A chloroplast is a tiny green structure inside plant cells that captures sunlight and transforms it into food through a process called photosynthesis. Think of chloroplasts as miniature solar-powered factories, working all day to convert light, water, and carbon dioxide into the sugars that plants need to grow.

These remarkable organelles contain a pigment called chlorophyll, which gives plants their green color and does the actual work of absorbing sunlight. A single leaf cell might contain dozens of chloroplasts, all working together. When you look at a green leaf, you're seeing millions of chloroplasts through the cell walls, each one busy making food.

Most plant cells and some algae have chloroplasts. Animal cells don't have them, which is why animals must eat plants (or eat other animals that eat plants) to get energy. Scientists believe chloroplasts were once independent bacteria that began living inside plant cells billions of years ago, a partnership so successful that plants and chloroplasts now depend on each other. Every bite of food you eat, whether it's an apple, a steak, or a slice of bread, traces its energy back to the sunlight captured by chloroplasts in plant cells.