1. Photosynthesis!

2. Plant questions? How do plants obtain energy?
Why do plants need light?
Why do plants need water?
Why are plants green?

3. The best known form of photosynthesis is the one carried out by higher plants and algae, as well as by cyanobacteria and their relatives, which are responsible for a major part of photosynthesis in oceans.

4. The very basics:
Energy from light is used to convert CO2, H2O into sugar
O2 is a byproduct or “leftover” and is released
Photosynthesis:
In: 6CO2+6H2O+Energy
Out: C6H12O6+6O2

5. Anatomy of a leaf (photosynthetic organ)
Leaf functions:
“Trap” sunlight
Perform photosynthesis
Move food to storage areas in the plant
Absorb CO2 from the air
Minimize water loss from evaporation
Leaf structure is related to function…

6. Why are leaves green?

7. Because….
Their cells are full of chloroplasts…which contain chlorophyll…a pigment that reflects green light…which we see….so leaves are green

9. Summary of chloroplast structure
Enclosed in a double membrane
Contain Thylakoid disks called grana (pigments embedded in Thylakoid membrane)
The liquid part of chloroplasts is the Stroma
Stroma contains
Electron Transport System
“Loose” enzymes

10. Light Dependent Reactions
Photosynthesis takes place in 2 stages – each made up of a set of reactions:
Light Dependent Reactions
Convert light energy to chemical energy in the form of ATP & NADPH
Light Independent Reactions (Calvin-Benson Cycle)
Convert chemical energy from ATP & NADPH to long term storage form: glucose/starch

11. Where does the light come from?
What are photons?
Light particles
No mass
Travel as a wave
Photons & Energy
The smaller the wavelength, the higher the energy per photon

12. Sunlight is a mixture of the colors of the rainbow

14. Photosynthetic Pigments: Light energy captors
Photosynthetic plant pigments
Embedded in membranes of thylakoid disks
Consist of different varieties of chlorophylls and other accessory pigments such as beta-carotene

15. Pigments
Pigments absorb light energy and convert it to chemical energy.
Chlorophyll: GREEN (most important in photosynthesis)
Carotenoids: YELLOW, ORANGE & RED.
Photosynthesis only takes place when chlorophyll is present.

16. Photosynthetic pigments absorb the energy in specific colors of light

17. What colors are absorbed. What colors reflected
What colors are absorbed? What colors reflected? Different pigments absorb different colors of light This allows plants to use most of the available light

19. 1. Light Reaction needs light energy takes place in the thylakoids
needs water (H2O), which is divided into electrons and oxygen (which is liberated)
uses 2 photosystems to capture the sun’s energy
produces ATP which is used in the dark rx (Calvin-Benson cycle)

20. The Light Reaction Two Steps: 1. Trapping Energy from the Sun.
2. Splitting of Water

21. Animation of the Light Reaction:

24. LIGHT REACTION PRODUCTS
Energy
ATP
NADPH
Oxygen (which is released into the atmosphere)

25. 2.The Dark Reaction (Calvin cycle)
- uses CO2 to make glucose (“fixation” of carbon dioxide)
- takes place in the stroma of the chloroplast
- also known as C3 bc of the 3 carbon molecule (PGA) that is formed
- there are 2 other methods that plants may use to make glucose… C4 and CAM

26. Calvin Cycle : the synthesis

27. The rate of photosynthesis
- which factors affect the rate of “fixed” glucose?
1) The rate of photosynthesis can be limited by physical factors such as temperature. The lower the temperature, the slower the photosynthesis.
2) The availability of light is a factor that limits the rate of photosynthesis. When the amount of light decreases, the rate of photosynthesis also decreases

28. The C4 & CAM plants The Calvin cycle and the “C4 Plants”
- in certain climates, the sun is too abundant, and it never limits photosynthesis
- however, these climates are also very try and hot
- here, it’s the CO2 that limits photosynthesis
- we can think of it as the availability and the loss of water (H2O)
- when the plant photosynthesises in the sun, the CO2 must enter the leaves through the stomatas (little holes under the leaves)
- but, when these holes are open, H2O is lost and the plant dehydrates

29. - if you close the stomatas, CO2 cannot enter so this limits photosynthesis
- in C4 plants, the stomatas are only partially opened during the day
- these plants have an enzyme that can transform the CO2 into a 4-carbon molecule
- these molecules are stored in the different cells and the CO2 can be released when the plant lacks any
Examples of C4 plants are corn, sugar canes

30. Crassulacean Acid Metabolism (CAM)
- the ultimate prevention of CO2 loss is found in desert plants like the cactus
- in these plants, the stomatas are only opened at night
- the plants fixes the CO2 into 4-carbon molecules during the night and transfer the carbon to the Calvin cycle during the day
- in the day, the stomatas are completely closed and there is no water loss

31. Comparison between photosynthesis and aerobic resp.
Global rx of photosynthesis:
6CO H2O + light energy → C6H12O O2
Global rx of aerobic cellular resp:
C6H12O O ADP P → 6CO H2O ATP
- in a way, photosynthesis is the opposite of aerobic resp.
- the products of photosynthesis are the raw materials (reactants) of resp.

32. Where? In cholorophyll-bearing cells In all cells
PHOTOSYNTHESIS RESPIRATION
Where? In cholorophyll-bearing cells In all cells
When? In the presence of light All the time
Input? Carbon dioxide and water Reduced carbon compounds and oxygen
Output? Reduced carbon compounds, Carbon dioxide and water
oxygen, and water
Energy sources? Light Chemical bonds
Energy result? Energy stored Energy released
Reaction ? Reduction of carbon Oxidation of carbon compounds compounds
Energy carrier(s) NADP NAD and FAD