Light Energizes Life

Energy Flows-Or Nothing Happens

Light is one kind of energy. There are many things about light that we don’t understand, but we only need three bits of very well established scientific fact to cover the most important aspects of how energy flows through the ecosystem to keep all of life alive.

1. Light is energy. We have defined energy as the ability to make actions happen, and light can make actions happen. For example, when light hits your eyes it activates molecules in a nerve cell that sends the message to your brain. That is one kind of work. Energy is the ability to do work.

2. According to the second law of thermodynamics, pushing anything from a lower level of organization to a higher level requires work. Work is necessary to push any kind of action “uphill,” but “downhill” actions can happen without help. It requires energy for you to climb the stairs to the top of the Empire State Building, but it requires no energy to get to the bottom if you fall off. In a more relevant example, anything that is more complicated or more powerful is “uphill.” To make a cake requires energy, but it can fall apart by itself. Cake is more complicated than flour. Life is the most complicated thing on earth. Cells require energy all the time in order to maintain their complex organization. They do this, with regard to energy, by balancing the “uphillness” of complexity with the degradation of energy. The light gives its energy to maintain the complexity of life. This is possible because energy takes different forms.

3. Some forms of energy are “uphill” from others. For example, light energy can release some of its energy to become heat, but heat energy can not spontaneously change back into light, because heat is a lower form of energy. Plants use light energy to make what I am referring to as organic energy (in food). Light energy is a higher form than organic energy, and organic energy is a higher form than heat energy.

So, the bottom line is that life maintains its “uphill” complexity, by changing light energy to organic energy and using the organic energy to feed the whole ecosystem. For some people, this is the definition of life. Life is working, working, working all the time to keep itself from falling apart, and — if it stops working — it does fall apart. It dies.

That’s why people are alive and cake is not. Once you turn off the oven, the cake has no way to maintain its high level of organization and eventually it will fall apart. The miracle of life is that it can use light energy to keep itself organized and functioning — and it does this inside of itself. Inside every cell in our bodies and every organism in the ecosystem. So far as we know, nothing else in the universe can do this. Only life.

So the first half of our life story is about the amazing way that plants, and some bacteria, are able to capture light energy and convert it to food energy that we have referred to as organic energy. The process happens only in green plants and bacteria and it is called photosynthesis. Photosynthesis is the process of capturing light energy and converting it to form the energy attractions that bond together groups of atoms and small molecules to make large organic molecules. They capture the light using a pigment molecule that is called chlorophyll.

Capturing, or absorbing light energy is no problem. Absorption of light energy happens all around us; it is what makes the colors. Pigment is any substance that absorbs light. Light from the sun includes (contains, is made of) several different kinds (different wave lengths or different energy types) of light. We see some of these in rainbows, and we can see them because our eyes are activated differently by the different wave lengths of light energy.
We see a cat because sunlight hits the cat and bounces off the cat into our eyes and energizes some nerve cells. This cat is orange, because only the orange light bounced off her. The other wavelengths were absorbed by the pigments in her hair. (We wrote a whole book about hair pigments, soon to be published, called The Colors of Mice, but that is blatant advertising and has nothing to do with our story here.)

The wavelengths that bounce off — that are not absorbed by the pigment — are still light energy; the wavelengths that are absorbed into the hairs change to a lower form of energy. For example, heat energy; that’s why the cat is stretched out in the sunlight on a cool day. It makes her feel warm and cozy. The pigment of a black cat absorbs most of the light that shines on it. A white cat reflects most of the different wavelengths of light. The green rug in this picture is reflecting green light back to our eyes and is absorbing the other wavelengths.

Plants, as you already realize, reflect the green light and keep the other wavelengths. Unlike cat hair pigment, however, the plant pigments (chlorphylls) do not allow the light energy to degrade into heat energy. Instead, the plant has a very complicated series of biochemical reactions that converts some of the light energy to make the energy bonds of large organic molecules. We will talk about the chemical reactions in some other post.

Absorbing the light into a pigment molecule of (mostly) plants –and then using the energy to make food molecules — is the first half of the flow of energy through the ecosystem.

The second half is distribution of the energy so that all the parts of the ecosystem can stay alive. We discussed last time why an internet requires all its parts if it is to maintain resilience and sustainability.

To recap, the energy that does all this work comes from food. And of course you know what happens when you have no food. The only food we can use to stay alive is organic molecules, and the organic molecules are made by plants. If someone tells you there is no limit to the energy available to us — because it comes from the sun — they are wrong. You and I both know we can not eat sunlight; our food comes from plants, and we are definitely limited by the amount of plants on earth, not by the amount of sunlight. If someone tells you we can make organic molecules for ourselves to eat, that is true, but unfortunately it takes more energy to make the food than we can get back when we eat it. And anyhow food is not the only thing that keeps the ecosystem alive. The ecosystem is an internet; it requires a lot of things, and the most important is to keep all those things in balance.

The whole ecosystem stays alive by keeping a critical balance among all the different life forms that do the various ecosystem jobs we talked about last time, and a balance among the three forms of energy, light energy, organic energy and heat energy.

The ecosystem stays alive because the energy from the sun flows from one of its life forms to another to another to another, doing the work of keeping cells alive. Cells of plants, cells of bacteria, cells of turnips, cells of your body, cells of trees, cells of potatoes, cells of tigers, cells of worms, cells of mosquitoes, grass, horses, fish. You get the idea but if you want a visual cue you can look to the elegant, if simplistic, diagram below.

Every time we eat a bite of food (with the energy it contains) and then our body breaks down the food to release the energy bonds, and uses that energy to do the work of keeping our cells alive — every time we do any of those things, some of the energy is lost as heat. Nobody can eat heat, so then some plant somewhere in the ecosystem must capture more light energy to make more organic energy for our next bite.

Of course we know energy is not the only good thing we get from food. We will discuss other things — primarily carbon, hydrogen, oxygen, nitrogen atoms and small molecules like water and carbon dioxide — in the third section of this book when we explain how the ecosystem recycles these materials into and out of our food. The point here is that the energy does not recycle. It is lost as heat. That’s why the plants must be constantly making more organic molecules to keep the entire ecosystem alive.

For the whole ecosystem to stay alive, it must provide food for every living part of itself. It must maintain the balance among the numbers of plants and the number of organisms that eat plants and the organisms that eat other organisms. And even more, the ecosystem must maintain the balance between the light energy that it uses to make organic energy, and the heat energy that is released when organic energy is burned to do work.

That’s why we have global warming. The energy balance is off. It has been for a good while.

Therefore, the only long-term cure for global warming is to help the ecosystem to restore her balance. We could do it, but not if we try to use any method that causes more heat to be released into the ecosystem. We can not cure global warming, and the starvation that comes with it, by burning anything or by growing our economy or our population.

Because growth Is what caused the problem in the first place.

“Men are not flattered by being shown that there is a difference between their purposes and those of God.” Abraham Lincoln