Microbial Culture - Class 12 Biotechnology - Chapter 6 - Notes, NCERT Solutions & Extra Questions
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Extra Questions - Microbial Culture | NCERT | Biotechnology | Class 12
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Describe the nutritional requirements of microorganisms.
Microorganisms require macronutrients (carbon, nitrogen, phosphorus, sulfur) and micronutrients (manganese, zinc, cobalt) for energy production and cellular functions. Carbon sources like glucose provide skeleton structures for organic molecules, while nitrogen is essential for proteins and nucleic acids. Phosphorus is used in ATP and nucleic acids, and sulfur in amino acids like cysteine. Also, growth factors like vitamins are crucial for those microbes that cannot synthesize them. Water, being a universal solvent, is essential for all biochemical reactions in microbial cells.
What is culture media? Classify the culture media.
Culture media are nutrient-rich preparations used to support the growth of microorganisms under laboratory conditions. They contain essential nutrients, carbon, energy sources, and possibly growth-promoting factors.
Culture media can be classified based on:
Chemical composition:
Synthetic (chemically defined): Composition is precisely known.
Complex (undefined): Contains some unknown components.
Consistency:
Liquid media (broth)
Solid media: Contains agar.
Semi-solid agar media
Function:
Selective media: Promotes growth of specific microbes.
Differential media: Differentiates between microbial types.
Enrichment media: Enhances growth of particular microbes.
Write an account of the growth curve analysis of a microorganism.
Growth curve analysis of microorganisms is performed by culturing microbes in a controlled environment and monitoring their growth over time. The growth curve typically follows four phases: the lag phase, where cells adapt to new conditions; the exponential phase, marked by rapid cell division; the stationary phase, where growth ceases due to nutrient depletion; and the death phase, characterized by a decline in viable cells due to adverse conditions. This analysis helps in understanding microbial growth dynamics, optimal growth conditions, and potential industrial applications.
Discuss any two methods to isolate a pure culture.
Methods to Isolate a Pure Culture
1. Streak Plate Method:An inoculating loop is used to streak a microbial suspension across an agar plate, creating areas of decreasing cell density. After incubation, isolated colonies form where individual cells, near the tail of the streak, have multiplied.
2. Pour Plate Method:A diluted microbial sample is mixed with molten agar and poured onto Petri dishes. On solidification and incubation, this allows separate colonies to arise from single cells, facilitating the isolation of pure cultures for further analysis.
Define sterilisation, disinfection and sanitisation.
Sterilisation is the complete elimination or destruction of all forms of microbial life, including bacterial spores, usually achieved through physical or chemical methods. Disinfection refers to the elimination of most pathogenic microorganisms (except bacterial spores) on inanimate objects using physical or chemical processes. Sanitisation is a process that effectively reduces the number of microorganisms to safe levels as determined by public health standards, typically through cleaning and disinfecting activities in food service and other environments.
Give a detailed account on the various methods of sterilisation.
Sterilisation ensures all living microorganisms, including spores, are eliminated. Heat sterilisation uses methods like boiling, autoclaving, and pasteurization. Radiation sterilisation, a cold process, uses UV, electron beams, or gamma rays to damage microbial DNA. Filtration, suitable for heat-sensitive liquids, removes microbes without killing, using membrane filters. Chemical methods involve substances like alcohols and aldehydes to disrupt microbial cell structures. Methods chosen depend on the materials to be sterilised and their tolerance of temperature, radiation, and chemicals.
Bacterial strains which do not require any organic supplement are called
(a) Auxotroph
(b) Prototroph
(c) Heterotroph
(d) Chemotroph
The correct answer is:
(b) Prototroph
Prototrophs are bacterial strains that can synthesize all the compounds they need for growth and therefore do not require any organic supplements in the culture medium. They are able to grow on minimal medium which lacks any nutritional supplements that auxotrophs would require.
Who was the first to develop the process of colony purification on solid media?
