PHOTOSYNTHESIS
Molecular Biology
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Chemical
Energy
and
ATP
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• Adenosine Triphosphate (ATP) is a
short term energy storage molecule.
ADP
ATP
Energy
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Adenosine triphosphate (ATP)
Fully
charged
battery
Chemical
Energy
and
ATP
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Examples of how ATP is used:
– active transport (Na+ and K+ pumps)
– movement of motor proteins
– protein synthesis
– photosynthesis
Energy
Flow
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Autotrophs - convert light energy from the
sun into stored chemical energy (sugar)
What
are
plants
made
of?
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• Plants are mainly carbohydrates.
sugar
C H O
6
12
2
6
• Where does the H2O come from?
• Where does the Carbon come from?
=
Photosynthesis
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Photo = Light
Synthesize = Combine together.
Photosynthesis a process that uses the
energy of sunlight to combine water and
carbon dioxide into sugar and oxygen.
Photosynthesis
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Light Energy
Chloroplast
CO2 + H2O
Sugars + O2
Understanding
Photosynthesis
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Jan van Helmont Experiment (1643)
– weighed a seedling and soil
– watered for 5 years
Results
– tree gained 75 kg
– mass of soil was unchanged.
Conclusion
– tree mass must have come from the water.
Understanding
Photosynthesis
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Joseph Priestly Experiment (1771)
– candle under a bell jar
– candle and mint plant
Results
– candle with plant burned longer
Conclusion
– Plants release oxygen
Understanding
Photosynthesis
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Jan Ingenhousz Experiment (1779)
– aquatic plants in light
– aquatic plants in dark
Results
– aquatic plants in light produce bubbles
Conclusion
– plants need sunlight to produce oxygen.
Understanding
Photosynthesis
______________________________________________
Theodor Engelmann Experiment (1882)
– used prism to divide light into component colors
– exposed photosynthetic algae to the light
Results
– oxygen-requiring bacteria concentrated where
oxygen levels were highest
Conclusion
– red and violet colors of light
drive photosynthesis
Light & Pigments
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• Chlorophyll a most common pigment
in plants, protists, and
bacteria.
Absorption of Light by Chlorophyll
Chlorophyll b
Chlorophyll a
Green Reflected
Red & Violet Absorbed
Chloroplast
______________________________________________
cross section
of leaf
• The chloroplast is the organelle that specializes in
photosynthesis.
– DNA
– Ribosomes
– Thylakoid (folded inner membrane)
chloroplasts
in plant cell
chloroplasts
contain
chlorophyll
Inside
a
Chloroplast
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• Chloroplast structure
– stroma
• fluid-filled interior
– thylakoid
• contains chlorophyll
• light reactions
– grana
• stacks of thylakoids
Photosynthesis
______________________________________________
light energy
water
carbon dioxide
glucose
oxygen
Photosynthesis
______________________________________________
• Photosynthesis occurs in two stages.
– light-dependent reactions
• driven by light
• occurs at the thylakoid membrane
– light-independent reactions
• light does not power these reactions
• occurs in the stroma
Light-Dependent
Reactions
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• Light-Dependent Reactions use sunlight
energy to form ATP (cellular energy).
Light-Independent
Reactions
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• Light-Independent Reactions or Calvin
Cycle, uses ATP and electrons captured
from the sun to form sugar compounds.
• Glucose C6H12O6
The calvin cycle was named after Melvin Calvin who traced
the chemical path that carbon follows to form glucose.
Photosynthesis:
Big
Picture
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Photosynthetic Sea Slug
The green sea slug is the first animal shown to make chlorophyll like a plant.