Answer:
4) The carbon dioxide comes from the animals and the oxygen comes from plants
7) Animals need to get their energy from other living things, but in order to do that said other living things need to have energy for the animals to get. Photosynthesis is the means by which plants and algae get their energy. Animals also need elemental oxygen,and photosynthesis produces this as a waste product as well
9) Fossil fuels consist mainly of carbon and hydrogen. When fossil fuels are combusted (burned), oxygen combines with carbon to form CO2 and with hydrogen to form water (H2O). These reactions release heat, which we use for energy
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