So, I'm writing a sci-fi, and of course, my alien life forms have special breathing needs. I've already started writing, but it's bothering me that the biology of these little, evil creatures doesn't quite add up. I don't know if anyone here could help me, because it's actually quite complicated, but I figured I'd give it a shot. My big issue is that Mars' air composition has Argon, a high CO2 content, and a few other trace elements or compounds. I want their respiration to be a lot like a plant's. What's got me beat, is that there is absolutely NO hydrogen (or at least not a usable/detectable amount). For every kind of anaerobic respiration I've researched, Nitrogen Fixation and the like, I can't seem to get past the hydrogen issue. I've looked into Cyanobacteria and everything, and hydrogen is just destroying me here. I know I should probably be presenting this issue somewhere else, but I don't like going to other places, and trying can't hurt, right? Any suggestions (even for ways to completely avoid their respiratory problems) would be really appreciated. Thanks. =)
I was a chemist, not a biochemist, but I don't see any way to make it work as a CO2-based respiration, especially considering how thin Mars' atmosphere is to begin with. The CO2 system in plants isn't an energy-producing system, in any case. It's an energy storage system, where sunlight is the primary energy source. Plants then break down the stored sugars in the very same way animals do. So the lack of free oxygen, and water as well, precludes a high metabolism resembling that of terrestrial life. I think your biochemistry will have to be substantially different from anything on Earth, and may not depend much upon the atmosphere at all. Keep in mind that movement requires energy, so your chemical reactions need to release enough energy to power such movement, along with all the processes needed to maintain the reaction environment (homeostasis in earthbound biology). Does your life form need to be native to Mars? Could it be dormant, from a more hospitable environment, waiting for conditions that could sustain growth?
Being that I'm trying to base it somewhat around a plant's respiration system, I was focusing more on the dark reaction in photosynthesis than the light ones. I wanted the biochemistry to be somewhat similar to that of Earth's organisms simply because of the fictional history of the planet that I've concoted. (prosperous, other creatures, water, etc.) I wanted their respiration to almost emulate a plant's because they can survive without any food, only with what they create in their own bodies. And I know that in photosynthesis the hydrogen in water carries electrons to the ETC, where they re-enter the cycle, which, of course is the tricky spot. Yes, the creatures are Mars natives. They can also respire aerobically. They're somewhat dormant, because they create energy so slowly, so they can only move every so often. There are Earth creatures that need no oxygen, and undergo Nitrogen Fixation, but they need hydrogen as well. Essentially all I need is another electron carrier in the respiration cycle itself. Thank you for the imput. =)
As someone with a little biochemistry experience, I think I might be able to shed some light. Plants use aerobic respiration on the cellular level that is near identical to that of our own cells. This process is of course glycolysis and the Krebs cycle. However I believe what you are trying to refer to is the process by which plants are able to synthesize sugars and other macromolecules by using photons as energy, photosynthesis and the Calvin cycle. There are variants in photosynthesis techniques and permutations on the Calvin cycle to enhance its efficiencies, but I'll spare you the details. However one important fact is that the photosynthesis uses photons to convert water into gaseous oxygen and protons (H+). This hydrogen can then be used in macromolecules. However another question about your organism: Does it have an amino acid synthesis pathway(s) or an alternative to amino acids that can be used to form enzymes and structural macromolecules? Does it have DNA-like macromolecules? If you have any other questions you can PM me and I'll try to give you my best answer or at least point you in the right direction.
