Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules, while freeing oxygen from water in plants. A chloroplast is a type of organelle known as a plastid, characterized by its two membranes and a high concentration of chlorophyll. Other plastid types, such as the leucoplast and the chromoplast, contain little chlorophyll and do not carry out photosynthesis.
Chloroplasts contain several important membranes, vital for their function. Like mitochondria, chloroplasts have a double-membrane envelope, called the chloroplast envelope, but unlike mitochondria, chloroplasts also have internal membrane structures called thylakoids.
Stroma, in botany, refers to the colorless fluid surrounding the grana within the chloroplast. Within the stroma are grana (stacks of thylakoid), and the sub-organelles or daughter cells, where photosynthesis is commenced before the chemical changes are completed in the stroma.
Thylakoids are membrane-bound compartments inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis. Thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana (singular: granum). Grana are connected by intergranal/ stroma thylakoids, which join granum stacks together as a single functional compartment.