Overview of Photosynthesis
Photosynthesis is the process in which plants turn sunlight into food. It happens in two stages: the light reaction of photosynthesis, which needs sunlight, and the dark reaction, which does not. The light reactions of photosynthesis take place in the thylakoid membranes of chloroplasts. Here, plants absorb sunlight and use it to produce energy in the form of ATP and glucose.
Reactants & Products
To understand what happens in light dependent reactions, we need to look at their inputs and outputs, as in any other chemical reaction. In this case, the inputs are water, carbon dioxide, and sunlight, while the outputs are oxygen, glucose, ATP, and NADPH. These outputs store and transfer energy to power the next stage of photosynthesis, called the Calvin cycle.
Light Reactions & Photolysis
During light-dependent reactions, light energy breaks down water molecules into oxygen, protons, and electrons. This process is call photolysis. In this phase, ATP is also created. The byproduct from the light-dependent reaction is oxygen, which is released into the atmosphere. Meanwhile, the electrons from photolysis are later used in the electron transport chain.
Photosystems
The light reaction of photosynthesis depends on two photosystems, namely, Photosystem II and Photosystem I. Despite being numbered this way, Photosystem II works first by capturing light energy to excite electrons. These electrons move through the electron transport chain and reach Photosystem I, where they gain more energy. So, what is the main purpose of the light dependent reactions? It's to produce ATP and NADPH, which are essential for the next stage of photosynthesis.
Electron Transport Chain
Which events take place in the light-dependent reactions of photosynthesis? One is the movement of energized electrons through the electron transport chain. When light energy excites electrons in Photosystem II, they travel through a series of proteins and lose energy as they go. The energy loss, in turn, helps create a proton gradient to assist ATP production. The electrons then reach Photosystem I, where they receive more energy before helping convert NADP+ into NADPH.
Products of Light Reactions
What are the products of light dependent reactions? They are ATP, NADPH, and oxygen. Oxygen is released as a waste product, while ATP and NADPH store energy for the dark reactions. Together, these products fuel the Calvin cycle, where glucose is made. The light reaction produces the energy needed to continue the process of photosynthesis.
Read Light Reaction of Photosynthesis | Definition, Diagram & Products Lesson
