In popular speech, plants is often multicellular plants. That include the vascular plants that have leaves, stems or stalks and roots.
Photosynthesis changes the earths atmosphere and it has been doing it for millions of years. Now it contains oxygen that animals and humans depend on. All plants uses photosynthesis to get energy and carbon to grow. That happens in the chloroplasts where plants convert sunlight, carbon and water to oxygen and glucose.
Humans are dependent on crops to get nutrient like grains, fruits and vegetables. Nutrients are released when glucose digests in the human body. Togheter with oxygen we breath, the waste when we breath out is carbon and water that plants uses to make oxygen.
(1) ( http://en.wikipedia.org/wiki/Plant , 24 mars 2013)
(2) ( http://en.wikipedia.org/wiki/Photosynthesis , 24 mars 2013 )
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