It's efficient in some way that we can recycle the same energy over and over again without losing the energy made. Take this chart for example:
The sun is the main source of energy.
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The plants grow through the help of the sun.
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The plants convert the energy into food.
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Let's say a pig ate that plant. That pig then gains energy from the plant.
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The pig is then turned into meat. We eat meat.
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And through that meat, we gain energy to do our daily activities.
