Photosynthesis: Light-Dependent and Light-Independent Reactions

Study Notes

Photosynthesis is a process of using light energy to build carbohydrates from water and carbon dioxide, releasing oxygen as a byproduct.
Net equation for photosynthesis: 6 CO2 + 6 H2O + light energy → C6H12O6 (glucose) + 6 O2.
Water and carbon dioxide enter the plant through roots and stomata, respectively. Oxygen is released through stomata.
Chloroplast is the organelle where photosynthesis occurs. Mitochondria are responsible for cellular respiration.
Chlorophyll, found in thylakoids, absorbs light energy for photosynthesis. Granum and stroma are parts of the chloroplast.
Photosynthesis consists of light-dependent reactions and light-independent reactions (Calvin cycle).
Chlorophyll absorbs blue and red light, reflects green light, giving plants their green color.
Light-dependent reactions occur in the thylakoid membrane, producing oxygen, ATP, and NADPH.
Water molecules are split into hydrogen ions and oxygen gas during the light-dependent reactions.
Electron transport chain in the thylakoid membrane facilitates the production of ATP through chemiosmosis.
Calvin cycle (light-independent reactions) takes place in the stroma, producing sugars from carbon dioxide using ATP and NADPH.
Carbon dioxide is fixed into 3-phosphoglycerate (PGAs) in the first step of the Calvin cycle.
Six PGAs are formed from three CO2 molecules and one Ribulose-1,5-bisphosphate (RuBP) molecule.
ATP is used to form one 1,3-bisphosphoglycerate (1,3-BPG) from three PGAs through the action of the enzyme PGA kinase.
NADPH reduces 1,3-BPG to glyceraldehyde-3-phosphate (G3P) during the second step of the Calvin cycle.
Six G3Ps are produced in total. One G3P is used to form glucose, while the other five are used to regenerate the three RuBP molecules.
The total number of carbons in the process is 18 (six PGAs + six G3Ps).- The Calvin cycle converts three molecules of CO2 into one molecule of glyceraldehyde-3-phosphate (G3P), resulting in a net gain of 12 carbons.
Each G3P molecule consists of three carbon atoms, along with a phosphate group on carbon 3.
The production of one molecule of glucose from six molecules of CO2 requires 18 ATP molecules and 12 NADPH molecules.
The light-dependent reactions and the Calvin cycle are the two processes that make up the process of photosynthesis.
The light-dependent reactions occur inside the thylakoid membrane, while the Calvin cycle takes place in the stroma of the chloroplasts.

Description

Test your knowledge of photosynthesis, a process in which light energy is used to produce carbohydrates from water and carbon dioxide, releasing oxygen. Learn about the net equation for photosynthesis, the role of chloroplasts, chlorophyll, and the processes of light-dependent reactions and the Calvin cycle.