1. Photosynthesis
2.9, 8.3

2. Photosynthesis 2.9 Understanding (Statement objectives)
Photosynthesis is the production of carbon compounds in cells using light energy.
Visible light has a range of wavelengths with violet the shortest wavelength and red the longest.
It should be known that visible light has wavelengths between 400 and 700 nanometres, but it is not required to be able to recall the wavelengths of specific colours of light.
Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours.
Oxygen is produced in photosynthesis from the photolysis of water.
Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide.
Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis.
Applications
Explain how photosynthesis is responsible for changes in the Earth’s atmosphere as well as oceans and rock deposition.
Nature of science
Skills
Draw an absorption spectrum for chlorophyll and an action spectrum for photosynthesis
Describe the design of experiments to investigate the effect of limiting factors on photosynthesis.
Water free of dissolved carbon dioxide for photosynthesis experiments can be produced by boiling and cooling water.
Separation of photosynthetic pigments by chromatograph.
Paper chromatography can be used to separate photosynthetic pigments but thin layer chromatography gives better results.
Explain the light-dependent reactions and light-independent reactions in photosynthesis.

3. Photosynthesis 8.3 Understanding
Light-dependent reactions take place in the intermembrane space of the thylakoids.
Light-independent reactions take place in the stroma.
Reduced NADP and ATP are produced in the light-dependent reactions.
Absorption of light by photosystems generates excited electrons.
Photolysis of water generates electrons for use in the light-dependent reactions.
Transfer of excited electrons occurs between carriers in thylakoid membranes.
Excited electrons from Photosystem II are used to contribute to generate a proton gradient.
ATP synthase in thylakoids generates ATP using the proton gradient.
Excited electrons from Photosystem I are used to reduce NADP.
In the light-independent reactions a carboxylase catalyses the carboxylation of ribulose bisphosphate.
Glycerate 3-phosphate is reduced to triose phosphate using reduced NADP and ATP.
Triose phosphate is used to regenerate RuBP and produce carbohydrates.
Ribulose bisphosphate is reformed using ATP.
The structure of the chloroplast is adapted to its function in photosynthesis.
Applications
Analyze Calvin’s experiment to elucidate the carboxylation of RuBP.
Nature of science
Explain developments in scientific research that follow improvements in apparatus—sources of 14C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation.
Skills
Annotate of a diagram to indicate the adaptations of a chloroplast to its function.
Explain the light-dependent reactions.
Explain the light-independent reactions.
Explain the relationship between the structure of the chloroplast and its function in photosynthesis.

4. Photosynthesis
Photosynthesis is the production of carbon compounds in cells using light energy

5. Photosynthesis

6. Summary of Photosynthesis

7. Visible Light
Visible light has a range of wavelengths, with violet being the shortest and red the longest
Falls between wavelengths

8. Photosynthetic Pigments
2 main categories
Chlorophylls
absorb red and blue-violet light
main photosynthetic pigment in plants
why leaves have green color
Carotenoids
absorb strongly in blue-violet
appear orange, yellow, or red
accessory pigments

9. Absorption
Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colors

10. Absorption Spectrum
Skill: Be able to sketch an absorption spectrum for chlorophyll

11. Action Spectrum
An action spectrum profiles the effectiveness of different wavelength light in fueling photosynthesis. It is obtained by plotting wavelength against some measure of photosynthetic rate (e.g. O2 production)
Skill: Also be able to sketch an action spectrum

12. Chloroplast Structure
Grana: stacks of thylakoid membranes containing chlorophyll
(“stack of pancakes” where a pankake is a thylakoid disk)
Stroma: liquid filled interior of chloroplast

13. Chloroplast Adaptation to Function
•Large surface area of thylakoids for light absorption.
•Small space inside thylakoids for accumulation of protons to create a concentration gradient
•Fluid filled stroma for the enzymes of the Calvin cycle
•Double membrane on the outside isolates the working parts and enzymes from the surrounding cytosol.

14. Practice

15. Stop and explain 1. the equation for photosynthesis
2. the absorption and action spectrum
3. indicate how the structure of a chloroplast relates to function

16. Biochem of Photosynthesis
Water is split and electrons are transferred together with hydrogen ions from water to CO2. The CO2 is reduced to sugar.
Sugar, oxygen and water are produced
as by-products.
Photosynthesis can be summarized as the
following chemical reaction:
6CO2 + 12H2O + light energy ➙ Glucose (C6H12O6) + 6O2 + 6H2O

17. Phases of Photosynthesis
There are 2 phases of photosynthesis
Light dependent phase
occurs in the intermembrane space of the thylakoid membranes of chloroplast
Light independent phase
occurs in the stroma of the chloroplasts

18. Light Dependent Reactions

19. Light Dependent Reactions

20. Light Dependent Reactions
Understanding: Absorption of light by photosystems generates excited electrons

21. Light Dependent Reactions
Photolysis of water generates electrons for use in the light-dependent reactions
Oxygen is produced from the photolysis of water

