MMBS111 Unit 3 Microbiology Study Guide – Step-by-Step Guidance

Q1. Explain the process of binary fission and explain how it differs from budding.

Background

Topic: Microbial Cell Division

This question tests your understanding of how prokaryotic cells (especially bacteria) reproduce, and how binary fission compares to budding, another form of asexual reproduction.

Key Terms:

• Binary fission: A method of asexual reproduction in which a cell divides into two genetically identical daughter cells.

• Budding: A form of asexual reproduction where a new organism develops from an outgrowth or bud due to cell division at one particular site.

Step-by-Step Guidance

1. Describe the main steps of binary fission in bacteria, including DNA replication, chromosome segregation, and cytokinesis.

2. Explain how the process ensures that each daughter cell receives a complete copy of the genome.

3. Contrast this with budding by describing how the new cell forms as an outgrowth from the parent cell, and how the size and genetic content of the offspring may differ.

4. Consider examples of organisms that use each method (e.g., most bacteria for binary fission, yeast for budding).

Try solving on your own before revealing the answer!

Final Answer:

Binary fission is a process where a bacterial cell duplicates its DNA, elongates, and divides into two equal daughter cells, each with identical genetic material. In contrast, budding involves the formation of a small bud on the parent cell, which grows and eventually detaches as a new organism; the bud may be smaller and sometimes genetically distinct due to uneven distribution of cytoplasmic contents. Most bacteria reproduce by binary fission, while some yeasts and a few bacteria reproduce by budding.

Q2. Which bacteria can use spores for asexual reproduction?

Background

Topic: Bacterial Reproduction and Survival Structures

This question focuses on which bacteria are capable of forming spores as a means of asexual reproduction and survival.

Key Terms:

• Spore: A resistant, dormant structure formed by some bacteria to survive harsh conditions.

• Asexual reproduction: Reproduction without the fusion of gametes, producing genetically identical offspring.

Step-by-Step Guidance

1. Recall which genera of bacteria are known for spore formation (think about Gram-positive rods).

2. Consider the difference between endospores (for survival) and reproductive spores (for propagation).

3. Identify examples of bacteria that use spores for reproduction, and note if this is common in bacteria or more typical in fungi.

Try solving on your own before revealing the answer!

Final Answer:

Some bacteria, such as those in the genera Bacillus and Clostridium, can form endospores, but these are primarily for survival, not reproduction. True asexual reproductive spores are rare in bacteria and more common in fungi; however, some actinomycetes (like Streptomyces) produce reproductive spores.

Q3. Outline the features of the four stages of bacterial growth in a closed batch system. Graph it out and describe what happens at each stage.

Background

Topic: Bacterial Growth Curve

This question tests your understanding of the classic bacterial growth curve in a closed system (like a flask or test tube), including the lag, log, stationary, and death phases.

Key Terms:

• Lag phase: Period of adaptation, no increase in cell number.

• Log (exponential) phase: Rapid cell division and population growth.

• Stationary phase: Growth rate slows; number of new cells equals number of dying cells.

• Death phase: Cells die at an exponential rate due to depletion of nutrients and accumulation of waste.

Step-by-Step Guidance

1. Draw a graph with time on the x-axis and number of viable cells (log scale) on the y-axis.

2. Label the four phases: lag, log, stationary, and death.

3. Describe what happens to the bacterial population in each phase, focusing on cell division, nutrient availability, and waste accumulation.

4. Explain why the transitions between phases occur (e.g., nutrient depletion, waste buildup).

Try solving on your own before revealing the answer!

Final Answer:

The four stages are: (1) Lag phase – cells adapt to the environment, no division; (2) Log phase – exponential growth and division; (3) Stationary phase – growth rate slows as nutrients deplete and waste accumulates; (4) Death phase – cells die faster than they divide. The graph is a sigmoidal curve with these phases clearly marked.

Q4. Explain why these four stages of growth might not occur in nature.

Background

Topic: Environmental Microbiology

This question asks you to consider how natural environments differ from laboratory batch cultures and how this affects bacterial growth patterns.

Key Concepts:

• Natural environments are open systems with fluctuating resources.

• Continuous input and removal of nutrients and waste.

Step-by-Step Guidance

1. Think about how nutrient availability and waste removal differ in nature compared to a closed system.

2. Consider environmental factors such as competition, predation, and changing conditions.

3. Explain why bacteria in nature may not experience clear-cut lag, log, stationary, and death phases.

Try solving on your own before revealing the answer!

Final Answer:

In nature, bacteria rarely experience the four distinct growth phases because resources and conditions are constantly changing, and there is often a continuous influx and removal of nutrients and waste. Environmental factors like competition, predation, and fluctuating conditions prevent the classic batch culture growth curve from occurring.

Q5. Describe psychrophiles, psychrotrophs, mesophiles, thermophiles, and extreme thermophiles. What are the temperature ranges they live in? Provide examples of each.

Background

Topic: Microbial Growth and Temperature Adaptation

This question tests your knowledge of how microbes are classified based on their preferred temperature ranges and examples of each group.

Key Terms:

• Psychrophiles: Cold-loving microbes.

• Psychrotrophs: Grow at low temperatures but have a broader range.

• Mesophiles: Prefer moderate temperatures.

• Thermophiles: Thrive at high temperatures.

• Extreme thermophiles: Grow at very high temperatures.

Step-by-Step Guidance

1. List the typical temperature ranges for each group (in °C).

2. Provide an example organism for each category (e.g., Pseudomonas for psychrotrophs).

3. Explain how their enzymes and cellular structures are adapted to their environments.

Try solving on your own before revealing the answer!

Final Answer:

Psychrophiles: -20°C to 10°C (e.g., Polaromonas vacuolata); Psychrotrophs: 0°C to 30°C (e.g., Listeria monocytogenes); Mesophiles: 20°C to 45°C (e.g., Escherichia coli); Thermophiles: 50°C to 60°C (e.g., Geobacillus stearothermophilus); Extreme thermophiles: 65°C to 120°C (e.g., Thermus aquaticus).