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Lesson Video: Aerobic Respiration Biology

In this video, we will learn how to recall the reactants and products of aerobic respiration, and explain the importance of respiration for organisms.

17:12

Video Transcript

In this video, we will learn about the process of cellular respiration and how it provides energy for cells and organisms. Then we’ll try some practice questions. And finally, we’ll summarize what we’ve learned.

You’re likely aware that our bodies use the food that we eat to generate energy. Recall that your body consists of many organ systems; each of which consists of many organs. Each organ is made of several tissues, and tissues consist of many cells. The cells of your body look something like this. And they contain several organelles, which are subcellular structures specialized to carry out a specific function. Do you know which organelle is responsible for producing cellular energy? Absolutely, the mitochondria produce cellular energy.

Our cells need energy to do work, and that work is different depending on the cell. Muscle cells need energy to contract and cause movement. Nerve cells need energy to carry impulses throughout your body. And your white blood cells need energy to fight off infections and keep you healthy. Cells need energy to carry out all the essential functions that keep us alive. And the mitochondria provide the energy that the cells need to do their jobs.

All living organisms use a form of cellular respiration to break down nutrients to generate energy. Usually this energy is in the form of a molecule called ATP, which we’re gonna discuss a little bit more next. If cellular respiration utilizes oxygen, we call it aerobic respiration. And if cellular respiration does not utilize oxygen, we refer to it as anaerobic respiration. An- is a prefix meaning not. For now, we’re gonna further investigate aerobic respiration, and we’re gonna start with this molecule ATP. ATP stands for adenosine triphosphate. It’s the molecule that provides the energy for almost all cellular processes in almost all living things.

You may be interested to know that adenosine triphosphate, or ATP, is composed of the nitrogen containing base adenine and a ribose sugar, which is hopefully reminding you of the structure of a nucleotide. However, instead of one phosphate group like a nucleotide, ATP has three, which is the origin of the tri- in triphosphate. ATP is an energy-rich molecule, meaning that there’s lots of energy stored within its chemical bonds, especially here between the second and third phosphate groups. So when our cells need energy to do their work, they take a molecule of ATP and break off that last phosphate group, freeing the energy stored in that high-energy chemical bond. The remaining molecule is called ADP or adenosine diphosphate, di- being a prefix meaning two.

Well, our cells need lots of energy, and it would take so much time and resources to make all of the ATP our cells need from scratch. Instead, one molecule of ATP can be recycled to ADP and back thousands of times. To provide power for cellular processes, energy is released from ATP by breaking off a phosphate group, creating ADP. That same ADP molecule can be converted back into ATP by reattaching a phosphate group. This occurs through a complex set of metabolic reactions known as cellular respiration. Cellular respiration is a chemical reaction, so we’ll represent it with a chemical equation. You might’ve learned in chemistry that the chemicals to the left of the arrow in a chemical reaction are the reactants and the chemicals to the right of the arrow are the products.

Well, since what we’re discussing is aerobic cellular respiration, we know that one of the reactants is oxygen. We also learned a little bit earlier that cellular respiration is the process of cells breaking down nutrients for energy. The nutrient that our cells typically use for cellular respiration is glucose, a type of simple sugar. The oxygen and glucose are broken down and rearranged into carbon dioxide and water, a process which releases energy that’s used to generate ATP. A chemical reaction that releases energy is called an exothermic reaction. In fact, some of the energy created during cellular respiration is actually given off as heat. Also important to know is that energy in this chemical equation is represented in parentheses or brackets. That’s because while energy is released, it’s not technically a product of the chemical reaction.

Now that we’ve explored the chemical equation for cellular respiration using words, we’ll go ahead and try to look at it using the proper chemical symbols. The chemical symbol for oxygen is O2 because there are two atoms of oxygen in every molecule of oxygen. The chemical symbol for glucose is C6H12O6, and a molecule of glucose looks something like this. If you counted up the atoms in this molecule, you would see that there are six atoms of carbon, 12 atoms of hydrogen, and six atoms of oxygen. For the sake of simplicity, we’ll represent the components of the glucose molecule like this. The chemical symbol for carbon dioxide is CO2 because carbon dioxide contains one atom of carbon and two atoms of oxygen. The chemical symbol for water is H2O. Water contains two atoms of hydrogen and one atom of oxygen.

So now we have represented our cellular respiration equation using chemical symbols. But the number of atoms that we have in our reactants is higher than the number we find in our products. In order for this to be a balanced chemical equation, we need to have the same number of carbon, hydrogen, and oxygen atoms in our reactants as we have in our products. In order to balance this chemical equation, we’ll need to add some coefficients. So our balanced chemical equation looks like this. It takes six molecules of oxygen and one molecule of glucose to generate six molecules of carbon dioxide and six molecules of water and to release the energy that our cells use to make ATP. Try counting up the atoms on each side of this equation to make sure that we balanced it properly.

Before we move on to our practice questions, let’s take a moment to look at how the process of breathing, also called respiration, is related to the process of cellular respiration. Cellular respiration primarily takes place within the mitochondria. Mitochondria are bean-shaped organelles that possess a folded inner membrane and many types of enzymes to facilitate the complex set of chemical reactions, which convert glucose and oxygen into carbon dioxide, water, and energy, which is used to generate ATP, which powers almost all of our cellular processes. Well, glucose is a sugar made from the nutrients we get from our food or, in plant cells, glucose is a product of photosynthesis. And the water in our bodies is recycled and used for many different purposes. But what about the oxygen and the carbon dioxide?

