Title: Energy Acquiring Pathways
1Energy - Acquiring Pathways
- Starr/Taggarts
- Biology
- The Unity and Diversity of Life, 9e
- Chapter 7
2Key Concepts
- Photosynthesis is the pathway by which carbon and
energy enter the web of life - Survival of nearly all organisms depends on
photosynthesis performed by autotrophs - Photosynthesis converts solar energy to chemical
energy - Photosynthesis is summarized this way
3The Equation
12H2O 6CO2
6O2 C6H12O6 6H2O
WATER
CARBON DIOXIDE
OXYGEN
GLUCOSE
WATER
in-text, p. 113
4Factors that influence photosynthetic rates
- 12H20 6CO2 ? 602 C6H12O6 6H2O
- Factors that would impact it
- CO2 carbon dioxide concentration
- Light intensity
- Water availability
- Minerals
- Temperature
5Where Photosynthesis Takes Place
- Chloroplasts
- Two outermost membranes surround interior stroma
- Inner thylakoid membrane system
6upper surface of leaf
photosynthetic cells
two outer membrane layers
part of thylakoid membrane system(the
chloroplasts innermost membrane)
(see next slide)
Fig. 7.3a, p. 114
stroma
7Inside the Chloroplast
Stroma
Thylakoid membranes
8Sunlight as an Energy Source
- Visible light is 380 - 750 nm
- Photoautotrophs use visible light energy
9Absorption Spectra
- Main pigments are Chlorophyll a and b
- Accessory pigments are carotenoids, anthocyanins,
and phycobilins
10Action Spectrum
http//cenocracy.topcities.com/spectrum.gif
11Chlorophyll and Solar Energy
- Solar energy is captured by pigment molecules in
the thylakoid membranes of chloroplasts. - Examples chlorophyll a and b, beta-carotene
- Electrons in these molecules get excited by
sunlight and move to higher energy levels
photosynthesis gets started.
12http//members.lycos.nl/rherold/science/extraction
/plantenextractie.htm
13Pigments
- Pigment structure
- Hydrocarbon backbones dissolve readily in lipid
bilayer of photosythetic cell membranes
14Photosystems
- Pigments are organized in photosystems
15What Happens to the Absorbed Energy?
- Energy flows randomly among pigments of a
photosystem until trapped by reaction center - Mixture of pigments
- Chloropyll a at center is important because of
its location
16Photosynthesis An Introduction
Light Dependent Rxns Thylakoid Membrane
Light Independent Rxns Stroma
17Sun Energy Source
Light Dependent Rxns Thylakoid Membrane
Light Independent Rxns Stroma
18Sun Energy Source
Chlorophyll absorbs solar energy
Light Dependent Rxns Thylakoid Membrane
Light Independent Rxns Stroma
19Sun Energy Source
Chlorophyll absorbs solar energy
1) Some energy used to make ATP
ATP
ADP P
Light Dependent Rxns Thylakoid Membrane
Light Independent Rxns Stroma
20Sun Energy Source
Chlorophyll absorbs solar energy
ATP
H2O reactant
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
21Sun Energy Source
Chlorophyll absorbs solar energy
2) Some energy used to split water hydrolysis
O
H
H2O reactant
H
H
O
H
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
22Sun Energy Source
Chlorophyll absorbs solar energy
H picked up by H carrier NADP
NADPH
O
H
H2O reactant
H
NADP
H
O
H
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
23Sun Energy Source
Chlorophyll absorbs solar energy
H picked up by H carrier NADP
NADPH
O
H
H2O reactant
H
H
O
H
O2 waste
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
24Sun Energy Source
CO2 reactant
Chlorophyll absorbs solar energy
NADPH
H2O reactant
O2 waste
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
25Sun Energy Source
CO2 reactant
Chlorophyll absorbs solar energy
ATP energy used to fix carbon
NADPH
C
C
O
H2O reactant
O
O
O
O2 waste
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
26Sun Energy Source
CO2 reactant
Chlorophyll absorbs solar energy
C
O
O
O
H
H
NADPH
H
NADPH drops off H
NADP
H2O reactant
H
C
O
O2 waste
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
27Glucose made with ATP energy
Sun Energy Source
Chlorophyll absorbs solar energy
NADP
H2O reactant
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
O2 waste
28Review
- Light-Dependent
- Sunlight drives ATP formation from ADP and Pi
- Water is split (hydrolysis)
- NADP picks up electrons and hydrogen
- Light - Independent
- ATP donates energy
- NADPH donates hydrogen
- CO2 donates carbon and oxygen
- Glucose (C6H12O6) is assembled
29Light - Dependent Reactions
- Relies on proteins in thylakoid membrane
- Pigments absorb photon energy
- Flow of electrons generates power to pump H ions
