1. Photosynthesis and Chemosynthesis
Chapter 23
Photosynthesis and Chemosynthesis

2. Photosynthetic pigments
Chlorophyll
Chlorophyll a
Chlorophyll b
Carotenoids
Carotene
Xanthophyll

3. Chlorophyll a is the most abundant and important photosynthetic pigment.
It is the primary pigment for photoexcitation.
The other photosynthetic pigments are called accessory pigments.
They enables the plant to absorb sunlight of greater range of wavelength.
They transfer the energy of the light they have absorbed to chlorophyll a for photoexcitation.
They protect chlorophyll a from destruction by absorbing excessive sunlight.

4. Absorption Spectrum

5. Action Spectrum
The action spectrum is highly correlated to the absorption spectrum.

6. for separation of photosynthetic pigments
Paper chromatography
for separation of photosynthetic pigments

7. Different photosynthetic pigment has different Rf value.
Rf value of a pigment = Distance travelled by the pigment
Distance travelled by the solvent front
The list below indicates the Rf value of the most common photosynthetic pigment using Petroleum ether: acetone(9:1) as a developing solvent:
Carotene 0.95
Xanthophyll 0.71
Chlorophyll a 0.65
Chlorophyll b 0.45

8. Chloroplast

9. Electromicrograph of Chloroplast
Light dependent stage of photosynthesis takes place in grana and intergrana.
Light independent stage of photosynthesis takes place in stroma.

10. Mechanism of Photosynthesis
Light dependent stage
1: Chlorophyll molecule is excitated from its ground state by a process called photoexcitation.
Ch  Ch+ + e-

11. Mechanism of Photosynthesis
Light dependent stage
2: The high energy electron is transferred via a series of electron transport chain.

12. Mechanism of Photosynthesis
Light dependent stage
3: The energy is handed over to form ATP, a process called photophosphorylation.

13. Mechanism of Photosynthesis
Light dependent stage
4: Water molecule is splitted up to give oxygen, hydrogen ion and electron, a process called photolysis. The H+ together with the e- via the electron transport chain reduce NADP to NADPH2. The electron returns the chlorophyll ion to its ground state.

14. Mechanism of Photosynthesis
Light dependent stage
Alternative explanation for step 4: Water is ionized to form hydrogen ion and hydroxide ion

15. Mechanism of Photosynthesis
Light dependent stage
4 OH-  2H2O + O2 + 4e-
The electron returns the chlorophyll ion to the ground state. The H+ together with the e- via the electron transport chain reduce NADP to NADPH2.

16. The main products formed by the light dependent stage are ATP and NADPH2 which will be used in the light independent stage of photosynthesis.
The light dependent stage is a series of photochemical reactions which are NOT controlled by enzymes. The rate is therefore NOT temperature dependent.
Light dependent stage takes place in grana and intergrana.
Light independent stage takes place in stroma.

17. Light independent stage: Carbon Fixation/ Calvin Cycle

18. Products of Photosynthesis
Some triose phosphate is to synthesize glucose and then sucrose and starch.

19. Products of Photosynthesis
Fatty acids and glycerol are produced from the 3-C compound and triose phosphate respectively. Lipids are formed by combining glycerol and fatty acids,

20. Products of Photosynthesis
Amino acids are formed from the 3-C compounds.

21. Factors affecting the rate of photosynthesis
Light intensity
Carbon dioxide concentration
Temperature

22. Concepts of Limiting factor
The rate of photosynthesis is controlled by light intensity, CO2 concentration and temperature.
The most unfavourable factor affects the rate of photosynthesis most. This factor is called Limiting factor. The change in other factors have no effect on the rate of photosynthesis.
When the limiting factor becomes favourable, it will no longer be limiting and the rate of photosynthesis increases accordingly until the other factors become limiting.

26. Chemosynthesis
Autotroph/ autotrophic organisms are able to synthesize their own food using the raw materials such as carbon dioxide and water.
Inorganic raw materials  Organic food
Inorganic raw materials  Organic food
Sunlight energy
Photo-autotroph:
Inorganic raw materials  Organic food
Chemical energy
Chemo-autotroph:

27. Examples of Chemo-autotrophs/ Chemosynthetic organisms
Iron bacteria:
Fe2+  Fe3+ + Energy
Inorganic raw materials  Organic food
Colourless sulphur bacteria:
S  SO4= + energy
Inorganic raw materials  Organic food

28. Chemosynthetic bacteria in Nitrogen Cycle

29. Nitrite bacteria
Nitrite bacteria oxidize the ammonium ion in the soil into nitrite ion with release of energy:
2 NH O2  2 NO H2O + 4 H+ + Energy
The energy is used to synthesize organic food for this bacteria.

30. Nitrate Bacteria
Nitrate bacteria oxidizes nitrite ion into nitrate ion with release of energy.
2 NO2- + O2  2 NO3- + Energy
The energy is used to synthesize organic food from inorganic raw materials.