Ribulose is a five-carbon sugar, specifically a pentose, that plays a crucial role in the process of photosynthesis. It is an important component of the Calvin cycle, where it combines with carbon dioxide to help produce glucose, a vital energy source for plants. In its phosphorylated form, ribulose bisphosphate (RuBP), it acts as a substrate for the enzyme ribulose bisphosphate carboxylase/oxygenase (RuBisCO). This enzyme catalyzes the first step of carbon fixation, making ribulose essential for converting atmospheric carbon into organic compounds that sustain life on Earth.