The Role of Chlorophyll

Photosynthesis

• Photosynthesis is the cyclical process where plants, certain bacteria and algae use energy from sunlight to convert water and carbon dioxide into oxygen and carbohydrates. Photosynthesis is divided into two phases called the light reactions, which require sunlight; and the dark reactions, which do not require light. During the light reactions, the plant creates high-energy molecules from the sunlight absorbed by the chlorophyll. During the dark reactions, the high-energy molecules power the production of carbohydrates.

Chlorophyll Function

• Chlorophyll is contained in a special compartment called a thylakoid, located in the part of the plant cell called the chloroplast. The thylakoid also contains pigments, called carotenoids, that absorb light wavelengths that the chlorophyll can't and pass that energy to the chlorophyll. The chlorophyll, other pigments, electron carriers and proteins form a light collecting unit, called a photosystem. Plants have two of these with different methods of absorbing light. After the photsystem absorbs enough light energy, the energy enters a chlorophyll molecule, called the reaction center, which releases a pair of excited electrons. These electrons help the plant form the molecules, nicotinamide adenine dinucleotide phosphate, or NADPH, and adenosine triphospate, or ATP.

Dark Reactions

• During the dark reactions, the energy provided by NADPH and ATP powers the processes where the plant converts carbon dioxide from the atmosphere into glucose. Glucose is the basis for a variety of carbohydrates including sugars, cellulose and starches. Plants use sugars, such as maltose and sucrose, as food for immediate energy. Plants store the starches in its leaves, fruit and roots for later consumption and use the cellulose for building the rigid cell walls that provide structure.

Importance

• Without the cycle of photosynthesis, earth wouldn't have any plants or life of any kind. Photosynthesis provides vital energy to nearly every form of life on earth. Plants and animals produce both fats and proteins from the carbohydrates created during dark reactions. Plants release oxygen into the atmosphere as a byproduct of the photosynthesis process. During respiration, animals breathe in oxygen and expel carbon dioxide. Plants absorb the carbon dioxide from the atmosphere and use it to create carbohydrates.