Life Requires Free Energy

Uploaded by bozemanbiology on 05.07.2011



Hi. It's Mr. Andersen and welcome to biology essentials video number 12. This
is on free energy and how life requires free energy. Now I am going to assume that you
know what free energy is. If you don't, make sure you watch the video that I made called
Gibbs Free Energy. And it talks you through that process in a real conceptual kind of
a way. But on our planet we get free energy from the sun. In other words we get a constant
supply of energy from the sun in the form of sunlight. And plants are able to use that
to convert that energy into sugars which we then breakdown. And so if it weren't for the
sun and if it weren't that available energy from the sun, life on our planet wouldn't
exist, at least the way it does today. And so today I'm going to talk about how we utilize
free energy. And so life requires free energy. Where do we get that free energy? We get it
from the environment. So we get it for the most part from the sun. How do we utilize
that energy? We utilize it through a series of chemical processes called metabolism. So
it's the sum of all of the chemical reactions inside our body. A specific one that I'm going
to talk about today is called glycolysis. And it's a series of chemical reactions. It
alway goes in a certain sequence. And the neat thing about it, is that you can jump
into at different points depending on what kind of energy or what kind of nutrients you're
getting. Next I'm going to talk specifically about how we organize, grow and reproduce.
So these are the three major things that we get from free energy. How we organize our
life. How we get bigger. How we develop. And then how do we finally pass on our genes.
Because that's the goal of all living things is to pass your genes on to the next generation.
To do this we must maintain homeostasis, which is an internal environment that remains stable.
Now there's an interesting relationship between the metabolism rate and your body weight.
And I'll finally talk about that. Now let's say we have some extra free energy. What do
we do with that? We can use that for storage. So we can use it later. And then the last
thing I'm going to talk about in this podcast is disruptions to free energy. If we get disruptions
to the free energy that we have in an individual that can lead to death. But also those disruptions
can lead to changes in a population or even an ecosystem. So that's what I want to talk
about. First thing that you should know is that life requires order. In other words it
requires a lack of entropy or a lack of disorder. Once we become disordered then we eventually
die. So to maintain that we require a constant supply of energy. So for example your brain
is the picture I have here. Twenty percent of the energy inside your body is going to
just maintaining the nervous system. And so that you actually, even though you might not
think your thinking, you're actually using a huge amount of that energy just to maintain
those nerves at a static state, yet alone to maintain the order inside our body. Now
there's two thermodynamic laws that I should briefly talk about. And you're very familiar
probably with the first one. The first law of thermodynamics says that energy can neither
be created nor destroyed. But it can be transferred. And so what that means is energy from the
sun is converted to energy in plants, in food. We eventually eat that. We convert that to
ATP and then we use that energy to maintain order. And so that energy that you're using
right now originally came from the sun. We don't make energy. We don't destroy energy.
But all that energy is eventually going to end up as heat or a lower form of energy.
So that's pretty straight forward. Second law of thermodynamics gives some people fits.
The second law of thermodynamics says that this, that every time we convert energy we
increase the entropy of the universe. Now what is entropy? Entropy is disorder of the
universe. And so from the origins of our universe, from that first big bang, to the formation
of the galaxies and the evolution of those through time, the randomness of the universe
is going to get greater and greater and greater. In other words we're going to become less
ordered as a universe. Now what's interesting about that is that some people have a problem
with that and they say that evolution violates that. They say that since entropy is increasing
over time how could you get something that is actually adding to the order of the universe?
Like evolution running almost in the opposite direction for that. And so example they say
is how could you get the formation of an eye from something as simple as just photoreceptors
if things become greater and greater as far as their level of disorder over time? They'd
be totally right if this was a closed system. In other words since we constantly get energy
from the sun, our planet does. And a constant supply of energy from the sun, we can actually
become evolved or we can gain greater order but we do that by increasing the disorder
of rest of the universe. And so the second law of thermodynamics only applies to a closed
system. And since the Earth is far from a closed system, it doesn't violate the second
law of thermodynamics. I love this progression right here on how we could go to the eye.
Because that was an argument that people had for evolution. How could you, what's the point
of having, for example, like a half of an eye? How could you have gone from simple photoreceptors
to an eye? Well if you think about it, each of these steps give you an advantage. So let's
say we have an organism that can just sense light, so like a flatworm. It only goes where
there is darkness so it can avoid being dried out. Well imagine if that membrane just gets
folded in on itself. What does that give you? Well these photoreceptors can see things coming
over here. These things can see things coming over here. And so what you get is you can
actually sense motion. And so the neat thing about evolution is that each of these steps
gives an advantage to that organism. And also we see organisms that have each of these different
types of eyes. And so I think that's fascinating. And it doesn't fly in the face of second law
of thermodynamics. It's an open system. And so we become more and more ordered at the
expense of the disorder of our planet. So I want to talk mostly about metabolism today
and how we utilize that energy. First process is called glycolysis. And this is shared by
almost all living things on our planet. So that suggests it goes pretty far back. So
to start glycolysis, which is the breakdown of glucose into pyruvate, you have to actually
add a little bit of ATP. But eventually what you do is you break it into two molecules
of pyruvate and you release more ATP and then a little bit of NADH. And we'll talk more
about that in cellular respiration. Now the process is not as simple as this. Like anything
in chemistry, it's much more complex than that. And so let me show you the different
steps in glycolysis. Glycolysis actually looks like this. So this would be right here, let
me get a different color, this would be glucose, which I just showed you. And then this would
be pyruvate and we're making ATP and we're making NADH down here as well. And so there's
a series of intermediates or steps that we must go through just to make that pyruvate.
