1. a b c Figure: 08-01 Title: Three types of photosynthesizers. Caption:
Photosynthesis is carried out not only by familiar plants, such as these sunflowers (a), but by algae, such as this giant kelp (b), and by some bacteria, such as these cyanobacteria (c). (magnified x 1025) a b c

2. Photosynthesis
Importance
Where, Who?
What is it?
Limitations

3. Photosynthesis (Phosyn) - conversion of light energy to chemical energy
Figure 7.1A
Figure 7.1B

4. Autotrophs = “self feeders” Includes plants, algae, some bacteria
Figure 7.1C
Figure 7.1D

5. Photosynthesis = light energy is used to make sugar and oxygen from CO2 and water
Carbon dioxide
Water
Glucose
Oxygen gas
PHOTOSYNTHESIS

6. Aquatic plant shows production of O2
Aerobic organisms dependent on this O2
Figure 7.3A

7. The location and structure of chloroplasts
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Inner membrane
Grana
Stroma
Thylakoid compartment
Stroma
Figure 7.2
Thylakoid

8. Photosynthesis is a redox process
Water molecules are split apart and electrons and H+ ions are removed, leaving O2 gas
These electrons and H+ ions are transferred to CO2, producing sugar
Reduction
Oxidation
Respiration
Oxidation
Reduction

9. CO2 sunlight H2O Calvin cycle ADP NADP+ O2 sugar NADPH ATP
Figure: 08-08
Title:
Summary of photosynthesis.
Caption:
In the light-dependent reactions, solar energy is converted to chemical energy in the thylakoids, and the chemical energy is stored temporarily in the form of ATP and NADPH. Water is required for this reaction, and oxygen is a by-product. The stored chemical energy is in turn used in the light-independent reactions (the Calvin cycle), taking place in the stroma, in which sugar is made from carbon dioxide and a low-energy sugar, RuBP. The sugar can be used for food, or may become part of the plant’s structure.
NADP+ O2
sugar

10. Certain wavelengths of visible light drive the light reactions of photosynthesis
Reflected light
Chloroplast
Absorbed light
Transmitted light
Figure 7.6B

11. How do photosystems capture solar power?
Each light-harvesting photosystem consists of:
an “antenna” of chlorophyll and other pigment molecules that absorb light
a primary electron acceptor that receives excited electrons from the reaction-center chlorophyll

12. Primary electron acceptor
PHOTOSYSTEM
Photon
Reaction center
Pigment molecules of antenna
Figure 7.7C

13. Primary electron acceptor
Excitation of chlorophyll in a chloroplast
Primary electron acceptor
Other compounds
Photon
Chlorophyll molecule
Figure 7.7B

14. Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product
Primary electron acceptor
Electron transport
Primary electron acceptor
Electron transport chain
Photons
Energy for synthesis of
PHOTOSYSTEM I
PHOTOSYSTEM II
by chemiosmosis
Figure 7.8

15. Chemiosmosis powers ATP synthesis in the light reactions
H+ produced by photolysis of H2O
electron transport chains pump H+ through the thylakoid membrane
The flow of H+ back into the stroma is harnessed by ATP synthase to make ATP
In the stroma, the H+ ions combine with NADP+ to form NADPH

16. thylakoid compartment
chloroplast
sunlight
PHOTOSYSTEM II
PHOTOSYSTEM I
Figure: 08-06
Title:
Light-dependent reactions.
Caption:
The light-dependent reactions take place in the thylakoid membranes within the chloroplasts. Electrons are donated by water molecules located in the thylakoid compartments. Powered by the Sun’s energy, these electrons are passed along the electron transport chain embedded in the thylakoid membrane and end up stored in NADPH in the stroma. An additional product of the splitting of water molecules is oxygen atoms, which quickly combine into the O2 form. This is the atmospheric oxygen that we breathe in. e-
NADPH
O2 + 4 H+
2 H2O
thylakoid compartment
thylakoid membrane
stoma

17. ATP and NADPH power sugar synthesis in the Calvin cycle
The Calvin cycle occurs in the chloroplast’s stroma,
where carbon fixation takes place and sugar is made
INPUT
CALVIN CYCLE
Figure 7.10A
OUTPUT:

