 Let's explore transportation in humans and in plants. In humans, the main organ for transportation is the heart. It pumps the blood to various parts of the body. It's the blood that carries the oxygen and the essential nutrients to the cell and then takes away all the unnecessary stuff like carbon dioxide and waste products from the cell. And in plants, the transportation system is the xylem and the phloem. The xylem carries the water, whereas the phloem carries the food. Let's first look at the transportation of the humans. Let's look at how the blood is pumped in the heart. Let's get some basics right. The top chambers of the heart is called the atrium. So this is the atrium, this is the atrium. And the bottom chambers are called the ventricles. This is the ventricle, this is the ventricle. Don't confuse your left and right. This is the right side. So this is the right atrium and this is the right ventricle. And this is the left side because that person is facing you. That's why this is the left. Then the blue represents the deoxygenated blood, but of course, blood is never blue in color. All blood is always red in color. It's just a way to represent that. And of course, the red over here represents the oxygenated blood. Finally, these two pumps are separate from each other. That's why this is called a double pump. And we say we have double circulation. All right, so let's look at the flow now. Remember that the blood always enters into your heart via the veins. Some basic stuff we should always be careful about. So even here, the blood always enters the heart through the veins. Then from the veins, the blood always enters into the atrium. The blood always enters into the atrium. From the atrium, the blood always goes into the ventricles. The blood always goes into the ventricles. From the ventricle, the ventricle pushes the blood. It always exits the heart from the ventricle through the arteries. Similarly, as the ventricle pushes the blood, the blood always exits the heart through the arteries. Of course, you can see there are multiple arteries over here. I'm not showing all of them. Now let's complete this whole circuit. From the artery, where does this blood go? Well, this is blue, so I know it's deoxygenated blood. Deoxygenated blood always goes into the lungs to get oxygenated. The lungs oxygenate the blood and then it has to reenter the heart. Remember, blood always enters the heart through the veins, so I know it has to go here now. Then from here, the blood exits the artery. Where does it go? Well, oxygenated blood from the heart goes to our cells. So it goes to all the cells. The cells use up the oxygen and deoxygenate the blood. And now this deoxygenated blood has to reenter the heart. Remember, blood always enters the heart through the veins. So it enters over here and that completes our cycle. Finally, from the blood capillaries due to the pressure, the plasma of the blood oozes out. And this particular fluid that oozes out and stays in between the tissues is called the tissue fluid or lymph. Lymph does not contain RBCs. That's why they are not red in color because RBCs are too big to ooze out from the capillaries. But they do contain some digested fat. Now it's important to put them back into the circulation. Otherwise, if the blood keeps on losing its liquid, it gets thicker and it becomes harder to circulate. So to put it back into the circuit, we have a separate network called the lymph network or the lymphatic system. So the lymphatic system suck all of these lymph fluid and put it back into the circulation. They connect it back to these veins. Now it's also possible that they might have picked up some unwanted stuff and therefore we have these things called as lymph nodes in between. There, there are WBCs. There's something that you can think of it as police that keeps a check of it so that by the time the lymph enters into the circulatory system, there are no unwanted stuff. They're all killed in the lymph nodes. One last thing I forgot to mention is that it's the ventricles that push the blood out of the heart. So it's the ventricles that are doing all the hard work. But which of the two ventricles must do more work? Can you pause and think about it? Well, notice this ventricle only has to pump the blood into the lungs and then take it back. So we don't need to do that much of compressing. Whereas this ventricle has to pump the blood such that the blood goes through all the cells and then come back. Which means this ventricle has to pump with a much higher pressure. So the left ventricles have the thickest muscular walls. Once you draw this diagram, you can see everything makes logical sense. Now let's look at the transport in the plants. The transport in the plants is mostly done by vascular bundles or vascular tissues which is made of xylem and phloem. Let's look at each one of them. Xylem mostly transports water and minerals and it's a one-way upward direction. Whereas phloem transports food and it's a bi-directional flow, both up and down, depending on where it needs to go. Xylem contains tracheates which are these cells which have tapering ends and it contains these vessels which are shorter but they are more broader compared to the tracheates. It's a single hollow tube over here and so the flow is much easier over here. How does the water go up? Well, one way is that the roots suck up water from the soil so that creates some pressure but this is not enough. The biggest pressure is created from the leaves where they lose water. The water evaporates from the stomach of the leaves which we call transpiration. This loss of water creates a suction and that sort of pulls the whole water column up. Now this process is a passive process meaning you don't have to spend energy. Transpiration happens automatically due to the sun and so the xylem is mostly a passive transport. That's why the xylem cells, the tracheates and the vessels, they are dead. You don't need them to be alive because they don't really have to do any work. Phloem contains these tubes called as sieve tubes. Sieves refers to the tiny holes that you can see over here which are there in the ends of the cells. Why is it like this and not completely hollow? Because these cells are alive. To keep them alive you need some cytoplasm, you need some boundaries and therefore you have perforations. Why do you need these cells to be alive? Because over here food is transported actively. So the way it works is wherever there's excess food that gets actively loaded using ATP, using energy, it's actively loaded into the sieve tubes. Now because of the increase in the concentration of the food over there, it sucks up water from the xylem and that increases the pressure over here. Now automatically it will tend to move. The whole sap tends to move towards the region of lower pressure and if that low pressure is say upwards then it'll move up. If that low pressure is downwards then it'll move down. If the lower pressure is upwards, in this example let's say it moves up and then wherever the food is needed it gets unloaded and then the water goes back. So notice this is an active process and therefore the cells need to be alive for that. But these cells are barely alive. So to keep them alive they have these things called companion cells. The companion cells have everything that a normal cell has and it's these cells that keep these cells alive and that's why they're called companions. And so this is how the xylem and the fluem transport stuff in plants.