere, leading to the evolution of multicellular life forms.
How were the theories of abiogenesis and spontaneous generation related? What were some observations believers used to validate spontaneous generation?
They both claim life was formed from nothing or randomly. There were arguments stating how “bad” air was the cause, or generation occurred due to a higher power.
How did the contributions of Hooke and van Leeuwenhoek contribute to the beginnings of microbiology?
Hooke was credited with the invention of the microscope, and credited with the discovery of microorganisms. Leeuwenhoek was credited with the discovery of microbial content in natural substances.
Why was Redi’s experiment not proof enough that biogenesis was a valid theory? What was the problem with his experiments?
People argued since meat still rotted when he did his experiments that abiogenesis was still a theory yet to be disproven for smaller organisms. The problem with his experiments lied with the gauze he used to cover the meat. This still allowed for organisms to seep through, because it was not fully covered.
What were Jablot and Needham attempting to prove or disprove with their experiments? Historically, how did this contribute to continued belief in spontaneous generation?
Jablot and Needham tried to prove that microbes are present in dust particles. They said that microbes were present in the air, and it was thought that air was necessary for spontaneous generation to occur, so this led to the continued belief in spontaneous generation.
How did the experiments of Pasteur finally invalidate the theory of spontaneous generation?
Pasteur used a swan-necked flask to show how after sterilizing liquid via extensive heating, microbes would be trapped in the neck of the flask instead of getting into the liquid. This showed that air was still present, disproving the theory of spontaneous generation.
How did Tyndall and Cohn lay the groundwork for the experiments performed by Pasteur? What did Cohn correctly predict the presence of? (Hint – this explained the discrepancies between Needham’s and Jablot’s experiments)
They performed many experiments using boiling infusions and received mixed results. They attributed their mixed results to the presence of heat resistant forms of life. Cohn predicting the presence of endospores (heat resistant forms of bacteria) which helped disprove Needham and Jablot’s experiments.
What policies and or practices did Ignaz Semmelweis implement in the Vienna hospital in which he practiced medicine? What important observation did he make that motivated him to implement his polices?
He introduced the idea of hand washing. He did this because he noticed deaths occurred more often when nurses received help from the medical students (worked with cadavers with many bacteria), so he implemented hand washing in hopes to reduce the spread of bacteria and the number of fatalities.
What is Joseph Lister considered the father of? What surgical practices did he implement? Whose work was essential to Lister’s proposals?
Joseph Lister is considered as the father of antisepsis. He would dress wounds with acid, which would reduce the amount of bacteria in wounds preventing them from getting infected.
What are Koch’s postulates? How did they further not only validate, but extend the work of Pasteur?
- Koch’s postulates are used to prove cause and effect in infectious diseases. The postulates were:
- 1.The disease-causing organism must always be present in animals suffering from the disease but not in healthy animals. 2. The organism must be cultivated in a pure culture away from the animal body.
- 3. The isolated organism must cause the disease when inoculated into healthy susceptible animals.
- 4. The organism must be isolated from the newly infected animals and cultured again in the laboratory, after which it should be seen to be the same as the original organism.
Do Koch’s postulates apply to all situations? Why or why not?
No, they do not. There are some organisms that cannot be grown in pure culture, and the infection can sometimes not be recreated due to different portals of entry.
John Snow proposed rudimentary spot maps in response to a cholera outbreak. His practices eventually became the foundation for what modern day science?
John Snow is the father of epidemiology.
What was Ehrlich referring to when he referenced the term “magic bullet”? What is the concept of selective toxicity?
He was referring to antibodies. Selective toxicity is the concept of causing harm to pathogens but not harming the host.
For what is Alexander Fleming given credit for? What is the term used to describe a successful antibiotic?
Fleming discovered the 1st
What two factors have contributed greatly to the increase of antibiotic resistant bacterial pathogens?
The ability for bacteria to generate quickly and adapt to biochemical changes and the over-prescription of antibiotics.
What important observation did Jenner make? How did he experimentally test his observations?
He noticed milkmaids did not acquire smallpox and he tested his observations by inoculating a child with cowpox and found that this person was protected against small pox.
What is the germ theory of disease? How does this compare with the ancient Greek’s idea of “miasma”
The Germ Theory of disease states that microorganisms can invade other organisms and cause disease. “Miasma” was the concept of bad air.
How did the contributions of Beijerinck build upon the original work of Koch and his assistant Petri?
Beijerinck’s greatest contribution to the field of microbiology was his formulation of the enrichment culture technique. This allowed for microorganisms to be isolated from natural samples using highly selective techniques.
Why was Winogradsky’s work important?
He proposed the concept of chemolithotrophy, the oxidation of inorganic compounds to yield energy. He also showed that these organisms (chemolithotrophs) obtained carbon from CO2
What is the difference between a true pathogen and an opportunistic pathogen? What is a saprobe?
