BIO.A.3 Bioenergetics
Topic Summary for Photosynthesis:
In eukaryotes, photosynthesis occurs in organelles called chloroplasts. Chloroplasts house light-absorbing chemicals.
Light is a form of energy. Sunlight is a mixture of all the different colors of visible light.
Light-absorbing molecules called pigments capture the sun’s energy.
Chlorophyll is the principal pigment in photosynthetic organisms. Chlorophyll absorbs blue-violet and red light but reflects green light.
Chloroplasts have a complex internal structure that includes:
• • thylakoids: saclike photosynthetic membranes that contain chlorophyll and other pigments and are arranged in stacks called grana.
• • stroma: the fluid portion outside of the thylakoids.
The energy in light raises some of the electrons in chlorophyll to higher energy levels. These high-energy electrons are used in photosynthesis.
Electron carriers are used to transport the electrons from chlorophyll to other molecules during photosynthesis.
NADP+ is a compound that can accept and hold 2 high-energy electrons and 1 hydrogen ion. This process converts NADP+ into NADPH.
Usually summarized by a simple chemical reaction, photosynthesis is a complex process that involves two interdependent sets of reactions.
The light-dependent reactions require light, light-absorbing pigments, and water to form NADPH, ATP, and oxygen.
The light-independent reactions do not use light energy. They use carbon dioxide from the atmosphere, NADPH, and ATP to make energy-rich carbon compounds.
The Light-Dependent Reactions: Generating ATP and NADPH
Photosynthesis begins with these reactions, which occur in thylakoid membranes.
Photosystems are clusters of proteins and chlorophyll in thylakoid membranes.
High-energy electrons form when pigments in photosystem II absorb light. The electrons pass through electron transport chains, a series of electron carrier proteins.
• • The movement of electrons through an electron transport chain causes a thylakoid to fill up with hydrogen ions and generates ATP and NADPH.
• • ATP synthase is a membrane protein through which excess hydrogen ions escape a thylakoid in a process that makes ATP.
The Light-Independent Reactions: Producing Sugars
They occur in the stroma of thylakoids and are commonly called the Calvin cycle.
Six carbon dioxide molecules from the atmosphere enter the Calvin cycle and combine with 5-carbon compounds already present. They produce twelve 3-carbon molecules.
Two 3-carbon molecules are removed from the cycle. They are used by the plant to build sugars, lipids, amino acids, and other compounds.
The remaining ten 3-carbon molecules are converted back to 5-carbon molecules and begin a new cycle.
Many factors influence the rate of photosynthesis, including temperature, light intensity, and availability of water affect photosynthesis.
C4 and CAM plants have a modified type of photosynthesis that enables the plants to conserve water in dry climates.
Topic Summary for Photosynthesis:
In eukaryotes, photosynthesis occurs in organelles called chloroplasts. Chloroplasts house light-absorbing chemicals.
Light is a form of energy. Sunlight is a mixture of all the different colors of visible light.
Light-absorbing molecules called pigments capture the sun’s energy.
Chlorophyll is the principal pigment in photosynthetic organisms. Chlorophyll absorbs blue-violet and red light but reflects green light.
Chloroplasts have a complex internal structure that includes:
• • thylakoids: saclike photosynthetic membranes that contain chlorophyll and other pigments and are arranged in stacks called grana.
• • stroma: the fluid portion outside of the thylakoids.
The energy in light raises some of the electrons in chlorophyll to higher energy levels. These high-energy electrons are used in photosynthesis.
Electron carriers are used to transport the electrons from chlorophyll to other molecules during photosynthesis.
NADP+ is a compound that can accept and hold 2 high-energy electrons and 1 hydrogen ion. This process converts NADP+ into NADPH.
Usually summarized by a simple chemical reaction, photosynthesis is a complex process that involves two interdependent sets of reactions.
The light-dependent reactions require light, light-absorbing pigments, and water to form NADPH, ATP, and oxygen.
The light-independent reactions do not use light energy. They use carbon dioxide from the atmosphere, NADPH, and ATP to make energy-rich carbon compounds.
The Light-Dependent Reactions: Generating ATP and NADPH
Photosynthesis begins with these reactions, which occur in thylakoid membranes.
Photosystems are clusters of proteins and chlorophyll in thylakoid membranes.
High-energy electrons form when pigments in photosystem II absorb light. The electrons pass through electron transport chains, a series of electron carrier proteins.
• • The movement of electrons through an electron transport chain causes a thylakoid to fill up with hydrogen ions and generates ATP and NADPH.
• • ATP synthase is a membrane protein through which excess hydrogen ions escape a thylakoid in a process that makes ATP.
The Light-Independent Reactions: Producing Sugars
They occur in the stroma of thylakoids and are commonly called the Calvin cycle.
Six carbon dioxide molecules from the atmosphere enter the Calvin cycle and combine with 5-carbon compounds already present. They produce twelve 3-carbon molecules.
Two 3-carbon molecules are removed from the cycle. They are used by the plant to build sugars, lipids, amino acids, and other compounds.
The remaining ten 3-carbon molecules are converted back to 5-carbon molecules and begin a new cycle.
Many factors influence the rate of photosynthesis, including temperature, light intensity, and availability of water affect photosynthesis.
C4 and CAM plants have a modified type of photosynthesis that enables the plants to conserve water in dry climates.