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Photosynthesis
Photosynthesis
• The process by which plants, algae, and some
microorganisms harness solar energy and convert
it into chem...
Photosynthesis Equation
Overall equation: 6CO2 + 6H2O  C6H12O6 + 6O2
Photosynthesis is a Redox Reaction
Redox-reactions
Photosynthesis/Respiration Cycle
Cellular
respiration
CO2 and H2O
ATP (available for
cellular tasks)
Heat energy
Atmospheric Oxygen
Light
• Light is the source of energy for
photosynthesis
– Made of photons—packets of kinetic energy
– Part of electromagn...
Light
Pigments
• Pigment—Substance that absorbs light energy
• Several types of pigments:
– Chlorophyll a—most abundant, green p...
Pigments
Pigment Color Organisms
Major Pigment
Chlorophyll a
green (or yellow) plants, algae, bacteria
Accessory Pigment
C...
Structure of a leaf
Structure of a leaf
Chloroplasts
• Mainly found in cells in the LEAF
– Lots of surface area to absorb light
– Has abundant water
– Main site o...
Chloroplasts
Chloroplasts
Chloroplasts
• Stroma—inner fluid with DNA, ribosomes, fluid
• Grana—Stacks of thylakoid
• Thylakoid—Disks, membranes with...
Chloroplasts
Chloroplasts
Photosynthesis Overview
• Happens in 2 stages
– Light Reactions—convert solar energy into
chemical energy
• Occurs in thyl...
Photosynthesis Overview
Photosynthesis Overview
Light Reactions: Photosystems
What happens if you could capture this
energy?
Light Reactions: Photosystems
Plants capture this energy!
Light Reactions: Photosystems
The Light Reactions
• Photosystem II
– Pigment molecules absorb light and transfer to
reaction center (chlorophyll a)
– Wa...
The Light Reactions—Photosystem II
ATP Generation—Photosystem II
The Light Reactions
• Photosystem I
– Pigment molecules absorb light and transfer to
reaction center (chlorophyll a)
– 2 e...
The Light Reactions—Photosystem I
NADPH Generation—Photosystem
I
Making ATP: Photophosphorylation
H+ gradient: as
electrons moved
within membrane,
H+ is pumped into
the thylakoid space
Making ATP: Photophosphorylation
ATP produced: ATP
synthase allows H+
to go down its
concentration
gradient, generates
ATP
ETC vs. Photophosphorylation
Energy source Final Electron Acceptor
The Carbon Reactions
• Also known as: Calvin Cycle, “Dark reactions”
• Occurs in the stroma
• Uses ATP and NADPH to make g...
Calvin Cycle
C3 Plants
• Calvin Cycle = C3 Pathway
• All plants use Calvin Cycle, but some plants ONLY
use C3 pathway
– 95% of plants a...
C4 Plants
• C4—adaptation to help minimize
photorespiration (1% of plants)
• C4 Plants—Separate light reactions and Calvin...
C3 and C4 Plant Anatomy
C4 plantC3 plant
Vein
Stoma
Mesophyll
cell
Bundle-
sheath cell Mesophyll
cell
Stoma
Vein
Bundle-
s...
CAM Plants
• Occurs in desert plants (3–4% of plants)
• Only open stomates at night to fix CO2, then
fix again during the ...
Pathway
C3 plant C4 plant CAM plant
Global Warming
Green house effect: radiant heat trapped by CO2
Global Warming
Ozone Depletion
Ozone: O3 (O2 converted to O3) filters out UV rays
Ozone Depletion
Chlorofluorocarbons: release chlorine which destroys
ozone
Antarctica
Ozone
Depletion
Chlorofluorocarbons:
release chlorine which
destroys ozone
Antarctica
Photosynthesis Updated
Photosynthesis Updated
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Photosynthesis Updated

