Metabolic Diversity in Microorganisms – Study Guide Walkthrough

Q1. Describe each type of microorganism. Be able to classify a microorganism into one of the four groups based on a description of the microorganism’s energy source and carbon source: Chemoheterotrophs, Chemoautotrophs, Photoautotrophs, Photoheterotrophs.

Background

Topic: Microbial Metabolism and Classification

This question tests your understanding of how microorganisms are classified based on their energy and carbon sources. This is a foundational concept in microbiology, especially for understanding microbial ecology and physiology.

Key Terms and Concepts:

• Energy source: The way a microorganism obtains energy (light or chemicals).

• Carbon source: The source of carbon for building cellular material (CO2 or organic compounds).

• Chemo-: Uses chemical compounds for energy.

• Photo-: Uses light for energy.

• -autotroph: Uses CO2 as a carbon source.

• -heterotroph: Uses organic compounds as a carbon source.

Step-by-Step Guidance

1. Recall the two main ways microorganisms obtain energy: from light (phototrophs) or from chemicals (chemotrophs).

2. Recall the two main ways microorganisms obtain carbon: from inorganic sources like CO2 (autotrophs) or from organic compounds (heterotrophs).

3. Combine these prefixes and suffixes to define each group:

   • Chemoheterotroph: chemical energy, organic carbon

   • Chemoautotroph: chemical energy, CO2 carbon

   • Photoautotroph: light energy, CO2 carbon

   • Photoheterotroph: light energy, organic carbon

4. Practice classifying a microorganism if given its energy and carbon source. For example, if a microbe uses light for energy and organic compounds for carbon, which group does it belong to?

Try classifying some example microbes on your own before checking the answers!

Q2. In which group of the four groups above would you find most of the medically important microbes?

Background

Topic: Medical Microbiology and Microbial Nutrition

This question asks you to connect metabolic classification to the types of microbes that are relevant in medicine, such as pathogens.

Key Terms:

• Medically important microbes: Microorganisms that cause disease or are relevant to human health.

• Review the definitions from the previous question.

Step-by-Step Guidance

1. Recall that most pathogens live in or on humans and must obtain both energy and carbon from their host.

2. Consider which metabolic group uses organic compounds for both energy and carbon, as these are abundant in living tissues.

3. Think about why this metabolic strategy is advantageous for microbes living in animal hosts.

Try to identify the group before checking the answer!

Q3. What are examples of final electron acceptors used by the various groups of chemoheterotrophs?

Background

Topic: Microbial Respiration and Metabolism

This question focuses on the diversity of metabolic pathways in chemoheterotrophs, specifically the molecules they use as final electron acceptors during energy production.

Key Terms and Concepts:

• Final electron acceptor: The molecule that receives electrons at the end of an electron transport chain.

• Aerobic respiration: Uses oxygen as the final electron acceptor.

• Anaerobic respiration: Uses other molecules (e.g., nitrate, sulfate) as final electron acceptors.

• Fermentation: Uses organic molecules as final electron acceptors.

Step-by-Step Guidance

1. Recall the difference between aerobic and anaerobic respiration in chemoheterotrophs.

2. List common final electron acceptors for aerobic respiration (think about what humans use).

3. List alternative final electron acceptors for anaerobic respiration (think about environments lacking oxygen).

4. Consider what happens during fermentation and what types of molecules serve as electron acceptors in this process.

Try listing examples for each type before checking the answer!

Q4. How might you classify microbes that survive underground in rocks with little or no access to organic material?

Background

Topic: Environmental Microbiology and Metabolic Adaptation

This question asks you to apply your knowledge of metabolic diversity to extreme environments, such as deep subsurface habitats.

Key Terms:

• Organic material: Compounds containing carbon-hydrogen bonds, typically from living organisms.

• Inorganic compounds: Compounds not containing carbon-hydrogen bonds (e.g., CO2, minerals).

Step-by-Step Guidance

1. Consider what sources of energy and carbon are available in deep underground environments (e.g., rocks, minerals, CO2).

2. Recall which metabolic groups can use inorganic compounds for energy and/or carbon.

3. Think about which group(s) would be best adapted to environments with little or no organic material.

Try to classify these microbes before checking the answer!

Q5. Background vocabulary to know and understand: Chemotroph, Phototroph, Oxygenic, Anoxygenic, Energy source, Carbon source, Final electron acceptor.

Background

Topic: Microbial Metabolic Terminology

This section is about mastering key vocabulary that will help you understand and answer questions about microbial metabolism.

Key Terms and Definitions:

• Chemotroph: Organism that obtains energy from chemical compounds.

• Phototroph: Organism that obtains energy from light.

• Oxygenic: Produces oxygen (usually during photosynthesis).

• Anoxygenic: Does not produce oxygen (during photosynthesis or other processes).

• Energy source: The source from which an organism derives energy (light or chemicals).

• Carbon source: The source from which an organism obtains carbon (CO2 or organic compounds).

• Final electron acceptor: The molecule that receives electrons at the end of an electron transport chain.

Try to write out your own definitions and examples for each term before checking the answer!