plants use nitrate to make proteins. where do they obtain this nitrate from?

Plants obtain the nitrate they use to make proteins mainly from the soil.

Where the nitrate comes from

• Nitrate is produced in soil when decomposers break down dead plants, animals, and waste, releasing ammonia that is converted by soil bacteria first into nitrite and then into nitrate (part of the nitrogen cycle).
• Farmers also add nitrogen fertilizers, which often contain nitrate or compounds that soil microbes quickly convert into nitrate, increasing what is available to plants.

How plants actually get the nitrate

• Plant roots absorb nitrate ions from the soil solution through specialized transport proteins in the root cell membranes.
• Once inside, the plant converts nitrate into ammonium and then into amino acids, which are joined together to build proteins.

So, in simple exam-style form:

Plants use nitrate to make proteins, and they obtain this nitrate from the soil, where it is supplied by the nitrogen cycle and by nitrogen fertilizers.