How do purple stem plants use there energy

Purple stem plants can be formed by genetics, they use their energy slightly different from other plants, they use less energy, but that may also be because of bad nutrition, and because they may be hungry for nutrients.

Photosynthesis (which literally means "light put together") is that very elegant chemical process that jump-started life as we know it some 4 billion years ago. So to answer your question, we’ll need a short chemistry lesson. Basically six molecules of water (H2O) plus six molecules of carbon dioxide (CO2) in the presence of light energy produce one molecule of glucose sugar (C6H12O6) and emit six molecules of oxygen (O2) as a by-product. That sugar molecule drives the living world.