through membrane - Hydrolysis provides replacement electrons to
pigments - Flow of electrons also used to build NADPH from
NADP and H - Cascade of H through ATP synthase makes ATP
30Light Dependent Reactions
http//www.stolaf.edu/people/giannini/flashanimat/
metabolism/photosynthesis.swf
Fig. 7.12a, p. 121
31ATP Formation in Chloroplasts
- Chemiosmotic Theory
- H released by hydrolysis (photolysis) of water
- More H accumulates as electron transport
systems operate - H concentration and electric gradients form
across the thylakoid membrane - Flow of ions from thylakoid compartment into the
stroma drives ATP formation
http//www.stolaf.edu/people/giannini/flashanimat/
metabolism/atpsyn1.swf
http//www.stolaf.edu/people/giannini/flashanimat/
metabolism/atpsyn2.swf
32Light-Independent Reactions
- Synthesis
- ATP delivers energy
- NADPH delivers hydrogen and electrons
- CO2 provides carbon and oxygen
33Calvin-Benson Cycle
- Carbon Fixation
- Occurs in the stroma
- Carbon atom of CO2 is attached to RuBP (ribulose
biphosphate) by the enzyme rubisco - Unstable six-carbon intermediate forms
- Intermediate splits to form two three-carbon
molecules of phosphoglycerate (PGA)
34Calvin-Benson Cycle
- Building Glucose
- Each PGA accepts a phosphate group from ATP and
electrons from NADPH - Two PGAL are formed
- To build one six-carbon sugar phosphate, twelve
PGAL must form - 10 PGAL rearrange to regenerate RuBP
- 2 PGAL combine to form phosphorylated glucose
35Glucose made with ATP energy
Sun Energy Source
Chlorophyll absorbs solar energy
NADP
H2O reactant
Light Independent Rxns Stroma
Light Dependent Rxns Thylakoid Membrane
O2 waste
36Pathways of ATP Formation
- Noncyclic Pathway (just studied)
- Electrons flow from water, through Type I and
Type II photosystems, then to NADP - ATP and NADH form
- Oxygen (O2) is a by-product
37Pathways of ATP Formation
- Cyclic Pathway
- ATP forms
- Electrons cycle from and back to a Type I
photosystem
38Photosynthetic Styles
- There are three styles of photosynthesis
- C3
- C4
- CAM
- They reflect the tension between a plant needing
carbon dioxide, but losing water
39Avoiding Photorespiration
If stomata close, CO2 levels fall, O2 levels rise
and a plant starts to do photorespiration fixes
O2 and not CO2
40C3 Photosynthesis
- Fix C once
- Performed by rice, wheat, soybeans, KY bluegrass
- Starts with 3-C molecule (3-PGA) in Light
Independent Reactions
41C4 Photosynthesis
- Fix C twice (once in the mesophyll, once in
bundle sheath) - Performed by crabgrass, corn, others
- Starts with 4-C oxaloacetate
- Twice the C fixation means that plants can extend
their sugar production - Guards against photorespiration - when Rubisco
accepts O2 vs. CO2 and attaches O2 to RuBP vs. CO2
42Fig. 7.16b, p. 124
43PEP and its enzyme have a high affinity for CO2
and work well when rubisco does not-when it is
hot and dry and the stomata are partially closed
http//www.bios.niu.edu/sims/metabolism/c038f3b.gi
f
44CAM Photosynthesis
- Fix CO2 at night!
- Performed by plants in deserts or dry
environments - C is stored in intermediate molecules and then
Calvin/Benson cycle occurs during the day. - This guards against water loss!
http//hcs.osu.edu/hcs200/images/leaves/SUCCUl.JPG
45Bottom Line
- All plants get CO2 through stomata. Stomata close
in hot, dry times. - Plants want to conserve H2O, but there is a
tension. Plants need CO2 to do photosynthesis.
http//gcte-focus1.org/activities/activity_13/task
_133/basin/tutorial/gifs_2/stomata.jpg
46upper leaf surface
vein
mesophyll cell
lower leaf surface
bundle-sheath cell
CO2 moves through stoma, into air spaces in leaf
Fig. 7.16b, p. 124
47CO2 or O2
CO2 H2O
Rubisco affixes O2 to RuBP.
one glycolate only one PGA (not two) decreased
CO2 uptake, fewer sugars can form
CALVIN- BENSON CYCLE
CO2
carbon fixation in mesophyll cells
oxaloacetate
C3 PLANTS. With low CO2 / high O2,
photorespiration predominates.
that carbon fixed again in bundle-sheath
cells CO2 level in leaf enhanced no
photorespiration
CALVIN- BENSON CYCLE
CO2
stomata open at night CO2 uptake but no water
loss
C4 PLANTS. With low CO2 / high O2, Calvin-Benson
cycle predominates.
CALVIN- BENSON CYCLE
stomata close during day CO2 in leaf used
Fig. 7.16a, p. 124
CAM PLANTS. With low CO2 / high O2, Calvin-Benson
cycle predominates.
48Englemanns Observational Test
- Oxygen-requiring bacteria congregated where
oxygen was being produced by algae