We and other animals rely on plants for energy. Without plants there would be no animals, no us. Plants have the same basic eukaryote cell 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 photon energy from the sun to convert carbon dioxide it takes from the air and water it takes from the roots into the simple sugar that is glucose (C6H12O6). The process releases oxygen. Glucose is an energy efficient structure but with an energy content that can be released by the process of respiration (a reverse of the photosynthesis process).
Plants use the simple sugar that is glucose to make the more complex sugars of starches or carbohydrates as they are called. It is how they grow and multiply the cell structures of their roots, stems, branches and leaves that go in search of energy and nutrients. They also create fruits with seeds containing genetic instructions enabling their replication. Many plants in winter shed their energy gathering leaves and survive on their energy stores.
We eat carbohydrates and break them down in our mouths and in our intestines to the simple sugar that is glucose. Our circling blood takes it and oxygen from our lungs. to trillions of our body cells. Any excess glucose is stored, for later use, as glycogen (a more complex sugar) in our liver or muscle cells. We don’t just get carbohydrates from plants. Dairy products are an animal source of carbohydrates.
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 needs energy and has an adequate supply of oxygen mitochondria organelles floating within the cell cytoplasm take two molecules of pyruvate and combine them with oxygen to release energy, water and carbon dioxide. The process is called aerobic respiration. We may view it as a complicated reversal of the photosynthesis process.
Mitochondria use the above energy release to convert ADP (adenodiphosphate) taken from the cell cytoplasm to create its higher energy form ATP (adenotriphosphate) that goes back into the cell cytoplasm. Understandably there are many more mitochondria in energy using muscl cells.
The ATP in cell cytoplasms are 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 cell 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 to be taken by the blood to the liver for processing back to glycogen or glucose.
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.
Now we know how we get energy how do we use it? When our brain requires an action a tiny electro-chemical energy pulse signal is transmitted down the long nerve cells of our central nervous system. The signal triggers selected cells to move chemicals across their membranes. Calcium that is short of electrons is moved close to muscle fibres (also long cells). The electron free spaces attract many of the electrons in the long cell structures that are muscle fibres, shortening them. That is how our muscles contract. Remove the electron shortage and the muscle relaxes. All muscles are somewhere between contracted and relaxed. Good for you if yours are more relaxed.
By way of an example the upper thigh muscle shown extends the leg by contracting. It relaxes when other muscles (not shown) at the rear of the leg contract to bend the leg. When extending the leg we apply a force between our foot and the ground so as to move us away from it. We will learn more about the nature of these forces later.
Movements we make are a mixture of contractions and relaxations of muscle cells. What seems to us as a smooth motion is actually a lot of on and off muscle actions. In the worlds strongest man competition we often see pronounced vibrations as muscles come under pressure. But in everyday use they provide for the most sensitive of touches. We are an assembly of many highly efficient energy systems with highly complex energy controls.
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.