1.
Bellringer
Without fail, I forget to water my plants. My
house’s temperature (electric heat = dry) is
kept at 72o F. Explain, using your
botannical vocabulary, why my house
plants shriveled up and died over the
winter.

2.
Set up lab, lecture, finish lab
• Today’s goal:
– Define pigment.
– Explain why plants are green.
– Give examples of the accessory pigments and
explain their role in photosynthesis.

3.
All you ever wanted to
know about photosynthesis
Part One

4.
• Photosynthesis is the process by which
autotrophic organisms use light energy to
make sugar and oxygen gas from carbon
dioxide and water
AN OVERVIEW OF PHOTOSYNTHESIS
Carbon
dioxide
Water Glucose Oxygen
gas
PHOTOSYNTHESIS

5.
Energy can be transformed from
one form to another
FREE ENERGY
(available for work)
vs.
HEAT
(not available for work)

6.
THE SUN: MAIN SOURCE OF
ENERGY FOR LIFE ON EARTH

7.
• Almost all plants are photosynthetic autotrophs, as
are some bacteria and protists
– Autotrophs generate their own organic matter through
photosynthesis
– Sunlight energy is transformed to energy stored in the
form of chemical bonds
(a) Mosses, ferns, and
flowering plants
(b) Kelp
(c) Euglena (d) Cyanobacteria
THE BASICS OF PHOTOSYNTHESIS

8.
Ingredients and Components
6 CO2 + 6 H2O + light energy → C6H12O6 + 6
O2

9.
Food Chain

10.
THE FOOD WEB

11.
WHY ARE PLANTS GREEN?
It's not that easy bein' green
Having to spend each day the color of the leaves
When I think it could be nicer being red or yellow or gold
Or something much more colorful like that…
Kermit the Frog

12.
Electromagnetic Spectrum and
Visible Light
Gamma
rays X-rays UV
Infrared &
Microwaves Radio waves
Visible light
Wavelength (nm)

13.
Sunlight
• Form of energy
(photons)
• Measured in
wavelengths
• Sun radiates full
spectrum, atmosphere
screens out most,
allows primarily only
visible light through
(380-750 nm)
• Amount of energy is
inversely related to
the wavelength of
light

14.
Different wavelengths of visible light are seen by
the human eye as different colors.
Gamma
rays
X-rays UV Infrared
Micro-
waves
Radio
waves
Visible light
Wavelength (nm)

15.
Pigment
• Substances that absorb visible light
• Different pigments absorb light of different
wavelengths
• Color we see is the color most reflected or
transmitted by the pigment

16.
Sunlight minus absorbed
wavelengths or colors
equals the apparent color
of an object.
The feathers of male cardinals
are loaded with carotenoid
pigments. These pigments
absorb some wavelengths of
light and reflect others.

17.
Why are plants green?
Transmitted light

18.
Chlorophyll a
•Chl a has a methyl
group
•Chl b has a carbonyl
group
Porphyrin ring
delocalized e-
Phytol tail

19.
Spectrophotometer

20.
WHY ARE PLANTS GREEN?

21.
Predict: action spectrum
• Measure photosynthetic output against the
various wavelengths of light…

22.
Action spectrum

23.
So chlorophyll isn’t the whole
story here…

24.
The Pigments
• Chlorophyll a: blue-green; only pigment that
can participate directly in photosynthesis
Accessory (antennae) pigments - absorb light
and transfer it to chlorophyll a:
• Chlorophyll b: yellow-green
• Carotenoids: various shades of yellow and
orange
• Xanthophylls: purples
• Anthocyanin: yellow

25.
Fall colors

26.
So what?
• Demonstration!

27.
Electron Excitation

28.
Excited
state
e
Heat
Light
Photon
Light
(fluorescence)
Chlorophyll
molecule
Ground
state
2
(a) Absorption of a photon
(b) fluorescence of isolated chlorophyll in
solution
Excitation of chlorophyll
in a chloroplast
e

29.
Okay…still, so what?

30.
Primary
electron acceptor
Primary
electron acceptor
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy for
synthesis of
by chemiosmosis
Noncyclic Photophosphorylation
• Photosystem II regains electrons by splitting
water, leaving O2 gas as a by-product

31.
Parts of the chloroplast
• Thylakoids: flattened
sac, pigments of
photosynthesis located
in their membranes
• Grana: stacks of
thylakoids (literally,
“stacks of coins”)
• Stroma: interior
portion

32.
• The location and structure of chloroplasts
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Inner
membrane
Thylakoid
compartment
Thylakoid
Stroma
Granum
Stroma
Grana

