They're the only vein that carries oygenated blood
Answer: Minerals
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The greenhouse effect occurs when rays enter our atmosphere and are reflected from the ground up. They get changed during their voyage through our atmosphere and they change in such a way that they can't leave the atmosphere anymore. Then they stay inside and heat up the planet which causes thing like global warming. That's what the greenhouse effect is.
The ultimate souce of energy for the food chain is solar energy from the sun. It allows plants to convert the solar energy to chemical energy for growth. The growing plants in turn allow heterotropic animals to consume them to obtain energy of their own.