The protoplasm and cytoplasm of a plant are interchangeable terms

No. These two terms aren't interchangeable. 
Protoplasm is the living content of a cell which is surrounded by a plasma membrane called the cell membrane. It is composed of a mixture of small molecules including ions, amino acids, monosaccharides and water, and macromolecules like nucleic acids, proteins, lipids and polysaccharides.
In eukaryotes,  the protoplasm surrounding the cell nucleus is known as the cytoplasm.