Cation Exchange

by Jason Amores Sumpter
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plants extract nutrients from the soil is ions. Most of this nutrient absorption is going to occur in the zone of maturation, which is behind the root tip and where you'll find all those root hairs. The reason for this is that root hairs significantly increase the surface area available for water and nutrient absorption. In fact, a single stock of a wry plant, which is kind of just like a wheat plant very similar. A single stock of that can have a root system with the surface area equal to that of a basketball court. Now that's pretty incredible. And it just goes to show how diffuse and how how diffuse the network of roots and root hairs is that it can create that much surface area yet not take up that much volume now. Ions, you might recall, come in. Two flavors we have are negatively charged an ions and are positively charged. Cat ions and ions air easier for plants. They're dissolved in water in the soil, and that makes them readily available for absorption. Unfortunately, irons dissolved in water are also easily leached from the soil. Leaching is the loss of nutrients through the movement of water. Now there's one exception to all of this. And that is phosphate, which is an an I am. It's p 03 I'm sorry, p 04 three minus very negatively charged and ion. But this is not dissolved in water and soil. It actually forms complexes with calcium and iron cat ions don't need to worry about that too much. Just wanted to point out that not every single anti and is gonna be dissolved in water. Now, cat irons, though they do dissolve in water in soil usually interact with clay and ions or organic acids. And these remember are going to come from humus thes, uh, because these, uh, our cat ions rather interact with clay and humus. It makes them harder for plants to extract. And here, in our example, you can see we have a clay particle with all of these cat ions interacting with it. That's because this clay particle has lots of negative charges. But this could also be a particle of humus, because it, uh, humans has all those organic acids which once they d protein, eight are of course, going to have a negative charge, which is why these cat ions air also going to interact with those organic acids. Now, plants do have a way of getting those cat ions from the soil. We call this cat ion exchange right. You don't get something for nothing. You got to give a little get a little. So basically the way it works is soluble cat ions like protons, and that's what plants they're gonna use. Though cat ion exchange can occur with other cat ions, these soluble cat ions are going to bind to the negatively charged soil particles and cause cat ions like magnesium and calcium, the ions that are nutrients, that the plants want to be released and allow the plants to absorb them. So basically what we're doing or what plants are doing is exchanging one cat iron for another. Remember earlier we said that plant roots will secrete protons, right? Secrete lots of protons. Well, that is to help with caddy. In exchange, it should be noted that humus has what's known as a higher cat ion exchange capacity than does clay. Basically, that means humus will more readily exchange it's cat ions than will a clay particle. Now, plants influence cat ion exchange by releasing Co two as well. And you might remember that CO two is a byproduct of cellular respiration. Right, So the plant roots carry out selling respiration. They're gonna release their CO two, and that CO two is gonna form carbonic acid in water that is found in the soil. So this is going to lead to the release of protons and help facilitate cata and exchange. And you can see that happening in this image here, the plant root is going to release that CO two, which is gonna turn into carbonic acid here. As you can see, it will deep protein ate here. Those protons and then those protons are going to trade places on this negatively charged soil particle with a cat ion. In this case, we have two protons. That's two plus charges so we can take one calcium away. So important to note there that it's not a direct exchange of particles, right? You don't just trade one proton for one magnesium, right? You have to balance charges. So it takes two protons to you protons, for example, to trade with the magnesium. Now it should be noted that if soil gets too acidic, the rain can wash away cat ions, right? Those congee leached from the soil just like the and ions, though it won't happen, is readily unless the soil is very acidic. With that, let's turn the page.