Chloroplast

Chloroplasts are the cytoplasmic organelles found in plant and algal cells. They are the most known plastids that contain high concentration of chlorophyll and are involved in photosynthesis. Other types of plastid include leucoplast and chromoplast that contains very less chlorophyll and are not involved in photosynthesis. Chloroplast contains chlorophyll and carotenoids and is the site of food synthesis and storage. They basically uses the light energy to convert carbon dioxide (CO₂) and water into carbohydrate and oxygen (O₂). This process is known as photosynthesis.

Chloroplast varies in their shape and size, the common being the oval shape with dimensions of 2 to 4 m by 5 to 10 m. They are embraced in two membranes: outer membrane and inner membrane; and the space between two membrane is known as intermembrane space. A matrix i.e. stroma lies within the inner membrane. The internal membrane system contains flattened, membrane bound compartment called thylakoids. It consists of thylakoid membrane that surrounds thylakoid lumen. Thylakoids are generally stacked on each other like coins to form grana (singular granum). Chlorophyll and electron transport components are present in thylakoid membrane.

Some part of photosynthetic reaction takes place in stroma and some takes place in thylakoid membrane. Reaction of CO₂ and water to form carbohydrate and dark reaction takes place in stroma. Whereas, the trapping of light energy to form ATP, NADPH, and O₂ , the light reaction takes place in thylakoid membranes.