Energy!

This post has the most monstrous image I’ve made to date.  I hope it will become more popular and useful than my current heavy hitters the cell and even Louis Pasteur’s experiment of spontaneous generation, which I’ve seen make the top ranks of both Google and Bing image search!

In this image, I’ve covered energy as it passes from the sun in the form of light to the chloroplast of plants. In the chloroplasts, there are structures called thylakoids where the magic happens. This is where photosynthesis takes place in two parts, 1) light-dependent reactions and, 2) Calvin Cycle.

The waste products here are eliminated and the useful products are then sent to the mitochondria.  The first step is 1) glycolysis, followed then by 2) the Krebs cycle (also called the Citric Acid Cycle) under aerobic conditions OR, 2) fermentation (under anaerobic conditions)

There’s a LOT of stuff that happens here. These are the basics.  This stuff can get extraordinarily complicated–the guy the Krebs cycle is named for won a Nobel prize for his work!

I’ve never, personally seen an image that attempted to go from the sun to photosynthesis to cellular respiration but I tried to keep it as simple as possible. That said, if you feel something’s missing, its probably because it is. Some steps weren’t explicitly mentioned for simplicity’s sake.

One final note: ATP gives you a burst of energy. If you need energy to do anything for longer than about a minute and a half, you want sugar. Sugars provide longer-lasting energy.  ATP (which makes up about a half-pound of your total body weight) doesn’t store, in other words, it gets used shortly after it’s made. ATP actually gets recycled over 1,000 times a day by humans!

Energy path thumb

Click for full size

Cellular Respiration

Heterotrophs need to obtain energy from consuming autotrophs.  Remember autotrophs turn light energy into chemical energy, which is stored as the sugar glucose.  The process of releasing energy by breaking down glucose and other food in the presence of oxygen is called cellular respiration.

Cellular respiration is not exactly, but can be roughly viewed as, the reverse process as photosynthesis.  Oxygen and glucose combine to breakdown and reassemble as carbon dioxide, water, and energy.

6O2 + C6H12O6 -> 6CO2 + 6H2O + ATP

oxygen + glucose -> carbon dioxide + water + energy

This process is simplified of course.  There’s a whole confusing mess of glycolysis, ATP, and NADH which the average high school bio teacher would want you to know, but honestly it’s overkill (…it’s not even in our state standards…).

Now there are cases when cells don’t get enough oxygen.  In this case, the cells produce nasty waste products that they remove from their body.  Some microorganisms, such as yeast, produce alcohol in the absence of oxygen.  This is called alcoholic fermentation.  Other organisms, such as yourself, produce lactic acid in the absence of oxygen.  Fittingly, this is called lactic acid fermentation.  Fermentation is vital in our food system.  Production of alcohol is quite the large business throughout the world; as is production of foods such as yogurt and pickles which utilize lactic acid.

One last point of overkill: the Krebs cycle and electron transport chain.  Unless you go to college for Biology, you have no need for this… and honestly, I went to college for Biology and I don’t have a use for it, short of torturing students with it if I was an evil person.

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