Photosynthesis
Photosynthesis is a complex process that involves the conversion of radiant energy
from the sun into chemical energy in the form of glucose. It consists of two sets of
reactions: light-dependent reactions and light-independent reactions.
During the light-dependent reactions, solar energy is captured and used to generate
ATP and NADPH. The process begins with the absorption of photons by pigments,
primarily chlorophylls, which are located in the thylakoid membrane of chloroplasts. The
absorbed energy excites electrons in the chlorophyll molecules, initiating a chain of
events.
The excited electrons are transferred to a primary electron acceptor via redox reactions.
This sets off an electron transport system, where the electrons pass through a series of
membrane-bound carriers. As the electrons are transferred, protons are pumped across
the thylakoid membrane, creating a proton gradient.
The generated proton gradient is then used to drive chemiosmosis, a process in which
protons flow through ATP synthase, leading to the synthesis of ATP from ADP and
inorganic phosphate. At the end of the light-dependent reactions, NADP+ molecules are
reduced to NADPH by accepting electrons, which are provided by the splitting of water
molecules in a process called photolysis. Oxygen gas is released as a byproduct of this
reaction.
The Calvin Cycle
The light-independent reactions, also known as the Calvin cycle, occur in the stroma of
chloroplasts. They utilize the ATP and NADPH generated in the light-dependent
reactions to convert carbon dioxide into glucose. The Calvin cycle consists of three
main stages: carbon fixation, reduction, and regeneration.
Carbon Fixation
During carbon fixation, carbon dioxide molecules are combined with a five-carbon
compound called ribulose-1,5-bisphosphate (RuBP) to form an unstable six-carbon
molecule. This molecule immediately breaks down into two molecules of
3-phosphoglycerate (PGA).
In the reduction stage, ATP and NADPH from the light-dependent reactions are used to
convert PGA into glyceraldehyde-3-phosphate (G3P), a three-carbon molecule. Some
G3P molecules leave the cycle to form glucose or other organic compounds, while
others remain to regenerate RuBP.
Photosynthesis is a complex process that involves the conversion of radiant energy
from the sun into chemical energy in the form of glucose. It consists of two sets of
reactions: light-dependent reactions and light-independent reactions.
During the light-dependent reactions, solar energy is captured and used to generate
ATP and NADPH. The process begins with the absorption of photons by pigments,
primarily chlorophylls, which are located in the thylakoid membrane of chloroplasts. The
absorbed energy excites electrons in the chlorophyll molecules, initiating a chain of
events.
The excited electrons are transferred to a primary electron acceptor via redox reactions.
This sets off an electron transport system, where the electrons pass through a series of
membrane-bound carriers. As the electrons are transferred, protons are pumped across
the thylakoid membrane, creating a proton gradient.
The generated proton gradient is then used to drive chemiosmosis, a process in which
protons flow through ATP synthase, leading to the synthesis of ATP from ADP and
inorganic phosphate. At the end of the light-dependent reactions, NADP+ molecules are
reduced to NADPH by accepting electrons, which are provided by the splitting of water
molecules in a process called photolysis. Oxygen gas is released as a byproduct of this
reaction.
The Calvin Cycle
The light-independent reactions, also known as the Calvin cycle, occur in the stroma of
chloroplasts. They utilize the ATP and NADPH generated in the light-dependent
reactions to convert carbon dioxide into glucose. The Calvin cycle consists of three
main stages: carbon fixation, reduction, and regeneration.
Carbon Fixation
During carbon fixation, carbon dioxide molecules are combined with a five-carbon
compound called ribulose-1,5-bisphosphate (RuBP) to form an unstable six-carbon
molecule. This molecule immediately breaks down into two molecules of
3-phosphoglycerate (PGA).
In the reduction stage, ATP and NADPH from the light-dependent reactions are used to
convert PGA into glyceraldehyde-3-phosphate (G3P), a three-carbon molecule. Some
G3P molecules leave the cycle to form glucose or other organic compounds, while
others remain to regenerate RuBP.
