Question

how do plants get nitrogen to synthesis protein​

Answer 1

they take nitrogen in two ways

1.during lightning the nitrogen that is released gets immediately mixed up with oxygen present in air to form nitrous oxide

then the plants take it through nitrogen cycle.

2. the roots of some plants had some swelling where nitrogen fixing bacteria are present .They provide some of the nitrogen and in return get some food from plant.

Hope it will help you

Answer 2

plants get nitrogen from soil which is taken from atmospheric nitrogen