1. PHOTOSYNTHESIS

2. Photosynthesis process by which green plants & some organisms
seaweed, algae & certain bacteria
use light energy to convert CO2 + water glucose
all life on Earth, directly or indirectly, depends on photosynthesis as source of food, energy & O2

4. Autotrophs self feeders
organisms that make their own organic matter from inorganic matter
producers
need inorganic molecules such as CO2, H2O & minerals to make organic molecules

5. Heterotrophs consumers other feeders
depend on glucose as energy source
cannot produce it
obtained by eating plants or animals that have eaten plants

6. Carbon and Energy Flow Light energy Heat energy CO2 + H2O
Photosynthesis
Carbs
Proteins
Lipids + O2
Cellular (Aerobic)
Respiration
(ATP Produced)

7. Food Chain byproduct of photosynthesis is O2
humans & other animals breathe in oxygen
used in cellular respiration

8. Other Benefits of Photosynthesis
humans depend on ancient products of photosynthesis
fossil fuels
natural gas, coal & petroleum
for modern industrial energy
represent remains of organisms that relied on photosynthesis millions of years ago

9. Photosynthesis plants produce more glucose than they use Stored
starch & other carbohydrates in roots, stems & leaves

10. Sites of Photosynthesis
leaves & green stems
cell organelles
chloroplasts
concentrated in green tissue of leaf
mesophyll
green due to presence of green pigment chlorophyll

11. Chloroplasts each cell has 40-50 chloroplasts
oval-shaped structures with double membrane
inner membrane encloses compartment filled with stroma
suspended in stroma are disk-shaped compartments-thylakoids
arranged vertically like stack of plates
one stack-granum (plural, grana)
embedded in membranes of thylakoids are hundreds of chlorophyll molecules

12. Chlorophyll
light-trapping pigment

13. How Photosynthesis Works
Requires
CO2
Water
Sunlight
Makes O2
Glucose

14. How Photosynthesis Works
CO2 enters plant via pores- stomata in leaves
water-absorbed by roots from soil
membranes in chloroplasts provide sites for reactions of photosynthesis
chlorophyll molecules in thylakoids capture energy from sunlight
chloroplasts rearrange atoms of inorganic molecules into sugars & other organic molecules

15. Photosynthesis redox reaction
6CO2 + 12H2OC6H12O6 + 6O2 + 6H2O in presence of light
must be an oxidation & a reduction
water is oxidized
loses electrons & hydrogen ions
carbon dioxide is reduced
gains electrons & hydrogens

16. Photosynthesis
relies on a flow of energy & electrons initiated by light energy
light energy causes electrons in chlorophyll pigments to boost electrons up & out of orbit
hydrogens along with electrons are transferred to CO2sugar
requires that H2O is split into H & O2
O2 escapes to air
light drives electrons from H2O to NADP+ which is oxidized NADPH which is reduced

18. Photosynthesis 2 stages light-dependent reactions
chloroplasts trap light energy
convert it to chemical energy
contained in nicotinamide adenine dinucleotide phosphate-(NADPH) & ATP
used in second stage
light-independent reactions
Calvin cycle
formerly called dark reactions
NADPH (electron carrier) provides hydrogens to form glucose
ATP provides energy

19. Light Dependent Reactions
convert light energy to chemical energy & produce oxygen
takes place- thylakoid membranes
solar energy absorbed by chlorophyllATP + NADPH

20. Light Energy for Photosynthesis
sun energy is radiation
electromagnetic energy
travels as waves
distance between 2 waves- wavelength
light contains many colors
each has range of wavelengths measured in nanometers
range of wavelengths is electromagnetic spectrum
part seen by humans
visible light

21. Pigments light absorbing molecules built into thylakoid membranes
absorb some wavelengths & reflect others
plants appear green because chlorophyll-does not absorb green light
reflected back.
as light is absorbedenergy is absorbed
chloroplasts contain several kinds of pigments
different pigments absorb different wavelengths of light
red & blue wavelengths are most effective in photosynthesis
other pigments are accessory pigments
absorb different wavelengths
enhance light-absorbing capacity of a leaf by capturing a broader spectrum of blue & red wavelengths along with yellow and orange wavelengths

22. Pigment Color & Maximum Absoption
Violet:   nm
Indigo:   nm
Blue:   nm
Green:   nm
Yellow:   nm
Orange:   nm
Red:   nm

23. Chlorophylls Chlorophyll A absorbs blue-violet & red light
reflects green
participates in light reactions
Chlorophyll B
absorbs blue & orange light
reflects yellow-green
does not directly participate in light reactions
broadens range of light plant can use by sending its absorbed energy to chlorophyll A

24. Carotenoids yellow-orange pigments absorb blue-green wavelengths
reflect yellow-orange
pass absorbed energy to chlorophyll A
protective function
absorb & dissipate excessive light energy that would damage chlorophylls

25. Light Energy
light behaves as discrete packages of energy called photons
fixed quantity of energy

26. Light Energy when pigment absorbs a photon
pigment’s electrons gains energy
electrons are excited
unstable
electrons do not stay in unstable state
fall back to original orbits
as electrons fall back to ground heat is released
absorbed energy is passed to neighboring molecules

