Chloroplasts are made up of light- soluble pigments involved in photosynthesis. These are known more commonly as green chlorophyll and yellow carotenoid. These light soluble pigments work by tapping sunlight energy, which is made up of different colours seen by the naked eye when a rainbow forms. Due to the chlorophyll being green this means the green light is reflected making the leaf appear green, while in the autumn the carotenoid becomes more dominant hence why they then appear yellow.

The chloroplasts transfer the energy they absorb from light in order to power a series of chemical reactions. These reactions lead to the splitting of water (H2O), which is taken in by the roots, into Hydrogen (H) and Oxygen (O). Meanwhile the leaf takes in Carbon dioxide through their stomata. This reacts with Hydrogen to form sugar glucose which is derived from the sunlight energy originally collected by the Chloroplasts.

For more on this see the book the science of Gardening by Professor peter Jones (2011)

In order to achieve this successfully Chloroplasts are adapted to aid their ability to carry out photosynthesis. This is though:

Them having a large surface area which maximises the amount of space for light to strike them.

They are located in the top two cell layers of the plant leaf to enable the most sun to be captured.

They are located near the spongy mesophyll layer which enables spaces for the hydrogen and Oxygen to diffuse in and out of the cell with ease.

They are near the veins of the leaf so the water, sourced from the roots, can diffuse in easily.

Oxygenic life exists for the water splitting activity done by chloroplasts. They were producing about 90% of the O2 in current air we can breathe. No plant exist without chloroplasts and the establishement of heritable endosymbiosis of photosynthetic bacteria gave rise to plants, with several nuclear genes active on chloroplasts life. Chloroplasts membrane is organized in an envelope and unique internal stacked structures, the thylakoids with a liquid media inside, the lumen. The liquid space out the thylakoid is the stroma and under light drives ATP synthesis due to a gradient in pH with lumen. Chlorophyll in different forms is active as prostetic group or light harvester in a series of different membrane proteins that can split water and generate NAPDH. Life of plants and life on Earth are after chloroplasts prevalence, but still now we do not are able to reproduce the extreme advantage of an artificial symbiosis like the one of plants. Please see Lynn Sagan Margulis history and related references.