# Do plants photosynthesize all the time?



## epicfish (Sep 11, 2006)

Yes, they do.

Remember that pearling occurs when the water is saturated with oxygen. I bet you that in the morning hours, the plants are still producing oxygen, but all the oxygen that is being produced is dissolved in the water. Hours later, the water becomes saturated and the oxygen is released in gaseous form.

However, I do have plants that pearl soon after my lights go on, and I'm assuming its because of oxygen saturation only in the region closest to the leaves, not throughout the entire tank.

Let's wait for Barr to chime in.


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## stagius (Nov 26, 2007)

plant only do photosynthesize when there is the presence of light.
Light is used as a form of energy to convert from CO2 to glucose. Glucose is then stored in plant cell. O2 is just a step before where H2O give up proton H+, resulting O2.

At night, when there is no light, plant use glucose to grown, where cell respiration, replication occur.


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## JSCOOK (Jan 7, 2008)

stagius said:


> plant only do photosynthesize when there is the presence of light.
> Light is used as a form of energy to convert from CO2 to glucose. Glucose is then stored in plant cell. O2 is just a step before where H2O give up proton H+, resulting O2.
> 
> At night, when there is no light, plant use glucose to grown, where cell respiration, replication occur.


I'll 2nd that ...


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## epicfish (Sep 11, 2006)

stagius said:


> plant only do photosynthesize when there is the presence of light.
> Light is used as a form of energy to convert from CO2 to glucose. Glucose is then stored in plant cell. O2 is just a step before where H2O give up proton H+, resulting O2.
> 
> At night, when there is no light, plant use glucose to grown, where cell respiration, replication occur.





JSCOOK said:


> I'll 2nd that ...



Not completely true. Light is used to create ATP + NADPH, precursors to the Calvin-Benson cycle. This cycle CAN operate in the dark. The Calvin-Benson cycle is actually where glucose production actually occurs.


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## dr.tran (Oct 8, 2007)

Also plants use the ATP at all times of the day. They can even grow during daytime. 

Hence they can use glucose at all times of the day.


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## mistergreen (Dec 9, 2006)

epicfish said:


> Yes, they do.
> 
> Remember that pearling occurs when the water is saturated with oxygen. I bet you that in the morning hours, the plants are still producing oxygen, but all the oxygen that is being produced is dissolved in the water. Hours later, the water becomes saturated and the oxygen is released in gaseous form.


Ah, interesting point.


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## Kayakbabe (Sep 4, 2005)

Plants only photosynthesis during light (photo = light)
But they do use CO2 both in the dark and the light. Just more so in the light.


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## plantbrain (Dec 15, 2003)

epicfish said:


> Not completely true. Light is used to create ATP + NADPH, precursors to the Calvin-Benson cycle. This cycle CAN operate in the dark. The Calvin-Benson cycle is actually where glucose production actually occurs.


You still need light for this to occur.:thumbsup: 
So the process of photosynthesis is still light driven ultimately.
The CB cycle is called the "dark" reactions but it still needs light to operate and run correctly.

O2 production is a sealed chamber aqueous shows how the Carbon is used and is what Calvin used with 14CO2. I also am using 14CO2 for my own research. 

If you do not resupply NADPH and ATP, the process of photosynthesis slows down and finally stops.

The plant has plenty of NADPH and ATP resupplied from all the reduced sugars/starch, sorbitol, mannitol etc to make it through the night or several days, weeks, months or year depending on the plant and or storage organ.

So like fat on us, it has plenty of back up.
The sun need not shine 24/7.

But they do respire(all the time), just like us, and we use ATP and NADP as well.

Regards, 
Tom Barr






Regards, 
Tom Barr


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## Kayakbabe (Sep 4, 2005)

The answer is NO. They only photosynthesis during light exposure. However, they do always have chemical reactions go on to keep them alive.

Here's a brief rundown:

Lights come on:
*Photosynthesis starts..*
The light energy is absorbed by the chlorphyl (green stuff) in the plant. cholorphyll can only hold so much energy before it starts to release it. It's kinda like an energy sponge. When it get's full.. that energy has to go somewhere. It goes to make ATP.

*
Plant makes ATP* ATP is basically an really available energy storage form. A plant will convert ATP to ADP and back and forth. ATP->ADP releases energy so the plant can do other chemical reactoins. ADP->ATP stores energy if some chemical reaction releases it. If it wasn't stored, it would remain as heat and the plant doesn't want to cook itself during the processes it needs just to grow and maintain life. Also 'why waste' energy, if you can save it and reuse it.. that is so much more efficient.

*Plant makes NADPH2*
The pearling is caused by breaking up a water molecule to get the two Hydrogens in order to make NADPH2. The oxygen molecules attract to each other to form O2 gas. The plant doesn't want to explode so it lets the O2 out of it's stomas (leave openings). The O2 dissolves into the water pretty fast, When lots of O2 is dissolved into your tank water, the O2 will form bubbles since it can't dissolve anymore.. that's pearling. So there is a time lag between when O2 starts forming and when you actually see pearling. 