27. Photosynthesis Pigments Absorb light Excites electrons
Energy passed to sites in cell
Energy used to make glucose

28. Photosystems
chlorophyll & other pigments are found clustered next to one another in a photosystem
two participate in light reactions

29. Photosystems photosystem I & II
each has specific chlorophyll at reaction center
photosystem II
chlorophyll P680
photosystem I
chlorophyll P700
named for type of light they absorb best
P700 absorbs light in far red region of electromagnetic spectrum

30. Reaction Center when photon strikes one pigment molecule
energy jumps from pigment to pigment until arrives at reaction center
electron acceptor traps a light excited electron from reaction center chlorophyll
passes it to electron transport chain which uses energy to make ATP & NADPH

31. Reaction Center

32. Light Reactions during process of making ATP & NADPH
electrons are removed from molecules of water
passed from photosystem II to photosystem I to NADP+

33. Photosystem II water is split
oxygen atom combines with oxygen from another split water forming molecular oxygen-O2
each excited electron passes from photosystem II to photosystem I via electron transport chain

35. Photosystem I primary electron acceptor captures an excited electron
excited electrons are passed through short electron transport chain to NADP+ reducing it to NADPH
NADP+ is final electron acceptor
electrons are stored in high state of potential energy in NADPH molecule
NADPH, ATP and O2 are products of light reactions

36. ATP Formation-Chemiosmosis
uses potential energy of hydrogen ion concentration gradient across membrane
gradient forms when electron transport chain pumps hydrogen ions across thylakoid membrane as it passes electrons down chain that connects two photosystems

37. ATP Formation-Chemiosmosis
ATP synthase (enzyme) uses energy stored by H gradient to make ATP
ATP is produced from ADP & Pi when hydrogen ions pass out of thylakoid through ATP synthase
photophosphorylation

38. Chemiosmosis H+ H+
pH 7
pH 8
Chemiosmosis

39. Substrate-level Phosphorylation

40. Calvin Cycle light independent reactions
depend on light indirectly to obtain inputs for cycle-ATP & NADPH
takes place in stroma of chloroplast
cycle of reactions
makes sugar from CO2 & energy
ATP provides chemical energy
NADPH provides high energy electrons for reduction of CO2 to sugar

41. Steps of Calvin Cycle starting material-ribulose bisphosphate (RuBP)
first step-carbon fixation
rubisco (an enzyme) attaches CO2 to RuBP
Next-reduction reaction takes place
NADPH reduces 3-phosphoglyceric acid (3-PGA) to glyceraldehye 3-phosphate (G3P) with assistance of ATP
to do this cycle uses carbons from 3 CO2 molecules
to complete cycle must regenerate beginning component-RuBP
for every 3 molecules of CO2 fixed, one G3P molecule leaves cycle as product of cycle
remaining 5 G3P molecules are rearranged using ATP to make 3 RuBP molecules

43. Calvin Cycle regenerated RuBP is used to start cycle again
process occurs repeatedly as long as CO2, ATP & NADPH are available
thousands of glucose molecules are produced
used by plants to produce energy in aerobic respiration
used as structural materials
stored

44. Photosynthesis Variations
plants vary in the way they produce glucose and when

45. C3 Plants use CO2 directly from air
first organic compound produced is a 3 carbon compound 3-PGA
reduce rate of photosynthesis in dry weather
CO2 enters plants through pores in leaves
on hot days stomata in leaves close partially to prevent escape of water
with pores slightly open, adequate amounts of CO2 cannot enter leaf
Calvin cycle comes to a halt
no sugar is made
in this situation rubisco adds O2 to RuBP
2-carbon product of this reaction is broken down by plant cells to CO2 + H20
Photorespiration
provides neither sugar nor ATP

46. C4 Plants
have special adaptations allowing them to save water without shutting down photosynthesis
corn, sugar cane & crabgrass
evolved in hot, dry environments
when hot & dry stomata are closed
saves water
sugar is made via another route
developed way to keep CO2 flowing without capturing it directly from air

47. C4 Plants
have enzymes that incorporate carbon from CO2 into 4-C compound
enzyme has an intense desire for CO2
can obtain it from air spaces even when levels are very low
4-C compound acts as a shuttle
transfers CO2 to nearby cells -bundle-sheath cells
found in vast quantities around veins of leaves
CO2 levels in these cells remain high enough for Calvin cycle to produce sugar

48. CAM Plants pineapple, some cacti & succulent plants
conserve water by opening stomata & letting CO2 in at night
CO2 is fixed into a 4-C compound
saves CO2 at night & releases it in the day
photosynthesis can take place without CO2 needing to be admitted during the day when conditions are hot and dry

49. Environmental Consequences of Photosynthesis
CO2 makes up 0.03% of air
provides plants with CO2 to make sugars
important in climates
retains heat from sun that would otherwise radiate from Earth
warms the Earth
greenhouse effect

50. Global Warming CO2 traps heatwarms air
maintains average temperature on Earth about 10 degrees C warmer than without it.
Earth may be in danger of overheating because of this greenhouse effect
CO2 in air is increasing because of industrialization
when oil, gas and coal are burned CO2 is released
levels in atmosphere have increased 30% since 1850
increasing concentrations have been linked to global warming
slow & steady rise in surface temperature of Earth
could have dire consequences for all life forms on Earth