PhotosynthesisMuhammad Tariq

Readings:Life Chapter 8

CO2 + H2O + Light energy Sugar + Oxygen

The food Chain

Autotrophs and Heterotrophs

Sun as god in cultures

• The Egyptian peoples honored the sun god

• For people in ancient Egypt, the sun was a source of life

• It was power and energy, light and warmth

• It was what made the crops grow each season

• 1/3rd of all the carbon fixed is used by humans• Law of conservation of energy

Photosynthesis

CO2 + H2O Carbohydates

• Conversion of energy from light to chemical bond in reduced electron carriers & ATP

• Sources of chemical energy in step 1 used to drive synthesis of carbohydrates from CO21/3rd of all the carbon fixed is used by humans

Photosynthetic reactants & Products• 3 principal ingredients: Water, CO2, Light• Not only produces CHO but also O2

CO2 + H2O + Light energy Sugar + Oxygen

Oxygen production

CO2 + H2O + Light energy Sugar + Oxygen

• What role does light play in this reaction???

• How carbon becomes linked to form sugar???

• O2 gas comes from CO2 or H2O???

6CO2 + 6H2O C6H12O6 + 6O2

Source of the Oxygen

6CO2 + 12H2O C6H12O6 + 6H2O + 6O2

http://bcs.whfreeman.com/thelifewire/content/chp08/0802001.html

Light as source of Energy

Visible spectrum

• Photon must be absorbed by receptive molecule

• Must have sufficient energy to perform chemical work

Light as source of Energy: Photon mediated activation

Receptivity of photon: pigments in photosynthesis

• Molecules that absorb wavelength in visible wavelength are called pigments

• Photon scattered• Photon transmitted• Photon absorbed, photon disappears but energy doesn’t

• Scattered and transmitted wavelengths make pigments appear to us colored

• Photosynthesis uses energy absorbed by several pigments• Several pigments, several absorbtion spectra• Chlorophyll, carotenoids, phycobillins• Chlorophyll a and b predominates

Pathways of Photosynthesis• Light reaction: driven by light, produces ATP and reduced electron

carrier NADPH+H+

• Calvin-Bensen reaction: doesn’t use light. Use ATP, NADPH+H+ from light reaction and CO2 to produce sugars

Absorbed wavelengths and biological activity

Blue and Red light cause highest rate of photosynthesis

Absorbtion spectrum

Action spectrum

Chlorophyll molecule

The light reaction

Energy absorbing antenna system

Converts absorbed light into chemical energy

Excited chlorophyll in reaction acts as reducing agent in electron transport

Oxidizing agent

• Chl acts as reducing agent and participates in a redox reaction

• Reduce electron carrier NADP+, generates a proton motive form used in ATP synthesis

The light reaction

The light reaction (Non cyclic photophosphorylation)

680nm 700nm

Photosystem II

Cyclic photophosphorylation (PSI)

Summary

Lumen

Light reaction summary

• http://bcs.whfreeman.com/thelifewire/content/chp08/0802002.html

Tracing the pathway of CO2

• http://bcs.whfreeman.com/thelifewire/content/chp08/0802003.html

Conclusion

The light independent reaction