In this video, we're going to compare and contrast photosynthesis versus cellular respiration. And so what you may have noticed is that photosynthesis and cellular respiration seem kind of similar when you compare their chemical equations. And so it turns out that photosynthesis and cellular respiration are both very ancient pathways that have been around for 1,000,000,000 years. And they are actually really highly connected to one another, and this is because each process produces the reactants that are necessary for the other process.

For example, photosynthesis produces products that are used as the reactants for cellular respiration, and cellular respiration produces products that are used as the reactants for photosynthesis. We'll be able to see this down below in our image. And also it turns out that photosynthesis and cellular respiration are almost exactly the opposite of each other in terms of their overall chemical equations. We'll be able to see that down below in our image as well.

In our example, we're going to be looking at the connection between cellular respiration and photosynthesis. Taking a look at the top half of the image up here, notice that it's occurring inside of the chloroplast organelle. This is the chemical equation for photosynthesis that we recently talked about in our last lesson video. Photosynthesis is going to take carbon dioxide, water, and sunlight energy from the atmosphere and convert those things into sugars such as glucose and oxygen gas as a byproduct.

But what you'll notice is that the products here of photosynthesis, which are glucose and oxygen, are actually used by mitochondria. You'll notice that glucose and oxygen here are being used by the mitochondria, and one thing to note about this image of the mitochondria is that it's actually flipped around so that the reactants are here on the right and the arrow is going from right to left. These over here are the products of cellular respiration, which we already covered in our previous lesson videos.

What you'll notice is that the reactants here of the mitochondria of cellular respiration are the products of photosynthesis. Cellular respiration converts oxygen and glucose into the products of carbon dioxide, water, and a lot of ATP energy. Carbon dioxide and water are products of cellular respiration, but they're actually used as the reactants for photosynthesis. You can see how each process is going to produce the reactants that are needed for the other process.

Now, you can also see that these two equations, the equation for photosynthesis and the equation for cellular respiration, are almost exactly opposites of each other. The reason for that is because carbon dioxide, water, and energy are all reactants for photosynthesis, whereas carbon dioxide, water, and energy are all products for cellular respiration. Remember, they're products because the arrow's going from right to left here.

In photosynthesis, glucose and oxygen are products for photosynthesis, But glucose and oxygen are reactants for cellular respiration. So really, when you compare these two equations side by side, they do line up similarly, and the only difference where they don't line up so similarly is the type of energy that's used or produced. Cellular respiration is going to be producing ATP, whereas photosynthesis is using solar energy or sunlight energy.

Another thing that you'll notice is that the substances in terms of being oxidized or reduced are flipped as well. In photosynthesis, carbon dioxide is being reduced to glucose. But down below in cellular respiration, glucose is being oxidized to carbon dioxide. And in photosynthesis, water is being oxidized to oxygen, whereas down below in cellular respiration, oxygen is being reduced to water, and so they are reversed in that respect.

One thing that helps me remember which substances are oxidized and reduced is that I know that photosynthesis is going to be synthesizing something, and that is going to be a glucose molecule. Glucose is going to be synthesized using carbon dioxide. It's literally able to take carbon dioxide gas from the atmosphere and use that carbon dioxide gas to build a glucose. Glucose has a lot more chemical bonds in it than carbon dioxide. These chemical bonds are going to be made using electrons. Carbon dioxide is going to need to gain a lot of electrons or it's going to need to be reduced in order to be used to create glucose.

This helps me remember that carbon dioxide has to be reduced. It has to gain a lot of electrons for it to make all of the chemical bonds that are found in glucose. And ultimately water is going to be oxidized. That means that water is going to be losing electrons and being used to produce oxygen. Now in cellular respiration, I know that glucose has a lot of chemical bonds in it. And glucose, because it has a lot of chemical bonds in it, it needs to be broken down. It needs to be stripped of electrons. It needs to lose electrons. And when it loses electrons, it's going to be converted into carbon dioxide.

Ultimately, the oxygen here we know is going to act as the final electron acceptor in cellular respiration. And so the oxygen, because it's acting as the final electron acceptor, it's going to be gaining the electrons or it's going to be reduced and be converted into water. So those are some ways to help you remember that photosynthesis and cellular respiration are very similar to each other, almost exact opposites. And once again, the only difference is that there's sunlight energy here, but down below, there's ATP energy here. And other than that, they are pretty much exactly the opposite of each other.

This here concludes our comparison of photosynthesis and cellular respiration and we'll be able to get some practice as we move forward in our course. And we'll also continue to talk more and more about photosynthesis. So I'll see you all in our next video.