True pathogens are capable of causing disease in healthy people with normal immune defenses. Opportunistic pathogens cause disease when the host’s defenses have been compromised. Saprobes are organisms that feed on nonliving or decaying organic matter.
What are some factors that have contributed to the need to return to the basic biological studies of pathogens we once considered conquered?
People now live longer so there is more susceptibility to a wide range of microbes; the population is more mobile, and there are emerging diseases.
What are some basic differences between prokaryotes and eukaryotes from a size standpoint? Metabolic standpoint? Structural standpoint?
Eukaryotes are generally much larger than prokaryotes. Metabolically they are extremely similar, but prokaryotes are generally more metabolically efficient. Structurally there are membrane-bound organelles in eukaryotes. Also,
What are the three basic shapes of the bacterial cell?
Spherical (coccus), Cylindrical shape (rod, bacillus) or spiral shaped (spirilla)
How are magnification and resolution related? What two factors of the standard bright field microscope affect resolution?
Magnification is the ability to increase the size of the image and resolution is the ability to distinguish two adjacent objects as distinct. The resolution is affected by the wavelength of light used and the numerical aperture (measure of light-gathering ability).
What is refraction? From a microscope standpoint, how does it affect resolution?
Refraction is the change in direction when light passes from one medium to another. Refraction generally improve resolution by allowing more light to go through a lens.
How does the use of oil of immersion with the proper objective enhance resolution?
Immersion oil increase the light-gathering ability of a lens by allowing some of the light rays emerging from the specimen at angles to be collected and viewed.
How do you determine the total magnification of a microscope?
The total magnification of a microscope is the product of the magnification of its objective and ocular lenses.
What is an easy method for improving the contrast of a final observed image under the microscope?
Dyes (staining) can be used to stain cells and increase their contrast so they can be seen more easily.
What are the two types of dyes used to stain organisms? Why are cationic dyes used for most general staining purposes?
There are basic stains and differential stains. Cationic dyes are used for most general staining because most cells have negatively charged surfaces so there will be better adherence to a positively charged stain.
What is a differential stain? How does the Gram stain subdivide bacteria into two general classes?
A differential stain makes cells different colors when stained. Bacteria can be divided into two groups: gram-positive and gram-negative. This is based on the cell wall structure differences.
What are the four steps of the Gram stain, and what would be the color of each class of bacteria after each step?
- Step 1: Flood the heat-fixed smear with crystal violet for 1 minute (all cells are purple)
- Step 2: Add iodine solution for 1 minute (all cells remain purple)
- Step 3: Decolorize with alcohol for 20 seconds (Gram positive cells are purple; Gram-negative cells are colorless)
- Step 4: Counter stain with safranin for 1-2 minutes (Gram Positive cells are purple; Gram-negative cells are pink)
Why is phase contrast microscopy with unstained specimens better than bright field images with stained specimens? What principle is phase contrast microscopy based upon?
Phase-contrast microscopy is based on the principle that cells differ in refractive index from their surroundings, so light passing through a cell differs in phase from light passing through surrounding liquid. This allows for the visualization of live samples without the use of a stain.
What is dark field microscopy commonly used for? Why is the resolution of a dark field microscope slightly better than an ordinary bright field microscope?
Dark-Field Microscopy is commonly used to observe motility in bacteria and the resolution is better because of the dark background, so specimens appear light.
Why is florescence microscopy so useful in the field of diagnostic microbiology? Microbial ecology? For fluorescence microscopy to be useful for diagnostics what important reagent is required? (Hint: it’s what makes it specific for detection purposes)
Florescence microscopy is so useful in diagnostic microbiology because bacteria can be examined in their natural environment. This allows for microbial ecologists to analyze bacteria in habitats such as soil, water and food. In order for it to be useful to diagnostics the reagent DAPI is used to complex with the cell’s DNA.
What makes confocal scanning laser microscopy useful? (Hint: think about a biofilm and then describe how a confocal works and relate it to microbial ecology and the identification of microorganisms)
Confocal scanning laser microscopy is so useful because it allows for 3D images of bacteria, which allows for analysis of thick specimens in biofilms.
What basic principle does the electron microscope take advantage of that results in such radical increases in resolution?
Electrons are used in electron microscopy instead of photons which allows for a much higher resolution.
What is the difference between SEM and TEM? (i.e. which method would you use for viewing intracellular structures? For external morphology?)
A transmission electron microscope (TEM) is generally used to observe intracellular structures of thin sections, whereas a scanning electron microscope (SEM) is more commonly used to observe surface structures.
What is a problem with TEM? What is SEM commonly used for?
For TEM, electrons do not penetrate well, so cells must be thinly sectioned in order to observe. SEM is used to observe intact cells or cell components.
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