The NADPH2 is used to make a lot of the more complex chemicals a plant needs. 

*here comes the CO2*
CO2 is brought in through the stroma (leafe openings) and in some complicated chemical stuff, the NADPH2 gives up it's Hydrogens. This forms glucose. That leaves NADP. The glucose can be added to in order to form more complex storage energy forms like startch or things that get stored away in tubers and rhizomes or in leaves. Or it can even be used later as an energy source.

*Lights go off*

The chemical processes that happened in the light will chug on for a while until most of the ATP made during "lights on" is used up. Since light isn't adding more easy energy to the plant. and the ATP can't be made easily anymore... the plant starts to do other things to make the energy it needs to live. The plant will still make ATP. But it has to get it in not so easy ways.
The next process is called respiration.

*Respiration takes over*

There are two ways a plant can respire. Both use the glucose (and other energy storage forms) made easily in the light. One way gives the plant a lot of energy and one way gives the plant just a little.

*Aerobic Respiration*
The lots of energy method actually uses Oxygen! Most of us never think about plants using oxygen. But they do in the dark. This method is called Aerobic respiration. This is a way to create ATP.

*Anerobic Respiration*
Here is the funny thing. The less energy method doesn't use O2 and is called Anerobic respiration. IN this process the plant will actually create Carbon Dioxide! Yes in the dark your planted tank plants actually give off CO2! This is an expensive way to create ATP. This process also gives off water as a by product.

*Overall*

The plant will still try to do what it needs in order to keep it's chemical processes working, but with light energy input, it can do it faster and use chemical reactions that require high energy. 

Photosynthesis which happens in the the cholorplasts (green stuff) can be thought of as solar cells. Photosynthesis converts light energy into energy a plant can use. (for us humans solar cells convert light energy into electricity for our gadets to use).

The chemical reactions that the high energy of light can give... allow the plant to give off Oxygen gas as a by product (pearling).

Without the high energy of light, the plant will go elsewhere to get it's energy for living. Those processes, give off Carbon Dioxide (CO2) and water as by products.

I think I got this right... IF you want more details, google on photosynthesis, calvin cycle, citric acid cycle, glycolosis, and Kreb's cycle. Those are all part of this huge chain of events from light to dark and back to light again in a plant.

Tom Barr does point out something that most of us forget. Respiration goes on all the time, in the dark and the light. The quick energy input by light though.. only occurs in the light.


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## teban (Feb 2, 2006)

very interesting facts stated here. Though with much of my understanding with kayakbabe's post. does this mean that extending the photoperiods (light exposure) actually give additional benefit or growth to our plants? 

the theory or hypothesis i really believed in before was that plants need "night time" in order to grow but it seems to be opposite in this post.


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## josh1604 (Mar 31, 2008)

Plants can only photosynthsize when in the presence of light photosynthesis is taking light enery along with CO2 and water and producing glucose and oxygen, 

light+6Co2+6h2o = c6h12o6(glucose) and 6o2

this is the reaction of photosynthesis 

it takes light six co2 and 6 waters produce one glucose molucule and six oxygen molecules

and to answer you last question i believe that if you want you plants to photosytesize properly you need to keep the co2 on as long as the lights are on

very nice kayakbabe very well described i know how confusing it came be as i am a biology major and you did as very good job describing it


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## ikuzo (Jul 11, 2006)

those detailed informations made me research. here's a good read :
http://en.wikipedia.org/wiki/Photosynthesis


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## josh1604 (Mar 31, 2008)

i forgot to post this in my other post, no leaving yuor lights on all the time is not good for your tank it can lead to algae problems you deffinetly need to have a night time


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## Naja002 (Oct 12, 2005)

Ok, I've read the thread and I basically understand what's been said, but it still leaves me with mistergreen's original question:




mistergreen said:


> Assuming there's light, CO2, and nutrients, *do they photosynthesize from the moment the light is on to the time the light is off?*


Emphasis added.


Here's is part of a post that I made a few days ago:




Naja002 said:


> First, plants have a basic schedule. Not "by the clock" or "time of day", but measured more in "hours". In short, after ~10hrs of photosynthesizing they are pretty much ready to close up shop for the day and start using the food (energy) that they made. So, lighting after ~10hrs is pretty much useless as far as the plants are concerned. But algae loves the extra light.....!


 Longer periods of lighting 

That's become my basic understanding from hanging around the forums--after ~10hrs the plants close up shop for the day. Observation indicates the same on many plants (leaves folding up). Is this correct? Not?

Thanx! :thumbsup:


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## mistergreen (Dec 9, 2006)

yeah, I got a lot of response to what photosynthesis is which we know but the time issue was kinda left unanswered. I think the people who study this know best.


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