Plant cells need nitrate ions (a source of nitrogen) in order to make proteins from glucose.

Quick Scoop: What do plants need (besides glucose) to make proteins?

To turn glucose into proteins, plants first use the carbon, hydrogen and oxygen in glucose, but they still need a good source of nitrogen. They usually get this nitrogen from nitrate ions in the soil , absorbed by their roots.

Once the plant has nitrate ions, it can combine the nitrogen from these nitrates with the carbon “skeletons” made from glucose to build amino acids , and then link those amino acids together to form proteins. School questions and practice quizzes that ask, “In order to make proteins from glucose, what other substance do plant cells need?” expect the one‑word answer: nitrate (or “nitrate ions”).

So, in exam-style wording:
In order to make proteins from glucose, plant cells need nitrate (nitrate ions) from the soil.

TL;DR:
In order to make proteins from glucose, plant cells need nitrate (nitrate ions, a source of nitrogen) absorbed from the soil.

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