What makes chloroplast appear completely different from other cell organelles?

It was not until 1954, that Daniel I. Arnon was able to break up plant cells so gently that whole chloroplasts could be obtained that could carry through photosynthesis. It has been found that the chloroplast is a membranous structure, consisting of 3 membranes.

The third layer forms stacked sack like structures called as grana. It is believed to be a site for trapping of solar energy. The intermediary fluid filled portion is called as stroma.

It is believed to be responsible for enzymatic reactions leading to the synthesis of glucose, which in turn join together to form starch.

Substances found in chloroplast which capture sunlight are called photosynthetic pigments. There are several types of photosynthetic pigments involved in the process to produce organic molecules like glucose in plants.

Chlorophyll is such a pigment which contain one atom of magnesium. It is similar in structure to the haem of haemoglobin.
(The iron containing red pigment that transports oxygen in blood.)

Two major kinds of chlorophylls are associated with thylakoid membranes. Chlorophyll ‘a’ is blue-green in colour and chlorophyll ‘b’ is yellow-green colour.

Around 250 to 400 pigment molecules are grouped as light harvesting complex or photosynthetic unit in each thylakoid. Such innumerable units function together in chloroplasts of green plants in the process of photosynthesis.

During photosynthesis several events occur in the chloroplast some of them are:

1. Conversion of light energy to chemical energy
2. Splitting of water molecule (photolysis of water)
3. Reduction of carbondioxide to carbohydrates

Light is required to initiate several events while several may continue even in absence of it. That would mean, once light energy has been captured it can help reactions to continue even in the dark. Light dependent events