Transcript http://vilenski.org/science/safari/cellstructure/chloroplasts.html AP BIOLOGY PHOTOSYNTHESIS Chapter 10 Light Reactions http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG Sunlight is made up of many different wavelengths _______________ of light Your eyes “see” different wavelengths as different colors ___________ http://www.simontucket.com/_Portfolio/PortLarge/L_Il_Prism.jpg.

http://vilenski.org/science/safari/cellstructure/chloroplasts.html
AP BIOLOGY
PHOTOSYNTHESIS
Chapter 10
Light Reactions
http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG
Sunlight is made up
of many different
wavelengths
_______________
of light
Your eyes “see”
different
wavelengths as
different
colors
___________
http://www.simontucket.com/_Portfolio/PortLarge/L_Il_Prism.jpg
Visible light is part of
electromagnetic spectrum
V
I
B
G
Y
O
R
Plants gather the sun’s energy with
light absorbing molecules called
_______________.
pigments
By: VanderWal
http://fig.cox.miami.edu/Faculty/Dana/chlorophyll.jpg
The main energy
absorbing molecule
in green plants is
__________________
CHLOROPHYLL a
http://www.rnzih.org.nz/images/gardenimages/carrots_d.jpg
CAROTENOID PIGMENTS appear
ORANGE, RED, and YELLOW
Carotene
appears orange
Xanthophyll
appears yellow
http://www.webexhibits.org/causesofcolor/images/content/7C_chlorophyll_in_leaves.jpg
Pigments of photosynthesis
• Chlorophyll & other pigments
– embedded in thylakoid membrane
– arranged in a “photosystem”
– structure-function relationship
Light: absorption spectra
Photosynthesis gets energy by absorbing
wavelengths of light
– chlorophyll a
• absorbs best in red & blue wavelengths & least in
green
– other pigments with different structures absorb
light of different wavelengths
WHY ARE PLANTS GREEN?
We “see” reflected light
Light wavelengths that are reflected
bounce back to your eyes . . .
so leaves “LOOK” green.
Image modified from: http://www.visibledreams.net/Web/color/color_3.html
WHY DON’T WE SEE THE OTHER
PIGMENTS?
Carotenoids are usually hidden by
the presence of chlorophyll
In the fall chlorophyll production
shuts down and other pigments
“show”
http://www.litzsinger.org/weblog/archives/email%20AutumnTrees5%20LREC%20102605.jpg
http://sps.k12.ar.us/massengale/ecology_notes_bi.htm
PHOTOSYNTHESIS HAPPENS IN
CHLOROPLASTS
THYLAKOIDS
= sac-like
photosynthetic
membranes
inside chloroplast
GRANUM (pl. grana)
= stack of thylakoids
Image from BIOLOGY by Miller and Levine; Prentice Hall Publishing©2006
THYLAKOID
SPACE
(lumen)
SPACES
STROMA
Gel-filled
space inside
chloroplast
surrounding
thylakoid sac
Gel-filled space
Inside the
thylakoid
sac
cytoplasm
Gel-filled space OUTSIDE
chloroplast but inside the cell
membrane http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG
PHOTOSYNTHESIS OVERVIEW
Pearson Education Inc; Publishing as Prentice Hall
LIGHT DEPENDENT REACTIONS
CHARGE UP ENERGY CARRIER
ATP
= _____
Adenine
Phosphate groups
Ribose
ATP
Energy for cellular work
(Energy- consuming)
Energy from catabolism
(Energy- yielding)
ADP +
P
i
NICOTINAMIDE ADENINE DINUCLEOTIDE PHOSPHATE
High energy
+
NADP
electron carrier = _____________
+
NADP
+
2e
+
+
H
→ NADPH
Photosynthesis
• Light reactions
– light-dependent reactions
– energy production reactions
• convert solar energy to chemical energy
• Make ATP & NADPH
• Calvin cycle
– light-independent reactions
– sugar production reactions
• use chemical energy (ATP & NADPH) to
reduce CO2 & synthesize C6H12O6
Photosystems of photosynthesis
2 photosystems in thylakoid membrane
– Both have a REACTION CENTER
• CHLOROPHYLL a molecules
• PRIMARY ELECTRON ACCEPTOR
– Surrounded by light-gathering “ANTENNA COMPLEX”
• Accessory pigments (chlorophyll b, carotenoids)
– Collect light energy and pass it on to chlorophyll a
– Photosystem II
• P680 = absorbs 680nm
wavelength red light
– Photosystem I
• P700 = absorbs 700nm
wavelength red light
ETC of Photosynthesis
Photosystem II
Photosystem I
ELECTRON TRANSPORT CHAIN
•
•
•
•
Plastoquinone
Cytochrome
Plastocyanin
Ferredoxin
Light Dependent reactions
Electron Transport Chain
+
H+
H
H+ H+H+
H+
– membrane-bound proteins in organelle
– electron acceptors
• NADPH
– proton (H+)
gradient across
inner membrane
• Where’s the double
membrane?
