1. 2.9 Photosynthesis

2. Understanding: Photosynthesis is the production of C compounds in cells using light energy
Photosynthesis = process of using light energy and inorganic compounds (CO2 & H2O) to make organic compounds (carb, protein, lipid)
Photosynthesis = energy conversion (light  chem)

3. What energy conversion is involved in photosynthesis?
Chem  light
Light  chem
Light  electrical
Electrical  chem

4. List 3 inputs needed for photosynthesis.
O2, glucose, light
Light, water, O2
Water, light, glucose
Water, light, CO2

5. Overview of Photosynthesis

6. Overview of Photosynthesis

7. What are the 2 main stages of photosynthesis, in order?
Light-dependent rxn, Calvin cycle
Light-independent rxn, light-dependent rxn
Calvin cycle, light-dependent rxn
Light rxn, Krebs cycle

8. Skill: Separating photosynthetic pigments by chromatography

9. What color wavelengths does chlorophyll a absorb the most?
Green
Yellow
Orange
Red & violet

10. Understanding: Visible light has a range of wavelengths with violet the shortest wavelength & red the longest.

11. What is the range of the visible light spectrum?
Violet 400nm – 700nm Red
Red 400nm – 700nm Violet
Violet 200nm – 800nm Red
Red 200nm – 800nm Violet

12. Understanding: Chlorophyll absorbs red & blue light most effectively & & reflects green light more than other colors.
Absorption of light = 1st stage of photosynthesis
Pigments = substances that absorb light
White = absorbs no colors (reflect all light)
Black = absorbs all colors (reflect no light)
Main pigment in photosynthesis = chlorophyll
Chlorophyll absorbs red and blue light very well
Reflects green light back to our eyes

13. Skill: Drawing an absorption spectrum for chlorophyll & an action spectrum for photosynthesis
ABSORPTION SPECTRUM = graph showing percentage of light absorbed at each wavelength of light by a pigment
ACTION SPECTRUM = graph showing rate of photosynthesis at each wavelength of light
Q: Why are absorption and action spectra very similar?
A: Photosynthesis can only occur in wavelengths of light that chlorophyll or other pigments can absorb

16. How is the x-axis labeled for both the action & absorption spectrum graphs?
Time
Wavelength of light
Rate of photosynthesis
% absorption

17. Which graph is pictured?
Action spectrum
Absorption spectrum

18. Understanding: Oxygen is produced in photosynthesis from photolysis of water.
Photolysis = using light to split water molecules
Water splits into hydrogen ions, electrons, and oxygen (this is where we get our O2!)
Hydrogen ions = used to set up concentration gradient so movement drives production of ATP
Electrons = used to replace lost electrons from chlorophyll (when light excited its electrons)
Oxygen = waste product of photosynthesis, diffuses out of leaf into air

19. What do you call the splitting of water molecules in photosynthesis?
Hydrolysis
Photolysis
Photosynthesis
Hydrosynthesis

20. Understanding: Changes to the Earth’s atmosphere, oceans & rock deposition due to photosynthesis.
Great Oxidation Event = the rising of the O2 concentration in the Earth’s atmosphere, caused by millions of years of photosynthesis by prokaryotes, plants & algae (2% by volume by 2200 mya)
This caused Ice Age: Great Oxidation Event  decrease in CH4 & CO2  decrease in greenhouse effect  fall in global temp
Also caused Banded Iron Formation: Great Oxidation Event  increased dissolved O2 in ocean  oxidation of dissolved Fe to form precipitate onto sea bed  rock formation with layers of iron oxide alternating with other minerals (banding pattern)  abundant resource of iron  lots of steel!
mya  O2 rose to 20%  same time big boost in multicellular organisms!

21. Understanding: Energy is needed to produce carbs & other C compounds from CO2.
Photosynthesis is ENDOTHERMIC = require putting in energy
Reactions that are usually endothermic:
Production of O2
Condensation synthesis
Energy needed for photosynthesis = Light energy
Light energy  chem energy

22. Understanding: Temp, light intensity & CO2 concentration are possible limiting factors on rate of photosynthesis.

23. Limiting Factors
Under any combination of light intensity, temp and CO2 conc, only ONE of the factors is actually limiting the rate of photosyn
Examples:
What is limiting factor…
At night?
When sun rises?
As temp increases during day?

24. Limiting Factors affecting rate of photosynthesis

25. Nature of Science: Experimental design: Controlling relevant variables in photosynthesis experiments is essential.
3 factors affect the rate of photosynthesis:
Temp
Light intensity
CO2 conc
Independent variable = the one that you deliberately vary with a range of levels that you choose = this will be one of the 3 limiting factors
Dependent variable = the one thing you measure to see if its affected by independent var = this will be how you will measure the rate of photosynthesis
Controlled variables = all other variables that might affect the independent var = keeping the other 2 limiting factors at a constant and optimal level

26. What are the 3 limiting factors in photosynthesis?
Temp, O2, light
Light, O2, CO2
Temp, CO2, light
Light, temp, O2

27. Skill: Design of experiments to investigate limiting factors on photosynthesis.
3 ways to measure photosynthesis:
1. Production of O2 (bubbles)
2. Uptake of CO2 (pH rises when CO2 absorbed from water)
3. Increase in biomass