Final answer:
A group of molecules known as organelles, specifically chloroplasts containing chlorophyll, captures sunlight and converts it into sugar via photosynthesis, forming the base of the food chain.
Step-by-step explanation:
The group of molecules that work together to capture sunlight and convert it into sugar in plants is known as organelles. Specifically, these organelles are called chloroplasts, and the key molecule involved in capturing the energy from sunlight is chlorophyll. Photosynthesis is the process by which plants, using chlorophyll within chloroplasts, convert light energy into the chemical energy of glucose, storing it for later use. This glucose is then used by both plants and animals for energy through cellular respiration, ultimately supporting life on Earth.