What is a Host in Biology? - Definition & Overview

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  • 0:00 An Excellent Host
  • 1:00 What Is a Biological Host?
  • 2:14 Other Types of Relationships
  • 3:35 Lesson Summary
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Lesson Transcript
Instructor: Ebony Potts

Ebony has taught middle and high school physical science, life science & biology. She's also been an assistant principal and has a doctorate in educational administration.

You might be familiar with the word 'host,' but it means something very different in biology than it does when you're talking about your home. In this lesson you'll learn the biological meaning of host, and why most of the time you don't want to be one.

An Excellent Host

Imagine that you live on a beautiful island. You have a gorgeous home with breathtaking views of the ocean. You often have visitors, because you like to open your home to those you love. During the frequent visits from family and friends, you serve food, provide shelter, and serve as a guide to the local tourist attractions. Everyone agrees that you are the best host any visitor could have.

But during one of your family visits, an uninvited guest shows up with one of your family members and decides to stay for an extended visit. At first, it's almost as if they're not there. They go about their day in a quiet manner, and take care not to disturb you. As time goes on, however, your house guest starts to eat more and more food, use more and more energy, and take up more and more space. You have had enough of your house guest, especially since you came home yesterday, and realized that he invited seven more guests to come and stay with you!

What is a Biological Host?

Sounds crazy, right? Who would ever allow someone to stay in their home who behaved like that?! What if I told you that the situation I just described is very similar to the biological definition of a host? The only difference is that the person does not have a guest staying in their home - the guest is in their body! The biological definition of a host is an organism that harbors another organism inside or near their body in a symbiotic relationship. A symbiotic relationship refers to two organisms living together.

Now, the guest in the story we described above is behaving like what scientists would call a parasite. A parasite is an organism that depends on another organism for food, shelter and basic needs, to the detriment of that other organism - its host. In our example, your house guest is not helping you at all. He is actually harming you, the host, because it is costing you money to house the guest. In a biological host, the parasite actually causes much more harm than in our example. Some parasites can cause extreme weight loss, fever, and even death! This harmful relationship between a parasite and host is called a parasitic relationship.

Hosts often end up with parasites through a cut in their skin or outer covering, from contact with animal waste, or from food that is not cooked well enough. The parasite makes its way into the host, lives out its life cycle, reproduces and has tiny babies inside the host that repeat the cycle. Intestinal tapeworms are an example of a parasite.

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