Conceptual Links Between Respiration and Photosynthesis

Let’s consider some conceptual links between the processes of aerobic respiration and photosynthesis.

1. Both processes are built around the same reaction:

2. Both processes are built around membrane proteins.



Now, refer to these figures to spot the other links.

3. Both processes use several membrane protein complexes to couple electron transport along the membrane with proton transport through the membrane.

4. Both processes thus generate a proton gradient that is in turn used to run the ATP synthase.

5. Photosynthesis uses photons to generate high energy electrons while respiration strips high energy electrons from sugars (which were originally formed by reactions tied to photosynthesis).

6. Photosynthesis strips electrons from water to generate oxygen, while respiration donates the electrons to oxygen to form water.

7. Respiration strips electrons from an electron carrier, nicotinamide adenine dinucleotide (NADH):



while photosynthesis donates electrons to a closely related electron carrier, nicotinamide adenine dinucleotide phosphate (NADP):



8. Both processes use three basic protein complexes, with the same one occupying the central position – cytochrome bc1 and b6f.

9. Both process also use Coenzyme Q to transport electron from the first complex to the second.

10. In photosynthesis, the first complex uses photons to generate high energy electrons and couples this to stripping them from water; in respiration the first complex accepts high energy electrons from the electron carrier, NADH.

11. In photosynthesis, the last complex passes electrons to the electron carrier, NADP; in respiration, the last complex passes electrons to oxygen to form water.

12. Both respiration and photosynthesis are the only two established examples whereby endosymbiosis generated an organelle for eukaryotes – mitochondria and chloroplasts.

13. While neither respiration nor photosynthesis is essential for life, mitochondria made it possible to evolve animals and chloroplasts made it possible to evolve plants.

Oh my.

2 responses to “Conceptual Links Between Respiration and Photosynthesis

  1. So cows and bunnies r responsible for global warming😉

    There is a video I watched once that asked Harvard graduates if they knew how a piece of wood from a tree was creatred. Some said dirt… yeah… they did.. nutrients, others said photosynthesis… oy vey….

    None could answer… and these are our brightest.

    I know u won’t agree Michael. But I tend to think the terraforming of earth was very rapid. I’m still not convinced of macro-evolution even with FL. Programmatically, FL makes more sense with variation on the edges.

    But what we observe today is rapid…

    If I were some intelligent agent… why wouldn’t I terraform with fully functional seedlings and lifeforms? Why would I wait a billion years or more for any kind of evolution, FL or not?

  2. Francois Savard

    A beautiful pair of reactions. The reverse similarity between them might speak of a common evolutionary origin?

    On another level, the ancient biologist and philosopher Aristotle would have been delighted with modern biochemistry, including these two reactions. He would have described it in terms of his doctrine of matter and form – radical principles of determinability and determination. In this sense, he might have honed in on the electron: in electronic orbitals, we have the radical indeterminacy of prime matter coming through in the indeterminate location of the electron; and we have the determination of substantial form coming through in the specific shape and size of the various orbitals. He would have had interesting things to say about the electron transfer chain. Lovely stuff. Long live biochemistry, long live Aristotle!

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