Structure of Chloroplast

The structure of the chloroplast is explained as follows:

Double Membrane Envelope

The chloroplast is enclosed by a double membrane envelope. The outer membrane act as a barrier between the chloroplast and the cell. The inner membrane regulates the passage of molecules in and out of the chloroplast. The space between them is referred to as periplastidial space (intermembrane space). A matrix is present inside these membranes. Carbohydrates are formed in this part, that is, the dark reaction of photosynthesis occurs.

Thylakoid Membranes (Lamellae)

The system is suspended in the stroma. There are large number of flattened, sac-like structures called thylakoids. These contain pigments, like chlorophyll, which capture sunlight energy during the light-dependent reactions of photosynthesis. The thylakoids are arranged in stacks referred to as grana and each granum consists of approximately 10-20 thylakoids.

Grana

Thylakoid membranes are structured into stacks called grana. It increase the surface area for light absorption and have the component necessary for the light-dependent reactions. The number of grana in a chloroplast can be up to 40-60. The particles present in it are referred to as quantasome. Each quantasome is made up of 200 green molecules. The width of the grana lamellae found in the grana is less than that of the stroma lamellae.

Stroma

The stroma is an aqueous, protein-rich, colorless fluid that enclose the thylakoids. It contains enzymes and substances necessary for the light-independent reactions of photosynthesis. Stroma also consists of various enzymes, DNA, ribosomes, and other substances. Stroma lamellae function by connecting the stacks of thylakoid sacs or grana.

Chlorophyll

Chlorophyll molecules are present in the thylakoid membranes. They are responsible for capturing light energy and come in different types (chlorophyll a and chlorophyll b) which is essential for photosynthesis.

DNA and Ribosomes

Chloroplasts contains its own DNA and ribosomes. It encodes proteins required for chloroplast function. The ribosomes present are involved in chloroplast protein synthesis.

Lipid and Starch Granules

Chloroplasts store lipids and starch granules. Lipids act as an energy reserve, and starch is a storage form of glucose that is produced during photosynthesis.

Envelope Pores

Protein channels present in the outer membrane, known as envelope pores, regulate the passage of molecules, such as ions and metabolites, into and out of the chloroplast.

The structure and function of chloroplast are adapted for photosynthesis. Chloroplast is an eukaryotic organelle found in plant cells and some algal cells which forms the site for photosynthesis. Chloroplasts contain the pigment chlorophyll, which captures light energy and uses it to synthesize organic compounds, including sugars, from carbon dioxide and water.

Chloroplasts give plants their green colour and are essential for their growth and survival. In this article, we will cover the structure and function of chloroplast, along with their diagram.