Definite volume refers to something which has a consistent, unchanging volume, which in practical terms may mean a static mass and density, or a predetermined shape, either of which will dictate volume. A cube with side length l has a definite volume because it can only be exactly one size.
One cup of raw plantains or one medium sized raw plantain contains: ~180-200 calories, 0.5 g total fat, 47-50 g carbohydrates, 3.5 g dietary fiber, 22 g sugar and 2 g protein. Because of it's high carbohydrate content, you need to monitor your portion, otherwise your blood sugars will spike.
Cellulose forms the structures that give plants their shape, and it's the main component of dietary fiber. Vegetables such as green beans, broccoli, and spinach contain less starch, but they have more cellulose. The difference between complex carbohydrates and simple carbohydrates is just the size of the molecules. Simple carbohydrates are made up of only one or two sugar units, whereas complex carbs contain at least three sugars.