Science Learning: The flow of free energy in biochemistry

Science learning doesn't have to be too complicated.

One of the main keys to understanding biochemistry is to think about the flow of energy. The second law of thermodynamics is a core concept for science learning. This video covers the basics of entropy and free energy. It's based on a single formula:


I'll explain the basics of this in the video. But when it comes down to it, learning science is all about mastering a few basic concepts. If you need help with the details, you can always ask me or someone else on the Science Learning Forum.

Anyway, here's the video:

I'll be posting more videos about biochemistry, especially respiration, in the near future. My own science learning has taken this direction lately, even though I'm getting more and more interested in physics.

But enough of me. Let's look at some biochemistry.

Energy is used by a system to create order. For example, you expend energy to fold your clothes, put things away, and otherwise clean up your room. When you don't expend energy to create order, your room falls into a state of disorder, or entropy. This can take the form of dust, clothes on the floor, a ruffled bed and so on.

Now let's apply this idea to science learning. When a plant uses photosynthesis to create carbohydrates, it is creating order--the carbohydrates are more orderly than the carbon and other elements from which they were made. Since energy was used or absorbed to make the carbohydrates, they contain energy and we say the system gained some energy.

But sooner or later the carbohydrates will burn. Maybe the tree catches on fire, or simply does and is slowly devoured and oxidized. More likely, however, the carbohydrates are broken down, releasing energy to do work for the plant. Either way, the result is the same. The system loses energy, and the carbohydrates are broken down into less-orderly molecules of carbon dioxide and water. Entropy takes place.

In the formula, ΔG = ΔH - TΔS,

ΔG stands for the change in free energy in the system.  ΔH stands for the total energy of the system, and T is the temperature in Kelvins of the system. ΔS stands for entropy. So we see, if there is a lot of entropy, the change in free energy will be negative--the system released energy. Likewise, the creation of order (or "negative entropy") would mean that energy was absorbed by the system and the change in energy was positive.

Of course, in a living system many such changes can happen in a tight sequence or even simultaneously. Somewhere in your science learning you've probably heard about ATP. When carbohydrates are broken down in a cell (producing entropy and releasing energy), the energy released is used to convert ADP into ATP (producing order and absorbing energy). Then the ATP breaks down to ADP, releasing energy to do some work in the cell, and creating entropy in the process.

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