22. Light Dependent Reactions
Excited electrons from Photosystem II are used to contribute to create a proton gradient

23. Light Dependent Reactions
Understanding: ATP synthase in thylakoids generates ATP using the proton gradient

24. Light Dependent Reactions
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Understanding: Excited electrons from Photosystem I are used to reduce NADP
Understanding: Reduced NADP and ATP are produced in the light dependent reactions

25. Light Dependent Reactions
When chlorophyll molecules absorb light, an electron is excited to a higher level. This electron is replaced to photosystem II in one of two ways:
In non-cyclic phosphorylation, the electrons lost to the electron transport chain are replaced by splitting a water molecule.
In cyclic phosphorylation electrons lost from photosystem II are replaced by those from photosystem I. ATP is generated but not NADPH
•Less common, probably when NADP+ is limited.

26. Cyclic Phosphorylation
Does not usually occur
No NADPH produced

27. Light Dependent Reactions

28. Light Dependent Reactions

29. Light Dependent Reactions
The light dependent reactions take place in the thylakoid membrane
Thylakoid membranes of the chloroplast provide a large surface area.
Chlorophyll is located in the membrane in groups of molecules called photosystems.
Photolysis of water occurs in thylakoid space and generates electrons for Photosystem II.
Absorption of light in the photosystems gives “excited electrons”.
Excited electrons from photosystem II are passed to electron carriers.
Electron carriers are embedded in the thylakoid membrane.
Excited electrons from photosystem I are used to reduce NADP+.
NADP+ accepts two high energy electrons and an H+ ion (proton) to form NADPH.
Electron flow through electron carriers causes H+ to be pumped into the thylakoid space
A proton concentration gradient is formed in the space between thylakoids.
ATP synthase is embedded in the thylakoid membrane
H+ ions flow back through ATP synthase channels to produces ATP by chemiosmosis.
ATP and NADPH (reduced NADP) are produced in the light dependent reactions

30. Stop and explain
the light dependent reactions

31. Part 2
The calvin cycle

32. Light Independent Reactions: The Calvin Cycle
Understanding: Glycerate 3-phosphate is reduced to triose phosphate using reduced NADP and ATP
Understanding: in the light-independent reactions a carboxylate catalyses the carboxylation of ribulose biphosphase
Understanding: Ribulose biphosphate is reformed using ATP
It could be worse
Understanding:Triose phosphate is used to regenerate RuBP and produce carbohydrates

33. Light Independent Reactions: The Calvin Cycle
ATP and NADPH produced in the light dependent reactions are used in the light independent reactions.
The light dependent reactions occur in stroma of chloroplast.
The enzyme ribulose bisphosphate carboxylase (Rubisco) catalyses attachment of CO2 to ribulose bisphosphate (RuBP).
This briefly forms an unstable six-carbon intermediate compound.
The six carbon compound splits to form two glycerate-3-phosphate (G-3-P) molecules.
Each (of the two) glycerate-3-phosphate then receives one phosphate from ATP;
Each (of two) phosphorylated glycerate-3-phosphate is reduced by NADPH + H;
The result is two molecules of triose phosphate (TP) for every six molecules of triose phosphate one goes to form glucose.
The five remaining TP molecules are reorganised to reform RuBP.
The reorganisation of TP into RuBP requires ATP.

34. Calvin’s Experiment
Animation and Explanation

35. Review
Stop and Explain
the light independent reactions

36. Factors Affecting Photosynthetic Rate
Amount of light available
Level of carbon dioxide
Temperature

37. Factors Affecting Photosynthetic Rate
Light Intensity
Increases rate until it reaches a plateau

38. Factors Affecting Photosynthetic Rate
Carbon dioxide concentration
Increases rate of photosynthesis until a plateau is reached

39. Factors Affecting Photosynthetic Rate
Temperature
Increases rate until it reaches a point where enzymes become denatured, where there is a sharp decline

40. Factors Affecting Photosynthetic Rate
Temperature
Increases rate until it reaches a point where enzymes become denatured, where there is a sharp decline

42. Factors Affecting Photosynthetic Rate

43. Review
What is the first identifiable product of carbon dioxide fixation in photosynthesis?
A. Ribulose bisphosphate (RuBP)
B. Glycerate 3-phosphate (GP)
C. Triose phosphate (TP)
D. Acetyl CoA

44. Review How is oxygen produced during photosynthesis?
A. Water molecules are split with energy from ATP.
B. Water molecules are split with energy from light.
C. Carbon dioxide molecules are split with energy
from ATP.
D. Carbon dioxide molecules are split with energy from light.

45. Chromatography
Paper chromatography
Thin layer chromatography
Both can be used to separate photosynthetic pigments, but TLC gives clearer results

46. Questions?