What are the products of the light reactions of photosynthesis that are required by the dark reactions?

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What substances are provided by the light reaction that are used in the light-independent reactions?

In the presence of light, water is split into H+ ions (protons) and electrons in a process called hydrolysis. This is very significant because light is an energy source that is converted from solar to chemical energy. Once light is absorbed by chlorophyll it helps provide the energy to transfer the electrons and H ions from water to a compound known as NADP+. This causes it to form NADPH which is a chemical energy source that is available to use in the light--independent reaction. It is a source of electrons that can be passed along an electron transport chain to an electron acceptor. This means that NADPH contains reducing power to help drive the next steps of photosynthesis.

Also generated in the light reaction is ATP which is formed by chemiosmosis in a process known as photophosphorylation. This step requires the presence of light to occur.

Both ATP along with NADPH provide energy from the light reactions to enable carbon dioxide to eventually form sugar in the light--independent reaction.


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Photosynthesis requires sunlight as a reactant and hence can be considered a light reaction. What you are referring to as 'dark reactions' are cellular respiration reactions and they do take place throughout the life of a plant. So, in reality they are not just dark reactions (since they take place 24 x 7).

Photosynthesis can be chemically represented by the following reaction:

`6CO_2 + 6H_2O + sunlight -> C_6H_12O_6 + 6O_2`

Here, carbon dioxide and water are converted (in the presence of sunlight) to glucose and oxygen. 

Cellular respiration is complementary to photosynthesis and uses the products of photosynthesis (that is, glucose and oxygen) as reactants. Cellular respiration can be represented as:

`C_6H_12O_6 + 6O_2 -> 6CO_2 + 6H_2O + ATP`

Here, glucose and oxygen (both generated from photosynthesis) are used and carbon dioxide and water are generated, along with energy molecules (ATP).

Hope this helps.

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