1. Higher Biology
Photosynthesis
Mr G Davidson

2. Pigments and Light White light is a form of radiant energy
it travels in the form of waves.
These waves always travel in straight lines.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

3. Pigments and Light
White light can be split into its coloured component if it is passed through a glass prism:
Red
Orange
Yellow
Green
Blue
Indigo
Violet.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

4. Pigments and Light
Each colour of the spectrum has a different wavelength
The wavelength of light is measured in nanometres (nm)
1 nm = 10-9m (1/1,000,000,000th metre)
red the longest – around 700 nm
violet the shortest – around 400 nm
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

5. Photosynthesis
Visible white light from the sun is the source of energy for photosynthesis.
Pigments in the leaf absorb light
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

6. Photosynthesis
When it strikes a green leaf light is absorbed by these pigments
A small percentage of this is used in photosynthesis.
The remainder of the light is either reflected from the leaf or transmitted through the leaf.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

7. Photosynthesis
Most leaves are green because they reflect green light and transmit green light.
Each of the pigments present in a leaf absorbs light of certain wavelengths therefore if a plant has different pigments, it can absorb a wider range of wavelengths of light.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

8. Absorption Spectrum Wavelength (nm)
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G Davidson

9. Photosynthesis
The pigments found in plants depend largely on where the plant is to be found e.g. shady plants need more pigment than canopy plants
Different sea weeds have a different range of pigments because of the reducing light intensity at greater depths of water.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

10. Fate of Light Striking a Leaf
100 % Sunlight
83 % absorbed
5 % transmitted
12 % reflected
Only a small percentage of absorbed light is used in photosynthesis
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

11. Chloroplasts Granum Double unit membranes Lamella Stroma
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

12. Chloroplast Structure Function Double unit membrane Enclose contents
Granum
Site of light dependent phase
Stroma
Site of carbon fixation
Lamella
Connect grana
Starch grains
Food Store
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

13. Chloroplasts
The light trapping pigments are to be found in the chloroplasts of plant cells.
Chloroplasts are relatively large organelles found in the cytoplasm, each one surrounded by a double unit membrane.
Inside the chloroplast are large starch grains which act as food stores.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

14. Chloroplasts
The main components of the chloroplast are grana which are interconnected by lamellae.
The grana are composed of flattened discs containing the pigments, and are the site of the light reaction.
The stroma is the site of carbon fixation and is the fluid part in the chloroplast.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

15. Chemistry of Photosynthesis
In the process of photosynthesis, raw materials carbon dioxide and water are assembled to make organic food molecules producing oxygen as a waste product.
Carbon dioxide
CO2
oxygen O2
glucose
C6H12O6
Light Pigments
water
H2O
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

16. Chloroplasts Photosynthesis occurs in two stages.
The first stage requires light and is called the light reaction or photolysis.
The second stage is a temperature dependent series of enzyme controlled reactions called carbon fixation or the Calvin Cycle.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

17. Photolysis
This is the trapping of sunlight energy by photosynthetic pigments to release chemical energy.
The light energy splits water into hydrogen and oxygen, the oxygen then being released as a by-product.
The hydrogen then combines with a hydrogen acceptor NAD to produce NADH2.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

18. Photolysis
At the same time, energy is also made available to convert ADP + Pi into the high energy molecule ATP.
This is a process known as photophosphorylation.
The NADH2 and ATP made by photolysis are passed to the carbon fixation stage.
Photolysis occurs on the grana of the chloroplasts.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

19. Photolysis NADH2 Carbon Fixation CO2 Sugar Water Photo-
phosphorylation
ATP
Photolysis
Sunlight
Oxygen
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

20. Calvin Cycle This is also referred to as carbon fixation.
This stage is a series of enzyme controlled chemical reactions in the form of a cycle.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

21. Calvin Cycle
As the carbon dioxide enters carbon fixation, it combines with a 5 carbon ribulose biphosphate (RuBP) to form an unstable 6 carbon compound which immediately splits into two molecules of 3 carbon glycerate phosphate.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

22. Calvin Cycle Glucose 5C 1C 3C 6C Triose phosphate Glycerate phosphate
ATP
ADP + Pi
NAD
NADH2
Triose phosphate
Glycerate phosphate
6 Carbon compound
CO2
RuBP
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

23. Calvin Cycle
Two molecules of glycerate phosphate are then converted via a triose phosphate into 6C sugar, using hydrogen and energy – both provided by photolysis.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

24. Calvin Cycle
Two molecules of triose phosphate are then used to make one molecule of 6 carbon glucose, which are then built to form starch or cellulose.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

25. Calvin Cycle
Not all triose phosphate molecules are used to make sugar, some are required to continue the cycle i.e. take it back to RuBP.
In doing this 5 molecules of 3 carbon triose phosphate become 3 molecules of 5 carbon RuBP using energy from ATP and so the Calvin cycle is allowed to continue.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

26. Limiting Factors
Chemical reactions such as photosynthesis can be speeded up or slowed down depending on certain conditions.
A condition which is able to limit the rate of a reaction is usually called a limiting factor.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

27. Elodea Bubbler
In the Elodea bubbler experiment we can alter light intensity, CO2 concentration and temperature, one at a time to show that they are all limiting factors.
The rate of photosynthesis is measured by counting the bubbles of oxygen released in a specific time.
Monday, 19 November 2018Monday, 19 November 2018
G Davidson

28. Elodea Bubbler
0.5% solution of sodium bicarbonate to provide a supply of CO2
Constant temperature
Monday, 19 November 2018Monday, 19 November 2018
G Davidson