The Anatomy of Chloroplasts

Chloroplast, structure within plant and green algae cells that is the site of photosynthesis, the process by which light energy is converted to chemical energy, resulting in the production of oxygen and energy-rich organic compounds. The endosymbiotic theory holds that chloroplasts and mitochondria (energy-producing organelles in eukaryotic cells) are descended from photosynthetic cyanobacteria, which are free-living close relatives of chloroplasts.

What are Chloroplasts?

Chloroplast is a plastid cell organelle found in plant cells and some protists such as algae and cyanobacteria. Chloroplasts are the cell’s food producers, converting sunlight’s light energy into sugar that the cell can use. 

This entire process is known as photosynthesis, and it is entirely dependent on a high concentration of chlorophyll, the molecule that absorbs light energy and gives plants and algae their green colour. As a result, the term chloroplast refers to plastids that contain chlorophyll. Chloroplasts, like mitochondria, are thought to have evolved from bacteria.

Functions of Chloroplasts

• Photosynthesis occurs in chloroplasts and consists of a series of light-dependent and light-independent reactions that harness solar energy and convert it to chemical energy.
• Chloroplast components are involved in a variety of cell regulatory functions as well as photorespiration.
• Chloroplasts also support plant cells’ metabolic activities, such as the synthesis of fatty acids, membrane lipids, isoprenoids, tetrapyrroles, starch, and hormones.
• Plants do not have specialised immune cells; instead, all plant cells participate in the plant response.

• The chloroplasts, along with the nucleus, cell membrane, and ER, are the primary organelles involved in pathogen defence.
• Chloroplasts have the potential to function as cellular sensors.

Structure of Chloroplasts

• Chloroplasts, like mitochondria, are oval and have two membranes: an outer membrane that forms the chloroplast’s external surface and an inner membrane that lies just beneath it. There is a thin intermembranous space about 10-20 nanometers wide between the outer and inner membranes. The stroma is the space within the inner membrane. The inner membranes of chloroplasts are smooth, whereas the inner membranes of mitochondria have many folds called cristae to absorb surface area. Chloroplasts, on the other hand, have many small disc-shaped sacs called thylakoids within their stroma.
• Thylakoids are stacked on top of one another in vascular plants and green algae, and a granum is a stack of thylakoids (plural: grana). The thylakoids contain chlorophylls and carotenoids, which absorb light during the photosynthesis process. Light-absorbing pigments combine with other molecules, such as proteins, to form photosystems. Photosystems I and II are the two types of photosystems, and they play different roles in light-dependent reactions.
• Enzymes in the stroma produce complex organic molecules used to store energy, such as carbohydrates. The stroma also has its DNA and ribosomes, both of which are found in photosynthetic bacteria. As a result, chloroplasts, like mitochondria, are thought to have evolved in eukaryotic cells from free-living bacteria.

Role of Chloroplasts in Photosynthesis

The primary function of chloroplasts in photosynthesis is to contain the majority of the reaction during photosynthesis. The plant will pump water into the leaves, which will absorb carbon dioxide as well. Inside the chloroplast, all of the thylakoids, chlorophyll, water, carbon dioxide, and so on are available. The entire photosynthesis process begins and ends inside the chloroplast. The chloroplast functions as the cell’s “powerhouse,” similar to the mitochondria, except that it produces its food, which is then used to power the plant.

Evolution of Chloroplasts

• Chloroplasts are thought to have entered certain eukaryotic cells in the same way that mitochondria did: as free-living cyanobacteria with a symbiotic relationship with a cell, producing energy for the cell in exchange for a safe place to live, and eventually evolving into a form that could no longer exist separately from the cell. This is referred to as the endosymbiotic theory.
• The evidence for chloroplast evolution from bacteria is very similar to that for mitochondria evolution from bacteria. Chloroplasts have their DNA, which is circular, similar to that of a bacterial cell, and is inherited maternally (only from the mother plant alga)
• Bacteria reproduce by binary fission, or splitting, which results in the formation of new chloroplasts. These types of evidence can be found in mitochondria as well. The only difference is that chloroplasts are thought to have evolved from cyanobacteria, whereas mitochondria are thought to have evolved from aerobic bacteria. (Mitochondria cannot photosynthesize; instead, cellular respiration occurs there.) Chloroplasts have a similar structure to cyanobacteria, with double membranes, circular DNA, ribosomes, and thylakoids. The majority of chloroplasts are thought to have descended from a single common ancestor that engulfed cyanobacteria between 600 and 1600 million years ago.

Conclusion 

Chloroplast, structure within plant and green algae cells that is the site of photosynthesis, the process by which light energy is converted to chemical energy, resulting in the production of oxygen and energy-rich organic compounds. This entire process is known as photosynthesis, and it is entirely dependent on a high concentration of chlorophyll, the molecule that absorbs light energy and gives plants and algae their green colour. Photosynthesis occurs in chloroplasts and consists of a series of light-dependent and light-independent reactions that harness solar energy and convert it to chemical energy. The chloroplasts, along with the nucleus, cell membrane, and ER, are the primary organelles involved in pathogen defence.