1. Light is central to the life of a plant
Life in the Sun
Light is central to the life of a plant
Photosynthesis is the most important chemical process on Earth
It provides food for virtually all organisms
Plant cells convert light into chemical signals that affect a plant’s life cycle

2. Light can influence the architecture of a plant
Plants that get adequate light are often bushy, with deep green leaves (filled with the photosynthetic machinery-chloroplasts)

3. 7.1 Autotrophs are the producers of the biosphere
Plants, some protists, and some bacteria are photosynthetic autotrophs. (Animals are not)
They are the ultimate producers of food consumed by virtually all organisms

4. On land, plants such as oak trees and cacti are the predominant producers
Figure 7.1A
Figure 7.1B

5. In aquatic environments, algae and photosynthetic bacteria are the main food producers
Figure 7.1C
Figure 7.1D

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

7. 7.3 Plants produce O2 gas by splitting water
The O2 liberated by photosynthesis is made from the oxygen in water
Figure 7.3A

8. Experiment 1 Not labeled Experiment 2 Labeled Reactants: Products:
Figure 7.3B
Reactants:
Products:
Figure 7.3C

9. 7.4 Photosynthesis is a redox process, as is cellular respiration
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
Figure 7.4A
Oxidation
Reduction
Figure 7.4B

10. 7.2 Photosynthesis occurs in chloroplasts
In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts

11. 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

12. A chloroplast contains: stroma, a fluid between grana
grana, stacks of thylakoids
The thylakoids contain chlorophyll
Chlorophyll is the green pigment that captures light for photosynthesis
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Inner membrane
Thylakoid compartment
Stroma
Thylakoid

13. 7.5 Overview: Photosynthesis occurs in two stages linked by ATP and NADPH
The complete process of photosynthesis consists of two linked sets of reactions:
the light reactions and the Calvin cycle
The light reactions convert light energy to chemical energy and produce O2
The Calvin cycle assembles sugar molecules from CO2 using the energy-carrying products of the light reactions

14. 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

15. 7.6 Visible radiation drives the light reactions
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY
7.6 Visible radiation drives the light reactions
Certain wavelengths of visible light drive the light reactions of photosynthesis
Gamma rays
Micro- waves
Radio
waves
X-rays UV
Infrared
Visible light
Wavelength (nm)
Figure 7.6A

16. Reflected light Light Chloroplast Absorbed light Transmitted light
Figure 7.6B

17. 7.7 Photosystems capture solar power
Each of the many light-harvesting photosystems 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

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

19. Fluorescence of isolated chlorophyll in solution
Heat
Photon (fluorescence)
Photon
Chlorophyll molecule
Figure 7.7A

20. Primary electron acceptor Electron transport chain
Excitation of chlorophyll in a chloroplast
Primary electron acceptor
Electron transport chain
Photon
Chlorophyll molecule
Figure 7.7B

21. 7.8 In the light reactions, electron transport chains generate ATP, NADPH, and 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. Where do the electrons come from that keep the light reactions running?
In photosystem I, electrons from the bottom of the cascade pass into its P700 chlorophyll

23. 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

24. 7.9 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
Thylakoid compartment (high H+)
Light
Light
Thylakoid membrane
Antenna molecules
Stroma (low H+)
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE
Figure 7.9

26. 7.10 ATP and NADPH power sugar synthesis in the Calvin cycle
THE CALVIN CYCLE: CONVERTING CO2 TO SUGARS
7.10 ATP and NADPH power sugar synthesis in the Calvin cycle
The Calvin cycle occurs in the chloroplast’s stroma
This is where carbon fixation takes place and sugar is manufactured
INPUT
CALVIN CYCLE
Figure 7.10A
OUTPUT:

27. The Calvin cycle constructs G3P using
carbon from atmospheric CO2
electrons and H+ from NADPH
energy from ATP
Energy-rich sugar is then converted into glucose

28. 7.11 Review: Photosynthesis uses light energy to make food molecules
PHOTOSYNTHESIS REVIEWED AND EXTENDED
7.11 Review: Photosynthesis uses light energy to make food molecules
A summary of the chemical processes of photo-synthesis
Chloroplast
Light
Photosystem II Electron transport chains Photosystem I
CALVIN CYCLE
Stroma
Electrons
Cellular respiration
Cellulose
Starch
Other organic compounds
LIGHT REACTIONS
CALVIN CYCLE
Figure 7.11

29. Many plants make more sugar than they need
The excess is stored in roots, tuber, and fruits
These are a major source of food for animals

30. 7.12 C4 and CAM plants have special adaptations that save water
Most plants are C3 plants, which take CO2 directly from the air and use it in the Calvin cycle
In these types of plants, stomata on the leaf surface close when the weather is hot
This causes a drop in CO2 and drop in G3P

31. 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

32. PHOTOSYNTHESIS, SOLAR RADIATION, AND EARTH’S ATMOSPHERE
7.13 Human activity is causing global warming; photosynthesis moderates it
Due to the increased burning of fossil fuels, atmospheric CO2 is increasing
CO2 warms Earth’s surface by trapping heat in the atmosphere
This is called the greenhouse effect

33. Sunlight
ATMOSPHERE
Radiant heat trapped by CO2 and other gases
Figure 7.13A & B

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

35. 7.14 Talking About Science: Mario Molina talks about Earth’s protective ozone layer
Mario Molino received a Nobel Prize in 1995 for his work on the ozone layer
His research focuses on how certain pollutants (greenhouse gases) damage that layer
Figure 7.14A

36. 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

37. International restrictions on these chemicals are allowing recovery
Industrial chemicals called CFCs have hastened 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