– ATP synthase
enzyme
ETC of Photosynthesis
Chloroplasts transform light
energy into chemical energy
of ATP

use electron carrier NADPH
LIGHT DEPENDENT REACTIONS
ETC produces from light energy
– ATP & NADPH
• go to Calvin cycle
PS II absorbs light
– excited electron passes from chlorophyll to
“primary electron acceptor”
– need to replace electron in chlorophyll
– enzyme extracts electrons from H2O &
supplies them to chlorophyll
• splits H2O
• O combines with another O to form O2
• O2 released to atmosphere
• and we breathe easier!
ETC of Photosynthesis
3
1
H+
4
H+
H+
H+
H+
H+
H+
H+
H+
ADP + Pi
ATP
H+
H+
to the
Calvin
Cycle
ETC of Photosynthesis
3
2
1
H+
4
H+
H+
H+
H+
H+
H+
H+
H+
ADP + Pi
ATP
H+
H+
to the
Calvin
Cycle
ETC of Photosynthesis
electron
carrier
6
5
$$ in the bank…
reducing power
to the
Calvin
Cycle
ETC of Photosynthesis
split H2O
MAKING ATP
•
•
•
•
•
moves the electrons
runs the pump
pumps the protons
forms the gradient
drives the flow of protons
through ATP synthase
• attaches Pi to ADP
• forms the ATP
H+
H+
H+
H+
H+
H+
H+
H+
ADP + Pi
ATP
H+
Noncyclic Photophosphorylation
• Light reactions elevate
electrons in
2 steps (PS II & PS I)
– PS II generates
energy as ATP
– PS I generates
reducing power as NADPH
Cyclic photophosphorylation
PS I doesn’t pass
electron to NADP…
it cycles back to ETC &
makes more ATP, but
no NADPH
– coordinates light
reactions to Calvin cycle
– Important in maintaining
proportion of ATP &
NADPH for Calvin
– Calvin cycle uses more
ATP than NADPH
X
Photophosphorylation
cyclic
photophosphorylation
noncyclic
photophosphorylation
Experimental evidence
• Where did the O2 come from?
– radioactive tracer = O18
Experiment 1
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Experiment 2
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Proved O2 came from H2O not CO2 = plants split H2O
LIGHT DEPENDENT REACTION
Requires ______________
LIGHT
Molecules embedded in
THYLAKOID membranes
________________________
Made up of __________________
PHOTOSYSTEMS II & I
connected by ______________________
ELECTRON TRANSPORT CHAIN
& ___________________
ATP SYNTHASE
Uses light energy to change
ATP
ADP + P → _______
NADPH
NADP+ + 2e- + H + → _________
Breaks apart ______
H20 molecules and
releases _____________
oxygen
LIGHT REACTIONS summary
Where did the energy come from?
sunlight
Where did the electrons come from?
From chlorophyll; replaced by H2O
Where did the H2O come from?
In through roots
Where did the O2 come from?
Made when water splits
Where did the O2 go?
Out through stomata
LIGHT REACTIONS summary
Where did the H+ come from?
Split off of water
Where did the ATP come from?
Produced by ATP synthase during light rxns
What will the ATP be used for?
