[Voiceover] I would like to welcome you to Biology at Khan Academy. And biology, as you might know, is the study of life. And I can't really imagine
anything more interesting than the study of life. And when I say "life," I'm not just talking
about us, human beings. I'm talking about all animals. I'm talking about plants. I'm talking about bacteria. And it really is fascinating. How do we start off with
inanimate molecules and atoms? You know, this right here
is a molecule of DNA. How do we start with things like that, and we get the complexity
of living things? And you might be saying, well, what makes something living? Well, living things convert
energy from one form to another. They use that energy to grow. They use that energy to change. And I guess growth is a form of change. They use that energy to reproduce. And these are all, in and of themselves, fascinating questions. How do they do this? You know, we look around us. How do we, you know, eat a muffin? And how does that allow us to move around and think, and do all the things we do? Where did the energy from
that muffin come from? How are we similar to
a plant or an insect? And we are eerily or strangely similar to these things. We actually have a lot more
in common with, you know, that tree outside your window, or that insect, that bee,
that might be buzzing around, than you realize. Even with the bacteria that you can only even see at a microscopic level. In fact, we have so much bacteria as part of what makes us, us. So these are fascinating questions. How did life even emerge? And so over the course of what you see in Biology on Khan Academy, we're going to answer these fundamental, fascinating questions. We're going to think
about things like energy and the role of energy in life. We're going to think about
important molecules in biology. And perhaps most importantly, DNA and its role in reproduction
and containing information. And we're going to study cells, which are the basic
building block of life. And as we'll see, even
though we view cells as these super, super small, small things, cells in and of themselves
are incredibly complex. And if you compare them
to an atomic scale, they're quite large. In fact, this entire blue
background that I have there, that's the surface of an immune cell. And what you see here emerging from it, these little yellow things. These are HIV viruses,
emerging from an immune cell. So even though you imagine cells as these very, very
small microscopic things, this incredible complexity. Even viruses. Viruses are one of
these fascinating things that kind of are right on the
edge between life and nonlife. They definitely reproduce,
and they definitely evolve. But they don't necessarily
have a metabolism. We'll learn a lot more about that. They don't necessarily
use energy and growth in the same way that we
would associate with life. And then perhaps one of the
biggest questions of all is how did life come about? And we will study that as we look at evolution
and natural selection. So welcome to Khan
Academy's Biology section. I think you're going
to find it fascinating. You're going to realize
that biology, in some way, is the most complex of the sciences. And in a lot of ways, the one
that we understand the least. It's going to be built
on top of chemistry, which in turn is built on top of physics, which in turn is built
on top of mathematics. And biology is one of our Frankly, even in the last hundred years, we're just starting to scratch the surface of understanding it. But what's really exciting is where the field of biology is going. As we understand things at a deeper level, at a molecular level, we're going to start thinking about how can we even do things
like engineer biology, or affect the world around us? It's going to raise all sorts of fascinating and deep
and ethical questions. So, hopefully you enjoy this. Biology is one of the most, arguably, maybe the most fascinating subject of all. I don't want to offend the chemists and the physicists out there. I actually find those
quite fascinating as well. But we're going to answer, or
attempt to start to answer, some of the most fundamental
questions of our existence.