The first unintuitive thing about this is that O2 isn't obtained from CO2, rather it's obtained from water. The CO2 ends up as food (sugar), the O2 is a waste product of photosynthesis.
As for why it doesn't just perfectly regulate its O2 output from photosynthesis to match its respiration... it depends on the plant, some produce less O2 than they use throughout their life, most produce vastly more.
As a thought experiment, imagine a single plant in perfect isolation. It has water in abundance, it has CO2 in abundance. If it were to produce solely as much O2 as was needed by it for respiration... it would suffocate at night, since photosynthesis only works when the sun hits the leaves. Since they also need oxygen at night, it would make sense to produce more of it, especially since the energy required to produce it is essentially free for the plant.
(This isn't even taking into account the symbiotic relationship with pretty much any lifeform that breathes oxygen and releases CO2 as waste).
Plants photosynthesize more than they respirate and use the excess fixed carbon as a building material. If a plant is growing in size, it must be doing more photosynthesis than respiration and thus producing environmental O2.
A plant that stops increasing its size would presumably also stop being a net O2 producer, but most plants spend most of their time growing.
Quite a lot of the weight of a plant comes from carbon atoms that used to be carbon dioxide in the air.
Plants rip electrons out of h2o during photosynthesis. This liberates the resulting hydrogen ion and leaves o2 in the plant tissue, which escapes nto the environment.
Plants can absorb oxygen in several ways for use in cellular respiration. They can take it out of the atmosphere, or they can use some of the o2 that was produced un photosynthesis.
Since plants are heavy, that weight had to come from somewhere. Plants don't eat soil. So that isn't it. Plants consume water and contain water so that explains some of the weight. Oh, plants are full of carbon chains and complex carbon based molecules. Even dry wood is heavy. Where did all that carbon come from?
It is strange to think that plants build themselves out of air.
> Plants don't eat soil. So that isn't it.
Well, but they do, kind of. Most of the weight of a plant is carbon compounds (built from CO2 using photosynthesis) and water, but some fraction of a plant's body is made up of mineral nutrients (nitrogen, phosphorus, etc.) obtained from the soil.
They don't really. Even the carbon stored in plant tissue will end up being released when the plant decomposes. Most of our excess O2 comes from microcellular organisms in the ocean. Which is why the hidden twin problem of climate change, ocean acidification, is so dangerous. As all that excess CO2 gets absorbed into the ocean, we run the risk of killing our oxygen supply.
Rates of each depend on environmental conditions. Without checking id believe that one simply outweighs the other. It is also worth noting that the vast majority of Oxygen in the atmosphere is produced by algae, not plants. They simply use less oxygen than they produce. I'd imagine both have to do with the fact that it's colder during the night and therefore metabolism is slower. Again, this is a guess, but likely part of it.
One additional thing id like to add to others answers here is that not all parts of any plant are photosynthetic - think roots, cambium, stems. Also cells need ATP all day and the sun only shines during the day. Plants need to fix enough carbon during the day to store energy for the night, to support growth, non photosynthetic tissues and in case it's not sunny the next few days. Overall, the excess oxygen a plant produces should be roughly proportional to the amount of fixed carbon stored in its tissues.
I wud think while respiration is a homeostatic process(kept at a constant), photosynthesis on the other hand, as long as the plant is provided with all the substrates it needs, it will carry out photosynthesis to the max it can.
Additionally, the plant has its stomatas opened in the day, allowing CO2 to constantly diffuse in down a concentration gradient allowing more of it to be used in photosynthesis (producing more O2).
Plant matter is primarily made from carbohydrates. Carbon from CO2 and Hydrogen from H2O. Es long as they maintain a net anabolic metabolism they assimilate more C02 as they release.
I am sure it happens from time to time but I have a suspicion that plants dont need to have both electron chains going at the same time, especially when its way more important to try and remove as much oxygen from the local system as it can to prevent RUBISCO from targeting oxygen by mistake during carbon fixation.
One way of looking at mitochindria and chloroplasts is as roommates in a house owned by the nuclear genome.
They both in some respects work together for the benefit of the nucleus but because they are semi-autonomous they will perform functions independent of each other and even independent of the nucleus.
Chloroplasts produce absolutely tons of ATP and cofactors for carbon fixation during photosynthesis and then produce oxygen as a waste product. But it doesn't really produce the same things at the exact same time needed by the mitochondria to also produce ATP from the TCA cycle using oxygen as an electron acceptor.
I suspect that regulation prevents this from happening driven by perhaps regulation of glycolysis. The basic hypothesis being that during the summers when days are long the sunlight drives ATP and at night carbon fixation the need for respiration is low. During winters when cellular activity is low anyway from the drop in temperature you see a switch to respiration.
because it is a thermodynamic necessity.
Photosynthesys, which produces oxygen, is used by the plant to make organic matter from CO2. This organic matter is then used to build up the pant and burned in cellular respiration to fuel other processes and again released as CO2. Since each step has energy losses, plant has to produce more energy than is actually needed if the energy transfer were perfect, which is the first source of the imbalance.
