Biotic and abiotic factors in Earth’s natural systems | High school biology | Khan Academy

This right over here is a picture of Earth. Not likely a surprise for most of y'all, but we're going to talk about in this video and future videos is how we can view Earth as a system. Many of y'all might be familiar with the term system; we talk about systems as a bunch of things interacting together in very, very complex ways.

Now, the first division that we can think about the constituent pieces of the system, we could think about what is living and what is not living. And that's where the title of this video comes from: biotic and abiotic factors. Now, what do you think biotic means? And I'll give you a hint: it has the word bio in it, which refers to life. Well, a biotic factor is a living factor, so this is a living factor.

Now what's a living factor in a system? For example, our bodies are a system. Our bodies are alive, but you also have biotic factors within that system. For example, you have gut bacteria inside of your intestines. That bacteria—they can live on their own if they needed to—but they are also part of your body's system. So, the bacteria in your gut is a biotic factor.

Some of you might be saying, "Hey, yeah, sometimes when I'm sick, my parents have given me antibiotics." Antibiotics are against living factors that are in your body. Now, antibiotics are usually if you have bad bacteria that are floating around you in your blood or some other place that you want to get rid of, but it can also affect your good biotic factors, say the gut bacteria that you actually need to help with your digestion.

So, we now know that a biotic factor is a living factor. So, what do you think abiotic means? Well, generally, when you have a "a" in front of something, it means not or the opposite of. So, an abiotic factor is a non-living factor.

Now, if you're thinking about an abiotic factor inside of a system, it might be the soil around you. It might be the air pressure, the molecules. It might be the water pressure, the temperature—things that are actually not living. And you could imagine that these, in many systems, will interact with each other.

So now that we have the basics of living factors and non-living factors, biotic and abiotic, let's start to break down Earth as a system into some of the highest-level systems that people will describe it, and these tend to be described as spheres.

Now, why spheres? Well, Earth itself is a sphere, and the four main spheres that Earth scientists, biologists, and other scientists will talk about are, in no particular order: the atmosphere, which is probably a term that you have heard of, and the "atmo" prefix is referring to all of the air around the Earth. We have about a 60-mile thick layer of atmosphere.

Now, 60 miles sounds thick to us, but it's a very thin layer if you think about it from Earth's point of view. You can barely see the little thin atmospheric layer in this image of Earth that I got from NASA. But the atmosphere is all the gases that surround the Earth. And why is it a sphere? If you don't consider all of the water, all of the land, all of the living organisms; well then, if Earth were to somehow maintain its shape, then that air, all of the gases around the Earth, would still be a sphere.

What other spheres are there? Well, there's the biosphere, which you can imagine is all of the living organisms on Earth. So once again, remove all the gas or don’t consider the gas, the land, and the water, but if all the living organisms stayed in place where they were—and we're talking about trillions and trillions of organisms all over Earth—they are for the most part at the surface or very close to the surface of Earth. It would still resemble a sphere.

Then another sphere that we could consider is all of the water, not only on the surface of the Earth but also below the surface of the Earth: the hydrosphere. So when you look at this picture, it's obvious that the oceans and seas are part of that, but also lakes and rivers, and actually any form of water.

We could even be talking about precipitation; we could be talking about rain; we could be talking about icebergs, because that too is water. And then the last sphere, which would really make up the bulk of the mass of Earth, all of the interior and surface of the Earth—including the rock, the continents, and the ocean floor—well then, you are talking about the geosphere: all of the non-water, non-gas, non-living things that make up Earth, which is really most of Earth.