Now this is found in almost all living things. And so bacteria for example, use glycolysis
just like we do. And it would be a pain if ate lasagne and we had to have one pathway
to release that energy and we drank milk or ate strawberries. And since they each have
a different sugar, it would be a waste if we couldn't just use this one process. And
so glycolysis is ubiquitous. It is used by almost all living things. So the neat thing
is simple sugars like glucose enter right here. Galactose is found in dairy products
and it will actually jump into the glucose 6-phosphate. Fructose can jump in farther
down the pathway. And glycogen, glycogen is a number of different sugar molecules that
we store. We use it for storage in living things. It can jump in right here. And so
I don't want you to memorize any of these intermediates. It's important in glycolysis
that you know where we start and where we begin. But also know this. It's a systematic
pathway and you can jump into it at different points along the way. So what is free energy
for? Well free energy really does these three things in living organisms. It allows us to
organize. It allows us to grow. And then it allows us to reproduce. Now like I said there's
an interesting relationship between metabolism and the size. And it kind of goes like this.
An elephant, which is a large organism has a relatively low metabolism. And a mouse which
is really small is going to have a high metabolism. Well, why is that? One of the reasons why
is that it has a hard time maintaining that homeostasis or that stable internal environment.
It losses a lot of it's energy to heat and so it has to crank up it's metabolism to accommodate
for that. And so what do we use free energy for? What do we use metabolism for? We use
it to organize. So we could say organization from the level of macromolecules all the way
to organelles, cells, organs, organ systems inside our body. We constantly are using an
influx of free energy to do that. And remember the coinage in life is ATP or adenosine triphosphate.
As we break that down into ADP that releases free energy and we can use it to do things.
For example, to maintain the sodium potassium pump that fires the nerves inside your brain.
We also grow through out our life. And that's not only development from this embryo to the
fetus to the baby. We also have to replace all those cells that are dying throughout
our life. And so we use free energy to do that. So we're using a lot of energy just
to organize ourselves, to grow and then maintain this homeostasis. We use extra energy to do
reproduction. And so the flowers of a plant are not there to maintain order or to grow,
they're used to pass their genes to the next generation. To pass sperm and fertilize egg.
And so reproduction is another way that we use metabolism inside our body. We always
maintain homeostasis. Homeostasis is that internal stable environment. Now these turtles
right here are ectotherms. And what that means is they maintain their body temperature by
using their external environment. And so a turtle will be the same temperature as their
surroundings. And so since metabolism is a bunch of chemical reactions, they don't run
really well at low temperature and so these guys are basking or sitting in the glow of
sunlight to warm up their bodies so they can actually use that. And then finally we can
store energy. I had said before that we can use it to store sugar and glycogen inside
our body. But plants will store that in starch. So potatoes are made up of starch, which is
a bunch of sugar molecules. And then they're using those to grow. And you see that if you
leave the potatoes in your closet too long, they'll actually start grow out of the closet
if you forget about them. And so the last thing I want to talk about is what happens
if we have disruptions to the amount of free energy that we have? Well if I get disruptions
to the amount of energy that I have, in other words I quit eating, that eventually leads
to death. And that's what always happen if we have a decrease in the amount of free energy.
But it gets more complex than that in life. In other words this is a food web. It shows
how the plants or the autotrophs in a population are fed on by herbivores and carnivores or
heterotrophs above that. And so if we have a decrease in the amount of free energy, so
a decrease in light for example, that's going to impact the plants and it's going to impact
this food web above them. Now it gets really complex. And so the example I have here, I
gathered from Jared Diamond's book which is Collapse. It's a great read. But this is Easter
Island and you know Easter Island for these giant statues that they built there at one
time. But what you probably didn't know about Easter Island is that it used to look a little
bit like Hawaii. Not quite as lush, but there were trees over the whole of Easter Island.
And the people that moved to Easter Island, they're pretty isolated, ended up cutting
down every tree on the island. As a result of that the population crashed. And so when
modern humans found the people on Easter Island, they were just holding on by a thread. Why
is that? Well, they were decreasing the amount of free energy and they had done that by decreasing
the plants on that, which they should have been using for life. And so they also couldn't
make transportation. The whole thing fell in on itself. But we could point to a decrease
in the amount of free energy that led to the collapse of Easter Island. And so that's free
energy. It's required for life. And I hope that's helpful.