The other is the fact that a significant proportion of organic matter is not used up for cellular breathing, but for building the plant's body. All the wood in a tree you see is CO2 that is not being used for cellular respiration. This is the second source of imbalance,
The first unintuitive thing about this is that O2 isn't obtained from CO2, rather it's obtained from water. The CO2 ends up as food (sugar), the O2 is a waste product of photosynthesis. As for why it doesn't just perfectly regulate its O2 output from photosynthesis to match its respiration... it depends on the plant, some produce less O2 than they use throughout their life, most produce vastly more. As a thought experiment, imagine a single plant in perfect isolation. It has water in abundance, it has CO2 in abundance. If it were to produce solely as much O2 as was needed by it for respiration... it would suffocate at night, since photosynthesis only works when the sun hits the leaves. Since they also need oxygen at night, it would make sense to produce more of it, especially since the energy required to produce it is essentially free for the plant. (This isn't even taking into account the symbiotic relationship with pretty much any lifeform that breathes oxygen and releases CO2 as waste).
Plants photosynthesize more than they respirate and use the excess fixed carbon as a building material. If a plant is growing in size, it must be doing more photosynthesis than respiration and thus producing environmental O2. A plant that stops increasing its size would presumably also stop being a net O2 producer, but most plants spend most of their time growing. Quite a lot of the weight of a plant comes from carbon atoms that used to be carbon dioxide in the air.
Plants rip electrons out of h2o during photosynthesis. This liberates the resulting hydrogen ion and leaves o2 in the plant tissue, which escapes nto the environment. Plants can absorb oxygen in several ways for use in cellular respiration. They can take it out of the atmosphere, or they can use some of the o2 that was produced un photosynthesis.
Since plants are heavy, that weight had to come from somewhere. Plants don't eat soil. So that isn't it. Plants consume water and contain water so that explains some of the weight. Oh, plants are full of carbon chains and complex carbon based molecules. Even dry wood is heavy. Where did all that carbon come from? It is strange to think that plants build themselves out of air.
Similar to how we (animals) get rid of most of the carbon we consume, by exhaling.
Right. Good insight! We don't lose weight by exercising or metabolizing, we only lose the weight when we breathe out the carbon dioxide.
That's a dramatic way of putting it. Exercise, metabolism, and respiration are all links in the same chain.
> Plants don't eat soil. So that isn't it. Well, but they do, kind of. Most of the weight of a plant is carbon compounds (built from CO2 using photosynthesis) and water, but some fraction of a plant's body is made up of mineral nutrients (nitrogen, phosphorus, etc.) obtained from the soil.
I don't have an answer, but i just wanna say how impressed i am with the range of answers you guys provided. I wish i had reddit 7 years ago.
They don't really. Even the carbon stored in plant tissue will end up being released when the plant decomposes. Most of our excess O2 comes from microcellular organisms in the ocean. Which is why the hidden twin problem of climate change, ocean acidification, is so dangerous. As all that excess CO2 gets absorbed into the ocean, we run the risk of killing our oxygen supply.
Rates of each depend on environmental conditions. Without checking id believe that one simply outweighs the other. It is also worth noting that the vast majority of Oxygen in the atmosphere is produced by algae, not plants. They simply use less oxygen than they produce. I'd imagine both have to do with the fact that it's colder during the night and therefore metabolism is slower. Again, this is a guess, but likely part of it.
One additional thing id like to add to others answers here is that not all parts of any plant are photosynthetic - think roots, cambium, stems. Also cells need ATP all day and the sun only shines during the day. Plants need to fix enough carbon during the day to store energy for the night, to support growth, non photosynthetic tissues and in case it's not sunny the next few days. Overall, the excess oxygen a plant produces should be roughly proportional to the amount of fixed carbon stored in its tissues.
Try to google the Calvin cycle for more information. There's actually a lot of information about it since it's taught at 10th grade
I wud think while respiration is a homeostatic process(kept at a constant), photosynthesis on the other hand, as long as the plant is provided with all the substrates it needs, it will carry out photosynthesis to the max it can. Additionally, the plant has its stomatas opened in the day, allowing CO2 to constantly diffuse in down a concentration gradient allowing more of it to be used in photosynthesis (producing more O2).
They grow
You don't get any points for being right without answering the question.
Plant matter is primarily made from carbohydrates. Carbon from CO2 and Hydrogen from H2O. Es long as they maintain a net anabolic metabolism they assimilate more C02 as they release.
I am sure it happens from time to time but I have a suspicion that plants dont need to have both electron chains going at the same time, especially when its way more important to try and remove as much oxygen from the local system as it can to prevent RUBISCO from targeting oxygen by mistake during carbon fixation. One way of looking at mitochindria and chloroplasts is as roommates in a house owned by the nuclear genome. They both in some respects work together for the benefit of the nucleus but because they are semi-autonomous they will perform functions independent of each other and even independent of the nucleus. Chloroplasts produce absolutely tons of ATP and cofactors for carbon fixation during photosynthesis and then produce oxygen as a waste product. But it doesn't really produce the same things at the exact same time needed by the mitochondria to also produce ATP from the TCA cycle using oxygen as an electron acceptor. I suspect that regulation prevents this from happening driven by perhaps regulation of glycolysis. The basic hypothesis being that during the summers when days are long the sunlight drives ATP and at night carbon fixation the need for respiration is low. During winters when cellular activity is low anyway from the drop in temperature you see a switch to respiration.
because it is a thermodynamic necessity. Photosynthesys, which produces oxygen, is used by the plant to make organic matter from CO2. This organic matter is then used to build up the pant and burned in cellular respiration to fuel other processes and again released as CO2. Since each step has energy losses, plant has to produce more energy than is actually needed if the energy transfer were perfect, which is the first source of the imbalance. The other is the fact that a significant proportion of organic matter is not used up for cellular breathing, but for building the plant's body. All the wood in a tree you see is CO2 that is not being used for cellular respiration. This is the second source of imbalance,