So now that we've recalled that,
let's think about the two Laws of Thermodynamics.
The second one is of particular interest to us
but it doesn't hurt to have an understanding of both.
The first law of thermodynamics states that energy
is not created or destroyed,
that means that energy is maintained consistently through systems.
It may change form but it still exists.
So for example, and this isn't a closed system,
an earth is not exactly a closed system.
But imagine that it is for a moment,
and we have energy from the sun,
which is passed on to the grass as it photosynthesizes and captures
carbon molecules and puts them together to form carbohydrates.
And those carbohydrates, the grass is eaten by our zebra,
and the zebra will then pass on its energy to a lion, a carnivore.
So we have this scheme on life of the energy pyramid
in which each level we lose some energy from the biomass.
So grass will have ten times the energy of the zebra,
and the zebra will have ten times the energy stored
in its biomass as the lion will eventually get.
But what happens to all of these other energy forms?
So we have biomass as potential energy,
and then we have the processes that say
the zebra does throughout its life
as it walks around and runs away from the lion,
so on and so forth.
And ten percent on average the ecological rule of efficiency, ten percent
of the energy that the zebra consumed will end up in its biomass.
The other ninety percent fuels the zebra's life. So it consumes
the grass and transforms the energy, stores it into ATP,
and uses the ATP to breath and so on and so forth.
The same thing happens at the level of the lion.
It puts ten percent of the zebra into its biomass
and the rest of it is creating energy that the lion can use
in the form of ATP to go about his daily business.
So energy, in the first law of thermodynamics,
energy is neither created nor destroyed.
We will see that there is always energy
although it may change forms in a closed system.
Naturally we lose some energy as heat,
and it makes its way out into space and goes who knows where,
but energy is not ever going to be destroyed.
Now the second law of thermodynamics states that
disorder is always increasing in universe.
Now it can be a little hard of a concept to wrap your head around
but I consider,
have you ever had a situation in your house
where the kitchen constantly becomes messier and messier,
and it takes a lot of thought and energy to get it together
to put it all back together.
It takes energy input to reorganize systems.
Not all of the energy that you put into reorganizing the system
though is going to available.
So much like this pile of bricks, if we want to organize it
into a wall, we have to put in some energy.
Now we could knock down that wall and release some energy
as gravity drags the bricks back towards the ground
but not all of the energy is going to be usable energy.
And so this brings us into biological systems
in which we have energy before a reaction
and energy after a reaction.
Some of it is usable.
For example, all the energy from the sun came into this plant,
and the plant photosynthesize and build some glucose molecules
in the form of carbohydrates.
Most of that energy is usable in the form of carbohydrates, but some
of it was probably released as heat or other unusable energy forms.
We have free energy being the usable energy,
we call it entropy.
I think EN-ergy entropy.
That's how I'd recall that entropy actually is the usable energy.