Which organelles are involved in photosynthesis?

Photosynthesis is a highly specialised biological process in which light energy is converted into chemical energy by autotrophic organisms like plants, algae and some protists. To understand which organelles are involved in photosynthesis, it is important to first clarify that the core reactions take place within specific compartments of the cell. However, some other organelles also support or regulate this process indirectly. Therefore, before discussing each organelle, it is essential to know that the primary site of photosynthesis is the chloroplast, but other organelles such as the endoplasmic reticulum, Golgi apparatus, and even the peroxisomes and vacuoles have supplementary roles in supporting photosynthesis-related functions.

1. Chloroplasts

Chloroplasts are the main organelles directly involved in photosynthesis. They are double-membrane-bound structures found in the cytoplasm of plant and algal cells. These organelles originated from an ancient symbiotic cyanobacterium, a theory known as endosymbiosis, which is supported by the fact that chloroplasts contain their own DNA, ribosomes and can synthesise some of their own proteins.

The internal organisation of chloroplasts includes structures like grana and stroma, which play specific roles in photosynthesis. Inside the chloroplast, the internal membrane system is organised into stacked disc-like structures called grana, formed by thylakoids, which are the actual sites of light-dependent reactions. These thylakoids contain chlorophyll a, chlorophyll b and accessory pigments like carotenoids, which absorb solar energy. The stroma, the enzyme-rich fluid surrounding the grana, is the site of the Calvin cycle or light-independent reactions, where CO₂ is fixed into carbohydrates using ATP and NADPH. Chloroplasts also play a role in starch synthesis and fatty acid metabolism.

The structure of the chloroplast allows compartmentalisation, which is essential for separating light and dark reactions, ensuring high efficiency. The involvement of chloroplasts in photosynthesis was established by Andreas Schimper (1883) and further elaborated by Melvin Calvin during his work on the dark reactions in the 1950s, which led to the naming of the Calvin cycle.
Chloroplasts are the main organelles directly involved in photosynthesis. They are double-membrane-bound structures found in the cytoplasm of plant and algal cells. These organelles originated from an ancient symbiotic cyanobacterium, a theory known as endosymbiosis, which is

2. Endoplasmic Reticulum (ER)

Although endoplasmic reticulum (ER) not directly performing photosynthesis, the rough ER helps in the synthesis and transport of proteins that are used in chloroplasts, including various enzymes required for photosynthetic pathways. The smooth ER plays a role in lipid synthesis that is necessary for membrane formation within the chloroplast.

3. Golgi Apparatus

The Golgi body modifies, packages, and transports proteins and lipids, many of which are necessary for chloroplast development and function. It is especially important for the transport of glycolipids and glycoproteins involved in chloroplast membrane composition.

4. Peroxisomes

During photorespiration, a process associated with photosynthesis in C₃ plants, peroxisomes work together with chloroplasts and mitochondria to metabolise 2-phosphoglycolate. This detoxification process helps recycle carbon atoms and protect the photosynthetic process.

5. Vacuole

The central vacuole of plant cells helps maintain turgor pressure, which is vital for keeping the leaf surface expanded to capture sunlight efficiently. It may also store ions and metabolites involved in photosynthesis.







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