33.
ALL YOU WANTED TO KNOW
ABOUT PHOTOSYNTHESIS
Day two

34.
• The Calvin cycle makes
sugar from carbon
dioxide
– ATP generated by the light
reactions provides the energy
for sugar synthesis
– The NADPH produced by the
light reactions provides the
electrons for the reduction of
carbon dioxide to glucose
Light
Chloroplast
Light
reactions
Calvin
cycle
NADP
ADP
+ P
• The light reactions
convert solar
energy to chemical
energy
– Produce ATP & NADPH
AN OVERVIEW OF PHOTOSYNTHESIS

35.
Review of photosynthesis…
• The reactants: CO2 and H2O
• Driving the reaction: sunlight
• Products: Glucose and O2
• Sunlight captured by pigments
(chlorophylls and others)
• Pigments located in the chloroplasts

36.
• Chloroplasts
absorb light
energy and
convert it to
chemical energy
Light
Reflected
light
Absorbed
light
Transmitted
light
Chloroplast

37.
What is a pigment?
Substance that absorbs visible light
Different pigments absorb light of
different wavelengths
Arranged into clusters called
photosystems (more on that later!)

38.
Chloroplasts: Sites of Photosynthesis
• Photosynthesis
– Occurs in chloroplasts, organelles in certain
plants
– All green plant parts have chloroplasts and carry
out photosynthesis
• The leaves have the most chloroplasts
• The green color comes from chlorophyll in the
chloroplasts
• The pigments absorb light energy

39.
Photosystems
• In the membrane of the thylakoid
• Contains several hundred molecules of
chlorophyll a and b along with accessory
pigments
• Named by the wavelength of light they
absorb (P680 and P700)

40.
Why have photosystems?
To harvest light over a larger surface
area and larger portion of the spectrum
than any single pigment could harvest.

41.
Primary
electron acceptor
Photon
Reaction
center
PHOTOSYSTEM
Pigment
molecules
of antenna
Molecular Game of “Hot Potato”

42.
Water-splitting
photosystem
NADPH-producing
photosystem
ATP
mill
• Two types of
photosystems
cooperate in the
light reactions

43.
Primary
electron acceptor
Primary
electron acceptor
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy for
synthesis of
by chemiosmosis
Noncyclic Photophosphorylation
• Photosystem II regains electrons by splitting
water, leaving O2 gas as a by-product

44.
• The O2 liberated by photosynthesis is made
from the oxygen in water (H+ and e-)
Plants produce O2 gas by splitting H2O

45.
2 H + 1/2
Water-splitting
photosystem
Reaction-
center
chlorophyll
Light
Primary
electron
acceptor
Energy
to make
Primary
electron
acceptor
Primary
electron
acceptor
NADPH-producing
photosystem
Light
NADP
1
2
3
How the Light Reactions Generate ATP and NADPH

46.
• Two connected photosystems collect
photons of light and transfer the energy to
chlorophyll electrons
• The excited electrons are passed from the
primary electron acceptor to electron
transport chains
– Their energy ends up in ATP and NADPH
In the light reactions, electron transport
chains generate ATP, NADPH, & O2

47.
• The electron transport chains are arranged
with the photosystems in the thylakoid
membranes and pump H+ through that
membrane
– The flow of H+ back through the membrane is
harnessed by ATP synthase to make ATP
– In the stroma, the H+ ions combine with NADP+
to form NADPH
Chemiosmosis powers ATP
synthesis in the light reactions

48.
• The production of ATP by chemiosmosis in
photosynthesis
Thylakoid
compartment
(high H+)
Thylakoid
membrane
Stroma
(low H+)
Light
Antenna
molecules
Light
ELECTRON TRANSPORT
CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

49.
Cyclic Pathway

50.
• A Photosynthesis Road Map
Chloroplast
Light
Stack of
thylakoids ADP
+ P
NADP
Stroma
Light
reactions
Calvin
cycle
Sugar used for
 Cellular respiration
 Cellulose
 Starch
 Other organic compounds

51.
Join me, on the dark side of
photosynthesis
https://www.youtube.com/watch?v=k-t2TeapTH8

52.
overview

53.
Redox reactions
• Reduction: gains electrons (escorted by
hyrdrogens)
• Oxidation: loses electrons

54.
• ATP is a limiting factor: more is used by
calvin cycle
• Need a way to fill deficit

55.
Cyclic Photophosphorylation
• Process for ATP generation associated with
some Photosynthetic Bacteria
• Reaction Center => 700 nm

56.
Review: Photosynthesis uses light
energy to make food molecules
Light
Chloroplast
Photosystem II
Electron
transport
chains
Photosystem I
CALVIN
CYCLE Stroma
LIGHT REACTIONS CALVIN CYCLE
Cellular
respiration
Cellulose
Starch
Other
organic
compounds
• A summary of
the chemical
processes of
photosynthesis

57.
It's not that
easy bein'
green… but it
is essential for
life on earth!

58.
Balancing Act

59.
climate

60.
photorespiration

61.
Adaptations
C4 Plants:
spatial separation
CAM Photosynthesis:
temporal separation