(a) Louis Pasteur
(b) Robert Koch
(c) Fannie Hesse
(d) Richard Petri
The first person to develop the process of colony purification on solid media was Robert Koch. This development was key for isolating pure cultures, which is essential for the identification of pathogenic organisms causing diseases.
Hence, the correct answer is: (b) Robert Koch
HTST and UHT methods belong to:
(a) Pasteurisation
(b) Isolation of pure culture
(c) Staining of bacteria
(d) Culture of bacteria
(a) Pasteurisation
Explanation: Both High Temperature Short Time (HTST) and Ultra-High Temperature (UHT) are methods used specifically for pasteurisation, particularly in the food and dairy industry, to kill pathogenic microorganisms in milk and other liquids while retaining the quality of the product.
Spontaneous generation was suggested by:
(a) Francesco Redi
(b) Lazzaro Spallanzani
(c) Robert Koch
(d) Louis Pasteur
None of the options provided were proponents of spontaneous generation. However, to address the context around each individual listed:
Francesco Redi and Louis Pasteur were notable for experiments that *disproved* spontaneous generation.
Lazzaro Spallanzani conducted experiments that also challenged the theory of spontaneous generation.
Robert Koch did not directly deal with spontaneous generation but made crucial contributions to microbiology and germ theory.
Thus, each of these scientists disproved or did not support the theory of spontaneous generation.
Please review if the options provided are correct or if the question is asking who disproved spontaneous generation. If the question is about disproving spontaneous generation, the correct answers would be from the given options: Francesco Redi (option a) and Louis Pasteur (option d).
Germ theory of disease was suggested by:
(a) Francesco Redi
(b) Lazzaro Spallanzani
(c) Robert Koch
(d) Louis Pasteur
The Germ theory of disease was suggested by:
(d) Louis Pasteur
Louis Pasteur's experiments disproved the theory of spontaneous generation, leading to the development of the germ theory of disease, which posits that microorganisms are the cause for infectious diseases.
Calculate the specific growth rate and generation time of a bacterial population in which the number of bacteria increases from 104 cells/mL to 107 cells/mL, during 4 hours of exponentail growth.
To calculate the specific growth rate (\mu) and generation time (t_d), we use:
[ \mu = 2.303 \frac{(\log X_t - \log X_0)}{t} ]
Where:
(X_0 = 10^4) cells/mL (initial concentration)
(X_t = 10^7) cells/mL (final concentration after 4 hours)
(t = 4) hours (time period)
Calculate (\mu):
[ \mu = 2.303 \frac{(\log 10^7 - \log 10^4)}{4} = 2.303 \frac{(7 - 4)}{4} = 1.72 , \text{hr}^{-1} ]
Calculate (t_d) (Doubling time):
[ t_d = \frac{0.693}{\mu} = \frac{0.693}{1.72} \approx 0.4 , \text{hours} = 24 , \text{minutes} ]
Thus, the specific growth rate (\mu) is 1.72 hr(^{-1}), and the generation time (t_d) is 0.4 hours or 24 minutes.
Assertion: Alcohol production by a batch culture of Saccharomyces starts declining steadily even though conditions like temperature are optimum.
Reason: Alcohol concentration of around 13% is toxic for yeast cells.
(a) Both assertion and reason are true and the reason is correct explanation of the assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
(a) Both assertion and reason are true and the reason is correct explanation of the assertion.
The assertion states that alcohol production by a batch culture of *Saccharomyces* starts declining even under optimum temperature conditions. This is true as yeast cells, which produce alcohol, eventually create an environment with an alcohol concentration high enough to inhibit their own growth and metabolism, leading to a decline in production.
The reason given is that an alcohol concentration of around 13% is toxic to yeast cells. This is also true; high concentrations of ethanol, which is the type of alcohol produced by yeast, can indeed be toxic to the cells. Ethanol disrupts the cell membrane and denatures proteins, leading to cell death.
