3. How we get energy

We and other animals rely on plants for energy. Without plants there would be no us.  Plant cells are of the same basic eukaryote type as us but with features that we and animals do not have. One such feature is chloroplasts that contain genetic material able to photosynthesize.

The photosynthesis process uses sun energy to convert carbon dioxide from the air and water from roots into the simple sugar that is glucose (C6H12O6). The process releases oxygen. The energy used to make glucose is stored in the structure of glucose and plant cells can extract that energy by respiring (reversing the photosynthesis process).

Plants use glucose to make the more complex sugars of starches (carbohydrates). It is how they grow and multiply the cell structures of their roots, stems, leaves and fruits. They reach out to the sun for summer energy and survive the winter on their energy stores.

We eat carbohydrates and break them down in our mouths and in our intestines to glucose. Our circling blood takes that glucose to all of our body cells along with oxygen from our lungs. Any excess glucose is stored as glycogen, a more complex sugar, in our liver or in our muscle cells for use as and when required. In the cytoplasm of our body cells each 6 carbon sugar molecule of glucose is broken down into 2 molecules of a 3 carbon sugar called pyruvate. The process is called glycolysis.

If the cell has an adequate supply of oxygen cell energy production continues in the mitochondria organelles floating within the cell cytoplasm. Here two molecules of pyruvate combine with oxygen to release energy, water and carbon dioxide. It is sort of complicated reverse of the photosynthesis process called aerobic respiration. Mitochondria use the energy released to convert cytoplasm obtained ADP (adenodiphosphate) into its higher energy form ATP (adenotriphosphate).  ATP in a cells cytoplasm is its energy store; a few seconds worth of power that when used returns ATP to ADP. This aerobic method of delivering cell energy is the preferred and more efficient way but not the only way that cells can get energy.

When exercise is vigorous and extended and their oxygen levels are depleted our cells get energy from the pyruvate in a less efficient but quicker way. The process is called anaerobic respiration. It is a fermentation process of the pyruvate that delivers ATP energy into the cytoplasm very quickly but less efficiently. The process produces the toxin lactic acid that quickly becomes lactate and is then taken by the blood to the liver. Here energy is used to combine it and pyruvate back to the simple sugar glucose for use by cells or to the more complex sugar glycogen for energy storage.

We don’t just get carbohydrates from plants. Dairy products are an animal source of carbohydrates. Animals, like plants also provide us with fats and proteins. Fats we process and store in our bodies. They provide cell protection, insulation and energy when carbohydrates are exhausted.  Proteins are chains of amino acids that our digestive system breaks down into simple amino acids. They are used by cells to build and repair structures and to create enzymes and hormone messengers that support body processes.  Proteins can be used as cell energy but only in an emergency when other sources are depleted.

In my previous article I said particles have energy desires and that cells developed because they more efficiently satisfied particle energy desires. In this article we see just a little of how the evolved highly complex, yet highly efficient electro- chemical processes within us satisfy and support those particle energy desires. They did not evolve and produce us for our benefit. They did it for their benefit.

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