Energy

What is energy?

We all “know” what energyThe capacity to do work or cause change. is—or do we? We all have a feel for what energy is, but try to come up with a good definition for it. It’s pretty difficult, isn’t it? You can probably think of examples of energy: your voice, a battery, burning wood, a light bulb emitting light, but a definition of energy is elusive since you can’t really hold it in your hand. 

Energy is the capacity to do work. This is a simple but profound definition.

Potential and Kinetic

Let’s describe some properties of energy that are important for understanding how energy drives the work of living systems. Energy can be in one of two forms: potential and kinetic. 

Potential energy is stored energy like a battery, a spring that hasn’t sprung, or Hypnotoad that has hopped.

Kinetic energy is energy that is in motion, like a frog in the process of jumping, a springing spring or the electronic device on which you are watching or listening.. 

Sparkzilla

Another great example are wind-up toys.  I, personally, had this toy when I was younger.  He did not emit actual sparks but he did walk forward. 

OK, so we turn the key (kinetic energyEnergy of motion.) in the back of Sparkzilla here and he traps that as potential energy in the mechanism.  Now Sparkzilla is ready to lumber forth and emit sparks.  Once you push his little button in the back, it releases the spring and he lumbers forth (again, kinetic energy) emitting sparks for all young children to enjoy safely. 

Properties of Energy

Now that we have a basicA solution with a pH above 7, having a lower concentration of H⁺ ions. understanding of how energy is defined, let’s consider some of the properties of energy.

First, energy can never be created nor destroyed. Energy can merely be converted from one form to another.

For example, your MP3 player does not create any new energy. Instead, it takes the potential energy of the battery and converts it to kinetic energy to drive the player. Once the potential energy of the battery is used up, you can no longer power the kinetic energy of the player until you restore the potential energy by charging or replacing the batteries.

Within a biological system such as a singular cell, this principle of energy conservation means we always need to make a complete accounting of the energy in and the energy out, and these two should exactly balance each other.

Converting energy

The second important property of energy is this: Every time energy is put to work or is converted from one form to another, some energy is lost as heat. Heat is also a form of energy, but it is so chaotic, so unorganized, and so spread out that it cannot be put to work.

Any energy converted to heat radiates out of the system and so can no longer be put to use by the system. Think of all the examples of non-living and living things that convert energy and generate heat as they do: light bulbs convert electric to light energy, cars convert the energy in gasoline into kinetic motion to move you forward, raising your engine’s temperature, your body sits somewhere near 37 degrees Celsius as it converts the energy of your food into ATPThe energy currency of cells used for muscle contraction., and plant-dense regions of the Earth emit more thermal energy than those less vegetated. 

As a complex organismA living individual made up of cells. you need a constant input of energy into your cellsThe basic structural and functional units of life. to make up for the energy that you are constantly losing as heat. Energy flows through a system, entering as food, being converted from one form to another, and exiting as heat. If you stop bringing energy in, heat is still lost, gradually decreasing the amount of energy available to your cells.

Okay, now that you understand what energy is and some of the basic principles surrounding its usage in living systems, we can ask a crucial question: What is work at the cellular level?

Cells are dynamos of work—breaking down raw materials, controlling the movementA fundamental property of life involving motion of the body or its parts. of materials across membranes, transporting materials throughout the cell, building new cell products, monitoring and adjusting to both internal and external stimuliChanges in the environment that are detected by sensory receptors., and providing for the next generation. All of these cellular processes require energy.

Chemical Energy

In a cell, the form of energy that drives most of this work is chemical energy. Any kind of macromolecule (carb, lipid, and protein in this case) can be broken down to serve as a source of energy. However, carbohydrates, glucoseA simple sugar that is the main source of energy for cells. in particular, serve as the universal fuel for our cells.

The potential chemical energy in food compounds is in bonds like the C-H and C-C bonds found in glucose. This chemical energy can be released when these bonds are broken and reformed. Some students develop the misconception that chemical energy is released because bonds are broken. Actually, it takes an input of energy to break bonds. But, when a new bond is formed, the extra energy is released. 

Heat is emitted by an organism as it grows as well as when it breaks down.  So ultimately, energy is given off as the bonds of the molecule are rearranged from high-energy bonds as those in glucose to lower-energy bonds such as those in carbon dioxide and waterThe universal solvent essential for life..