 Let's explore respiration and breathing. Wait, aren't they the same thing? No. Breathing is where we get oxygen from air or water into our bodies. Respiration is once the oxygen enters into the cell, the cell uses that oxygen to break sugars down to give us energy. Let's start with respiration. I remember respiration is the exact opposite of photosynthesis. In photosynthesis, you take carbon dioxide, water and sunlight to give us glucose and oxygen. Well, here's the exact opposite. There it absorbs energy, here it releases energy. But wait, this is not a one-step process. This is a multi-multi-step complex process, but it can... There are two big stages for this. The first stage is to break down glucose into pyruvate. Pyruvate. Glucose is a six-carbon molecule. Pyruvate is a three-carbon molecule. We don't need the formula. So there will be two pyruvate molecules. Now in this stage itself, there is a tiny amount of energy released. Then that pyruvate is further broken down using oxygen to give us carbon dioxide, water and even more energies released. But what if this oxygen is insufficient, not available, and we need a lot of energy? Say, during exercising. Then that pyruvate can be broken down, usually by your muscles, even without oxygen. When that happens, you don't get this, you get lactic acid. And that's why during strenuous workout, lactic acid gets built up in our muscles. But there's yet another way in which pyruvate can be broken down without oxygen. Yeast, for example. When they break down pyruvate, they don't give you lactic acid. They give you carbon dioxide and alcohol. Yes, this is how we produce alcohol in your wines, beers, or whatever that is we use for consumption. So you can see actually there are two kinds of respiration. One in which we use oxygen. This is called aerobic respiration. And the one in which we do not use oxygen. This is called anaerobic respiration. So let's look at some similarities and differences. The similarity is that in both these cases, the first stage is the same. You break down glucose to get pyruvate. Okay, now what are the differences? Well, clearly here you use oxygen to break down pyruvate. Here you don't use oxygen to break down pyruvate. What are the differences? Well, this happens inside the mitochondria, which is the powerhouse of our cell. So for aerobic respiration, the pyruvate has to go inside our mitochondria. The oxygen has to go inside the mitochondria and then we get this. Whereas anaerobic and all the other stages, everything else that happens outside of mitochondria in the cytoplasm of our cell, which is basically in this space over here. But there's a third important difference and that is in aerobic, you get a lot of energy released when you break down pyruvate using oxygen. But in anaerobic, you don't get any extra energy when you break down pyruvate. You only get some little energy in the first stage. Now let's talk about breathing. How exactly do we get oxygen into our blood? Well, it's all thanks to our lungs and the diaphragm. When we inhale, our lung size increases. How exactly? Well, have a look at this animation. Keep your eye on the diaphragm. See what happens to it. What did you see? Can you see that the diaphragm actually moves down? Look at that. So the diaphragm moves down making space for the lungs to expand downwards. And then also look at what happens to the rib cage. Have a look at that. You see the rib cage actually expands and goes a little up as well. So the ribs move up and out. The diaphragm moves down. That increases the space inside your lungs, decreasing the air pressure inside. And that sucks in more air from the atmosphere. Kind of like when you pull the syringe back, it sucks in water. Okay, what happens then? Well, for that, let's look inside our lungs now. The trachea divides into two branches called the bronchi. Singular is broncus. And then the bronchi also keep dividing into smaller and smaller bronchi, which then divide into bronchiolas. What's the difference between the two? Well, bronchiolas are usually much thinner than the bronchi, but the main difference is that bronchi has these cartilages that even the trachea has. Cartilage helps maintain their structure and ensures that under low pressure, they don't collapse. But once they get too small, the cartilage disappears and that's when we call them bronchioles. Eventually the bronchioles end into these tiny balloon shaped air sacs called alveoli. And these sacs are wrapped in blood capillaries. So what happens over there? Well, if you zoom in, because you inhaled air, your alveoli contains oxygen. Whereas over here you have the deoxynated blood. Since these are microscopic structures, diffusion works now. So carbon dioxide diffuses into the alveoli and the oxygen diffuses into the blood. In fact, they get attracted by the hemoglobin inside the RBCs and then they are carried to the different parts of the body. And now when you breathe out, when you exhale that carbon dioxide eventually goes out. But finally, why do we have alveoli in the first place? Why can't we just wrap these blood vessels directly around the lungs? Because the lungs do not have the necessary surface area. When you divide them into eventually alveoli, if you look at the surface area, that increases tremendously. So alveoli helps increase the surface area, which eventually helps increase the amount of diffusion and exchange that happens. And this is how oxygen from the air moves into our blood. Isn't that amazing?