Explanation: Plants and animals need nitrogen to make proteins but they cannot take it in from the air. Because nitrogen is unreactive as a gas, it has to be transformed into a new molecule. When bacteria in the soil takes nitrogen from the air, it becomes nitrates. Finally, it can move through the food chain in this form.
The endosymbiotic theory hypothesizes that mitochondria and chloroplasts were formed when <u>prokaryotic </u>cells were engulfed by larger cells that were precursors to <u>eukaryotic </u>cells.