18. 3 molecules 3 molecules of RuBP rubisco 6 molecules of 3-PGA 1. carbon
fixation 3
ADP 6
ATP 3
ATP
4. regeneration
of RuBP
2. energizing
the sugar 6
ADP
3 molecules
of G3P
Figure: 08-07
Title:
Calvin cycle.
Caption:
Overview: CO2, ATP and electrons (contained in hydrogen atoms) from NADPH are the input into the Calvin cycle, while a sugar (G3P) is its output. 1. Carbon fixation. The enzyme rubisco brings together three molecules of CO2 with three molecules of the five-carbon sugar RuBP; the three resulting six-carbon molecules are immediately split into six three-carbon molecules named 3-PGA (3-phosphoglyceric acid). 2. Energizing the Sugar. In two separate reactions, (a) Six ATP molecules react with six 3-PGA, in each case transferring a phosphate onto the 3-PGA. (b) The six 3-PGA derivatives oxidize (gain electrons from) six NADPH molecules; in so doing, they are transformed into the energy-rich sugar G3P (glyceraldehyde 3-phosphate). 3. Exit of product. One molecule of G3P exits as the output of the Calvin cycle. This molecule, the product of photosynthesis, can be used for energy or transformed into materials that make up the plant. 4. Regeneration of RuBP. In several reactions, five molecules of G3P are transformed into three molecules of RuBP.
3. exit of
product
6 molecules
of 3-PGA derivative
1 molecule
of G3P 6
NADPH 6
NADP+
6 molecules
of G3P
glucose and
other
derivatives

19. LIGHT REACTIONS (in grana) CALVIN CYCLE (in stroma)
An overview of photosynthesis
H2O
CO2
Chloroplast
Light
NADP+
ADP + P
LIGHT REACTIONS (in grana)
CALVIN CYCLE (in stroma)
ATP
Electrons
NADPH O2
Sugar
Figure 7.5

20. Photorespiration occurs as O2 increases and CO2 decreases
Plants close their stomates to conserve water.
Result: CO2 cannot reach the mesophyll cells.
Photorespiration occurs as O2 increases and CO2 decreases

21. Photorespiration in a C3 plant
CALVIN CYCLE
2-C compound
Figure 7.12A

22. This molecule can then donate CO2 to the Calvin cycle
Some plants have special adaptations that enable them to save water
Special cells in C4 plants—corn and sugarcane—incorporate CO2 into a four-carbon molecule
This molecule can then donate CO2 to the Calvin cycle
4-C compound
CALVIN CYCLE
3-C sugar
Figure 7.12B

23. Stomates open at night; plants make a four-carbon compound
CAM plants—pineapples, most cacti, and succulents—employ a different mechanism
Stomates open at night; plants make a four-carbon compound
Then use this as a CO2 source in the same cell during the day
4-C compound
Night
Day
CALVIN CYCLE
3-C sugar
Figure 7.12C

24. Is global warming really a threat to life?
Due to the increased burning of fossil fuels, atmospheric CO2 is increasing (+30% since 1900)
CO2 warms Earth’s surface by trapping heat in the atmosphere = greenhouse effect

25. Greenhouse gases trap solar energy in the atmosphere
- gases include CO2 and methane
Sunlight
ATMOSPHERE
Radiant heat trapped by CO2 and other gases
Figure 7.13A & B

26. What is the effect on phosyn?
Consequences predicted by models:
world temp may rise from 1 to 6 degrees C by 2100
Polar ice melts, sea levels rise
Drastic weather changes
Spread of tropical pests and diseases
Extinction of many species
What is the effect on phosyn?

28. Effects of deforestation?
How can warming be stopped?
1. Plant more crops - phosyn removes CO2
Effects of deforestation?
Stop adding CO2, methane
- Change from fossil fuel to other energy
- Don’t eat hamburgers.

29. Solar radiation converts O2 high in the atmosphere to ozone (O3)
The O2 in the atmosphere results from photosynthesis
Solar radiation converts O2 high in the atmosphere to ozone (O3)
Ozone shields organisms on the Earth’s surface from the damaging effects of UV radiation

30. International restrictions on these chemicals are allowing recovery
Industrial chemicals called CFCs speed up ozone breakdown, causing dangerous thinning of the ozone layer
International restrictions on these chemicals are allowing recovery
Sunlight
Southern tip of South America
Antarctica
Figure 7.14B

31. Figure: 08-11
Title:
Dry-weather photosynthesis.
Caption:
Plants such as this saguaro cactus in Arizona utilize CAM photosynthesis, thereby preserving precious water.