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Structure of Chloroplasts

Chloroplasts are double membraned cell organelles responsible for photosynthesis. These vary in shape and size but are typically disc shaped. The algal chloroplasts are lens shaped but might also show star shape as in case of zygnema or spiral as in case of spirogyra. Algae like oedogonium show irregular outline.
Significant advances have been made towards the study of chloroplasts and understand the molecular structure, especially the proteins and lipids orientation and polypeptide associated with light harvesting pigment protein complexes.
The module you are about to see contains all these interesting facts and helps you understand the structure better. The intricate cellular differentiation and interesting facts found in chloroplast might help you understand of why some plants leaf colour look little different than others or why a plant in shade might look greener than the one in in direct Sun.
The double membraned chloroplasts contain the grana, which are stacks of disc like structures with chloroplast pigments inside. These thylakoids are stacked in single lamella or in pairs. The most common form of thylakoids found in chloroplasts is of course the arrangement of three.
Next to thylakoids, the presence of single pyrenoid is seen in chloroplast where the densely packed fine granular materials are present. These pyrenoids which are seen in the centre of chloroplasts can be seen in primitive red algae and are characterised by undulating membranous structure.
The stroma present in chloroplasts is a fluid filled matrix where the light independent photosynthesis takes place. Oil droplets and starch grains are also found inside stroma.
The role of grana membrane is to providing large surface area for the attaching pigments like chlorophyll and carotenoids, enzymes and electron carriers used for light dependent reaction.
These granal membranes have enzymes like ATP synthase which help in manufacture ATP through chemiosmosis.
The endoplasmic reticulum completely surrounds each of the chloroplasts lobe having ribosomes, on chloroplast surface.

 

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