Photosyntheis: Part 2

Chlorophyll and other plant pigment

• Chlorophyll- is the green pigment in plants

that absorbs radiant energy from the sun.

It is essential in the conversion of radiant

energy into chemical energy during

photosynthesis.

• wavelenghts: 400-500 nm(violet-blue) and

600-700 nm(orange-red).

• light brings life- meaning electrons of chlorophyll becomes excited as it is hit by light.– part of it becomes chemical energy and are

used as food for plants.

– as electrons jumps back to its original level, the rest of the energy is released in the form of red light( is lower than the first)

– reddish afterglow or fluorescence.

– dissipated in form of heat.

– light is also important for CHLOROPHYLL SYNTHESIS

• Choloroplast- membrane bound cytoplasmic organelles.– where chlorophyll is found.

– site of photosynthesis.

– found in numerous quantity inside the mesophyll.

– may also contain other pigments like carotenoids and xanthophylls( which has a color ranging from purple-orange)

• Grana- looks like stacked sheets; in between are molecules of fats and chlorophyll.

• Stroma- gelatinous matrix where grana is suspended.

How do producers use light energy to

manufacture food?

• 6CO2+12H2O C6H12O6+

6H2O+6O2

Light Dependent Phase: Photosynthesis

• "Photochemical reaction"

• occurs in granum: requires light to happen.

• prerequisite to light independent phase.

• 3 major events:

a. Chlorophyll Photoactivation- capture of light energy by chlorophyll

- energized electrons will be released

b. Photolysis- light activated Chlorophyll splits H2O into Hydrogen ions, electrons and oxygen gas.

c. Photophosporylation- transfer of energy absorbed by chlorophyll into molecules of ATP.

– simple adding of additional Phosphate group to ADP( adenosine diphosphate) to ATP( adenosine triphosphate) the energy currency of cell.

– Light----chlorophyll catch-----electrons release----hydrogen protons---additional energy----phosphate group---added to ADP---ATP.

• NADP+- a hydrogen carrier and electron

acceptor in cell.

– accepts Hydrogen ion from water

– accepts energized electrons from chlorophyll

– it becomes NADPH- after absorption

– Summary:( products of light dependent)

• Oxygen gas is the gaseous product.

• NADPH-

• ATP

Light independent phase

• 2nd phase

• involves the use of NADPH- and ATP for the conversion of CO2 to carbohydrates.

• according to Melvin Calvin

– CO2 is fixed into prefabricated 5-carbon sugar phosphate called RIBULOSE BIPHOSPHATE or RuBP.( Carbon fixation or Calvin cycle)

– RuBP is combined to CO2= unstable 6 carbon cpds.-----breaks into 2 molecules of PGA( phosphoglyceric acid- is the first stable product of carbon fixation; a carbon-3 cpd)

• Breaking of 6 carbon cpd to 3 carbon(

PGA)---C3 Cycle.

• PGA---BPGA( biphosphoglyceric

acid)*ATP

• BPGA----

PGAL(phosphoglyceraldehyde)*H+ from

NADPH-

• 2 molecules of PGAL-----(C-3, H-6, O-3)

final product-----glucose( C6H12O6)

• 4 things may happen to glucose:

– converted to sucrose( to be used by plants)

– converted to starch( stored for future)

– for animal and human consumption

– raw material( substrate for cell respiration and

major source of energy)

Ans: Reflections pp 111