Cellular respiration is one of the fundamental processes that facilitate cellular life and function. Without cellular respiration, living organisms would not be able to survive.
If you’re interested in learning more about cellular respiration, one of the best tools at your disposal will be a diagram depicting the process.
A cellular respiration diagram will allow you to visualize the process of respiration as it occurs in cells, meaning that you will be better able to understand how cells survive as they do.
This article will provide you with the basic information you need to understand cellular respiration, alongside a diagram to illustrate how this process works.
What Is Cellular Respiration?
First of all, what is cellular respiration? Cellular respiration is the term for a series of metabolic processes that occur on a cellular level.
In order for cellular respiration to occur, both oxygen and nutrients (glucose) from food sources need to be present so that the chemical energy they contain can then be converted into adenosine triphosphate.
This is an organic compound that is, in itself, a source of energy. That energy is then used by the cells to complete other important processes.
The Cellular Respiration Equation
Cellular respiration is often depicted in the form of an equation. This equation is one of the most important in cellular biology:
C6H12O6 + O2 → H2O + CO2 + 36ATP
In order for cellular respiration to take place, the chemical bonds found in glucose molecules need to be broken down to produce energy.
The glucose bonds are represented by the chemical formula C6H12O6, whereas the oxygen required for this metabolic reaction is written as O2.
Then, on the other end of the equation, you can see the substances produced as a result of the reaction between glucose and oxygen: H2O (water), CO2 (carbon dioxide), and 36ATP (36 adenosine triphosphate molecules).
A Cellular Respiration Diagram
Equations can be difficult to understand if you’re not familiar with chemical formulae.
These equations don’t always help with visualization, either, which can be difficult when you’re trying to understand a biological concept. That’s why we prefer to explain cellular respiration using a diagram like this one:
How Cellular Respiration Works
Hopefully, the above diagram will have given you a better understanding of the process of cellular respiration.
However, if you’re interested in how cellular respiration actually works and the science behind it, here is a more in-depth explanation of each aspect of the process:
Cellular respiration is a process in itself, but it can be broken down further into 3 stages.
The first stage is glycolysis, the second stage is something called the Krebs cycle, and the final stage is known as electron chain transport. Let’s take a closer look at all of the stages involved in cellular respiration.
Step 1: Glycolysis
The first stage in cellular respiration is called glycolysis. The word literally translates to ‘splitting sugars’, and it refers to the breaking down of the bonds of glucose.
Glycolysis initially occurs in a cell’s cytoplasm, but the process ends in the mitochondria (famously referred to as the powerhouse of the cell).
During glycolysis, the molecules of simple sugar get broken down through the oxidation of carbon and a reduction in oxygen levels. This is known as an oxygen-reduction process or reaction.
Only 2 molecules of ATP (adenosine triphosphate) are produced during glycolysis. As you can see from the equation and the diagram above, cellular respiration produces 36 ATP molecules in total.
If you’re wondering where the other 34 molecules come from, they are the result of an aerobic reaction that happens when the glucose is exposed to oxygen.
Whether cellular respiration is taking place anaerobically (without oxygen) or aerobically (with oxygen), glycolysis can still take place.
When the glucose molecule breaks down, several chemical reactions are triggered, producing a substance called pyruvate, otherwise known as pyruvic acid.
This molecule is what causes the transition from the glycolysis stage of cellular respiration to the next stage, which is the Krebs cycle.
Step 2: The Krebs Cycle
You may also hear the Krebs cycle during cellular respiration being referred to as the tricarboxylic acid cycle – but the Krebs cycle is easier to say and spell, so it tends to be used more often in general discussion.
When the molecule of pyruvate produced during glycolysis transports a liquid called cytosol into the mitochondrion, the pyruvate tracts with a microenzyme called coenzyme A. This microenzyme is responsible for creating Acetyl CoA, which you don’t need to know much about at this stage.
What you do need to know is that Acetyl CoA is produced by removing a carbon molecule and two molecules of oxygen.
Several more chemical reactions then take place, with the end result being the production of six carbon dioxide molecules alongside two molecules of adenosine triphosphate and, of course, the Acetyl CoA mentioned earlier.
But these aren’t the only molecules produced during the Krebs cycle. The chemical reactions during this cycle also produce compounds called flavin adenine dinucleotide (commonly known as FAD) and nicotinamide dinucleotide (NAD). These molecules can store high-energy electrons.
Although the Krebs cycle takes place aerobically (oxygen is present in the environment), no oxygen is actually used during the cycle.
Step 3: Electron Chain Transport
The third and final stage of cellular respiration is electron chain transport, also known as the electron transport chain or oxidative phosphorylation process. This is also illustrated in the diagram.
During electron chain transport, energy is released. Unlike the Krebs cycle, which doesn’t use oxygen even though it can only take place in oxygenated environments, the electron transport chain directly uses oxygen molecules.
The electron transport chain involves electrons in the organic acids produced during the Krebs cycle being passed over to the electron acceptor (nicotinamide adenine dinucleotide, or NAD, which you can also see labeled on the diagram).
A chain reaction occurs after the transfer of acids, at which point, the energy produced is handed over to the electron carriers (FADH2 and NADH). It’s this process that ultimately causes adenosine triphosphate molecules to be produced.
The Results Of Cellular Respiration
As you can see in the diagram, and as explained above, different stages of cellular respiration produce ATP molecules in various quantities.
During the glycolysis process, just two ATP molecules are produced, although four molecules of NADH are produced at the same time.
These NADH molecules are converted into the same number of ATP molecules in the mitochondria. In some cases, eight ATP molecules may be produced, but this is not normally the case.
Then, when Acetyl CoA molecules are formed, two more NADH molecules are produced, and these are also converted in the mitochondria into six molecules of ATP.
Finally, the six NADH molecules produced during the Krebs cycle become 18 molecules of ATP, while the FADH2 molecules turn from two into four.
There are also two ATP molecules produced at this stage. As a result, the ATP yield of cellular respiration comes to either 26 or 36 molecules of ATP in total.
Thank you for reading our guide to cellular respiration. We hope that this information, alongside the diagram and equation for cellular respiration, has helped you to grasp the stages that make up this complex and important chemical reaction.
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