Chapter 8: PhotosynthesisChapter 8: Photosynthesis
ATP: The Energy unit of the Cell
ATP (adenosine triphosphate,三磷酸腺苷)
O O O O CH2
H
OH OH
H
N
H H
O
NC
HC
N CC
N
NH2Adenine
RibosePhosphate groups
O
O O
O
O
O
-
- - -
CH
Cell Energy use in Active Transport
• Energy is released from ATP (-30.54 kJ/mol)– When the 3rd phosphate bond is broken
Trapping Energy from Sunlight
• The process that uses the sun’s energy to make simple sugars is called photosynthesis
• Bases of all ecosystems on Earth
6 CO2 + 6 H2O + Light energy C6H12O6 + 6 O2
Vein
Leaf cross section
Mesophyll
CO2 O2
Stomata
Where Does CO2 come from?•Enters leafs through the stomata
Where does H2O come from?•Absorbed by roots and pulled up to the leaves by cohesion and adhesion
(transpiration)
Where does Light Energy come from?
• Energy from the sun must be absorbed by pigments, light absorbing molecules
• Inside a chloroplasts are thylakoids and inside their membranes are pigments
• What wavelength of light do the pigments not absorb?– Green; reason why plants
are green
Photosynthesis: 2 Reaction Set
1) Light-dependent reactions chemical reactions driven by light energy absorbed by pigments
2) Light-independent reactions chemical reactions that use ATP and NADPH to create sugars out of CO2
H2O CO2
Light
LIGHT REACTIONSCALVINCYCLE
Chloroplast
[CH2O](sugar)
NADPH
NADP
ADP
+ P
O2
ATP
The Light-Dependent reactions
LightReflectedLight
Chloroplast
Absorbedlight
Granum
Transmittedlight
Pigments- light absorbing moleculesChlorophyll main light absorbing pigment
Light-dependent reactions are broken into two systems:Photosystem II and Photosystem I
Photosystem II• Chlorophyll absorbs light energy
into electrons
• Electrons passed through protein carriers (Electron Transport Chain)
• Energy used to move H+ into thylakoid
• Photosystem II breaks water (photolysis) to get more electrons and H+ produces O2
Photosystem I• Electrons re-energized by chlorophyll
in the photosystem
• Electrons passed to enzyme to change NADP+ (nicotinamide adenin dinucleotide phosphate) into NADPH
• NADPH carries H+ and energized electrons to light-independent reactions
• ATP synthase uses H+ ions in thylakoid to make ATP
ATP-Synthase
• Makes ADP + Pi into ATP
• Powered by Chemiosmosis:– Movement of chemicals across a
selectively- permeable membrane
– H+ concentration gradient was made by photosystem II, now it is used to make ATP through facilitated diffusion
3H+= 1 ATP
The Light-Dependent reactions
Photolysis
H2O CO2
Light
LIGHT REACTIONSCALVINCYCLE
Chloroplast
[CH2O](sugar)
NADPH
NADP
ADP
+ P
O2
ATP
The Light-Independent reactions
Final NumbersUse Produce
Light-Dependent Reactions
Sunlight NADPH
H2O ATP
NADP+/ADP/Pi O2
Use Produce
Light-Independent Reactions
(Calvin Cycle)
NADPH
RuBP
RuBP (recycled to keep
cycle going)
ATP PGAL (Which form sugars)
CO2 NADP+/ADP/Pi
Alternate Pathways: C4 and CAM
• Plants in hot/dry areas lose H2O quickly if they open their stomata but they need CO2
• 2 Pathways to fix this:1) C4 allows plant to change O2 into
CO2 but it costs ATP so it is less energy efficient• Corn and sugar cane
2) CAM Collect CO2 at night and store it as an acid then use the acid to make CO2 during the day time• Pineapple trees and cactus plants
P 242
Homework
• Read Ch. 9 and do Ch. 9 vocabulary
• Ch. 8 Apply Vocabulary and Questions 1-18 on p. 205-206