Which organism is not correctly matched to its energy source?

• A. Escherichia coli — uses glucose as an energy source
• B. Methanogens — use oxygen as an energy source
• C. Cyanobacteria — uses light as an energy source
• D. Nitrosomonas — uses ammonia as an energy source

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the types of organisms and their typical energy sources. Organisms can be classified based on their energy source as phototrophs (using light), chemotrophs (using chemical compounds), and further by their electron donors and carbon sources.
2. Step 2: Review each organism's known metabolism: Escherichia coli is a chemoheterotroph that commonly uses glucose as an energy source; Cyanobacteria are photoautotrophs that use light as an energy source; Nitrosomonas are chemolithoautotrophs that oxidize ammonia for energy.
3. Step 3: Analyze the statement about methanogens. Methanogens are a group of Archaea that produce methane and are obligate anaerobes, meaning they do not use oxygen as an energy source but rather obtain energy through the reduction of carbon compounds in anaerobic conditions.
4. Step 4: Identify the mismatch by comparing the energy source listed for methanogens (oxygen) with their actual metabolism (anaerobic methane production). This indicates the incorrect match.
5. Step 5: Conclude that the incorrect match is 'Methanogens — use oxygen as an energy source' because methanogens do not use oxygen but instead thrive in anaerobic environments.