The chemical element essential for photosynthesis is chlorophyll, which contains magnesium at its core. During the photosynthesis process, plants convert sunlight into chemical energy using chlorophyll to capture light energy from the sun. This energy helps convert carbon dioxide and water into glucose and oxygen, essential for plant growth and providing energy for other organisms in the food chain. Without chlorophyll, plants wouldn't be able to harness sunlight effectively, drastically impacting the Earth's ecosystems and food sources.