Water, Hydrogen, and Oxygen, and where we get our energy

 

The above equation is a simple way of showing what happens during photosynthesis. There are more detailed ways to show it. Photosynthesis is a complicated process, or processes. But, at its heart, it may be summarized simply.

As you know, there's a lot of water on the earth. As you also know, water consists of two elements, Hydrogen and Oxygen. As you may not know, the energy you need is intimately connected to water. I'm using energy to type this, and you are using energy to move your eyes as you read it. What's that got to do with water?

Our food comes from photosynthesis. Green plants absorb light, and produce various molecules that we use as food, such as starches, sugars, several vitamins, and proteins.

 Light energy is used to split water, and the Hydrogen split off is then available for the manufacture of Carbon-containing molecules, like glucose, food molecules, which can be stored, broken down to release energy, or moved to parts of the organism where they are needed. Some of the need is to release energy. Most foods you buy at a grocery store, or a restaurant, come with a calorie number. That number indicates the amount of energy you would expect to get if you ate and digested that food. The energy comes from energy-storing molecules, like glucose. The Carbon-containing molecules, which have Hydrogen added to the Carbon, may also be used to produce important molecules like enzymes, vitamins, hormones and proteins. (Oxygen, Nitrogen, Sulfur and other elements may be added to a Carbon-based structure.)

Organic molecules, like glucose, will burn. Burning uses Oxygen to carry on combustion. There is a process, used by nearly all organisms, called cellular respiration. That process also uses Oxygen to create water, and, in the process, releases energy for use in our cells. So, putting it very simply, photosynthesis uses light energy to break water, and cellular respiration puts water back together, and releases energy.

I'm bald-headed. So lots of light hits my head. My cells, like yours, have lots of water. So why doesn't that light, on my scalp cells, split water and make glucose? The answer is that various helping molecules, molecular tools, as it were, are necessary for photosynthesis to occur. These include chlorophyll and several enzymes, which I don't have in my scalp cells.

Isn't God great? Thanks for reading.

Trees and Oxygen

A recent letter to the editor, in our local paper, complained that we should be careful not to cut down trees, because we need them to provide Oxygen for us. The author was, no doubt, well-intentioned, but wrong.

It is true that photosynthesis, carried out by trees and other green plants, releases Oxygen. But, as the Wikipedia article on the Atmosphere of Earth tells us, about one-fifth of the earth's atmosphere is Oxygen. As this article tells us, it would take about 2,000 years for us to use up all the Oxygen in the atmosphere, if no more were released by photosynthesis. (We would become extinct much sooner than that, if photosynthesis ceased, because we would run out of food.) The article also tells us that the Oxygen released by forests is almost entirely used up by those same forests. This is because, to obtain energy from stored plant material, most organisms use cellular respiration, which takes up Oxygen, and generates Carbon Dioxide. Even trees use cellular respiration to release the energy they store through photosynthesis..

The letter might much better have warned us that indiscriminate tree-cutting would be expected to mean that less Carbon Dioxide was taken up by photosynthesis, and, hence, the amount of CO2 in the atmosphere would increase. The result would be that the atmosphere would be less likely to allow heat radiation to pass through it, which would contribute to global warming. (See this Wikipedia article on Carbon Dioxide in the atmosphere.) Burning fossil fuels is the main culprit in the recent increases in CO2 in the atmosphere, but cutting forests is the second largest contributor.

Thanks for reading. Be glad that there is Oxygen enough to breathe, and be careful to save as many green plants as possible, so that global climate change can be slowed down.