1. Photosynthesis

2. Life on Earth is largely solar powered
Photosynthesis produces 160 billion metric tons of carbohydrates each year

3. Life in the Sun -Photosynthesis provides food for most organisms.
(Some autotrophic bacteria use chemosynthesis, which makes food from inorganic compounds)
Light is central to the life of a plant, It provides food for virtually all organisms

4. Examples of photosynthetic autotrophs: plants, some protists (algae) and some bacteria
photosynthetic autotrophs = They generate their own organic matter through photosynthesis
(c) Euglena
(d) Cyanobacteria
(b) Kelp
Mosses, ferns,
and flowering plants

5. In aquatic environments, algae and photosynthetic bacteria are the main food producers.

6. Each square millimeter of a leaf contains about 500,000 photosynthesis factories called chloroplasts

7. Chloroplasts: Sites of Photosynthesis
Are found in the cells of the mesophyll
Enclosed by two membranes
Contain stroma, a thick fluid
Contain thylakoids, membranous sacs, that are stacked together

8. Vein Chloroplast Outer membrane Inner membrane Stomata
Mesophyll
Inner
membrane
Stomata
Leaf cross section
Mesophyll
cell
Thylakoid
Stroma
Thylakoid
space
Grana

9. The Overall Equation for Photosynthesis
Light energy
Photosynthesis
Water
Glucose
Carbon
dioxide
Oxygen
gas

10. Plants produce O2 gas by splitting water
The O2 released by photosynthesis is made from the oxygen in water

11. Photosynthesis occurs in two parts
Light reactions: Solar energy is converted into chemical energy (NADPH and ATP) when H2O splits. Oxygen is released.
2) Calvin Cycle: CO2 combines with NADPH and ATP (from the light reactions) to make organic compounds (sugars).

12. An overview of photosynthesis
CO2
Chloroplast
Light
NADP+
ADP +P
CALVIN CYCLE (in stroma)
LIGHT REACTIONS (in grana)
Photosynthesis is a two-step process
1. The light reactions convert solar energy to chemical energy
2. The Calvin cycle makes sugar from carbon dioxide
ATP
Electrons
NADPH O2
Sugar

13. THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY
Sunlight is a type of energy called radiation, or electromagnetic energy

14. The full range of radiation is called the electro-magnetic spectrum
Increasing energy
The full range of radiation is called the electro-magnetic spectrum
Gamma
rays
Micro-
waves
Radio
waves
X-rays UV
Infrared
Visible light
Wavelength (nm)
600 nm

15. Chloroplast Pigments Chloroplasts contain several pigments
Chlorophyll a
Chlorophyll b
Carotenoids
Xanthophyll

16. Chlorophyll: Occurs in two forms, chlorophyll a and b
Absorbs light in the blue-violet and orange-red regions, thus appears green
Occurs in two forms, chlorophyll a and b
Chlorin
ring Mg
Chlorophyll a, b and other associated pigments are assembled in clusters in the thylakoid membrane
Hydrocarbon
tail

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

18. Harvesting Light Energy
Light behaves as photons, discrete packets of energy
Chlorophyll molecules absorb photons
- Electrons in the pigment gain energy
- The energy is released and used

19. Absorption of a photon (light energy)
Excited state 2 1
Heat
Light
Light
(fluores-
cence)
Photon
Ground
state
Chlorophyll
molecule
Absorption of a photon (light energy)

20. A photosystem
Is an organized group of chlorophyll and other pigment molecules
Is a light-gathering antenna
Cluster of
pigment
molecules
embedded
in membrane
Chloroplast
Primary
electron
acceptor
Photon
Electron
transfer
Granum
(stack of
thylakoids)
Reaction
center
A chlorophyll a molecule located at the center of the pigment cluster receives light energy from the pigment of cluster and forms part of the reaction center
Each of the many light-harvesting photosystems consists of:
an “antenna” of chlorophyll and other pigment molecules (carotenoids, phycobilins, phycocyanins) that absorb light
a primary electron acceptor that receives excited electrons from the reaction-center chlorophyll
Reaction-
center
chlorophyll a
Transfer
of energy
Thylakoid membrane
Antenna pigment
molecules
Photosystem

21. Primary electron acceptor
PHOTOSYSTEM
Photon
Chlorophyll a
Pigment molecules of antenna

22. I. LIGHT REACTIONS:
Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons
The excited electrons are passed from down the electron transport chains
Their energy ends up in ATP and NADPH

23. How the Light Reactions Generate ATP and NADPH
Primary
electron
acceptor
NADP
Energy
to make 3
Primary
electron
acceptor 2
2e-
Light
Electron transport chain
Light
Primary
electron
acceptor
Reaction-
center
chlorophyll 1
NADPH-producing
Photosystem I
Water-splitting
Photosystem II
2H + 1/2

24. Electron Transport Chains (ETC)
Connect the two photosystems
Release energy that the chloroplast uses to make ATP

25. II. THE CALVIN CYCLE
Functions like a sugar factory within a chloroplast
Regenerates the starting material with each turn

26. ATP and NADPH power sugar synthesis in the Calvin cycle
The Calvin cycle occurs in the chloroplast’s stroma
The carbon atoms from CO2 are used to make organic compounds like sugar.
INPUT
CALVIN CYCLE
OUTPUT:

27. Most plants make more sugar than they need
The excess is stored in roots, tubers, and fruits and seeds
These are a major source of food for animals

28. A review of photosynthesis
Light
Chloroplast
NADP
RuBP
ADP
+ P
3-PGA
Calvin
cycle
Light
reactions
Electrons
G3P
Cellular
respiration
Cellulose
Starch
Other organic
compounds

29. Photosynthesis & the Greenhouse Effect

30. The Greenhouse effect:
Warms the atmosphere
Is caused by atmospheric CO2
Sunlight
Atmosphere
Radiant
heat
trapped
by CO2

31. Photosynthesis has an enormous impact on the atmosphere
It swaps O2 for CO2

32. Because photosynthesis removes CO2 from the atmosphere, it moderates the greenhouse effect
Unfortunately, deforestation may cause a decline in global photosynthesis