1. Photosynthesis
Mrs Martin

2. Plants and animals are dependent upon the products of photosynthesis.
They use the products of photosynthesis to for respiration
6CO2 + 6H2O (+ light energy) - C6H12O O2
C6H12O O2  6CO2 + 6H2O
Photoautotrophs and heterotrophs can release the chemical potential energy in complex organic molecules during photosynthesis. They can also use the waste product Oxygen produced by photosynthesis for aerobic respiration.

3. Autotroph Chemoautotroph
Organisms that can produce their own complex organic compounds, using light energy or chemical energy, from inorganic sources.
Chemoautotroph
Prokaryotes that use the energy from exergonic reactions (chemical reactions that release heat) to synthesise complex organic compounds
Nitrifying bacteria that oxidise ammonia to nitrate or oxidising nitrite to nitrate.
Bacteria using sulphur rich substances bubbling from the vents of volcanoes. These bacteria help to support food chains living in those areas.

4. Photoautotroph Heterotrophs
Use the sun as their energy source and the inorganic molecules carbon dioxide and water. Most of the world’s food chains have photoautotrophs as their producers
Heterotrophs
These organisms cannot make their own food and are reliant on digesting other organisms to obtain their complex organic molecules into more simple soluble molecules. These simple molecules can then be rebuilt to produce proteins, lipids and nucleic acids.

5. Structure of the chloroplast

6. Chloroplasts- main regions
Stroma
Fluid filled matrix contains starch grains, oil droplets, DNA and and prokaryote-type ribosomes
Chloroplast DNA and ribosomes can make some proteins needed for photosynthesis
Site of light independent reactions
Enzymes needed for these reactions are found here
Surrounds Grana so products of light dependent reactions can easily pass into the stroma

7. Chloroplasts- main regions
Grana
Stacks of flattened membrane compartments – thylakoids
Up to 100 stacks
Provides large surface area for photosynthetic pigments, electron carriers and ATP synthase (required for light dependent reactions)
Can only be seen using an electron microscope
Site of light dependent reactions
Light is absorbed and ATP synthesised
Contain Photosynthetic pigments arranged into photosystems

8. Photosystem
Photosystem, a funnel shaped light harvesting cluster of photosynthetic pigments held in place by proteins in the thylakoid membrane.
The primary pigment reaction centre is a molecule of Chlorophyll a. The accessory pigments consist of molecules of chlorophyll b and carotenoids.

9. Structure of chlorophyll a
Essential molecule in the process of photosynthesis.
Gives plants their intense green colour
When vegetation is cooked the central magnesium is replaced with a hydrogen ion. This changes the colour of the leaves

10. Chlorophyll a
Active part of the chlorophyll molecule. Central Mg bonded to 4 N atoms. Changes in the electrons in this part of the molecule enable it to absorb light very strongly
Hydrocarbon tail is non-polar. It is hydrophilic so sticks into the thylakoid membrane

11. Photosynthetic pigments
Substances that absorb some wavelengths of light and reflect others.
The colour they appear is the colour they are reflecting
This light is reflected

12. Pigments Two forms of chlorophyll a
P680 absorbs at 680nm- found in photosystem II
P700 absorbs at 700nm- found in photosystem I
Both also absorb blue light at around 450nm
Chlorophyll b absorbs around 500nm & 640nm
Carotenoids absorb blue light and reflect orange/yellow light
Pigments

13. Knowledge check What is a chemoautotroph? Can you name an example
What type of trophic organism are the majority of food chains reliant upon?
Name the membrane that makes up the grana
Suggest what this membrane is composed of
Suggest why scientists have proposed the idea of endosymbiosis
State where the light independent reactions of photosynthesis take place
Explain why the majority of plants are green
Suggest why in the autumn leaves may turn red
Explain how a chlorophyll molecule is adapted for its function
Describe how a photosystem is able to maximise the amount of energy it can obtain from light

14. (b) Formation of ATP during non-cyclic photophosphorylation
(a) The distribution of photosystems on granal and intergranal lamellae;
(b) Formation of ATP during non-cyclic photophosphorylation
(b)
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15. The Z-scheme 15 © Pearson Education Ltd 2009
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16. Light dependent reactions- non-cyclic photophosphorylation
Light energy strikes photosystem II and cascades through to the primary pigment reaction centre
If enough energy strikes the primary pigment molecule the energy levels of a pair of electrons are raised. The electrons leave the chlorophyll molecule to an electron transport chain
As the electrons go down the electron transport chain they lose energy which is used to convert ADP + Pi  ATP
New electrons are needed to replace the electrons lost from photosystem II

17. Photolysis of water H20  2H+ + 2e- + ½ O2 enzyme Protons
Used for NADP
Waste product
Electrons used as a
Replacement for PS II

18. OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons
Light energy also hits photosystem I. If enough light hits the photosystem II electrons are lost from the primary pigment centre.
The electrons are replaced by the electrons from photosystem II
The electrons again leave to the electron transport chain
The electrons lose energy as they go down the chain. This energy is used to make reduced NADP (rNADP)
OILRIG
OXIDATION Is Loss of electrons
REDUCTION Is Gain of electrons

19. OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons
NADP H e-  Reduced NADP
Energy source
Protons from
photolysis
of water
From
Photosystem II
OILRIG
OXIDATION Is Loss of electrons
REDUCTION Is Gain of electrons

20. OXIDATION Is Loss of electrons REDUCTION Is Gain of electrons
REMEMBER!!!
OILRIG
OXIDATION Is Loss of electrons
REDUCTION Is Gain of electrons

21. Cyclic Phosphorylation
Only photosystem I is used
Excited electrons are passed to an electron receptor and back to the chlorophyll molecule from which they were lost
No photolysis of water
Small amounts of ATP are produced which maybe used in photosynthesis or by guard cells to bring in K ions lowering water potential and causing water to enter by osmosis. This causes the guard cells to swell and open, allowing exchange of gas.

22. Light dependent photosynthesis
The Z-scheme
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23. (b) Formation of ATP during non-cyclic photophosphorylation
(a) The distribution of photosystems on granal and intergranal lamellae;
(b) Formation of ATP during non-cyclic photophosphorylation
(b)
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24. Explain the role of carbon dioxide in the light-independent stage.
Week 10
Outline how the products of the light-dependent stage are used in the light-independent stage (Calvin cycle) to produce triose phosphate (TP), referring also to ribulose bisphosphate (RuBP), ribulose bisphosphate carboxylase (rubisco) and glycerate 3-phosphate (GP).
Explain the role of carbon dioxide in the light-independent stage.
State that TP (and GP) can be used to make carbohydrates, lipids and amino acids.
State that most TP is recycled to RuBP.
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25. Light independent photosynthesis
The reactions are not truly independent of light as the ATP and rNADP could not be produced without light.
The light independent reactions occur within the stroma.
Carbon Dioxide is needed to produce all large organic molecules. These molecules are used as structures or act as energy stores or sources for all the carbon based life forms on this planet

26. Calvin Cycle Inorganic form Of Carbon 3CO2 Rubisco
2x Glycerate 3 phosphate GP
(2x 3C, not sugar)
Now has carboxy group
5C acceptor
Ribulose bisphosphate
(RuBP) 5C Sugar
This reaction is catalysed by Ribulose Bisphosphate Carboxylase Oxygenase Rubisco. Described as the most important enzyme on earth.
Read Stretch and challenge on page 65!

27. Calvin Cycle GP Reduced and phosphorylated ATP ADP + Pi
2x triose phosphate (3C)
Ose= sugar
NADP
rNADP
5 of every 6 molecules of TP are recycled by phosphorylation (using ATP from light dependent reaction, to 3 molecules of RuBP (5C)

28. Calvin cycle 28 © Pearson Education Ltd 2009
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29. Limiting Factors Lesson Objective
To discuss the factors that limit photosynthesis
Design an experiment to test one factor that affects photosynthesis

30. Limiting Factors Law of limiting Factors states
At any given moment, the rate of metabolic process is limited by the factor that is present at its least favourable (lowest) value

31. Limiting factors
At any given moment, the rate of metabolic process is limited by the factor that is present at its least favourable (lowest) value

32. Light Intensity
When light is the limiting factor the rate of photosynthesis is directly proportional to the light intensity.
What does this mean?
Light causes the stomata to open so that Carbon dioxide can enter the leaves
Light is trapped by chlorophyll where it excites electrons
It splits water molecules to produce protons
Electrons and protons are involved are involved in photophosphorylation producing ATP for the fixation of carbon dioxide

33. Questions
Which stage of photosynthesis will affected by temperature? And why?
Why does light intensity affect the rate of photosynthesis?
Why would burning an oil-fired stove in a greenhouse increase the growth of plants in a greenhouse?

34. Questions
Which stage of photosynthesis will affected by temperature? And why?
The light independent Calvin cycle.
As many of the reactions are catalysed by enzymes, the rate rises between 0-25oC. At the rate plateaus and fall as enzymes work less efficiently and as oxygen competes more successfully than carbon dioxide for the active site of rubisco

35. Questions Why does light intensity affect the rate of photosynthesis?
Which stage of photosynthesis will affected by temperature? And why?
Why does light intensity affect the rate of photosynthesis?
Light is required for the light dependent phase, as photons hit the photosystem electrons are excited which then leave the photosystem via electron carriers and passed along a series of protein electron carriers which eventually produce ATP and rNADP. A reduced light intensity will reduce these levels. G3P will accumulate as it is not reduced to triose phosphate (calvin cycle). Ribulose bisphosphate levels will fall as it is not being regenerated

36. Questions
Which stage of photosynthesis will affected by temperature? And why?
Why does light intensity affect the rate of photosynthesis?
Why would burning an oil-fired stove in a greenhouse increase the growth of plants in a greenhouse
Burning hydrocarbons (oil, coal, natural gas) will produce Carbon Dioxide
Burning fuel will also increase the temperature of the greenhouse

37. Use your knowledge to explain the graph

38. Use your knowledge to explain the graph