Final answer:
The substance that combines with carbon dioxide in a chloroplast to initiate the process of photosynthesis is ribulose bisphosphate (RuBP). The enzyme RuBisCO facilitates this reaction, starting the Calvin cycle.
Step-by-step explanation:
The substance that combines with carbon dioxide in a chloroplast is ribulose bisphosphate (RuBP). In the process of photosynthesis, RuBP is a five-carbon sugar that reacts with carbon dioxide with the help of the enzyme RuBisCO. This reaction kicks off the Calvin cycle, which eventually leads to the production of glucose and other carbohydrates that serve as energy sources for the plant.
Answering review question 20, ribulose-1,5-bisphosphate carboxylase/oxygenase, abbreviated as RuBisCO, catalyzes the reaction between carbon dioxide and RuBP in photosynthesis. This is an essential step in the process because it initiates the conversion of inorganic carbon into organic forms that can be used by the plant and other organisms for energy and growth.