1. PHOTOSYNTHESIS

2. Fundamental biological processes for making and using energy
Photosynthesis: process by which plants convert radiant energy to chemical energy
Respiration: process by which glucose molecules are broken down and stored energy is released
Photosynthesis - autotrophs make glucose
Respiration – organisms break down glucose

3. TYPES OF ORGANISMS BY ENERGY PRODUCTION
Autotrophs
organisms that produce organic molecules from inorganic substances (photosynthesis)
- Photoautotrophs- use light energy to make food (plants, algae, cyanobacteria)
- Chemiautotrophs oxidize inorganic chemicals to drive food making reactions (bacteria, fungi)
Heterotrophs
- organisms that obtain energy from other organisms
(heterotrophs or autotrophs)
- do not make own food

4. Location of photosynthesis
Chloroplast- double membrane organelle Thylakoid discs (photosystem: thylakoids) - Harvest sunlight - Contains chlorophyll and accessory pigments - Photosystem I and II are linked structurally and functionally Grana (stacks of thylakoid discs) location of light reactions Stroma (protein rich solution, outside grana) location of Calvin Cycle Mesophyll: location of chloroplasts Stomata: pores in leaf CO2 enters/ O2 exits Chlorophyll: pigiment in thylakoids

5. 6 CO2 + 6 H2O + light energy  C6H12O6 + 6 O2
PHOTOSYNTHESIS
6 CO H2O + light energy  C6H12O O2
process whereby autotrophs (plants) take in light energy and convert it to chemical energy (sugar)
Redox Reactions
water is split  e- transferred with H+ to CO2  sugar
biochemical pathway- series of linked redox reactions where product of one reaction is consumed by the next reaction
Endergonic- absorbs solar energy
Exergonic- releases energy for organism

6. Tracking Atoms through Photosynthesis
Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis (C.B. van Niel)
Reactants:
Products:
6 CO2
12 H2O
C6H12O6
6 H2O
6 O2
6 CO2

7. Photosynthesis = Light Reactions + Calvin Cycle “photo” “synthesis” energy building sugar building reactions reactions

8. Light Energy and Pigments
Comes from radiation (energy that travels in waves) from the sun
photon- particles which have energy
wavelength- crest to crest of wave
sunlight- mixture of all visible wavelengths
white light- all wavelengths reflected equally so looks white
visible spectrum- all colors of white light

9. graph plotting pigment light absorption vs wavelength
Pigment: substance that absorbs light
- photosynthesis: absorbed light energy is used to make chemical bond energy
- wavelengths not absorbed are reflected (color we see)
Absorption spectrum
graph plotting pigment light absorption vs wavelength
representation of how well particular pigment absorbs different wavelengths of white light

10. Photosynthetic pigments
chlorophyll a (blue green)
- primary photosynthetic pigment
- directly involved in converting light  chemical energy
- hides other pigments
chlorophyll b (yellow green)
- accessory pigment
- absorbs light and transfers energy to chlorophyll a
carotenoids (orange, yellow)
- xanthophylls (yellow) / carotenes (orange)
- accessory pigments
- converts energy to chloro. a
- seen in autumn when chloro. breaks down
- photoprotection for chlorophyll
anthocyanin (red, purple, blue): antioxidants
- non photosynthetic parts of plant (flowers/fruits)
- absorb different pigments so we see other colors

11. Determining Absorption Spectrum

12. Action Spectrum Action spectrum plots rate of photosynthesis of
different wavelengths,
i.e. CO2 consumption , O2 release
(different than absorption spectrum)
Englemann’s experiment:
Used alga and bacteria
Measured O2 output
Result: violet-blue and red
wavelengths caused
most photosynthesis

13. * *Move from ground state to excited state**
Electron Excitement
light is made of photons
(particles which carry fixed amount of energy)
when light strikes chlorophyll , some of its atoms absorb the photons
energy is transferred to the atoms
electrons and excites them to jump to next level
* *Move from ground state to excited state**
- excess energy is released as light or heat