Make sugar in Calvin cycle
Where did the NADPH come from?
Receives e-’s at end of ETC
What will the NADPH be used for?
Make sugar in Calvin cycle
…stay tuned for the Calvin cycle
PHOTOSYNTHESIS
Light &
Water
Light-Dependent
Reaction
Oxygen
ATP
NADPH
Carbon
Dioxide
Light-Independent
Reactions
CALVIN CYCLE
(CH2O)n
http://vilenski.org/science/safari/cellstructure/chloroplasts.html
CALVIN CYCLE
http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0076.JPG
Calvin Cycle
*
Molecules you
*
need to know
*
*
X2
See
Calvin cycle
animation
CALVIN CYCLE MOLECULES
5 carbon CO2 acceptor that combines with
CO2 in the first step of the Calvin cycle
________________________________
Ribulose bisphosphate (RuBP)
Enzyme that catalyzes the addition of CO2 to
RuBP
RuBP
carboxylase (RUBISCO)
________________________
3 carbon sugar produced during the Calvin
cycle that can be used to build glucose
and other organic molecules
Glyceraldehyde-3-phosphate (G3P)
______________________________
CALVIN CYCLE
LIGHT INDEPENDENT
(also called _________________________)
DOES NOT require ____________
LIGHT
____________
Happens in _________
STROMA between thylakoids
NADPH donates Hydrogen
_______________
ions + electrons
ATP donates _________________
ENERGY
CO2 donates ______________
Carbon & oxygen
to make __________________________
glyceraldehyde-3-phosphate
(G3P)
http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookCHEM2.html
To make one glucose molecule
C6H12O6
the Calvin cycle uses
6 molecules of CO2
_____
18 molecules of ATP
_____
12 molecules of NADPH
_____
Campbell concept check 10.3
CALVIN CYCLE summary
Where does the C in G3P come from? CO2
Where does the H in G3P come from? From H2O
via NADPH
Where does the O in G3P come from?
CO2
Where does the ADP & NADP+ go? Back to light reaction
to recharge
Where does the G3P go? Used to make glucose and
other organic molecules
STOMA (pl. STOMATA)
GUARD CELLS
http://www.cbu.edu/~seisen/Stomata.jpg
PROBLEMS ON HOT DRY DAYS
• If stomata are open to receive CO2 . . .
results in water loss
• On hot, dry days if plant shuts stomata to
conserve water . . . photosynthesis slows
http://www.ipm.iastate.edu/ipm/icm/files/images/spider-mite-field.jpg
C3 plants (Ex: rice, wheat, soybeans)
____
(1st product of carbon fixation has 3 C’s- 3PG)
On hot, dry days when plant shuts stomata
plant switches to ______________________
PHOTORESPIRATION
Rubisco adds O2 to Calvin cycle instead of CO2
Product broken down by
mitochondria/peroxisomes to release CO2
COUNTERPRODUCTIVE:
Makes NO ATP
Makes NO sugar
Uses ATP
Decreases photosynthesis by siphoning molecules
from Calvin cycle
ALTERNATIVE METHODS of
CARBON FIXATION
•
C
4
______
plants
(Ex: corn & sugarcane
CAM
• ______ Crassulacean acid metabolism
(Ex: succulents, cactus, pineapple,)
WAYS TO AVOID DECREASE IN
PHOTOSYNTHESIS DUE TO
PHOTORESPIRATION
SEE ANIMATION
CALVIN CYCLE found in BUNDLE
SHEATH CELLS in C4 plants
*
PEP CARBOXYLASE
________________________
adds CO2 to make a 4 carbon
molecule before entering
Calvin Cycle
Process of using H+ gradient to generate ATP
chemiosmosis
= ________________________
(Can refer to ATP made in mitochondria too)
Process of creating ATP using a Proton gradient created by
the energy gathered from sunlight.
photophosphorylation
= ________________________
Process that consumes oxygen, releases CO2, generates no
ATP, and decreases photosynthetic output; generally occurs
on hot, dry, bright days, when stomata close and the oxygen
concentration in the leaf exceeds that of carbon dioxide
photorespiration
= ___________________________________