Cyclic vs. Noncyclic

For those who have stumbled upon the terms cyclic and noncyclic photophosphorylation, you probably don’t understand what the differences are. First off, let’s define what photophosphorylation is. To understand the definition, we have to establish what photosynthesis is, and photosynthesis, according to your grade school science teacher, is the production of carbohydrates by green plants under sunlight. If you don’t remember, this process is actually a two-step approach: light reaction and dark reaction. The light reaction process happens in the part of the plant where light energy is converted to chemical energy.

When we talk about photophosphorylation, we talk about the addition of phosphate in the presence of light when undergoing the light reaction process. Here is where the two types of photophosphorylation come in: cyclic and non-cyclic.

There are a few things you need to know in cyclic photophosphorylation. First off, electrons travel in a cyclic manner, hence the name of the process. Furthermore, only the ATP chemical is produced, and that oxygen is in no way evolved. This system is usually seen in bacteria.

Non-cyclic photophosphorylation, on the other hand, means that electron travel in a non-cyclic manner. So the name really suggests the transport of these electrons especially in terms of direction. Under this system, two chemicals are produced: ATP and NADPH. Water splitting is actually present here, as opposed to the cyclic counterpart, and that oxygen is evolved. In fact, oxygen is a by-product of this system. It is easy to see that green plants have a non-cyclic photophosphorylation as oxygen is often times the product of photosynthesis.

There are other technicalities, of course, between the two terms, but the ones discussed should give you insights on the main differences of the two systems as well as an idea of how different these two are and where these systems are usually found.


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