ALL of the energy in our bodies started off as sunlight! Plants use energy from the sun to take the elements in water and carbon dioxide and put them together as sugar. Oxygen is left over. When we eat plants, or things that ate plants, we are harvesting energy in our food that started off as sunlight.

We don’t get all the energy that the plant got, even if we eat the entire plant, from the top of the plant to the bottom of its roots. Every time energy changes form, some is lost as heat that drifts away. Also, the plant has already used some of the sun energy for its own needs. When an animal eats a plant, it only gets about 10% of the energy that the plant took in as light. When an animal eats another animal, it gets a maximum of about 10% of the energy that its prey ate.

Why do you think that there are so few carnivores (meat eaters) compared to herbivores (plant eaters)? In other words, why are you a lot more likely to see a deer than a mountain lion?

If these questions interest you, check out a career in ecology.

Since humans eat organisms that directly or indirectly get their energy from the sun, yes we do have a fraction of the energy of the sun.

The energy of the sun is sent to the Earth through “thermal radiation.” When this radiation hits certain molecules, they start vibrating or move faster which increases their energy. In the case of plants, they use this energy from the sun to turn carbon dioxide and water into sugar. When we eat the sugar in the plants, we are indirectly absorbing some of the energy the sun gave to make the sugar in the first place.

Interestingly though, not every organism on the planet gets its energy from the sun. The organisms that live around deep sea vents rely solely on the chemicals dissolved in the vents, which does not come from the sun. These ecosystems deep under the ocean are considered to be independent of solar energy, so if you ate one of those organisms, you wouldn’t get any energy from the sun. Of course, nobody would ever eat a deep sea vent critter.

We sure do! Plants are only able to harvest a small fraction of the light energy and turn it into chemical energy. When we consume plants that transfer of energy is an even smaller proportion. This is called the 2nd Law of Thermodynamics: With each transfer of energy, heat is lost.

Thus we have to eat a lot of plants to fulfill our energy needs.

We have a fraction of the *power* of the sun in our solar system. Power is energy expended over time. The sun continually emits more energy, thus having a certain level of power. The power reaching the Earth is a fraction of that, the power taken up by plants is less still, and the power that we take from plants is even less still, but yes, it is a fraction of the sun's power.

Yes, definitely. Almost all living things on earth are fueled by the sun either directly or indirectly. (The exception is organisms that live near volcanic vents deep in the ocean.) Energy from the sun is taken in by plants and eaten by animals. Without the sun, that foundation level of energy would be gone, and no large life on earth would exist. So yes, we definitely do have fractions of the sun's energy in our system. Even cooler, the universe many billion years ago was almost entirely hydrogen. It took a whole generation of stars to take the hydrogen and turn it into heavier elements like carbon and oxygen and iron. What this means is that our bodies are literally made of matter from dead stars.

We have definitely used the suns energy, but the sun's energy has been converted into a form that we can use in our bodies. The plants transform the sunlight into energy that they use to grow things like leaves and fruits. In the same way, when we eat those leaves and fruits, we transform the plant's energy into bones, muscles, activity, etc.