Plant Respiration: Definition & Process

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  • 0:00 What is Respiration?
  • 1:01 Why Respiration Matters
  • 1:46 Step 1: Glycolysis
  • 3:06 Step 2: The Krebs Cycle
  • 4:01 Step 3: Oxidative…
  • 5:40 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Cellular respiration is essential to the survival of all plants and animals. In this lesson, we'll look at what plant respiration is, why it is important, and the three main phases involved in the process.

What Is Respiration?

I want you to take a deep breath in, then let it out. Breathing might be the first thing that comes to mind when you think of respiration, but respiration on a cellular level is more than just the exchange of the oxygen you take in and the carbon dioxide you let out. In fact, cellular respiration is critical to an organism's survival because it's the conversion of sugars into usable energy.

When you eat a sandwich for lunch, your body breaks that down and then converts those nutrients into energy that your cells can actually use. Plants don't eat sandwiches, but they do get their food in the form of sunlight. However, that food doesn't magically turn into energy just because the plant takes in sunlight. It has to process that sunlight, turn it into sugars, and then turn those sugars into energy that the plant's cells can use, just like your body does with your sandwich. While the source may be different, the end goal is the same for both plants and animals.

So let's dig a little deeper to see what cellular respiration in plants is all about.

Why Respiration Matters

Before we get into the process of cellular respiration itself, let's take a step back to discuss why respiration is so important. We already know that respiration converts sugars into usable energy, but what is that energy used for?

Well, in both plants and animals, the energy provided by cellular respiration goes to cell growth, repair, and new cell production as well as the many processes that occur in your body that you don't even realize are going on. Things like breathing, thinking, pumping blood through your body, and maintaining a stable body temperature are all process that occur whether you like it or not, and all of them require energy! In short, cellular respiration provides the energy cells need to do work, which is what keeps an organism alive.

Step 1: Glycolysis

During photosynthesis, water, carbon dioxide, and light energy are combined to yield glucose (sugar) and oxygen. We can even write this as an equation:

water + carbon dioxide + sunlight (energy) = glucose + oxygen

After photosynthesis, the plant then has to break down the glucose so that the energy can be used for cellular processes. Here, we find that

glucose + oxygen = water + carbon dioxide + energy

Does this equation for respiration look familiar? It should because it's the exact opposite of photosynthesis! Instead of building sugars from energy, we're breaking down sugars into energy. Cool, huh?

There are three steps involved in plant respiration that we need to be familiar with in order to better understand the process. First is glycolysis, which splits a glucose molecule into two pyruvate molecules. This step occurs in the cytosol, or inner fluid of the cell. To remember the name of this first step, just remember that we're splitting glucose, and 'lysis' means to break down. Of note, with glycolysis is that it does not produce much energy (in the form of ATP molecules), nor does it require oxygen to occur; however, this is the only step without this requirement.

Step 2: The Krebs Cycle

The next step along the respiration pathway is the Krebs cycle, also called the citric acid cycle. This step involves the oxidation of the pyruvate molecules produced in glycolysis and occurs in the mitochondria of the cell.

To describe the Krebs cycle completely would take an entirely separate lesson, possibly a few days sitting in a biology lecture hall. I'm not here to put you to sleep, so let me summarize by explaining it like this: this cycle is where, through a sequence of repeating steps, the sugars the plant created in photosynthesis are broken down chemically until their energy is released into the plant's cells. It is catalyzed by enzymes, requires oxygen, and generally requires two full runs through the cycle to be complete. In the end, the plant is left with 2 energy molecules (ATP), carbon dioxide, and two electron carriers called NADH and FADH2.

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