Chlorophyll is the green pigment found in plants. This organelle is mainly responsible for capturing the sunlight and using it for photosynthesis. It absorbs blue-violet and red light and reflects green light.

The model below shows how photosynthesis is involved in the carbon and energy cycles through the atmosphere and the biosphere.

The model below shows how photosynthesis is involved in the carbon and energy cycles through the atmosphere and the biosphere. (Click to see the diagram)

The roles of ADP and ATP during light-dependent and light-independent reactions are:

1. ADP
Light-dependent reaction:
ADP combines with phosphate to form ATP.

Light-independent reaction:
ADP is the product when a phosphate group is removed in ATP. Once ADP is recycled and recharged, it comes out again as ATP.

2. ATP
Light-dependent reaction:
ATP is produced by the chloroplasts during this stage. It becomes the energy required during the light-independent reaction.

Light-independent reaction:
ATP provides energy when the cells construct organic compounds using carbon dioxide and water during light-independent reactions. Eventually, these organic compounds become sugar.

During photosynthesis, two types of reaction occur. Light-dependent reactions occur in the thylakoid membranes of a chloroplast. This process converts solar energy into the molecules that are used for the light-independent reaction. Once the light from the sun is absorbed by the chloroplasts, high-energy electrons are transported into the different chemical reactions that produce ATP and NADPH. These molecules are used for producing high-energy sugars during the next stage of photosynthesis.

On the other hand, the light-independent reaction, which is also known as the Calvin cycle, takes place in the stroma of the chloroplasts. It uses carbon dioxide, ATP and NADPH to produce high-energy molecules, such as glucose. This cycle does not require the presence of light.