1. Photosynthesis

2. Photosynthesis
The process by which plants and other producers convert the energy of sunlight into the energy, stored in organic molecules. (Carbon Compounds) Plants and other photosynthetic organisms produce the food that start the food chain.

3. Pigment Chlorophyll For most plants chlorophyll is the main pigment
Gives green color
Photosystems – groups of pigment molecules

4. Types of Chlorophyll Pigments
Chlorophyll a – absorbs mainly blue-violet and red light; reflects green light
Chlorophyll b – (helper pigment) absorb mainly
blue and orange light; reflects yellow-green (looks light frees)
Carotenoids – (many types) absorb mainly blue-
green light; reflect yellow-orange
Xanthophyll - a yellow or brown carotenoid plant pigment that causes the autumn colors of leaves

5. Absorption Spectra

6. Electromagnetic Spectrum
The range of types of electromagnetic energy; from the very short wavelength (gamma rays) to the very long wavelength (radio waves)

7. Electromagnetic Spectrum
ROYGBIV

8. Electromagnetic Spectrum
Plants use the same part of the electromagnetic spectrum that our eyes are able to see.

9. Electromagnetic Spectrum
Those wavelength that your eyes can see as different colors
Make a small fraction of the electromagnetic spectrum
Shorter wavelengths (violet/indigo) have more energy than longer wavelengths (red)
Actually shorter wavelengths can damage organic molecules like proteins and nucleic acids
This is why U.V. rays cause sunburns and can lead to skin cancer

10. Electromagnetic Spectrum
Substances can do one of only 2 things when struck by a particular wavelength of light:
Absorbed
Reflected
Pigments in the leaf’s chloroplast absorb blue-violet and red very well

11. Wavelength

12. Chloroplast

13. Chloroplast

14. Photosynthesis
ATP and H2 generated from light dependent stage used to covert CO2 and H2O into organic compounds (like glucose)
6CO H2O C6H12O O2
This carbon fixation…turning inorganic to organic
Fixation requires energy—all comes from sun

15. Photosynthesis Two Main Stages
Stage I Light Reaction (Light Dependent)
Convert the energy in sunlight to chemical energy
Takes place in the thylakoid membrane
1st – Chlorophyll molecules in the membrane
capture light energy
2nd – Chloroplast use energy to remove eˉ (excites)
from water (photolysis)
This splits H⁺ + O₂
O₂ is the “waste product” for photosynthesis

16. Photosynthesis Stage 1
Photolysis – when a water molecule is split into its component elements
Hydrogen and water
Generates electrons in light dependent reaction

17. Results of Light Reaction – NADPH + ATP
Photosynthesis Stage 1
O₂ escape into the atmosphere via the stoma (on leaves)
3rd – Chloroplast use H₂O eˉ and H⁺ ions to
(make energy rich molecules) NADH
found in cellular respiration.
4th – (finally) ATP is made in chloroplast
Excited e⁻ from Photosystem II are used to generate a proton gradient
Results of Light Reaction – NADPH + ATP

18. Photosynthesis Stage 1
Because of the proton gradient created by Photosystem II:
ATP synthase located in the thylakoid membranes allows the protons to diffuse back across the membrane to the stroma and uses energy that the protons release as they diffuse down the concentration gradient to produce ATP
This is called chemiosmosis
Photophosphorylation – using light energy absorbed to create ATP

19. Photosynthesis Stage 1 Photosystem I
A pair of excited e⁻ is emitted from the reaction center of photosystem I and passes a short chain of e⁻ acceptors.
At the end of the chain e⁻ are passed to NADP in the stroma.
NADP is reduced to NADPH

20. Side Bar
1st organisms to release O₂ in the atmosphere happened 2.4 – 2.2 billion years ago
O₂ was at 2%
This caused dissolved iron in the oceans to precipitate as iron oxide.
Sank to the bottom of the oceans and formed banded iron formations
750 million yrs ago it was 30% now it’s 20%

21. Photosynthesis Stage 1
Transfer of excited electrons occurs between carriers in the thylakoid membrane

22. Photosynthesis Stage 1
In photosynthesis light-excited eˉ for the electron transport from chlorophyll travel down the chain. (P680/P700 are pigments)

