 Carbon supports life on Earth as we know it. In fact, we humans are 18.5% carbon. Our plant friends produce carbon through a process called photosynthesis. Through photosynthesis, plants provide that delicious oxygen that humans and other animals need and love. So understanding how much photosynthesis is happening tells us a lot about how healthy the plants are in an ecosystem. Now, we know photosynthesis is happening all around us. We see plants growing and reproducing every day. But how do us science-minded humans measure how much photosynthesis is happening in plants in order to grow and produce oxygen? How we measure photosynthesis is the topic of this video. So let's first talk about that carbon-generating process called photosynthesis. The photo part in photosynthesis relates to light. Plants use energy from light to grow. Now, synthesis relates to biosynthesis, or the process in which plants synthesize light, carbon dioxide, or CO2, and water to grow. Now, to support growth, plants absorb CO2 from the atmosphere through small pores in their leaves called stomata. Using energy from sunlight, CO2 and water are synthesized to create sugar. This sugar is then converted into energy that plants need to grow through a process called respiration. So the delicious CO2 that plants absorbed, mixed with some sun and water, creates the perfect cocktail to produce that energy that plants need to grow. And if that's not important enough, through photosynthesis, plants also provide clean air for us to breathe. But how do we actually measure photosynthesis? Well, one way to measure photosynthesis is to measure how much CO2 plant leaves absorb. Because we know that a plant that is actively absorbing CO2 is also performing photosynthesis. But how do we actually measure CO2 uptake by a plant? Well, let's first place a leaf in a closed chamber that's filled with CO2-rich air. Think about it, if the leaf in the chamber is alive, it will uptake CO2 to produce the energy that it needs to grow. Now, one way to measure the CO2 in that chamber is to use light. The method of using light to measure things in science is called spectroscopy. Spectroscopy methods measure how much matter, like CO2, absorbs, reflects, or transmits light. Now, CO2 loves to absorb infrared light. So if we fill a chamber with a lot of CO2 and we shine infrared light into the chamber, a lot of that light will get absorbed. Now, on the other hand, if the chamber doesn't have a lot of CO2 in it, only a small amount of that light gets absorbed. Now, equip the chamber with a detector that can measure the amount of light that makes it to that end of the chamber. The detector is calibrated, which means that it relates the amount of light recorded in the box to a specific amount of CO2. So more light recorded means less CO2 in the chamber, and less light recorded means more CO2 in the chamber. This chamber system is called an infrared gas analyzer. Infrared gas analyzers are commonly used to measure CO2 uptake. So now that we understand the basics of spectroscopy, how do we measure CO2 uptake of an individual leaf? Well, we can use our infrared gas analyzer chamber system. First, add a reference chamber on the left. We'll flow CO2-rich air through this reference chamber and use the infrared light detector to measure how much CO2 is in the air. Next, add a second sample chamber on the right. Air flows from the reference chamber to the chamber with the leaf in it and into the sample chamber. The sample chamber uses infrared light detector to measure the amount of CO2 in the air after the leaf absorbs what it needs to grow. We can control the volume of air moving through the chambers using a flow meter, so we know how much air is in each chamber. Here comes the interesting part. We can calculate the difference in the amount of CO2 measured in our reference chamber compared to the CO2 measured in our sample chamber. The difference between CO2 and the two chambers is the flux, which represents the amount of CO2 taken up by the leaf inside the chamber for photosynthesis. The measurement of the difference in CO2 between the two chambers is called net assimilation, or ANET. The infrared gas analyzer can be used to estimate how much photosynthesis is occurring. But if that's not powerful enough, it can also be used to measure how temperature and moisture changes in our climate impact carbon uptake. We can also add additional meters to the setup that control things like temperature and humidity in the chamber. So we can adjust the temperature of the chamber and measure how that affects CO2 uptake of our plant. These measurements can also be combined with other techniques that measure and estimate carbon over large areas. For example, the National Ecological Observatory Network, or the NEON project, uses an infrared gas analyzer installed on its towers across the United States to measure carbon in the atmosphere. NEON will also be combining this atmosphere carbon data with airborne remote sensing to model carbon across entire forests in over larger landscapes. And so to sum this all up, plants use CO2 to perform photosynthesis to grow and provide oxygen. We can measure CO2 uptake with spectroscopy or light measures using an infrared gas analyzer. These measurements can help us understand both how healthy plants are in an ecosystem and also how changes in climate affect plant growth. And that, my friends, is how and why we measure photosynthesis.