Biology lesson on photosynthesis

1. The Marvels of Photosynthesis
Unleashing the Power of Sunlight

2. The Evolution of Photosynthesis
From Cyanobacteria to Green Plants

3. The Origins of Photosynthesis
● Photosynthesis emerged around 3.5 billion
years ago
● Early prokaryotes used simple pigments to
harness energy from the Sun
● First photosynthetic organisms were likely
anoxygenic
● The process shaped Earth's atmosphere and
paved the way for further evolution
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4. The Purple Earth Hypothesis
● The idea that chlorophyll evolved in a
time when there were only purple
photosynthetic organisms on earth
● Our (Previously) Purple Planet.
●
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5. The Rise of Cyanobacteria
● Cyanobacteria evolved around 2.5 billion
years ago
● They developed oxygen-generating
photosynthesis
● Oxygen production caused the Great
Oxygenation Event
● Cyanobacteria became the dominant
photosynthetic organisms
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6. Endosymbiosis and Eukaryotic
Photosynthesis
● Endosymbiotic events led to the origin of
eukaryotes
● Chloroplasts originated from engulfed
cyanobacteria
● Mitochondria and chloroplasts share a similar
evolutionary history
● Eukaryotes evolved more efficient
photosynthetic mechanisms

7. Adaptations in Photosynthetic
Organisms
● Plants developed complex tissues and
specialized structures
● Leaves evolved to maximize light absorption
and minimize water loss
● C4 and CAM photosynthesis arose as
efficient adaptations
● Photosynthetic pigments diversified to
maximize light capture
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8. The Marvels of Photosynthesis
Unleashing the Power of Sunlight

9. Introduction to Photosynthesis
● Photosynthesis is the process by which
plants convert sunlight into energy.
● Plants capture carbon dioxide and release
oxygen as a byproduct.
● Chlorophyll, found in chloroplasts, is the key
pigment responsible for capturing light.
● Photosynthesis plays a vital role in the
Earth's oxygen supply.
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10. The Sunlight Dependence
● Photosynthesis is the process by which
plants convert sunlight into chemical energy.
● Chlorophyll is a pigment that captures light
energy from the sun.
● Light-dependent reactions occur in the
thylakoid membranes of chloroplasts.
● Water is split, producing oxygen and protons
to fuel subsequent reactions.
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11. Light Absorption by Chlorophyll
● Chlorophyll absorbs red and blue light most
efficiently.
● It reflects green light, giving plants their
characteristic color.
● Accessory pigments like carotenoids
broaden the spectrum of light absorption.
● Light energy is used to excite electrons in the
chlorophyll molecules.
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12. Introduction to Photosynthesis
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13. Introduction to Photosynthesis
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14. Light Dependent Reactions
● Light-dependent reactions occur in the
thylakoid membrane of chloroplasts.
● They convert light energy into
chemical energy in the form of ATP and
NADPH.
● Water molecules are split, releasing
oxygen as a byproduct.
● The energy carriers ATP and NADPH
are used in the next stage of
photosynthesis.
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15. How Photosystems work
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16. Light Dependent Reactions
Unveiling the Power of Sunlight

17. Introduction to Light Dependent
Reactions
● The first step in photosynthesis
● Converts light energy from the sun
● Occurs in thylakoid membranes of
chloroplasts
● Produces ATP and NADPH

18. Introduction to Light Dependent
Reactions
● The first step in photosynthesis
● Converts light energy from the sun
● Occurs in thylakoid membranes of
chloroplasts
● Produces ATP and NADPH

19. Photosystem II
● Located in the thylakoid
membrane
● Absorbs photon energy and
splits water
● Releases oxygen as a
byproduct
● Produces electrons and
protons
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20. Electron Transport Chain
● Transports electrons from photosystem II to
photosystem I
● Establishes a proton gradient across
thylakoid membrane
● Generates ATP through chemiosmosis
● Electrons end up in NADP+ to form NADPH
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21. Photosystem I
● Transfers electrons from electron transport
chain
● Re-energizes electrons using light
● Produces more ATP and NADPH
● Electrons eventually combine with NADP+ to
form NADPH
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22. Unveiling the Calvin Cycle
Illuminating the Pathway to Photosynthesis

