Photosynthesis

PhotosynthesisPigments are proteins that

reflect varying wavelengths of light, making them appear to be different colors.

They are necessary to absorb the energy from the sun.

Pigments can be separated through a process called paper chromatography.

Light

•light energy has to be captured for photosynthesis to begin

•pigments absorb light energy

•white light is composed of colors of the visible spectrum

Electromagnetic Spectrum

•chlorophylls a and b and other pigments (beta carotenes, for example) absorb certain wavelengths of light energy

•pigments can be separated by a process known as chromatography

The Chloroplast

2 Major Stages of Photosynthesis

•Light Reactions (Light Dependent Reactions) – take place in thylakoids

•Light Independent Reactions (Calvin Cycle) – take place in stroma

Overall Summary Equation

6CO2 + 6H2O C6H12O6 + 6O2

Melvin Calvin

Determined the reactions of the light independent reactions and won a Nobel prize

In the light reactions, energy from the sun is captured by the pigments, water is split to release oxygen and ATP and NADPH are produced

In the Calvin cycle, CO2

combines with the high energy H electrons in NADPH to make glucose; ATP provides energy for the reactions

What happens in the light reactions?

• Light excites electrons in PSII and PSI

• H20 is broken down to replace PSII electrons; O2 is released as by-product

• Electrons from PSII go down electron transport pulling H+ through membrane

• H+ diffuse back across thylakoid membranes through ATP synthase

• ATP synthase uses their energy to make ATP

• Excited electrons from PSI bond to NADP+; H+ that diffused across membrane bond to NADP+; this makes NADPH

• ATP and NADPH are used in the Calvin cycle

What happens in the Calvin cycle?

• CO2 is fixed (bonded) to RuBP to form 3-phosphoglycerate

• ATP is needed for energy to rearrange the 3-phosphoglycerate

• High energy electrons from NADPH are bonded

• Some product forms glucose

• Remaining product reforms additional RuBP to keep the cycle going

REVIEW!!!

• What is the source of the O2 released in photosynthesis?

• Which photosystem releases high energy electrons that bond to NADP+?

• H+ diffuse out of the thylakoids through what protein?

• In what organelle does photosynthesis occur and in what part of that organelle do the light reactions and Calvin cycle occur?

• What happens during electron transport?

• Where is the energy in glucose?