What is chloroplast: definition, function, structure, adaptation

What is chloroplast: definition, function, structure, adaptation

What is chloroplast

Chloroplast is a plastid containing chlorophyll, and is used as a place for photosynthesis to take place. Chloroplasts are membrane-bound cell organelles found only in plant cells.


Chloroplasts are also plastids that are green in color which contain a pigment called chlorophyll. Chloroplast Lens-shaped or grain and flattened that can be seen under a microscope with the strongest magnification light. In higher plants, chloroplasts are oval in shape, while at lower levels they tend to be rounded.

Chloroplast Functions

The main function of chloroplasts is as a site for photosynthesis. Photosynthesis is a reaction to the formation of ATP and involves the transport of hydrogen and electrons in compounds such as NADH and cytochromes.

This photosynthesis will convert carbon dioxide into sugar, which is a source of chemical energy and food for plants. Photosynthesis uses light as an energy source, CO2, water which will produce oxygen and carbohydrates.

Chloroplast Structure


The chloroplast membrane is a double membrane structure that exists in the outer membrane as well as the inner membrane. Each of these membranes is a phospholipid bilayer, and is also about 6 to 8 nm thick. A thick space is present about 10 to 20 nm between the 2 membranes which is often known as the space between membranes.


The stroma is a fluid that is in a double membrane membrane which is often called the stroma. The internal components and some solutes are scattered on the stroma. The stroma is rich in protein, and also contains many enzymes that are needed for important cellular processes. Chloroplast DNA is also present in the stroma along with ribosomes and also other molecules that will be needed for protein synthesis. Starch is synthesized through photosynthesis and is stored in the stroma in the form of a granule.


In addition there are membranes that make up the membrane, the chloroplast will contain a third internal membrane system which is commonly called the thylakoid membrane. The internal thylakoid in a membrane bound compartment will be formed by the thylakoid membrane itself. The internal part of the thylakoids is called the thylakoid lumen, and contains plastocyanin or other molecules needed for the transport of an electron.


Some of the thylakoids are arranged in the form of a disc which will be stacked between each other. These piles are usually called grana, grana will be connected to one another through thylakoid intergrana to thylakoid stroma.


It is in the thylakoid membrane. Photosystem is a structural and functional unit that can utilize solar energy. A photosystem consists of a reaction center that will be surrounded by a sunlight catcher or a complex antenna that will release chlorophyll, carotenoids, other photosynthetic pigments, and proteins.

Peripheral Reticulum

Certain plant chloroplasts contain an additional package of tubular membrane, often called the peripheral reticulum, which originates from the membrane present in the membrane. Small bud vesicles that detach from the inner membrane of the chloroplast, will gather to form a tubule of the peripheral reticulum.

Chloroplast membrane

The membrane system in chloroplasts is also known as the three membrane system, because it consists of an outer membrane, an inner membrane, and a thylakoid membrane. Like the outer membrane of the mitochondria, the outer membrane of the chloroplast also contains porin which makes this membrane permeable to molecules with a size of 10,000 daltons. In contrast, the inner membrane is relatively more selectively permeable so that it has transport proteins to regulate the entry and exit of substances from and into the chloroplast (Taiz and Zeiger, 2002).

The transport protein contained in the chloroplast membrane is a complex called TOC and TIC. The TIC and TOC complexes are translocons located in the chloroplasts of eukaryotic cells, namely protein complexes that facilitate the transfer of proteins into and out of the chloroplast membrane. The TIC (translocon on the inner chloroplast membrane) complex is located in the inner envelope of the chloroplast. The TOC (translocon on the outer chloroplast membrane) complex is located on the outer membrane of the chloroplast. This complex transports proteins synthesized in the cytoplasm across the chloroplast membrane (Alberts et al, 2008).

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