Metabolic Diversity: Choosing an Electron Donor and Acceptor
Microbes are classified by where they get carbon, where they get energy and what they pass electrons to at the end. The energy available depends on the gap between donor and acceptor, which is why oxygen respirers outgrow the alternatives when oxygen is present.
What a learner can do afterwards
- Classifies an organism from its carbon source, energy source and terminal acceptor.
- Ranks acceptors by the energy yield they allow and explains the ranking.
- Predicts which metabolism dominates as a sediment loses oxygen with depth.
1 · Read
Imagine sorting microbes the way you sort lunchboxes. Ask where carbon comes from: air gas or ready made organics. Ask where energy comes from: light or chemicals. Then ask what catches electrons at the end. Those three answers fix the lifestyle completely.
Now rank the catchers the way athletes rank medals. Oxygen accepts most willingly, then nitrate, then sulfate and carbon dioxide last. The wider the gap between giver and catcher, the more energy each fuel molecule banks. That sliding scale is why oxygen users outgrow the rest wherever oxygen reaches.
Picture the mud under a pond sorted by depth for you. Near the top the oxygen users grow fastest on the full payoff. Below them come the nitrate users, and deep down in the oxygen free dark sit the sulfate breathers and methane makers. Read the oxygen profile and you predict the stack.
Two small extras complete your map. Without an outside catcher, cells dump electrons back onto their own waste just to keep going, and most fuel energy stays locked inside: tiny yield. With a catcher, electron flow pumps a gradient whose return through the synthase mints the energy coins.
You read the carbon, energy, and final catcher to predict who wins each layer.
2 · Watch
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Where it sits
Learn first
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.