 Let's explore excretion in humans and in plants. In humans, the main parts of the system is the kidneys which form the urine, the ureter which passes the urine down into the bladder where the urine is stored until you evacuate it. If we look into a little bit of more detail, the blood from the heart comes from the renal artery. This is the renal artery. And renal, the word comes, it means kidneys actually. The blood from the renal artery enters into the kidney. In the kidney, the blood gets filtered out. All the unwanted stuff comes out and forms the urine. But of course the cells also use of the oxygen from that blood and then the deoxygenated blood, but the filtered blood now enters into the veins and then it goes through this main vein which we call the renal vein. From here it goes back to the heart. And then what happens to the urine? Well, the urine that is formed goes through the ureter. It comes down through the ureter into the bladder. It sits over here until you're ready to expel it. But you may be wondering, how exactly does the filtration happens inside the kidney? For that, let's look inside the kidney and zoom in and zoom in a little bit more. You will eventually arrive at the main part of the kidney that's responsible for the filtration, the nephron. Filtration actually happens in two stages. The first stage happens over here. This is the opening of the nephron. You can see a blood capillary that is convoluted over here. That is called the glomerulus. This capillary actually came from this renal artery. It kept branching, branching. Eventually you got the capillary. And this cup sort of shape, which is the opening of the nephron, which surrounds the glomerulus, that's called the Bowman's capsule. So what happens is because of the pressure, there is a lot of stuff that actually oozes out of the glomerulus and enters into the Bowman's capsule and enters into the nephron. And this is where all the filtration is happening. Is it amazing that the entire filtration that happens in your body is actually happening in this tiny region? Of course, we have millions of these nephrons, but it's actually happening over here. But then you might wonder, well, why do we have the rest of the nephron if all the filtration is happening here? Because not only the unwanted stuff like the urea, which we don't want, not only that comes out, but along with that, even the wanted stuff like some salts, sugars, like glucose, and even water comes out from here. And the thing is you may want this back in your blood capillary, right? And that's where the second stage comes. So as this filtered stuff goes through this entire loop, through the nephron, there is some reabsorption that happens. Some water gets reabsorbed over here, maybe some salts get reabsorbed, we're not getting into the details of it, but all the reabsorption happens. And then eventually what is left over here is the ultimately what we don't want, which is urine. And then the urine from all these pipes get collected together into the ureter, goes into the bladder and then finally comes out. Which means the first part of filtration happens over here from the glomerulus into the Bowman's capsule, but then we realize too many things have also gone out, we want to reabsorb a few things and the rest of the nephron is to reabsorb. And finally, whatever remains is the urine that goes into the ureter, goes into the bladder and comes out. What about excretion in plants? They don't have such sophisticated systems, things are much more simpler over here. So if they want to get rid of say oxygen or carbon dioxide, well that happens through the stomata that we've seen earlier as well, right? So that's one. What about the other waste products? Well, cells usually like to store it in their cell vacuoles. You might know that plant cells have huge vacuoles. So they can store waste products over there inside the vacuoles. But what if the vacuoles get full? Well, then they can transport it to other parts like the tree bark or leaves and eventually shed them off because a lot of these things die. So they can just get rid of their waste products by shedding off barks or leaves. And of course, there are other ways as well. For example, they can also excrete through soil. They can also put some of the waste products out into the soil.