Cellular Respiration With Photosynthesis

Light is captured by the leaves of a plant.

Photosynthesis is the act by which an organism collects light energy for use in cellular respiration, converting it to chemical energy. The process is present in plants, algae and some bacteria. Because it uses water and carbon dioxide and produces oxygen and glucose as byproducts, it is in many ways the opposite of metabolism in animals, which uses glucose and oxygen by giving off water and carbon dioxide.

Chloroplasts

Complex photosynthetic organisms have organelles inside their cells called chloroplasts, where most of the process occurs. Two outer membranes bound the chloroplast, and inside is a semi-fluid interior called the stroma. A thylakoid membrane is a series of compartments within the chloroplast stacked together and linked by channels.

Photosynthesis

In the light-dependent reactions, light energy is captured by molecules of pigment, which reflect light and give organisms like plants their color. Light harvesting complexes are circular clusters of pigments and other proteins embedded in the thylakoid membrane. Light that hits each pigment excites electrons within pigments, and this energy is passed back and forth.

Released Electrons

When the energy reaches an area called photosystem II, it finally causes electrons to release and enter an electron transfer chain. Lost electrons are immediately replenished by pulling electrons from nearby water molecules. The oxygen atom from the water is lost as a byproduct, while the hydrogen atoms continue on as ions (charged particle).

Electron Transfer Chain

As the electrons move through the transfer chain, they compel the hydrogen ions to move across the thylakoid membrane again and again, forming an electric gradient which drives the synthesis of ATP, the main energy carrier of the cell, and eventually attract the hydrogen to the stroma. The remaining electrons pass through photosystem I and along with the hydrogen are transferred to a molecule of NADP, which is used to transport electrons, in order to form NADPH. Both NADPH and ATP are necessary in the light-independent reactions.

LIght-Independent Reaction

The Calvin-Benson cycle forms the integral part of the light-independent reactions in the stroma. Carbon dioxide, which is captured from the air in plants and the water in algae, enters the cycle and is slowly modified into a variety of molecules by ATP, which contributes a phosphate group, and NADPH, which contributes electrons and hydrogen. Glucose is eventually formed, and later on it will be converted to either sucrose or starch. Sucrose is a transportable form of carbohydrates that provides immediate energy, while starch can be stored for later use.

References

• Estrella Mountain Community College: Photosynthesis