Complex sentence: The mechanism of photosynthesis remained a mystery until the mid 19th century when Sachs, in 1862, noted that starch was formed in green cells only in the presence of light and in 1882 he confirmed carbohydrates as the starting point for all other organic compounds in plants.
Split into simpler sentences: The mechanism of photosynthesis remained a mystery until the mid 19th century when Sachs, in 1862, noted that starch was formed in green cells only in the presence of light. It was only in 1882 that Sachs confirmed carbohydrates as the starting point for all other organic compounds in plants.