Video Transcript: Photosynthesis

Today we are going to talk about an incredible process that uses light carbon dioxide and water to make something awesome that we all love, sugar. Unfortunately, we cannot do this amazing, incredible process, which is known as photosynthesis. Some types of protists can do photosynthesis, some types of bacteria can. And of course plants can, plants will be our focus for this video clip, animals and amoebas just sort of missed out on this ability. But we do benefit from it greatly as this process also produces oxygen, the very gas that we need in order to breathe. So this process is important for us to understand.

First, a little background, plants and animals need sugar, specifically glucose. Plants, as well as animals use glucose to make ATP energy in a process known as cellular respiration. ATP energy is critical for cells to be able to carry out their cellular activities. But while we have to be in search of food to get glucose plants instead can do photosynthesis to make their own glucose. So that's kind of nice, because they don't have to go anywhere to get it. Plants have adaptations to make them able to carry out photosynthesis in a variety of environments. Here is the formula for photosynthesis, on the left side of the formula, you will find the reactants, that means these are the inputs, the plant has to have these in order to do photosynthesis. On the right side of the formula, you will see the products that means those are the items that are produced by the plant the outputs. Now sometimes the formula is written a little differently. Technically, it needs to be balanced. And sometimes light is written on top of the arrow just to show that it's in the presence of light. So it may instead look like this. The C₆H₁₂O_6. That product, it's a sugar, specifically glucose. Now photosynthesis it's not just a formula. Have you ever tried to capture light before? It's hard; plants have light capturing molecules called pigments that help them do this. See visible light it has different wavelengths, different wavelengths of light have different colors. If you've ever played with a prism before, you may have been able to see how light can be divided up into a rainbow of colors. Due to these different wavelengths. 

Well, one pigment that plants use for photosynthesis is called chlorophyll. Chlorophyll is an expert at absorbing red and blue light, but not so much green light. Because it does not absorb very much green light, it actually reflects green light. Therefore, many plants appear green to our eyes. There are more pigments besides chlorophyll that work with different wavelengths of light. And this can explain why green is not the only color that you see in plants. 

Chlorophyll is a pigment found in the chloroplast of plant cells. Convenient they sound similar. This amazing organelle is not found in animal cells. There are two major reactions that occur in the chloroplasts that together make up photosynthesis, the light dependent reaction and the light independent reaction. The light independent reaction, by the way, is also called the Kelvin cycle, or dark reaction. So let's talk about these two reactions. The light dependent reaction happens in thylakoids. What are thylakoids? Well, there are little compartments in the chloroplast. And they contain the pigment, they tend to be nicely stacked is a collective stack, we call it a green thumb, the best way to describe a green thumb is that it looks like a stack of green pancakes. Very, very small green pancakes. In the light dependent reaction light is converted by means of a complex process that involves multiple photosystems, into chemical energy. By chemical energy, I mean ATP. We've mentioned that before, that's energy and NADPH. We'll get to that later. During the light dependent reaction. Water which is needed for this process to work is split. That means if you think of the chemical formula for water, it's H₂O. It is split so that you get electrons, protons and oxygen. So oxygen is also a product of this reaction. So let's take a look at our formula to see what just happened. The light in the water on the reactant side were used in the light dependent reaction, and the oxygen that was produced was also from this light dependent reaction. Now, what about the other items in the formula? And why would you make this ATP and NADPH?

What do they do? Where are they going to come in? Well, that's the next step, the light independent reaction. The light independent reaction also occurs in the chloroplast. But the name is misleading. It doesn't happen in the dark. It needs items from the light dependent reactions, so they happen at the same time. Now, while it still happens in the chloroplast, as with plants, we're not going to be getting out of the chloroplast. With this part, it does not happen in the thylakoids. Instead, it happens in the stroma. And the stroma is a fluid outside of the thylakoid. In this reaction, carbon dioxide must be fixed. What do I mean by fix? Well, nothing was wrong with it. By fixed I mean that with the additional help of a major enzyme, the inorganic carbon dioxide is changed to a more usable organic form. The ATP from the light dependent reaction helps supply energy and the NADPH from the light dependent reaction supplies reducing power. By that I mean that it helps add high energy electrons to this process. So in a very complex series of pathways, the fixed carbon dioxide, the ATP, and the NADPH are used to make a product that can ultimately be converted into glucose. Phew.

So let's take a look at this formula. Last time, I promise. So we have here the circled items already that came from the light dependent reaction. Now notice the other items, the carbon dioxide on the reactant side, and the glucose which was on the product side. Those were from the light independent reaction. Together the light dependent reaction and the light independent reaction, which happens simultaneously create the glucose that plants need to survive. The process of photosynthesis is necessary for plants to make sugar. Photosynthesis also supplies organisms with the oxygen they need because remember, oxygen was a product. Also, since plants are the producers and food webs. Photosynthesis is important because plants supply the energy for a lot of hungry consumers. Well, that's it for the amoeba sisters and remind you to stay curious