1. 8.3 Photosynthesis Applications:
Calvin’s experiment to elucidate the carboxylation of RuBP
Understanding:
Light-dependent reactions take place in the intermembrane space of the thylakoids
Reduced NADP and ATP are produced in the light-dependent reactions
Light-independent reactions take place in the stroma
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 generate a proton gradient
In the light-independent reactions a carboxylation of ribulose bisphosphate
Glycerate 3-phoshpate is reduced to triose phosphate using reduced NADP and ATP
Triose phosphate is used to regenerate RuBP and produce carbohydrates
Skills:
Annotation of a diagram to indicate the adaptations of a chloroplast to its function
Nature of science:
- Developments in scientific research follow improvemnts in apparatus: sources of 14C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation
Understanding:
Ribulose bisphosphate is reformed using ATP
The structure of the chloroplast is adapted to its function in photosynthesis

2. Chloroplast structure
Chloroplasts are adapted to their function
Draw a chloroplast and label the following onto it:
Thylakoid
Granum
Inner membrane
Outer membrane
Stroma

3. Chloroplast structure

4. Chloroplast structure
Thylakoids – flattened membrane sacs with components for the absorption of light (first step of photosynthesis) Grana – Stacked up thylakoids = more photosynthesis. Contains chlorophyll. Stroma – fluid outside of the grana. Contains many enzymes and chemicals for photosynthesis.

5. Chloroplast structure
Function Allowed
Extensive membrane surface area of the thylakoids
Small space (lumen) within the thylakoids
Stroma region similar to the cytosol of the cell
Double membrane on the outside

6. Chloroplast structure
Function Allowed
Extensive membrane surface area of the thylakoids
Greater absorption of light by photosystems
Small space (lumen) within the thylakoids
Faster accumulation of protons to create a concentration gradient
Stroma region similar to the cytosol of the cell
Area for the enzymes necessary for the Calvin cycle to work
Double membrane on the outside
Isolates the working parts and enzymes of the chloroplast from the surrounding cytosol

7. Photosynthesis

8. Photosynthesis vs respiration
Essentially the opposite Respiration = catabolism (breaks down molecules into smaller units to release energy) Photosynthesis = anabolism (construct large molecules from smaller units using energy)

9. Light dependent reactions Light independent reactions
Photosynthesis
Light dependent reactions Light independent reactions

10. Light dependent reactions
Thylakoid membrane
Uses light directly
Use pigments to absorb the light (chlorophyll/carotenoids…)
Pigments organised into photosystems in thylakoids
Photosystems include:
Chlorophyll a molecules
Accessory pigments
Reaction centre
A reaction centre in these photosystems contains:
Pair of chlorophyll a molecules
A Primary electron acceptor

11. Light dependent reactions
Modern day plants have 2 photosystems Each absorbs light efficiently at different wavelengths Photosystem I: 700nm (P700) Photosystem II: 680nm (P680) Work together to to transfer electrons to create energy

14. Photosystem II
A photon of light is absorbed by a pigment in Photosystem II and is transferred to other pigment molecules until it reaches chlorophyll a. (Photoactivation)
Water split by enzymes to produce e-, H+ and oxygen – driven by light energy (photolysis)
Electrons supplied one by one to chlorophyll a
The photon energy excites a chlorophyll a electron to a higher energy state
Electron captured by primary acceptor of the reaction centre

15. Electron transport chain
6. Excited electrons pass from primary acceptor down electron transport chain, losing energy at each step
Involves Plastoquinone (electron carrier) and plastocyanin (electron acceptor)
Involves cytochrome complex where the e- transport chain occurs)
7. Protons pumped into thylakoid space against concentration gradient
This stored energy drives chemiosmosis – phosphorylation of ADP to ATP using ATP synthase
(ATP is the first product)

16. Photosystem I
8. Another photon of light is absorbed by a pigment in Photosystem I. 9. Energy is transferred until it reaches chlorophyll a 10. Electron is energised and transferred to primary electron acceptor 11. De-energised electron from Photosystem II fills the void left by the newly energised electron

17. Electron transport chain
12. High energy electron passed down a second electron transport chain that involves ferredoxin (electron carrier) 13. Enzyme NADP reductase catalyses the transfer of electron form ferredoxin to energy carrier NADP electrons are needed to fully reduce NADP+ to NADPH (NADPH is the second product)

18. Light dependent reactions
NADPH and ATP are the final products Supply energy for the light independent reactions to occur Also where oxygen is released (water splitting in the first few steps)

19. ATP
ATP production in photosynthesis and respiration are similar Both use chemiosmosis to phosphorylate ADP to ATP (ATP synthase enzyme) When it is produced using light = photophosphorylation

20. Chemiosmosis Respiration chemiosmosis Photosynthesis chemiosmosis
Electron transport chain in cristae membranes
Energy released when electrons are exchanged from one carrier to another
Energy used to pump H+ into intermembrane space
H+ ions come from matrix
H+ ions diffuse back into matrix through channels of ATP synthase
ATP synthase catalyses the phosphorylation of ADP to ATP
Electron transport chain in thylakoid membranes
Energy used to pump H+ into thylakoid space
H+ ions come from the stroma
H+ ions diffuse back into stroma through channels of ATP synthase
ATP synthase catalyses the photophosphorylation of ADP to ATP

21. Light Independent Reactions
In the stroma (contains enzymes)
Uses ATP and NADPH from light dependent reaction
Involves the Calvin cycle (begins and ends with the same substance)

22. Carbon Fixation
5-carbon compound Ribulose bisphosphate (RuBP) binds to an incoming carbon dioxide molecule
Catalysed by enzyme RuBP carboxylase (rubisco) – results in an unstable 6-carbon compound
Breaks down into two 3-carbon compounds called glycerate 3-phosphate (GP)

23. Reduction
GP uses ATP and NADPH to form triose phosphate (TP) – REDUCTION
TP can go in 2 directions

24. Regeneration
Some leave cycle to become sugar phosphates that become more complex carbohydrates (STARCH)
Most continue in the cycle to reproduce the originating compound of RuBP (uses ATP) REGENERATION
As much RuBP must be produced as is consumed.
Example:
3 RuBP used = 6 TP molecules produced
5 used to regenerate RuBP – 1 used to produce carbohydrates

25. Annotate onto your diagrams
To form one 6 carbon sugar molecule: 12 TP molecules 6 RuBP molecules 12 NADPH 18 ATP

26. Calvin’s experiment
Calvin and his team worked out carbon fixation in plants.
Research the lollipop experiment
What is it?
What is the process?
What did he find out?

27. Photosynthesis summary
Involves light dependent and light independent reactions Light dependent reactions produce ATP and NADPH for the light independent reactions Light is needed for the light independent reactions to occur – but not directly.

28. Photosynthesis summary
Light dependent
Light independent
Occurs in thylakoids
Uses light energy to form ATP and NADPH
Splits water in photolysis to proved replacement e- and H+ and to release oxygen to atmosphere
Includes 2 electron transport chains and photosystems I and II
Occurs in the stroma
Uses ATP and NADPH to form triose phosphate
Returns ADP, inorganic phosphate and NADP to the light dependent reactions
Involves the Calvin cycle