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Author Topic: Does photosynthesis increase the earth's mass?  (Read 4676 times)

Offline Kharposht

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Does photosynthesis increase the earth's mass?
« on: 30/08/2007 13:24:04 »
Hi, Iím a bit confused, can any one help Ė

Plants use light energy to grow. I believe that this means that some of the energy of the incident photons is absorbed by the plantís pigments, and the rest comes out of the plant as green light.

The plant uses the absorbed energy to synthesise sugars from CO2 and water that it uses to grow, and it thus increases its mass.

 So, my question is, If they are absorbing somthing from the sun,
does photosynthesis directly increase the mass of the earth through photon absorption or does light only act as a catalyst for changing mass that already exists from one substance into another?


 

Offline lightarrow

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Does photosynthesis increase the earth's mass?
« Reply #1 on: 30/08/2007 20:15:02 »
Hi, Iím a bit confused, can any one help Ė

Plants use light energy to grow. I believe that this means that some of the energy of the incident photons is absorbed by the plantís pigments, and the rest comes out of the plant as green light.

The plant uses the absorbed energy to synthesise sugars from CO2 and water that it uses to grow, and it thus increases its mass.

 So, my question is, If they are absorbing somthing from the sun,
does photosynthesis directly increase the mass of the earth through photon absorption or does light only act as a catalyst for changing mass that already exists from one substance into another?
The absorption of energy is converted into mass.
 

Offline Soul Surfer

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Does photosynthesis increase the earth's mass?
« Reply #2 on: 31/08/2007 09:37:31 »
No there is no effective net change in mass.  Photons in their own right are massless and consist of energy.  In absorbing them photosynthesis converts the light energy into chemical bond energies and other photons of lower energy in the form of heat.  this heat is eventually radiated back into space.  (except for the tiny bit that contributers to global warming).  The chemical bond energies are eventually broken down to make more photons (and eventually radiated as above)when the materials break down to be recycled in the carbon cycle.

To be pedantic the chemical bond energy of a compound will probably contribute an incredibly tiny amount to the mass of a molecule over the total mass of its constituent elements while it exists but this is only a temporary feature and in the long term the absorption of photons from the sun by the earth does not increase the mass of the earth because the whole proces is cyclic.
« Last Edit: 31/08/2007 09:39:33 by Soul Surfer »
 

lyner

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Does photosynthesis increase the earth's mass?
« Reply #3 on: 02/09/2007 21:56:16 »
E= mc^2 - or rather   ΔE = Δm c^2 (which describes the relationship between  change in mass and energy)
applies to any energy change.
c^2 is such a big number that it's only for nuclear changes / reactions that the Δm is relevant.
 

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Does photosynthesis increase the earth's mass?
« Reply #3 on: 02/09/2007 21:56:16 »

 

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