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Photosynthesis: An Overview
Warm up 11/12 Define these words
Pigment Chlorophyll Thylakoid Stroma Light dependent reactions Light independent reaction
Learning Objectives Explain the role of light and pigments in photosynthesis. Explain the role of electron carrier molecules in
photosynthesis. State the overall equation for photosynthesis.
Light
• Light energy from the sun must be captured for photosynthesis to occur.
• Sunlight is “white” light—actually a mixture of different wavelengths. (ROY-G-BIV)
Pigments
Pigments – plants gather the suns energy with light absorbing molecules called pigment
What role do pigments play in the process of photosynthesis?• Photosynthetic organisms capture energy from sunlight
with pigments
Chlorophyll
Photosynthetic organisms capture energy from sunlight with pigments—principally with chlorophyll.
Chlorophyll – green pigments
2 main types of chlorophyll• Chlorophyll a and Chlorophyll b
• Absorbs light very well in the blue-violet spectrum and red regions of visible spectrum
• Chlorophyll a – found in all plants, algae, and cyanobacteria
• Chlorophyll b – found in all plants, and green algae
Chlorophyll
Photosynthesis takes place inside organelles called chloroplasts.
Plant Cell
Chloroplast
Chloroplast
Chloroplasts contain• Thylakoids- saclike photosynthetic membranes
• Chlorophyll is located in thylakoid membrane• Grana – thylakoids are interconnected and arranged
in stacks known as grana• Stroma – fluid portion of the chloroplast, outside of the
thylakoids
Chloroplast
In plants, photosynthesis takes place inside chloroplasts.
ThylakoidGranum
Thylakoid membrane
Stroma
Chloroplasts and light transmission
What is so special about chlorophyll that makes it so important for photosynthesis?
• light is a form of energy, any compound that absorbs light absorbs energy
High Energy Electrons
The high-energy electrons produced by chlorophyll are highly reactive and require a special “carrier.”
High Energy Electrons
An electron carrier is a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule.
NADP+ accepts and holds 2 high energy electrons, along with a hydrogen ion (H+) NADP+ NADPHThis is one way in which energy from sunlight can be trapped in chemical form.
High Energy Electrons
NADPH can carry the high-energy electrons that were produced by light absorption in chlorophyll to chemical reactions elsewhere in the cell.
An Overview of Photosynthesis
Photosynthesis uses the energy of sunlight to convert water and carbon dioxide (low-energy reactants) into high-energy sugars and oxygen (products).
Carbon dioxide + Water → Sugars + Oxygenlight
light+ → +
C6H12O66CO2 6H2O 6O2
Photosynthesis and Light
Photosynthesis involves two sets of reactions: Light-dependent reactions Light-independent reactions
Light-Dependent Reactions
Light-dependent reactions require the direct involvement of light and light-absorbing pigments.
Water
Oxygen
• Uses energy from sunlight to produce energy rich compounds like ATP
• Takes place in the Thylakoid
• Input: Water• Output:
Oxygen (O2)
Light-Independent ReactionsLight-independent reactions use ATP and NADPH molecules produced in the light-dependent reactions to produce high-energy sugars from carbon dioxide
Sugars andCarbohydrates
Carbon Dioxide
• No light is required • Take place outside the
thylakoids, in the stroma• Input: CO2
• Output: sugar
Interdependence of ReactionsLight-dependent and light-independent reactions have an interdependent relationship.
work together to capture the energy of sunlight and transform it into energy rich compounds like carbohydrates