Podcast
Questions and Answers
During which growth phase are cells observed to be maximum in size?
During which growth phase are cells observed to be maximum in size?
What characteristic is observed in cells during the Stationary Phase?
What characteristic is observed in cells during the Stationary Phase?
What is the purpose of performing serial dilutions?
What is the purpose of performing serial dilutions?
What is a likely issue if a Petri plate contains more than 250 colonies?
What is a likely issue if a Petri plate contains more than 250 colonies?
Signup and view all the answers
What occurs when a sample with 10,000 bacteria per milliliter is plated without dilution?
What occurs when a sample with 10,000 bacteria per milliliter is plated without dilution?
Signup and view all the answers
What is a major disadvantage of the pour plate method?
What is a major disadvantage of the pour plate method?
Signup and view all the answers
Which group of microorganisms grows optimally at temperatures between 25˚C to 40˚C?
Which group of microorganisms grows optimally at temperatures between 25˚C to 40˚C?
Signup and view all the answers
When performing a plate count using the spread plate method, what characteristic of islands is crucial for diagnostic purposes?
When performing a plate count using the spread plate method, what characteristic of islands is crucial for diagnostic purposes?
Signup and view all the answers
What is a characteristic of extreme halophiles regarding their environmental adaptation?
What is a characteristic of extreme halophiles regarding their environmental adaptation?
Signup and view all the answers
Which of the following statements about acidophiles is true?
Which of the following statements about acidophiles is true?
Signup and view all the answers
What happens to bacterial cells under high osmotic pressure?
What happens to bacterial cells under high osmotic pressure?
Signup and view all the answers
Which phase of bacterial growth is characterized by adjusting to new environments without significant cell division?
Which phase of bacterial growth is characterized by adjusting to new environments without significant cell division?
Signup and view all the answers
In a serial dilution, if a sample is diluted 1:10 and then plated, how many colonies might be expected from 100 bacteria in the original sample?
In a serial dilution, if a sample is diluted 1:10 and then plated, how many colonies might be expected from 100 bacteria in the original sample?
Signup and view all the answers
What is the primary characteristic of the lag phase in bacterial growth?
What is the primary characteristic of the lag phase in bacterial growth?
Signup and view all the answers
What technique involves diluting a sample to obtain a countable number of colonies?
What technique involves diluting a sample to obtain a countable number of colonies?
Signup and view all the answers
In the pour plate method, what happens to the bacteria during the plating process?
In the pour plate method, what happens to the bacteria during the plating process?
Signup and view all the answers
Which of the following accurately describes the definition of generation time in bacterial growth?
Which of the following accurately describes the definition of generation time in bacterial growth?
Signup and view all the answers
During which growth phase does rapid population increase occur?
During which growth phase does rapid population increase occur?
Signup and view all the answers
Which method allows for estimating the number of viable bacteria in a sample by creating a dilution series?
Which method allows for estimating the number of viable bacteria in a sample by creating a dilution series?
Signup and view all the answers
What is a significant factor that can influence bacterial generation time?
What is a significant factor that can influence bacterial generation time?
Signup and view all the answers
In the spread plate technique, how are bacteria typically deposited onto the agar?
In the spread plate technique, how are bacteria typically deposited onto the agar?
Signup and view all the answers
Study Notes
Association of Growth and Cell Changes
- Lag Phase: Phase where maximum cell size is reached towards the end, preparation for division occurs.
- Log Phase: Characterized by smaller cells that stain uniformly, rapid cell division happens.
- Stationary Phase: Cells become Gram variable and exhibit irregular staining due to intracellular granules; sporulation occurs.
- Decline Phase: Involution forms become common as resources deplete.
Plate Counts
- Measures viable cell counts; results reported as colony-forming units (CFU).
- Visible colonies require about 24 hours or more to develop.
- Serial dilution is performed to ensure colony counts are between 25 and 250 to avoid overcrowding on plates.
Serial Dilutions
- Example: A milk sample with 10,000 bacteria/ml would yield too many colonies if 1 ml is plated.
- Dilution process starts by mixing 1 ml of the milk sample with 9 ml of water, reducing the concentration to 1,000 bacteria/ml.
- Further dilution (1 ml into 9 ml of water) reduces concentration to 100 bacteria/ml, yielding a countable number of colonies.
Pour Plates and Spread Plates
- Plate count methods include the pour plate and spread plate techniques for isolating colonies.
Pour Plates: Disadvantages
- Heat-sensitive microorganisms may be damaged during the melting of agar, failing to form colonies.
- Differential media may require distinct colony appearances on the surface, which is problematic in pour plates.
Filtration
- Employed when bacterial quantities are minimal, allowing for concentration and isolation of bacteria.
Physical Requirements: Temperature
- Psychrophiles: Grow optimally at -10°C to 20°C.
- Mesophiles: Thrive between 10°C to 50°C, optimal growth at 25°C to 40°C.
- Thermophiles: Prefer 40°C to 70°C with a peak around 50°C to 60°C.
- Psychrotrophs: Spoilage organisms, grow from 0°C to 30°C.
- Hyperthermophiles/Extreme Thermophiles: Optimal growth at 65°C to 110°C.
Physical Requirements: pH
- Most bacteria flourish at pH 6.5-7.5; very few survive below pH 4.
- Acidophiles: Remarkably tolerant to acidic conditions.
Physical Requirements: Osmotic Pressure
- High osmotic pressure can lead to plasmolysis, causing cell shrinkage due to water loss.
- Extreme Halophiles: Thrive in high salt concentrations, with some requiring it for growth.
Growth Curve: Bacterial Growth
- Defined as an increase in bacterial numbers rather than cell size, measured directly or indirectly.
Bacterial Division
- Binary Fission: The primary method of asexual reproduction, yielding two daughter cells.
- Budding: Asexual reproduction creating outgrowths or buds from mature cells; separation occurs when the bud reaches parent cell size.
Generation Time
- Refers to the time required for a cell to divide and for the population to double.
- Most bacteria have a generation time of 1-3 hours, while some species may take up to 24 hours.
Phases of Growth
- Bacterial growth is influenced by the nutritional environment, leading to an increase in cell numbers under suitable conditions.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your knowledge on the phases of cell growth and the significance of plate counts in microbiology. This quiz covers key concepts such as the lag, log, stationary, and decline phases of cell changes, as well as methods for measuring viable cells. Perfect for students studying microbiology or cellular biology.
