This tiny saucer-shaped organelle acts as a biological solar cell that captures the energy which originated in outer space and powers virtually all the biological processes on the planet, either directly or indirectly. Not only is this energy free, but producing it also makes the environment cleaner and greener as chloroplasts capture carbon dioxide and release oxygen during the process as well.
You can think of chloroplast as mitochondria’s cooler cousin. Where, mitochondria break down complex biomolecules into chemical energy that is needed to power the cells, the chloroplast, on the other hand, converts energy traveling from the sun, nearly 150 million kilometers away into adenosine-triphosphate (ATP), and ultimately into energy-rich biomolecule in a process called photosynthesis.
Chloroplasts are membrane-bound organelles that contain chlorophyll i.e., the most important green in the world. Chlorophyll is packed into disc-shaped structures known as thylakoids within the chloroplast along with other protein complexes known as light-harvesting complexes or photosystems. In the first step, thylakoids capture the light energy in the form of excited electrons which then travel through the electron transport chain that drives the production of ATP. These ATPs then move to the stroma of chloroplasts, just outside the thylakoids, and in a process called the Calvin cycle, these energy-rich ATP molecules are used to produce glucose —the ultimate biological fuel.