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What is the structure of chloroplast?

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Surrounding the grana (sing. granum; stack of thylakoids), and the stroma is the inner membrane. Each thylakoid stack is connected by lamellae (the skeleton of the chloroplast). The outer membrane is a further protective layer.

See the image for an overview. In addition, here are some notes on the major structures:

Outer Membrane - porous, such that small molecules (smaller than proteins) and charged particles can move freely.

Inner Membrane - again, regulates the passage of molecules in and out of the chloroplast. Also where fatty acids, lipids and carotenoids are synthesised.

Stroma - protein rich fluid - also contains ribosomes and DNA. The stroma is where biochemical synthesis occurs. 

Thylakoid - the thylakoids contain the chlorophyll required for photosynthesis.

Lamellae - these structures ensure that the thylakoid stacks are arranged in a useful way - so that there is no overlapping or entanglement - such that photosynthesis is as efficient as possible.

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user2260781 | Student

The chloroplast is about 3-10 micrometer in diameter.

It is surrounded by two membranes which form the chloroplast envelope.

The inner membrane is folded forming thylakoids.The thylakoids a flattened,fluid-filled sacs which form stacks called grana at intervals,with layers between the grana.

It also consist of the chloroplast DNA,starch grain,lipid droplets and ribosomes.