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I 'm aware when plants are not in the light they respire just as we do. I also know the products of photosynthesis are sugar and oxygen. My questions are:
How do plants get energy when they are in the light if photosynthesis produces no ATP? Do plants always have to respire with the sugar produced from photosynthesis? Or is there some energy made from photosynthesis and if so in what form?

Question Date: 2013-11-12
Answer 1:

During photosynthesis, plants use the energy from the sun in order to split water molecules into their hydrogen and oxygen components. The oxygen is then emitted into the atmosphere for us animals to use to breathe. The hydrogen is used to create cellular energy in the form of adenosine 5'-triphosphate (ATP) and through a more complicated process into glucose. These reactions are called photochemical or light reactions because they require light to occur.

Check out this neat video describing the process of photosynthetic electron transport and ATP synthesis:

video click here

If plants do not have access to light they can break down glucose for energy. If they already have enough glucose for the time being they store it in the form of a complex carbohydrate molecule called starch, which can be broken down for energy later.

For more detailed information, check out this article describing in detail the process of how cell's (both eukaryotic and prokaryotic) get their energy: cell energy and cell functions

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