Phases of Photosynthesis & Its Location

By John Newton
The leaves are the primary location in which photosynthesis takes place.
Leaf image by Pablo Gonzales from Fotolia.com

Photosynthesis is a process in which plants and some bacteria use energy from sunlight to produce sugar, or glucose, as explained by Estrella Mountain Community College. The sugar is converted by cellular respiration into adensoine triphosphate (ATP), providing the plant with energy. Photosynthesis is the primary function of the leaves and requires carbon dioxide, water and sunlight, which are used to produce glucose and oxygen, as can be seen from the photosynthesis equation: 6CO2 + 6H2O + energy from light ' C6H12O6 + 6O2 (Carbon Dioxide + Water + energy from light ' glucose and oxygen)

Obtaining Carbon Dioxide and Water

Water enters plants by osmosis through the root hairs, according to Estrella Mountain Community College. This water is then drawn up to the leaves along specialized xylem cells. The leaves obtain carbon dioxide for use in photosynthesis via the stomata, which are microscopic pores that open during the day and close at night to reduce water lost by transpiration.

The Light-Dependent Reactions

Photosynthesis takes place in the chloroplasts within plant leaves, with the light-dependent reactions occurring in membrane -bound compartments in the chloroplasts called thylakoids. Jones and Jones demonstrate how chlorophyll molecules embedded in the thylakoid membrane absorb light energy, which is used to split water in the photolysis reaction, create ATP in a process called photophosphorylation and to produce nicotinamide adenine dinucleotide phosphate (NADP), a molecule used in the light-independent reactions.

The Light-Independent Reactions

Jones and Jones report that the light-independent reactions take place in the stroma, a fluid containing enzymes that use ATP, generated in the light-dependent reactions. The stroma is located in the chloroplasts. The light-independent reactions are kept separate from other reactions in the cell by the outer chloroplast membranes. The light-independent reactions use energy and electrons produced from the light-dependent reactions to reduce carbon dioxide and convert it into sugar, or carbohydrate (glucose).

Products of Photosynthesis

The carbohydrates produced from photosynthesis provide a longer-term store of energy and can be used to produce other organic molecules, such as fats and proteins necessary for growth and repair. Jones and Jones show how excess carbohydrate produced during photosynthesis is stored in starch grains in the chloroplasts. The other product of photosynthesis, oxygen, is released into the atmosphere.

About the Author

Based in Manchester, England, John Newton has been writing since 2006. His work has appeared in "Floreat Castellum" and "The Castle Society" magazine. He holds a Bachelor of Science in geography from Durham University.