23. Photosynthesis Stage 2
Stage II The Calvin Cycle (takes place in Stoma)
Makes sugar from the atoms in CO₂ + the H ions and high-energy eˉ carried by NADPH
Enzymes for the Calvin Cycle are located outside the thylakoids and are dissolved in the stoma
ATP made in Light Reaction provides energy to make sugar (carbohydrates or other carbon compounds)
Calvin Cycle AKA “Light Independent Reactions” because it does not require light to begin reaction

24. Photosynthesis Stage 2
ATP synthase in thylakoids generates ATP using the proton gradient.

25. Photosynthesis Stage 2 Carboxylation of RuBP
Ribulose biphosphate (RuBP), 5 carbon compound, binds with CO₂ in a process called carbon fixation.
Catalyzed by an enzyme called RuBP carboxylase (rubisco).
Result: 6 carbon compound
The unstable 6-carbon breaks down into 2 3 carbon compounds (Glycerate 3 – phosphate GP)
GP = what we called G3P!!!!!
Done by reducing NADP and ATP

26. Photosynthesis Stage 2
The 3 carbon molecules of GP are acted upon by ATP and NADPH from the light-dependent reaction to form 2 other 3-carbon molecules called triose phosphate (TP). This is a reduction reaction.
The molecules of TP then do one of 2 things: some leave the cycle to become sugar phosphates that may become more complex carbohydrates. The others continue in the cycle and reproduce RuBP.
ATP is used to regain RuBP

27. Calvin Cycle

28. The Calvin Cycle

29. Photosynthesis-rates
Photosynthesis does not occur at such a steady rate
Greatly affected by intensity of light, temperature, and CO2 levels
Can be measured directly via CO2 intake and O2 production amounts IF adjusted to account for respiration
Biomass (amount of plant/size) is an indirect method of measuring rate of photosynthesis—indirect b/c a lot of other potential factors

30. Photosynthesis O2 released + Photosynthesis Respiration O2 taken in --
Respiration
O2 taken in --
Day 1
Night 1
Day 2
Night 2

31. Photosynthesis
Light intensity—varies inversely with the square of the distance (farther away, less intense)
At low light, the rate of photolysis is limited by the amount of light absorbed
Light is used for the production of ATP and high energy electrons which are needed for the conversion of CO₂
Limits glucose production

32. Photosynthesis
At low Temps all of the enzymes that catalyze the conversion of CO₂ into carbohydrates work slowly
Below 5℃ there is little or no photosynthesis in many plants
At 30℃ rubisco is decreased effectively although not denatured
So temperature is a limiting factor at both high and low temperatures.

33. Effects of Temperature

34. Photosynthesis Below .01% CO₂ rubisco is not effective in many plants
So no photosynthesis
Between .01 and .04 concentration of CO₂ is often a limiting facture

35. Photosynthesis Summary
Light Reaction – takes place in the thylakoid
membrane
Convert light energy to chemical energy (ATP) and NADPH
Calvin Cycle – takes place in the stroma; uses ATP and NADPH to convert CO₂ to sugar.

36. Calvin’s Experiments
Calvin cycle was discovered by Melvin Calvin & Andrew Benson in the 1950’s

37. Calvin’s Experiments

38. Calvin’s Experiments Improvements in apparatus Radioactive Labelling
Radioisotopes of elements have the same chemical properties as other isotopes of an element but can be ID’d because they are radioactive
They can be used to label organic compounds in biochemistry experiments
¹⁴C (discovered in 1940) so CO₂ and hydrogen carbonate labelled with ¹⁴C could be produced and made available to researchers

39. Calvin’s Experiments Improvements in apparatus
Double-way paper chromatography
A first solvent is run up through the paper to separate the mixture partially in one direction. The paper is dried and then a second solvent is run up at 90° to the first spreading the mixture in a second dimension
This procedure is ideal for separating and identifying the initial products of carbon fixation

40. Calvin’s Experiments Improvements in apparatus Autoradiography
Using X-ray film to find the location of isotopes.
When atoms of ¹⁴C decay they give off radiation which makes a small spot in an adjacent X-ray film.
To find radioisotopes in a sheet of chromatography paper it is placed next of film that is of the same size
They are kept in the darkness for several weeks
The film is then developed, black patches appear in areas where the adjacent chromatography paper contained radioisotopes