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Photosynthesis Updated

  1. 1. Photosynthesis
  2. 2. Photosynthesis • The process by which plants, algae, and some microorganisms harness solar energy and convert it into chemical energy. • Endergonic reaction • Redox reaction • Only done by autotrophs • Glucose used for: fuel own plant respiration (50%), growth, make other important compounds (amino acids, cellulose, starch, sucrose) 6CO2 + 6H2O C6H12O6 + 6O2
  3. 3. Photosynthesis Equation Overall equation: 6CO2 + 6H2O  C6H12O6 + 6O2
  4. 4. Photosynthesis is a Redox Reaction Redox-reactions
  5. 5. Photosynthesis/Respiration Cycle Cellular respiration CO2 and H2O ATP (available for cellular tasks) Heat energy
  6. 6. Atmospheric Oxygen
  7. 7. Light • Light is the source of energy for photosynthesis – Made of photons—packets of kinetic energy – Part of electromagnetic spectrum – 3 types from the sun get to the earth • Ultraviolet • Visible • Infrared
  8. 8. Light
  9. 9. Pigments • Pigment—Substance that absorbs light energy • Several types of pigments: – Chlorophyll a—most abundant, green pigment, absorb blue/red, reflect green – Accessory Pigments: • Chlorophyll b—absorb blue/red, reflect green • Carotenes—absorb blue, reflect orange/red • Xanthophylls—absorb purple/blue/ green, reflect yellow
  10. 10. Pigments Pigment Color Organisms Major Pigment Chlorophyll a green (or yellow) plants, algae, bacteria Accessory Pigment Chlorophyll b yellow plants, algae Carotenoids (xanthophylls and carotenes) orange, red, yellow plants, algae, bacteria, archaea
  11. 11. Structure of a leaf
  12. 12. Structure of a leaf
  13. 13. Chloroplasts • Mainly found in cells in the LEAF – Lots of surface area to absorb light – Has abundant water – Main site of gas exchange • Exchange occurs through stomata surrounded by guard cells – Mainly located in mesophyll
  14. 14. Chloroplasts Chloroplasts
  15. 15. Chloroplasts • Stroma—inner fluid with DNA, ribosomes, fluid • Grana—Stacks of thylakoid • Thylakoid—Disks, membranes with photosynthetic pigments • Photosystem—in thylakoid membrane – Chlorophyll a (approx. 300 molecules) • Reaction Center – Accessory pigments (approx. 50 molecules) • Antenna pigment to funnel light to reaction center – Proteins
  16. 16. Chloroplasts
  17. 17. Chloroplasts
  18. 18. Photosynthesis Overview • Happens in 2 stages – Light Reactions—convert solar energy into chemical energy • Occurs in thylakoid membrane – Carbon Reactions—use ATP and NADPH to reduce CO2 to glucose • Occurs in the stroma
  19. 19. Photosynthesis Overview
  20. 20. Photosynthesis Overview
  21. 21. Light Reactions: Photosystems What happens if you could capture this energy?
  22. 22. Light Reactions: Photosystems Plants capture this energy!
  23. 23. Light Reactions: Photosystems
  24. 24. The Light Reactions • Photosystem II – Pigment molecules absorb light and transfer to reaction center (chlorophyll a) – Water is split into 2H+ and ½ O2 – Water donates 2 electrons – Energy “excites” 2 electrons to a higher energy orbital – Chlorophyll a ejects “excited” electrons to first electron transport chain (ETC) – ETC makes a proton gradient from stroma into the thylakoid space – ATP synthase uses proton gradient to make ATP (chemiosmotic phosphorylation) • Used in carbon reactions
  25. 25. The Light Reactions—Photosystem II
  26. 26. ATP Generation—Photosystem II
  27. 27. The Light Reactions • Photosystem I – Pigment molecules absorb light and transfer to reaction center (chlorophyll a) – 2 electrons come from first ETC – Energy “excites” 2 electrons to a higher energy orbital – Chlorophyll a ejects “excited” electrons to first electron transport chain (ETC) – Electrons are passed to NADP+ to reduce it to NADPH (used in carbon reactions)
  28. 28. The Light Reactions—Photosystem I
  29. 29. NADPH Generation—Photosystem I
  30. 30. Making ATP: Photophosphorylation H+ gradient: as electrons moved within membrane, H+ is pumped into the thylakoid space
  31. 31. Making ATP: Photophosphorylation ATP produced: ATP synthase allows H+ to go down its concentration gradient, generates ATP
  32. 32. ETC vs. Photophosphorylation Energy source Final Electron Acceptor
  33. 33. The Carbon Reactions • Also known as: Calvin Cycle, “Dark reactions” • Occurs in the stroma • Uses ATP and NADPH to make glucose from CO2 • Calvin Cycle: – Step 1: Carbon fixation—incorporation of CO2 into an organic molecule • CO2 combines with RuBP, using enzyme called rubisco – Step 2: PGAL Synthesis – Step3: PGAL makes glucose – Step 4: Regeneration of RuBP
  34. 34. Calvin Cycle
  35. 35. C3 Plants • Calvin Cycle = C3 Pathway • All plants use Calvin Cycle, but some plants ONLY use C3 pathway – 95% of plants are this way • Inefficient—lose some energy to heat – 30% on the best sunny day – In Photorespiration rubisco uses O2 instead of CO2 as a substrate – Stomates open, O2 diffuses out, CO2 is used – Hot dry climates, stomates cannot stay open—lost water, O2 builds up, photorespiration takes over
  36. 36. C4 Plants • C4—adaptation to help minimize photorespiration (1% of plants) • C4 Plants—Separate light reactions and Calvin Cycle into different cells – Light reactions and carbon fixation—mesophyll – CO2 combines with 3 carbon molecule to make 4 carbon—C4 – C4—(malate) moves to bundle sheath cells, rest of Calvin Cycle • Bundle sheath cells NOT exposed to O2
  37. 37. C3 and C4 Plant Anatomy C4 plantC3 plant Vein Stoma Mesophyll cell Bundle- sheath cell Mesophyll cell Stoma Vein Bundle- sheath cell
  38. 38. CAM Plants • Occurs in desert plants (3–4% of plants) • Only open stomates at night to fix CO2, then fix again during the day using Calvin Cycle – Store night time CO2 as malate in vacuoles – Stomates open, malate to chloroplast, release CO2, used in Calvin Cycle • Happens in same cells
  39. 39. Pathway C3 plant C4 plant CAM plant
  40. 40. Global Warming Green house effect: radiant heat trapped by CO2
  41. 41. Global Warming
  42. 42. Ozone Depletion Ozone: O3 (O2 converted to O3) filters out UV rays
  43. 43. Ozone Depletion Chlorofluorocarbons: release chlorine which destroys ozone Antarctica
  44. 44. Ozone Depletion Chlorofluorocarbons: release chlorine which destroys ozone Antarctica

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