1. Photosynthesis
Biology

2. Know why plants tend to be green in appearance.
LEARNING OBJECTIVES
By the end of this lecture you will be able to:
Explain why photosynthesis is so important to energy and material flow for life on earth.
Know why plants tend to be green in appearance.
Describe the organization of the chloroplast – the organelle of photosynthesis in eukaryotes
Understand that photosynthesis is a two fold process composed of the light-dependent reactions and the light independent reactions
Explain where the light reactions and the CO2 fixation reactions occur in the chloroplast.
Define photosynthetic pigment composition and structure.
Explain the absorption spectrum of chlorophyll and compare it to the action spectrum of photosynthesis.

3. PHOTOSYNTHESIS
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
(c) Euglena
(d) Cyanobacteria
(b) Kelp
(a) Mosses, ferns, and
flowering plants

4. Harvesting Light Energy
PHOTOSYNTHESIS
Harvesting Light Energy
6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

5. WHY ARE PLANTS GREEN? PHOTOSYNTHESIS
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

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

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

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

9. Why are plants green?
Reflected light
Transmitted light

10. WHY ARE PLANTS GREEN? Plant Cells have Green Chloroplasts
The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

11. Pigments Pigments are lipids
Plants use PIGMENTS to capture sun’s energy
A pigment is a substance that absorbs and reflects light.
The main pigment in plants is chlorophyll a
Chlorophyll b
Carotenoids

12. THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED
Chlorophyll molecules are embedded in the thylakoid membrane
Act like a light “antenna”
These molecules can absorb sunlight energy
Reflected
light
Light
Absorbed
light
Transmitted
light
Chloroplast

13. Chlorophyll a Chlorophyll b Carotenoids Chloroplast Pigments
Chloroplasts contain several pigments
Chlorophyll a
Chlorophyll b
Carotenoids
Figure 7.7

14. Different pigments absorb light differently
Chloroplast Pigments
Different pigments absorb light differently

15. PHOTOSYNTHESIS
Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
6CO2 + 12H2O  C6H12O6 + 6O2 + 6H2O
Carbon dioxide
Water
Glucose
Oxygen gas
PHOTOSYNTHESIS
carbon dioxide + water  glucose + oxygen + water + energy

16. PHOTOSYNTHESIS
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 visible light energy
What wavelength is reflected?
internal leaf structure
chloroplasts
outer membrane
thylakoid
inner membrane

17. Chloroplasts: Sites of Photosynthesis
In most plants, photosynthesis occurs primarily in the chloroplasts in the leaves
A chloroplast contains:
stroma, a fluid
grana, stacks of thylakoids
The thylakoids contain chlorophyll
Chlorophyll is the green pigment that captures light for photosynthesis

18. Structure of Chloroplast
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Inner membrane
Grana
Stroma
Thylakoid compartment
Stroma
Thylakoid

19. The light reactions convert solar energy to chemical energy
PHOTOSYNTHESIS
The light reactions convert solar energy to chemical energy
Produce ATP & NADPH
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
NADP
ADP
+ P
Calvin
cycle
Light
reactions

20. Excitation of chlorophyll in a chloroplast
ELECTRONS AGAIN!
Excitation of chlorophyll in a chloroplast
Loss of energy due to heat causes the photons of light to be less energetic.
Less energy translates into longer wavelength.
Transition toward the red end of the visible spectrum. e
Excited
state 2
Heat
Light
Light
(fluorescence)
Photon
Chlorophyll
molecule
Ground
state
(a) Absorption of a photon
(b) fluorescence of isolated chlorophyll in solution

21. Photosynthesis
In the light reactions, electron transport chains generate ATP, NADPH, & O2
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

22. How the Light Reactions Generate ATP and NADPH
Photosynthesis
How the Light Reactions Generate ATP and NADPH
Primary
electron
acceptor
Primary electron acceptor
Electron transport chain
Electron transport
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy for synthesis of
by chemiosmosis
Primary
electron
acceptor
Primary
electron
acceptor
Reaction-
center
chlorophyll 1

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

24. Chemiosmosis powers ATP synthesis in the light reactions
Photosynthesis
Chemiosmosis powers ATP synthesis in the light reactions
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

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

26. The Calvin Cycle a.k.a. the “dark reactions”
WARNING: DOES NOT ONLY TAKE PLACE IN THE DARK!
Accomplishes “carbon fixation” taking carbon from inorganic molecules and putting it into organic molecules (CO2  sugars) .

27. The Calvin Cycle
The quantities listed are for the production of one glucose molecule which is produced from six turns of the cycle .

28. Photosynthesis Chloroplast Light Stroma NADP Stack of thylakoids ADP
reactions
Calvin
cycle
Sugar used for
 Cellular respiration
 Cellulose
 Starch
 Other organic compounds

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