Well, you may have already guessed. When we breathe in, oxygen from the air enters our lungs. And from there it’s pumped through the bloodstream to each of our cells, where the mitochondria use it to carry out cellular respiration, producing carbon dioxide as a waste product, which enters the blood and is pumped back to the lungs, where it’s removed from our bodies when we exhale. And this is why the respiration which occurs in our cells and the respiration which occurs in our lungs have the same name.

This also helps to explain why cells that are more active will have more mitochondria inside of them. For example, you could expect to find more mitochondria in a muscle cell than in a skin cell. This also helps to explain why as you do more physical activity, like exercise, your respiration rate or breathing rate will increase. When you’re more physically active, you need to breathe in more oxygen so that your cells can make more ATP to keep your body moving.

Well, now that we’ve learned a little bit about aerobic respiration, why don’t we try some practice questions together?

Not including energy or ATP, state the correct word equation for aerobic respiration.

This question is asking us to recall the word equation for aerobic respiration. Since our final product will be a word equation, while knowing the chemical symbols will come in handy, we’re not going to include them in our final answer. Another thing we’ve been told not to include is energy or ATP in this word equation. So while we know that they’re the purpose of aerobic respiration, we’re gonna go ahead and leave them out of our answer. Our final word equation should have the reactants for aerobic respiration on the left side of an arrow and the products on the right.

In order to answer this question, let’s review what we know about aerobic respiration. Here, we see our busy biology student. They are breathing, they’re eating an apple as a healthy snack, and their heart is beating, pumping blood all throughout their body. And all of these things are essential to the process of aerobic respiration. Cellular respiration is the process of breaking down nutrients for energy. And every living organism carries out some form of cellular respiration. And the word aerobic means that this is specifically a type of cellular respiration that uses oxygen. So we know that our reactants have to include some type of nutrients as well as oxygen.

Let’s take a closer look at our student and his cells. Our student receives their nutrients from the food they eat. They’re broken down in the small intestine and absorbed into the bloodstream, where they’re transported to our cells primarily in the form of glucose. Our student also breathes in oxygen from the air, which enters the lungs and is absorbed into the bloodstream, which distributes it to the cells of our bodies. Recall that each cell contains mitochondria, which are bean-shaped organelles that are the site of cellular respiration. They possess a folded inner membrane and several different types of enzymes that facilitate the complex metabolic reactions that allow them to convert oxygen and glucose into carbon dioxide and water and releasing energy that’s used to form ATP, which is a molecule that powers almost all of our cells’ essential functions.

The water is largely recycled, but the carbon dioxide diffuses out of the cells and back into the bloodstream, which carries it back to the lungs, where it’s removed from our bodies when we exhale. So breathing takes in oxygen and removes carbon dioxide, eating provides nutrients, especially glucose, and your circulatory system, driven by your heart, carries all of these materials from place to place, which allows our cells to make the ATP that provides the cellular energy that they use to do their jobs. So in response to our question, aerobic respiration is the process of converting oxygen and glucose into carbon dioxide and water, which releases energy to power our cells.

Let’s try another practice question.

Which of the following is correct about cell activity and the number of mitochondria? (A) The more active the cell, the lower the number of mitochondria. (B) There is no correlation between the activity of the cell and the number of mitochondria it contains. Or (C) the more active the cell, the higher the number of mitochondria.

This question is asking us to read each of the statements and to choose the one that is correct or true about the relationship between cell activity and the number of mitochondria. In order to visualize information regarding relationships, it’s often helpful to sketch a little graph. We’ll let the 𝑥-axis represent cell activity and the 𝑦-axis represent the number of mitochondria. Choice (A) states, the more active the cell, the lower the number of mitochondria. So we can expect this graph to look something like this. Choice (B) states that there’s no correlation between cell activity and mitochondria number. So we might expect a graph of this information to look like this. Choice (C) says the more active the cell, the higher the number of mitochondria. So we can expect a graph of this information to look something like this.

Well, what do we know about mitochondria? Recall that mitochondria are bean-shaped organelles found inside of almost all eukaryotic cells. Also recall that mitochondria are the site of cellular respiration, a process that converts oxygen and glucose into carbon dioxide and water, a process which releases energy. This energy is used to produce a molecule called ATP, which is used to power almost all cellular activities or functions. So if a cell is more active, it would require more energy, which is generated in the mitochondria.

So as cellular activity increases, you expect the cell’s need for energy to also increase. And since mitochondria produce cellular energy through cellular respiration, it’s also reasonable to expect their number to increase. So returning to our answer choices, the statement that’s correct about the relationship between cell activity and the number of mitochondria is the more active the cell, the higher the number of mitochondria.

Let’s take just a moment to review what we’ve learned in this video. We’ve learned that cellular respiration is the process of breaking down nutrients to release energy and that aerobic is a word that means using oxygen. So aerobic respiration is cellular respiration that uses oxygen. We also learned about the chemical equations that represent the complex metabolic processes that go into cellular respiration. And we reviewed how your lungs and mitochondria work together in this process to produce a molecule called ATP that’s used to power almost all of our cells’ activities.

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