Plant cells produce oxygen gas by splitting carbon dioxide. by splitting ribulose bisphosphate. by breaking down glucose by splitting molecules of water.

Almost all the oxygen you breathe comes from green plants. They produce oxygen during a process called photosynthesis. During photosynthesis green plants manufacture the sugar moleculesfructose and glucose. Green plants use energy from sunlight to build sugarmolecules from carbon dioxide and 

A) early horses is your answer

The first means of speeding up reactions mentioned by the speaker is raising the enzymes