Nematode Circulatory System

Instructor: Dominic Corsini
Why do living things pump blood throughout their bodies? What purpose does the circulatory system serve? This lesson investigates circulation in nematodes, the most numerous worms on Earth. A brief quiz and summation are included.

What is Circulation?

To begin, let's start with a question. What does the network of blood vessels throughout your body actually do? The simple answer is that it delivers blood to your tissues. But why does this have to occur? The more detailed answer is that living organisms need to exchange material, such as gasses, with their environment to maintain their basic metabolism. Specifically, living organisms need move nutrients throughout their bodies and remove waste. The delivery/removal of these items is performed in part by circulation. Living organisms perform circulation in different ways. Mammals rely on blood vessels, trees have tiny openings in their trunks, and nematodes utilize a process called diffusion. Nematodes are the most numerous microscopic worms on Earth, and amazingly, they have no circulatory system (we'll talk about this in a minute). Diffusion is a process where substances move from an area of high concentration to an area of low concentration. Below is an illustration for your reference.


How Nematode Circulation Works

First off, understand that nematodes are worms. In case you've never seen one, have a look at this photo for reference.


As microscopic worms, nematodes don't have lungs, blood vessels or any other type of circulatory apparatus. Remember, a primary function of your circulatory system is moving materials throughout the body. For example, circulation transports oxygen to your cells and removes carbon dioxide. Instead of using blood vessels for this, nematodes exchange materials through their skin as a form of circulation. Here's how this works. Nematodes, like all living organisms, must respire (exchange gasses) to stay alive. Much like us, they use oxygen and produce carbon dioxide (CO2) gas as a waste product. Therefore, because they are using oxygen, an imbalance is created between the amounts of oxygen on the inside and outside of their bodies. This imbalance is called a concentration gradient, and it is the driving force behind diffusion.

Examples of concentration gradients and diffusion are everywhere. Consider when someone cooks bacon for breakfast. The highly concentrated smell of bacon diffuses across the room until everyone can smell it cooking. Or, perhaps an even better example, if you place a drop of food coloring into a glass of water, the drop will eventually diffuse and stain the entire water column. Initially, the drop of food coloring would be highly concentrated, but then would diffuse into areas of lower concentration. Remember, diffusion is the movement of material from areas of high concentration to areas of low concentration.

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