Is the oxygen exhaled by plants during the day compensated by inhalation of carbon dioxide at night?
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$\begingroup$ Green-plant respirate (O2 ---> CO2 ) throughout day and night. But the total rate of photosynthesis (that happens only at day) throughout world is so greater than respiration of animals+plants for (day+night) is so grater, that CO2 can't accumulate. speed of photosynthesis is greater than the plant's own respiration otherwise it could not be able to accumulate foods and grow. $\endgroup$– user25568Commented Sep 11, 2016 at 9:20
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$\begingroup$ The confusion takes place because it is not about stoichiometry (chemical arithmetic) or balance; but it is about reaction-rate (speed) with time. $\endgroup$– user25568Commented Sep 11, 2016 at 9:23
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$\begingroup$ In night, the plant do-not intake any CO2. You can consider them like animals when it is night. $\endgroup$– user25568Commented Sep 11, 2016 at 9:27
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$\begingroup$ Are you confused about "dark-phase" of photosynthesis (where CO2) is taken? The term is misleading and another synonym for it is "light independent phase". All school-textbook on photosynthesis-chapter; mentions it so-far I can recall. $\endgroup$– user25568Commented Sep 11, 2016 at 9:29
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$\begingroup$ If you block the light; there would be a deficit of pre-requisit-compounds for another-phase (so-called dark-phase). So with turning off light, within very short, momentary time the dark-phase stops. Dark-phase (light-independent phase) though indirectly, dependent on light. $\endgroup$– user25568Commented Sep 11, 2016 at 9:33
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2 Answers
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All green plants do Photosynthesis as well as Respiration.
Plants respire during the day and night, but they only photosynthesis during the day when it is light: there is equations for aerobic respiration and photosynthesis:
C6H12O6 + 6O2 → 6CO2 + 6H2O (aerobic respiration)
6CO2 + 6H2O → C6H12O6 + 6O2 (photosynthesis)
In terms of reactants and products, they are the reverse of each other. In terms of gas exchange:
Process -------Carbon dioxide -----------------Oxygen
Respiration -----------Out ---------------------------- In
Photosynthesis -------In ---------------------------- Out
Photosynthesis is only in the presence of Sunlight . So it occurs only during the day .
For photosynthesis they require Carbon Dioxide gas ( CO2 gas )
This gas enters the leaves through tiny pores on them called stomata .
The byproduct of photosynthesis is Oxygen gas ( O2 gas )
It is either passes out through the same stomata OR used for respiration
For respiration they require O2 gas . It enters the leaves through the same pores or stomata .
The by product of respiration is CO2 gas .
During day time it is immediately used for photosynthesis .
During night time the CO2 gas is released in the atmosphere
Net gas exchange
The net (overall) effect depends on the time of day and the light intensity. Photosynthesis doesn’t occur at night. When there is no photosynthesis, there is a net release of carbon dioxide and a net uptake of oxygen.
If there is enough light during the day, then:
the rate of photosynthesis is higher than the rate of respiration
there is a net release of oxygen and a net uptake of carbon dioxide
(consider CAM plants)
in a plant using full CAM, the stomata in the leaves remain shut during the day to reduce evapotranspiration, but open at night to collect carbon dioxide (CO2)
https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism#During_the_night
this link help you understand the process better by simple language :
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It's impossible for a plant to use more oxygen in the long term. As @BlueFoxy explained, whenever a plant is using oxygen it is to oxidise sugar ($C_6H_{12}O_6$). These sugars were made by the plant itself using $CO_2$, $H_2O$ and sunlight, so it can't oxidise more sugar than it produced in the first place.
If the plant is growing then some of the carbon removed from $CO_2$ will be used to form the plant's tissues, causing a net increase in oxygen in the atmosphere. If the plant isn't growing it'll probably be oxygen neutral.
There are probably some weird parasitic plants that break this pattern by stealing other plants' carbon, but in general the rule holds.
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1$\begingroup$ "There are probably some weird parasitic plants that break this pattern by stealing other plants' carbon" - Monotropha uniflora is parasitic on mycorrhizal fungi, so does this indirectly. $\endgroup$ Commented Sep 5, 2016 at 10:46
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1$\begingroup$ @arboviral Cuscuta reflexa or anysuch parasitic plant would be more direct example because they donot require mediators like mycorrhizal fungi. $\endgroup$– user25568Commented Sep 11, 2016 at 9:42
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1$\begingroup$ @AlwaysConfused good catch - I'd forgotten about dodder. However, Cuscuta reflexa can actually photosynthesize a bit; a species which is thought to be entirely dependent on the host plants for nutrition such as C. europaea would be an even better example. $\endgroup$ Commented Sep 11, 2016 at 19:05
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$\begingroup$ @arboviral Thanks I did not knew C. reflexa can do little amount of photosynthesis. Great info! $\endgroup$– user25568Commented Dec 21, 2016 at 16:43