Photosynthesis is arguably one of the most important chemical reactions on Earth because it provides the basis for the energy of our ecosystem. In photosynthesis, there are two very crucial phases, which are light reaction and dark reaction. Today, we're going to take a closer look at how these two processes work.
First, let's start with the light reaction. The light reaction takes place on the thylakoid membrane of the plant chloroplast, and this process requires sunlight. You can think of thylakoids as solar panels, and their job is to capture sunlight and convert it into chemical energy.
The light reaction is divided into two main phases, photosystem II and photosystem I. In the photoreaction phase, the chlorophyll molecules in the chloroplast absorb sunlight, causing the electrons to be excited and jump to a high energy level. These energetic electrons undergo a complex series of transport processes and are finally sent to the photosystemi. In this process, water molecules are broken down into oxygen and hydrogen ions, which are emitted into the atmosphere through the pores, and hydrogen ions are used for subsequent energy conversion.
Next, we come to the second stage of the light reaction. Here, the energetic electrons are excited again, this time to a molecule called coenzyme NADP+, which is reduced to NADPH. At the same time, hydrogen ions form a gradient difference on the thylakoid membrane, which is like a ready stream of water that stores a large amount of potential energy.
Now, we have two important energy carriers for the light reaction: NADPH and hydrogen ion gradients. These energy carriers will play a role in the following dark reactions.
The dark reaction, also known as the Calvin cycle, takes place in the matrix of chloroplasts. This process does not directly depend on light, hence the name "dark" reaction, but in reality they also occur simultaneously during the day. The goal of the dark reaction is to convert carbon dioxide into organic molecules such as glucose using the energy carrier produced by the light reaction.
In the first stage of the dark reaction, the carbon dioxide molecule is captured by an enzyme called RUBP, a five-carbon ribulose. After a series of chemical reactions, two three-carbon compounds, 3-phospho-glyceric acid, are finally formed. This stage is known as carbon fixation because it "fixes" carbon dioxide in the atmosphere.
Next, 3-phospho-glycerate moves on to the second stage, which consumes two energy carriers, ATP and Nadph. In this process, 3-phospho-glyceric acid is reduced to glyceraldehyde-3-phosphate, which is an important intermediate in the synthesis of glucose and other organic matter.
Finally, a portion of glyceraldehyde-3-phosphate is used to generate glucose, while the other part is re-entered into the dark reaction cycle to regenerate RUBP to keep the reaction going. It is worth mentioning that in addition to Calvin cycle carbon sequestration in the dark reaction stage, some plants have other carbon sequestration pathways, and everyone who is interested can go down to popularize science on their own. Light reaction and dark reaction are the two core parts of photosynthesis. The light reaction is responsible for capturing solar energy and converting it into chemical energy; Dark reactions, on the other hand, use this energy to convert carbon dioxide into organic matter. These two processes are interdependent and together support the growth of plants and provide the basic energy for the entire ecosystem**.
Through this process, we can see how subtle and efficient the energy conversion in nature is. Photosynthesis in plants not only provides them with the energy they need to survive, but also provides the starting point of the food chain for other organisms. It's like a huge solar factory on Earth, constantly powering our life activities. Well, that's all for today's popular science. If you are more interested in photosynthesis or energy conversion in plants, you can leave a message in the comment area and we will discuss it together. Don't forget to like and follow me.