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Why do animals need energy from the sun even if they get energy from the food they eat?
Answer 1:

You are right, some animals get energy not just from their food, but also from the sun. The most common examples I can think of are reptiles. They are cold blooded, which means that they heat themselves using heat from outside. It's not so much that these animals need to do it this way, but that it is advantageous for them to do it that way. Most animals that do that live in hot places, and so the heat they get from the sun is pretty much free. On the other hand, if you needed to use food energy to heat your body, it would mean that you'd have to eat a lot more food. So, in environments where heat is easier to find than food, it makes sense for animals to save their efforts and rely on the sun to heat themselves up. That's what crocodiles and large snakes do. They can go weeks and months between meals and part of that is because they don't need to waste food energy to heat themselves up.


Answer 2:

Animals don't need energy from the sun, not directly anyway. Animals get energy from the food they eat. However, that food either got its energy by eating other food, or by photosynthesis, and sooner or later almost all energy on Earth comes from the sun. There are some ecosystems in the deep ocean that use geothermal energy, but we use sunlight, because we eat plants, or we eat things that themselves eat plants, etc.


Answer 3:

You are right that animals get their energy from the food that they eat. Our bodies do not get energy directly from the sun (other than getting warmed up by standing in sunlight). But without the sun, we would have no food. Plants need the sun for energy and we eat those plants or the animals that ate the plants.

At each level, a lot of energy is lost. Only a tiny bit of all of the sunlight falling on Earth is captured by things doing photosynthesis. Plants, algae, and other photosynthesizers use a lot of that energy for things like fighting diseases, making chemicals, and other things that don’t produce food. So if we eat corn, for example, we are only getting a fraction of the energy that was in light that hit the corn plant. If we feed corn to chickens, then eat the chickens, we get even less of the energy in the light that hit the corn plant. The chickens use energy eating and digesting, walking around, fighting disease, and all of their other body functions. A rough estimate is that about 10% of the energy at one level of the food chain makes it into the next link up the chain.

What happens to the rest of the energy? It can’t just disappear. It becomes heat. The heat spreads out. If we tried to gather that energy up to do work, it would take more energy than we would get, so the energy is “lost” to the ecosystem, even though it doesn’t disappear.

We also use energy from the sun for solar power. When we burn fossil fuels (gas, coal, oil, etc.), we are burning the remains of living things that got their energy from the sun, either directly (plants) or indirectly (animals). These things died millions of years ago and became coal, oil, and natural gas. Even wind energy is caused by the sun heating some places more than others.

Can you think of any forms of energy that do not come from the sun?

Thanks for asking,


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