Chloroplast are the structure within the cells of plants and green algae which is the site of photosynthesis, a process by which sunlight energy gets converted into chemical energy, resulting in production of oxygen and energy-rich organic compounds. So, Chloroplasts can be considers as food producers of the cell. Animal cells do not have chloroplasts.


Plants are the basis of entire life on Earth. They are classified as the producers of world. During the process of photosynthesis, plants create sugars and release oxygen. This oxygen released by the chloroplasts is the same oxygen all living creatures breathe every day. Mitochondria works in the opposite direction. They use utilize oxygen in releasing chemical energy from sugars.


Chloroplasts Structure


On high level, two membranes contains and protects the inner parts of chloroplasts. And they are named appropriately as outer and inner membranes. The inner membrane of chloroplast surrounds the stroma and the grana (grana are stacks of thylakoid). One thylakoid stack is called a granum.


Chlorophyll molecules sit on the surface of every thylakoid and captures the light energy from the sun. As these energy rich molecules are prepared by the light-dependent reactions, they moves to the stroma where carbon can be fixed and sugars are then synthesized.


Chloroplast are of 10 microns long and 0.5 to 2.0 microns thick and it may vary based on size and type of the cells especially among algae. It is surrounded by outer and inner membrane. In addition chloroplasts consist of interconnected extensive sacs called Thylakoids which are of disc shaped. These are stalked (20-50 no’s) to form Grana and embedded in a matrix called Stroma.


The stacks of the thylakoid sacs are well connected by stroma lamellae. This lamellae acts just like the skeleton of chloroplasts, thus keeping all the sacs at a safe distance from each other and thereby maximizing the efficiency of the organelle. Because if all of thylakoids were overlapping and bunched together, there would be such efficient way to capture the Sun’s light energy.


                                                          Chloroplast by Kelvinsong (CC0 1.0)


Stroma is a semi fluid, colloidal and colorless complex contains DNA, RNA, ribosomes (70s type) and many other enzymes. Its DNA is circular. Matrix may consist as starch as storage material. Thylakoids are occur as inner membrane of chloroplast.

Nearly 40-100 grana may occur in a chloroplast. Many membranous tubules called stroma lamellae inter connect thylakoids of different grana.

The mechanism of ATP production is similar to Mitochondria.

Thylakoid membrane consist of photosynthetic pigments called as “Chlorophyll” and other pigments that absorb light and generate ATP during photosynthesis. Some of the ATP’s are used to convert CO2 into three carbon intermediates which are then converted to sugars.


Making Food

The sole purpose of the chloroplasts is to make sugars that feeds the cell’s machinery. Photosynthesis is the plant’s process taking energy from Sun and preparing sugars. When the energy from Sun hits the chloroplasts and chlorophyll molecules, the corresponding light energy gets converted into chemical energy found in compounds like ATP and NADPH.

Those energy-rich compounds then moves into the stroma where enzymes fixes the carbon atoms from carbon dioxide. Animals and plants then use the sugars (or glucose) for food and energy.

Different Chlorophyll molecules

Not all of the chlorophyll molecules are same. Several types of chlorophyll molecules can be involved in photosynthesis. All of the chlorophyll are varieties of green and have a common chemical structure known as porphyrin ring.

There are also other molecules which are also photosynthetic like carotenoids in carrots, fucoxanthin in brown algae, phycoerythrin in algae or phycocynanin in bacteria. While these compounds might be indirectly involved in photosynthesis, they are not all green or have the same structures as chlorophyll. Accessory pigments like carotenoids and fucoxanthin passes absorbed light energy to its neighbor chlorophyll molecules, instead of using itself.


                                                          Chloroplast by Kelvinsong (CC0 1.0)

By | 2015-08-23T15:42:54+00:00 March 26th, 2013|Cell organelles|0 Comments

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