Effect of Temperature on Cellular Respiration

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  • 0:01 What Is Cellular Respiration?
  • 1:37 Optimal Temperature
  • 2:40 Testing the Effect of…
  • 5:52 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
In this lesson, we'll explain the basic steps of cellular respiration. Then we'll go over why temperature has an effect on this process, what the optimal temperature is for yeast and how you can test this at home.

What Is Cellular Respiration?

Imagine being outside in winter. There are snowflakes falling, and you have to be careful not to slip on the ice. Even when you're in a cold environment, your body still tries to keep itself the same temperature inside, 98.6 degrees Fahrenheit. Conversely, if you get too hot, your body starts to sweat to cool you down.

The reason your body works so hard to maintain this balance is because your cells work best at that temperature. Within your cells, tiny molecules called enzymes are responsible for chemical reactions that allow the cells to make energy so your body can stay alive. The process the enzymes use to make energy inside cells is called cellular respiration. During cellular respiration, cells take glucose (sugar), and oxygen and make ATP (cellular energy), carbon dioxide, and water.

There are three main steps to cellular respiration: glycolysis, the citric acid cycle, and oxidative phosphorylation. Glycolysis begins with bringing glucose into the cell. This step makes a few molecules of ATP, but the main purpose is to collect electrons and make pyruvate, which is needed for the next step. Pyruvate is converted to another molecule, acetyl Co-A, and enters the citric acid cycle. It is in this step that carbon dioxide is made and many more electrons are collected. In the next step, the cell harvests the energy collected in the electrons and makes ATP. Here, the oxygen we breathe combines with hydrogen ions to make water.

Optimal Temperature

These reactions work best at an optimal temperature, and for us that is 98.6 degrees Fahrenheit, our body temperature. At the optimal temperature, the enzyme activity, or how fast it works, is the highest. But since all organisms have a different internal temperature, the optimal temperature will vary a little bit. However, in general, cooler temperatures make enzymes work slower, since the molecules inside them move slower also. Picture this: when ice freezes, the water molecules slow down and eventually stop moving to form a solid. The same thing happens with the molecules that make up enzymes inside our cells.

When the temperature increases, molecules start to move a little faster and the reactions go faster too. But if you keep increasing temperature, eventually the enzyme breaks apart, or denatures. Now the enzyme won't work anymore and cellular respiration cannot proceed. The optimal temperature is kind of like a Goldilocks temperature. The temperature cannot be too hot or too cold; it has to be just right for the enzyme to function efficiently.

Testing the Effect of Temperature

As it turns out, there are some cool experiments you can try to test this out. The yeast you use for baking has the same type of cell structure as humans and does cellular respiration the same way, so it is a convenient and inexpensive model for our tests. While one way to find the rate of cellular respiration at different temperatures involves measuring oxygen consumption, you would need lab equipment. So today, we're going to test carbon dioxide production, since you can do this at home.

Do you remember which step makes carbon dioxide? It's the citric acid cycle. So if our cells make carbon dioxide, we know that they must be running the citric acid cycle. For the citric acid cycle to keep going, oxidative phosphorylation must use up the electrons collected to make ATP. So we can infer that if we get carbon dioxide, we are also getting ATP and the cell is doing cellular respiration. If the cell is at an optimal temperature, then cellular respiration will happen faster and we'll get more carbon dioxide in the same amount of time compared to other temperatures.

Now how will we measure the production of a gas we can't see? Since we're doing this in our kitchen, you won't need any fancy sensors here. We're going to use balloons. Think about how you blow up a balloon. What do you exhale? Carbon dioxide, which is the product of all the cellular respiration happening in your body at once. The only reason we exhale carbon dioxide is because it is made from cellular respiration. It's toxic, so our body exhales to get rid of it and keep us safe. The yeast we'll be using produces carbon dioxide too.

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