Furthermore, the reason correctly explains the assertion. The toxicity of the produced alcohol at certain concentrations leads to a decrease in yeast viability and activity, thereby causing a decline in alcohol production, even when other conditions are maintained optimally.
Assertion: A selection medium containing Ampicillin is sterilised by autoclaving. Both AmpS and AmpR microbes show growth on the medium.
Reason: To inhibit the growth of AmpS microbe ampicillin should not have been autoclaved but sterilised by using micro-filters before adding to the medium.
(a) Both assertion and reason are true and reason is correct explanation of the assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
(a) Both assertion and reason are true and reason is correct explanation of the asssertion.
Explanation:
Assertion (True): When a selection medium containing ampicillin is sterilized by autoclaving, heat-sensitive ampicillin is likely denatured, making it ineffective at inhibiting the growth of ampicillin-sensitive (AmpS) microbes. Thus, both ampicillin-resistant (AmpR) and AmpS microbes show growth.
Reason (True and Correct Explanation): Ampicillin is a β-lactam antibiotic which is heat sensitive. Autoclaving (using high heat and pressure) can degrade ampicillin's effectiveness. Hence, to maintain the antibiotic's activity, ampicillin should be added to the sterilized medium after autoclaving has been completed. The filtration, not autoclaving, is the suitable method for sterilizing heat-labile substances like ampicillin, thus correctly explaining why AmpS microbes were not inhibited in the provided scenario.
Assertion: Microorganisms are able to grow and multiply over a wide range of temperatures.
Reason: Extreme thermophiles can tolerate temperatures of above 100°C.
(a) Both assertion and reason are true and reason is the correct explanation of the assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.
Explanation:
The assertion is true as microorganisms, depending on their type, can grow over a wide range of temperatures from cold-loving psychrophiles to heat-loving thermophiles and extreme thermophiles.
The reason is also true; extreme thermophiles can indeed tolerate temperatures above 100°C.
However, the reason is not the correct explanation for the assertion because the ability of microorganisms to grow over a wide range of temperatures is not solely because extreme thermophiles can tolerate very high temperatures. Rather, it's due to the existence of diverse groups of microorganisms, each adapted to different temperature ranges.
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Comprehensive Class 12 Notes on Microbial Culture: Key Concepts and Study Guide
Introduction to Microbial Culture
Microbial culture is the process of growing and studying microorganisms in a controlled environment. This field has significant importance in various scientific domains including medicine, agriculture, and biotechnology. Let's delve into the historical background, essential culture media, nutritional requirements, and other facets of microbial culture.
Historical Perspective
The Discovery of the Microscope
The invention of the microscope was a pivotal moment in the history of microbiology. Anton van Leeuwenhoek, a Dutch merchant in the 1670s, developed one of the first microscopes and discovered microscopic organisms, which he referred to as "animalcules." His discoveries lay the groundwork for further advancements in microbiology.
Contributions of Louis Pasteur and Robert Koch
Louis Pasteur, through his groundbreaking experiments, proved that microorganisms could cause diseases, leading to the germ theory. Robert Koch further solidified this theory by establishing a set of criteria known as Koch's Postulates, which identify microorganisms as causative agents of diseases.
Importance of Culture Media
Development of Media for Microbial Growth
The development of various media has been crucial for microbial studies. Ferdinand Cohn, Louis Pasteur, and Robert Koch were instrumental in refining media that provided essential nutrients for microbial growth.
Types of Culture Media
- Synthetic or Chemically Defined Media: These media have known chemical compositions and are often used in research. For instance, M9 medium is used for cultivating E. coli.
- Complex Media: These have some components with unknown compositions, such as peptones and yeast extract, and are suitable for growing a wide variety of microorganisms.
Nutritional Requirements for Microbial Growth
Microorganisms require various nutrients for growth and reproduction, including:
- Macronutrients: Carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus, potassium, calcium, magnesium, and iron.