23. Light Independent Reactions
● Also known as the Calvin/Benson
cycle, it takes place in the stroma
of chloroplasts.
● Carbon dioxide is converted into
sugar molecules using ATP and
NADPH.
● The cycle requires the enzyme
RuBisCO and several
intermediate reactions.
● It plays a critical role in fixing
carbon and creating organic
molecules.
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24. Introduction to the Calvin Cycle
● Essential process in photosynthesis
● Occurs in the stroma of chloroplasts
● Converts carbon dioxide into glucose
● Requires ATP and NADPH as energy and
reducing power
● Driven by the enzyme RuBisCO
● Engine of life on Earth
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25. Step 1: Carbon Fixation
● RuBisCO enzyme combines carbon dioxide
with RuBP
● Forms unstable 6-carbon molecule, which
immediately splits
● Produces two molecules of
3-phosphoglycerate (3-PGA)
● Requires the input of ATP
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26. Step 2: Reduction
● ATP and NADPH are used to convert 3-PGA
into glyceraldehyde 3-phosphate (G3P)
● One molecule of G3P is formed while the
other molecules are used to regenerate RuBP
● NADPH is oxidized in the process
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27. Step 3: Regeneration of RuBP
● Remaining G3P molecules are rearranged
and used to regenerate RuBP
● Requires ATP as an energy source
● Regeneration makes the cycle continuous
● Great video explaining the regeneration of
RuBP
○ Nature's smallest factory: The Calvin
cycle - Cathy Symington
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28. Factors Affecting
Photosynthesis
● Temperature, light intensity, and carbon
dioxide availability strongly influence
photosynthesis.
● Different plants have varying optimal
conditions for efficient photosynthesis.
● High temperatures can lead to enzyme
denaturation and reduced photosynthetic
rates.
● Photosynthesis can be limited by low light
intensity or insufficient carbon dioxide.
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29. C3, C4, CAM Plants: Strategies for Photosynthesis
Adaptations in Carbon Fixation Among Different Plant Species

30. Introduction to C3, C4, and
CAM Plants
● C3, C4, and CAM plants are named after the
type of photosynthesis they use.
● The terms refer to different pathways plants
have evolved for carbon fixation.
● Carbon fixation is the process of converting
carbon dioxide into organic compounds.
● Understanding these pathways helps us
appreciate plant diversity and survival
strategies.
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31. C3 Plants – The Most Common
Type
● C3 plants use the Calvin cycle exclusively for
carbon fixation.
● They typically have lower photosynthetic
efficiency in hot, dry conditions.
● Common C3 plants include rice, wheat, and
soybeans.
● In the cool, moist climates, C3 plants
dominate plant communities.
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32. C4 Plants – Efficient in High
Temperatures
● PHYSICALLY Separate different aspects of
photosynthesis
● C4 plants use an additional biochemical
pathway called the C4 pathway.
● They have specialized leaf anatomy and can
fix more carbon dioxide.
● These plants thrive in hot, arid conditions
with intense sunlight.
● Examples of C4 plants include maize,
sugarcane, and many grasses.
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33. C4 Plants – Efficient in High
Temperatures
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34. CAM Plants – Surviving in
Extreme Environments
● TEMPORALLY separate different parts of
photosynthesis
● CAM plants, or crassulacean acid metabolism
plants, use a specialized variant of the C4
pathway.
● They open their stomata at night to minimize
water loss.
● During the day, the stored carbon dioxide is
released for photosynthesis.
● CAM plants are well-suited for deserts and
other water-limited environments
● Include succulents, pineapples.
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35. CAM Plants – Surviving in
Extreme Environments
● TEMPORALLY separate different parts of
photosynthesis
● CAM plants, or crassulacean acid metabolism
plants, use a specialized variant of the C4
pathway.
● They open their stomata at night to minimize
water loss.
● During the day, the stored carbon dioxide is
released for photosynthesis.
● CAM plants are well-suited for deserts and
other water-limited environments
● Include succulents, pineapples.
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36. The Secrets of Photosynthesis
Unraveling the Mysteries of Nature's Energy Conversion

37. The History of Photosynthesis
● Early scientists wondered how plants grew
and produced energy.
● In the 18th century, Joseph Priestley
discovered the presence of a gas that
supported combustion.
● Jan Ingenhousz revealed that plants produce
oxygen in sunlight.
● These findings laid the groundwork for
understanding photosynthesis.
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