Krebs Cycle

Today, we are learning about the Krebs cycle. Wait! Come back!
 
The Krebs cycle is how plants get energy from their food. Also known as the citric acid cycle, it won’t tell you how to grow bigger tomatoes or sweeter melons, but understanding the Krebs cycle gives you a better understanding of how plants grow and what they go through to make all those delicious things we eat.

Chef Krebs ready to cook up some food (Isuru Prabath) Pixabay

We’ve already discussed the nitrogen cycle, the carbon cycle, and the water cycle. Those cycles describe how things needed by plants become available (and unavailable) as they change forms, moving through the environment.

​We’ve also discussed the Calvin cycle, which is part of photosynthesis. In the Calvin cycle, several anaerobic chemical reactions occur that allow plants to transform the carbon from CO2 into sugars. After those sugars are formed, the Krebs cycle begins.

Messrs. Krebs and Johnson
 
In 1937, a man by the name of Albert Szent-Györgyi was studying pigeon muscles. Stay with me, now! He received a Nobel Prize for his efforts, part of which was discovering several aspects of what later became known as the citric acid cycle. His discoveries were taken further that same year by Hans Adolf Krebs and William Arthur Johnson. [I guess they decided the Johnson cycle didn’t sound as impressive.] Krebs received the Nobel Prize for Physiology in 1953 for that work. [I don’t know why Johnson didn’t. Maybe he was too difficult to work with. I don’t know.] The Krebs cycle is part of the aerobic respiration process plants use to produce usable energy.

Respiration, not what I expected

When I hear “aerobic respiration” I start thinking about increased heart rates and time spent on a treadmill, but that’s not it. Aerobic respiration refers to one way that usable energy is formed. That usable energy is adenosine triphosphate or ADT. ATP is a molecule that carries usable energy around within a cell, taking it wherever it is needed. ADT is created when food (sugar) is burned with oxygen. I don’t know how plants burn anything but I keep getting images of little campfires in plant cells, so that’s kinda fun.

Sugar as plant food

I always thought plants simply drank sugar solution as food, but that’s not exactly how it works. Let’s put our steampunk magnifiers on and see what’s really going.

Plant cell (Lady of Hats) Public Domain

How plants convert sugar into energy is far more complex and amazing than my little campfire, especially when you think of the scale at which all of this is happening. Plant cells are 10 to 100 micrometers across, depending on the species. This means you could put approximately 180 to 1,800 plant cells across the top of an American dime. [Human and animal cells are even smaller and they do similarly impressive things.] Now back to converting sugar.

Sugar crystals at x50 and x300 magnification (Gabriela P.) CC BY 4.0

To start, you need to know that sugar molecules are relatively large. To use them, plant enzymes go to work, breaking down those acidic glucose molecules into energy and pyruvic acid. That process is called glycolysis. More reactions occur, breaking the remaining bits down into carbon dioxide. As energy is released through these processes, it is moved to other molecules, called electron carriers. Electron carriers are like tiny cargo trucks. They form a chain called the electron transport chain. This transport chain creates ATP. As a side benefit, the processes also create the building blocks of several other molecules, such as amino acids.

For perspective, let’s say that a plant cell is the size of Arizona and the mitochondria are Phoenix. Arizona has a railway system that transports food. All the food comes from Texas and is too big to be packaged. This giant-sized food is taken to Phoenix where it goes through a 9-step process that converts the giant food into snack-sized portions that are small enough to fit on the trains. The trains take the food wherever it is needed. Put simply, that’s the Krebs cycle.

But what does all this have to do with your garden?

The bottom line, healthy plants produce bigger, tastier crops with less effort on our part. They are better able to defend themselves against pests, diseases, and weather extremes. All you have to do is make sure they get the right amount of water regularly and that the soil they are growing in contains the correct range of nutrients.

Have you had your soil tested yet? What did you learn?