7. where does oxygen come from in nature?

Most of Earth's oxygen comes from tiny ocean plants – called phytoplankton – that live near the water's surface and drift with the currents. So, mostly from plants, trees etc...

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Most of Earth's oxygen comes from tiny ocean plants called phytoplankton that live near the water's surface and drift with the currents.

Explanation:

answer: grassland biomes are closer to the equator and receive more rain.

grasslands are biomes that are dominated by grasses rather shrubs and trees. savanna are biomes that exhibit grasses, shrubs and small tree as vegetation. grasslands are located near the equator of the earth. these are found in north america. savanna biomes are found in africa, south america, australia and india. grassland exhibit moderate climatic conditions, it receives   amount of rainfall higher than savanna.   therefore, savanna exhibit dry and hot climatic conditions.