14. Photosystems
Photosystem: reaction center (proteins that hold special pair of chlorophyll a molecules) + light harvesting complexes (cloro. a & b, carotenoids bound to proteins)
- located in thylakoid discs
- absorb light energy
Primary electron acceptor: accepts electrons and becomes reduced (electrons move to higher energy level)
Photosystem I: chlorophyll a absorbs at 700 nm- far red (p700)
Photosystem II: chlorophyll a absorbs at 680 nm- red (p680)

15. Overview of Stages of Photosynthesis 2 Stage Process
light reactions (needs light)
- occurs in thylakoid membranes
4 basic steps
- sun’s energy is trapped by chlorophyll
- electron transport (linear/cyclical)
- water is split and oxygen is released (O2 production)
- ATP and NADPH are formed and released into stroma
- purpose: to make ATP and NADPH (energy carrier molecule)

16. Calvin Cycle:
- occurs after light reactions
- can occur in light or dark
3 basic steps
- carbon fixation to glucose
- reduction of NADP to NADPH
- regeneration of RuBP to start cycle over again

17. Light Reactions Electron Flow
Two routes for electron flow: A. Linear (non-cyclic) electron flow B. Cyclic electron flow

18. STEPS OF LIGHT REACTION
1. photosystem II absorbs light and excites electrons of chlorophyll a
- molecules and electrons are forced to higher energy level (reaction center)
***purpose of photosystem II is to generate ATP and supply electrons to photosystem I ***
2. excited electrons leave chlorophyll a molecule (oxidation reaction)

19. NON-CYCLICAL PHOTOPHOYPHORYLATION
primary electron acceptor sends electrons into ETC
- reduction reaction
- chain uses energy of electrons to make ATP
- water is split (photolysis) and O2 is released into atmosphere
- electrons from water replace those lost in Photosystem II
- pumps H+ ions (from splitting of water) to interior of grana (lumen)
- inside grana , there is a high concentration (proton gradient) of H+ ions
- chemiosmosis occurs (making of ATP)
- H+ ions back move across grana membranes (ATPsynthase)
LINEAR ELECTRON FLOW
NON-CYCLICAL PHOTOPHOYPHORYLATION

20. NON-CYCLICAL PHOTOPHOYPHORYLATION
at end of ETC, electrons are passed to photosystem I thru the
(cytochrome complex = plastiquinone Pq (e- carrier) and plastocyanin Pc (protein)
- photosystem also absorbs light to excite electrons in chloro. A
- electrons go thru separate electron transport chain in photosystem I to a different primary electron acceptor
ferradoxin Fd (protein) facilitates movement of e-
- purpose of photosystem I is to generate NADPH
5. NADP+
- accepts electrons and H+ ions (reduces it to NADPH)
- NADPH and ATP move into stroma
LINEAR ELECTRON FLOW
NON-CYCLICAL PHOTOPHOYPHORYLATION

21. produces ATP for Calvin Cycle
Cyclic Electron Flow:
uses PSI only
produces ATP for Calvin Cycle
animation

22. Cyclic
PS I only
Reaction center is P700
Electrons travel back to PS I
Only ATP is produced
No photolysis of water
No O2 involved
Predominant in bacteria
Non cyclic
PS II and I
Reaction center is P680
Both ATP and NADPH are produced
Photolysis (splitting) of water occurs
O2 is by-product
Predominant in green plants

23. End products of light reactions
1. ATP and NADPH: needed to power dark reactions
2. O2:
by product
released into atmosphere

24. Chemiosmosis in Chloroplasts and Mitochondria
Respiration and photosynthesis use chemiosmosis to generate ATP
ETCs pump protons (H+)
across membrane from
areas of low concentration
to high concentration
Protons then diffuse back
across membrane thru
ATPsynthase to make ATP
H+ reserviors for each organelle
mitochondria- matrix
chloroplast – lumen
Mitochondria:high energy e- come from organic molecules
Chloroplasts: high energy e- come from water

