44 votes

Why isn't Fluorine, or Neon, the final electron acceptor in cellular respiration?

One of the main reasons that modern(!) biology uses oxygen as an electron acceptor is availability. Around 2.45 billion years ago, oxygen (O$_2$) started being built up in the atmosphere (which ...
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31 votes

Why isn't Fluorine, or Neon, the final electron acceptor in cellular respiration?

Availability and applicability. Availability. In the beginning, there was CO2. It was abundant in the atmosphere, and later, the oceans. Fluorine and neon weren't, and so respiration evolved around ...
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  • 546
29 votes
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Why is the Krebs cycle considered a part of aerobic metabolism if molecular oxygen is not involved in any of the reactions in the cycle

Oxygen is actually not needed in the Krebs cycle - it is needed in the electron transport chain that is downstream of the Krebs cycle to regenerate NAD+ from NADH. NAD+ is a co-enzyme and acts as an ...
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25 votes

Why don't we breathe nitrogen when it makes up most of the air?

Animals use oxygen as a chemical energy source because oxygen gas can react with many other compounds to form oxides, which releases energy and happen spontaneously. Both carbon and nitrogen can be ...
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19 votes
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Why don't we breathe nitrogen when it makes up most of the air?

I'd argue that we do "breathe" all those gases. Air that we inhale (at sea level) is about 78% N$_2$, 20.9% O$_2$, 1% argon, and smaller percentages of CO$_2$, neon, methane, etc. So all those gases ...
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14 votes

Why isn't Fluorine, or Neon, the final electron acceptor in cellular respiration?

The atomic radius of fluorine is just slightly larger than that of carbon. When a fluorine atom bonds to a carbon atom that is part of a carbon backbone, the fluorine atom covers up not only the C-F ...
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  • 501
13 votes
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Why does NAD+ become reduced if it gains a hydrogen proton?

You are correct that reduction is simply a gain of electrons. This results in a decrease in oxidation number. You know that NAD+ is reduced by this process because it starts off with a positive ...
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13 votes
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Why is ATP produced in photosynthesis used to synthesize glucose?

As far as I can understand your question, you wish to know why a plant cell consumes ATP to produce glucose when it can directly use the ATP as an energy molecule. ATP is an energy currency and is ...
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11 votes

What is the ultimate source of ADP/ATP in humans?

Phosphorus is a very common nutrient, found in high levels in proteins, which are in such foods as milk and milk products, meat, beans, lentils, nuts, and grains, especially whole grains. Phosphorus ...
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10 votes

Why is ATP synthase sometimes referred to as ATPase?

The way we were To understand why you may encounter ATP synthase referred to as ATPase, you need to be aware of the historical context — the experimental work that preceded the knowledge of the ...
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10 votes
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Is pyruvate considered a high energy molecule like ATP or NADH?

Summary Do not use the term ‘high-energy’ to refer to biochemical intermediates because many people (including the OP) do not understand what it is supposed to mean. However, if you insist in using it ...
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9 votes

What does the human body use oxygen for besides the final electron acceptor in the electron transport chain?

Another small addition There is class of oxidoreductases called oxygenases which incorporate molecular oxygen into the substrates and not just use it as an electron acceptor like in oxidases (note ...
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9 votes

How many molecules NADH are produced in the Krebs Cycle?

This is slightly depending on which reaction you want to include into the cycle. I count four: One when Pyruvate is converted to Acetyl-CoA, one when Isocitrate is converted to α-...
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9 votes

Why is carbon dioxide produced in alcohol fermentation but not in lactic acid fermentation?

Glycolysis needs a steady supply of NAD+ to happen - this is the driver for the anaerobic oxidation to lactate and ethanol, although this is energetically much less favorable than the complete ...
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9 votes

Why isn't Fluorine, or Neon, the final electron acceptor in cellular respiration?

Neon just does not work as an electron acceptor. It is that inert that there are currently no known Neon compounds at all. Fluorine would work in principle, but it is rare compared to oxygen and its ...
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7 votes

Why don't we breathe nitrogen when it makes up most of the air?

Nitrogen is much less reactive than oxygen. Indeed, if I haven't totally forgotten my long-ago chemistry courses, most chemical reactions involving N2 are energy-consuming. Thus you get nitrogen ...
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7 votes

Why is oxygen needed for the electron transfer phosphorylation?

Aren't there any other alternatives for this acceptor? Yes, there are multiple other acceptors used by anaerobic bacteria. Iron is probably the most common other acceptor used by a range of organisms ...
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7 votes
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Why is oxygen needed for the electron transfer phosphorylation?

Aren't there any other alternatives for this acceptor? Not that we're aware of. Every other alternative requires an anaerobic environment - which means small, and often less efficient. Oxygen is ...
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7 votes
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Violation of the law of energy conservation between photosynthesis and respiration?

The Fallacies in the argument The question contains two main fallacies (some would say sleights of hand) in the energetic comparison of glucose synthesis from CO2 in the Calvin cycle and glucose ...
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7 votes
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Why do zoologists classify sponges as animals rather than plants?

Organisms are classified, not by their behavior, but by their phylogeny (evolutionary relationships). Sponges have unique and complex molecules in their intracellular matrix that developed in a common ...
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  • 7,529
7 votes

How can the leakage of mitochondrial protons generate heat?

Uncoupling ATP synthesis from the ETC (electron transfer chain; this is where oxidation takes place) by thermogenin or any other method means that the energy used to generate or uphold the proton ...
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6 votes
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Membrane Permeability to Pyruvate

Pyruvate is negatively charged and quite polar, which makes it unfavourable to diffuse directly through any membrane. The outer mitochondrial membrane contains porins, which allow small molecules, ...
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6 votes
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Why don't protons diffuse out of the mitochondria during chemiosmosis?

Diffusion, is by definition (Ficks Law) describing movement along or against some gradient (here its concentration) even if the mechanism of transport differ: active, passive, facilitated. The setup ...
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  • 397
6 votes

How much oxygen does a plant use up at night?

Roughly, half of the CO2 assimilated annually through photosynthesis is released back to the atmosphere by plant respiration (Gifford, 1994; Amthor, 1995). Source: https://academic.oup.com/aob/...
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6 votes
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Facultative anaerobic organism

There are organisms with anaerobic metabolism that tolerate oxygen: aerotolerant anaerobes. "Anaerobic" refers to the metabolic system. You cannot be sure of oxygen tolerance based solely on ...
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6 votes
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ATP production via aerobic respiration

In short, the difference stems from different values regarding the number of ATP attributed to the electron carriers in the electron transport chain (ETC). My guess is that your class didn't go too ...
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5 votes
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Fermentation to acetic acid

There are some recipes available on the web, my answer is based on this webpage and this information: The process itself is rather easy and you can either use ready bought apple juice, homemade juice ...
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5 votes
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Mitochondria - are they really separate organisms that once merged into eukaryotic cells?

Yes. But it is incorrect to call mitochondria an organism now. Most of their genes were lost and are now encoded in the nuclear genome It gets most of its metabolites It is not known. See the other ...
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5 votes
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Cellular Respiration/Fermentation Problem Leading to Lack of Energy

Short answer (A) is a possible answer and is indeed cause for fatigue, as pyruvate is needed for the Krebs cycle to run. The krebs cycle is an essential step in the generation of ATP in aerobic ...
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5 votes
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If higher levels of atmospheric oxygen can lead to larger animals, can it also lead to larger plants?

Oxygen is good for animals because our basic metabolism is this: High energy carbon molecules + O2 → energy + H2O + CO2 Plants do that too at night, but during the day, they mostly do this: ...
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