Chapter 7: PHOTOSYNTHESIS - Los Angeles Mission … Chapter 7.pdf · Chapter 7: PHOTOSYNTHESIS 2....
Transcript of Chapter 7: PHOTOSYNTHESIS - Los Angeles Mission … Chapter 7.pdf · Chapter 7: PHOTOSYNTHESIS 2....
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Chapter 7:PHOTOSYNTHESIS
2. The “Light” Reactions
1. Overview of Photosynthesis
3. The “Dark” Reactions
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1. Overview of Photosynthesis
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What is Photosynthesis?The process of converting light energy (kinetic)into energy stored in the covalent bonds of glucose molecules (potential).
• carried out by photoautotrophs• plants, phytoplankton, cyanobacteria (any
photosynthetic organism)
• the basis of almost all ecosystems• all “food energy” ultimately comes from the sun• source of all atmospheric oxygen (O2)
Lightenergy
PHOTOSYNTHESIS
6 CO2 6+ H2O
Carbon dioxide Water
C6H12O6 6+ O2
Glucose Oxygen gas
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Photosynthesis vs Respirationessentially the
reverseof each other
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Leaf Cross Section
Leaf
Mesophyll Cell
CO2 O2
Chloroplast
Chloroplast
Photosynthesis occurs in Chloroplasts
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The Chloroplastouter membrane
inner membrane
granum
thylakoid
stroma
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Photosynthesis consists of 2 sets of Reactions
The light-dependent or “Light” Reactions:• convert sunlightenergy intochemical energy(stored in ATP &NADPH)
“Dark” Reactions(Calvin cycle):
• use chemicalenergy fromlight reactionsto make glucose
Light
CO2H2OChloroplast
LIGHTREACTIONS(in thylakoids)
CALVINCYCLE
(in stroma)
NADP+
ADP+ P
ATP
NADPH
O Sugar
Electrons
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2. Light-dependent(“Light”) Reactions
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Light Reactions occur in Thylakoids
A variety of light-absorbing
pigments &electron transport
proteins areembedded within
the thylakoidmembrane
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The Pigments absorb “Visible” Light
Chlorophyll a & b:• the major pigments (absorb red, blue…, reflect green)
Carotenoids (e.g., β-carotene)• accessory pigments (absorb green, blue, reflect red, yellow)
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blue red
Absorption Range for each Pigment
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Transmittedlight
Absorbedlight
Reflectedlight
Light
Chloroplast
Chlorophyll absorbs “non-green” light energy
• green lightpasses onthrough oris reflected,causing theleaves to appear green
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1H2O ½ O2 + 2 H+ + 2 *e-
2e- transport chain(ETC) pumps H+
into thylakoid
PS I
PS II
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3 ATP Synthaseuses H+ flow tomake ATP
4 2 e- toNADPHPS II
PS I
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Light Energy absorbed by Pigments Fuels 4 General Steps of the “Light Reactions”:
1) H2O split to O, 2 H+ & 2 high energy e- (*e-) in PS II
H2O O2 + H+ + *e-sunlight
2) Energy released by a series of *e- transfers is used to generate H+ gradient• H+ accumulates inside the thylakoid membrane
• *e- ends up in NADPH (an electron carrier)
3) H+ gradient used to make ATP (chemiosmosis)
4) *e- “re-energized” in PS I, passed on to NADP+
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e–
ATP
MillmakesATP
Phot
on
Phot
on
Photosystem II Photosystem I
NADPHe–
e–e–
e–
e–
e–
Analogy of Light reactions
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Chloroplast
Stroma (low H+ concentration)
Light Light
NADP+ + H+ NADPH
H+
H+
H+
H+
ATPPADP +
Thylakoidmembrane
H2O 1
2O2 + 2 H+ H+
H+
H+ H+
H+
H+
H+ H+
H+
H+
Photosystem II Electrontransport chain
Photosystem I ATP synthase
Thylakoid space(high H+ concentration)
Summary of the“Light” Reactions
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3. Light-independent(“Dark”) Reactions
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The “Dark” ReactionsA series of reactions called the Calvin cycle that synthesize glucose from CO2 and H2O:
CO2 + H2O C6H12O6 (glucose)ATP, NADPH
• can occur in dark (doesn’t require light directly)• also occurs during daylight!
• takes place in the stroma of chloroplasts• outside the thylakoids
• uses energy stored in ATP and NADPH• produced by the light reactions
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“Dark” Reactions
Don’tmemorize
this!!
Involves an anabolicpathway known as theCalvin cycle:
• endergonic reactions ofthis pathway are fueled byATP & NADPH from the“light” reactions
• resulting sugars can beused as a source ofenergy or to build otherorganic molecules
Calvincycle
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Summary of Photosynthesis
stroma
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Key Terms for Chapter 7
• chlorophyll, carotenoids
Relevant Review Questions: 1-6, 8-10, 12
• ATP synthase
• ATP, NADPH
• electron transport chain (ETC)
• photoautotroph
• chloroplast, thylakoid, stroma
• Light reactions, dark reactions, Calvin cycle