- Micronutrients: Trace elements like manganese, zinc, copper, and cobalt, usually present in small quantities in culture media.
Nutritional Categories
-
Autotrophs: Obtain their carbon from carbon dioxide.
- Photoautotrophs: Use light energy.
- Chemoautotrophs: Use chemical oxidation of inorganic molecules.
-
Heterotrophs: Obtain their carbon from organic molecules.
- Chemoheterotrophs: Obtain energy by chemical oxidation of organic molecules.
- Photoheterotrophs: Obtain light energy for photosynthesis.
Types of Culture Media
On the Basis of Chemical Composition
- Synthetic or Chemically Defined Media: Used in research for specific nutrient requirements.
- Complex Media: Useful for a range of microorganisms; includes nutrient broth and MacConkey agar.
On the Basis of Consistency
- Liquid Media or Broth: Used for large-scale culture preparations.
- Solid Media: Includes agar, which provides a solid surface for microbial growth.
- Semi-Solid Media: Contains lower concentrations of agar, used for specific types of microbial culture.
Based on Application and Function
- Selective Media: Favour the growth of a particular microorganism while inhibiting others.
- Differential Media: Differentiate between microorganisms based on their appearance on the media.
- Enrichment Media: Enhance the growth of specific microorganisms by adjusting the nutritional environment.
Sterilisation Methods
Importance of Sterilisation
Sterilisation ensures that all living microorganisms, including bacterial spores, are eliminated. Various methods include:
- Heat: Boiling, autoclaving, pasteurisation, and flaming.
- Radiation: UV rays and gamma rays for cold sterilisation.
- Filtration: Used for heat-sensitive solutions.
- Chemical Methods: Use of alcohols, aldehydes, and heavy metals for surface sterilisation.
Pure Culture Techniques
Obtaining a pure culture is crucial for studying specific microorganisms. Key techniques include:
- Streak Plate Method: Involves streaking a bacterial suspension on a solid agar plate to isolate colonies.
- Pour Plate Method: Diluted samples are mixed with molten agar to form colonies.
- Spread Plate Technique: A diluted bacterial mixture is spread evenly over the surface of an agar plate.
Factors Affecting Microbial Growth
Microbial growth can be influenced by several environmental factors like:
- Temperature: Mesophiles, thermophiles, and extreme thermophiles grow at different temperature ranges.
- pH: Most bacteria grow best around neutrality (pH 7), while fungi prefer slightly acidic conditions.
- Oxygen: Microorganisms can be aerobes, anaerobes, or facultative anaerobes.
- Carbon Dioxide: Essential for autotrophic organisms.
- Light: Required for photosynthetic microorganisms.
The Microbial Growth Curve
The growth of microorganisms can be illustrated using a growth curve with four distinct phases:
- Lag Phase: Cells are metabolically active but not dividing.
- Exponential Phase: Cells divide at a consistent rate.
- Stationary Phase: Growth rate equals the death rate.
- Death Phase: Viable cell numbers decline.
graph TD;
A[Microbial Culture] -->|Historical Perspective| B[Microscope Discovery];
A -->|Development of Media| C[Culture Media Types];
A -->|Nutritional Needs| D[Nutritional Categories];
A -->|Sterilisation| E[Sterilisation Methods];
A -->|Pure Culture| F[Pure Culture Techniques];
A -->|Growth Factors| G[Factors Affecting Growth];
A -->|Growth Curve| H[Growth Curve Phases];
Applications of Microbial Culture
The applications of microbial culture are vast and diverse:
- Medicine: Production of antibiotics and vaccines.
- Biotechnology: Production of human hormones, blood-clotting factors, and genetically modified organisms (GMOs).
Conclusion
Understanding microbial culture is pivotal for various scientific advancements. From historical discoveries to modern applications in biotechnology and medicine, microbial culture continues to play an essential role in numerous fields.
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