25. Thylakoid Membrane Organization
Proton motive force (H+ gradient) generated by:
H+ from water
H+ pumped across by cytochrome
Removal of H+ from stroma when NADP+ is reduced

26. Calvin Cycle - occurs in stroma
- light independent: can occur in light or darkness, always after light rxns
- occurs in stroma
purpose: Carbon fixation to glucose molecule (from CO2 in atmosphere)
Uses ATP and NADPH
3 Phases
1. carbon fixation
2. reduction
3. regeneration of RuBP (CO2 acceptor)

27. Steps of Calvin Cycle
1. Carbon fixation
- 3 CO2 enters plant from atmosphere and binds with RuBP ribulose biphosphate (5 C sugar)
- catalyzed by rubisco enzyme
( RuBP carboxylase)
- forms unstable 6 C intermediate sugar
- this splits into 2 PGA per CO phosphoglycerate molecules
net: 6 PGA

28. Reduction (PGA to G3P)
2 steps
- each PGA gets phosphate
from ATP
- then each molecule reacts with H from NADPH and breaks phosphate bond
- net gain: 1 molecule of G3P (glyceraldehydre 3 phosphate)
- 6 G3P formed, but
- 1 molecule used to make sugar
- 5 molecules used to regenerate RuBP
6 ATP and 6 NADPH needed to produce 1 net G3P

29. 3 ATP needed to regenerate RuBP
Regeneration of RuBP from G3P
- series of reactions results in the regeneration of 3 RuBP molecules
(cyclical – continues over and over again)
3 ATP needed to regenerate RuBP
animation

30. End product of Calvin Cycle
Glucose
*6 turns of cycle needed to make 1 molecule of glucose*
Calvin Cycle uses:
3 CO2, 9 ATP, 6 NADPH
animation
1 C6H12O6 molecule = 6 CO2, 18 ATP, 12 NADPH

31. Evolutionary Advantages
- Calvin cycle is most common pathway for carbon fixation
- C3 plants: plants that fix C thru calvin cycle (because of 3 C PGA that is initially formed)
- other plants fix C through alternative pathways and then release it into Calvin cycle
- alternative pathways found in plants in dry hot climates
- these plants use STOMATA (pores on undersurface of leaves)
- major passageways thru which O2 and CO2 goes in and out - major passageways of water loss

32. Alternative Pathways of Carbon Fixation
1. C4 Pathway
- during hottest part of day, stomata are partially closed
- plants fix CO2 into 4 C compounds when CO2 is low
- mesophyll: PEP carboxylase fixes CO2 (4-C)
pumps CO2 to bundle sheath
- bundle sheath: CO2 used in Calvin Cycle
- lose less water than C3 plants
- corn, sugarcane, crabgrass
advantage in hot sunny areas

33. Alternative Pathways of Carbon Fixation, cont.
CAM Pathway
- Crassulacean acid metabolism (CAM)
- stomata open at night, closed during day
- night: plants take in CO2 and fix into many compounds, stored in mesophyll cells
- day: light reactions supply ATP, NADPH; CO released from organic acids for Calvin cycle
- lose less water than C3 and C4 plants
- cactus, pineapples
advantage in arid areas

34. C fixation and Calvin Cycle together
C fixation and Calvin Cycle in different CELLS
C fixation and Calvin Cycle at different TIMES

35. Factors Affecting Rate of Photosynthesis
Environmental Variables 1. Light intensity/ direction of incoming light
- high intensity = high rate
- saturation point: levels off after certain
intensity because pigments can only
absorb so much light
2 Light color
3..CO2 levels
- same mechanism as light
4. temperature
- higher temp = higher rate unless enzymes denature
5. pH of leaf

36. Factors Affecting Rate of Photosynthesis
Plant Variables 1. leaf color/ variegation- amount of chlorophyll 2. leaf size 3. stomata density and distribution 4. leaf age