Photosynthesis Overview video 3 mins Overview video 3 mins

Photosynthesis over view  Carbon Dioxide + Water + SUNLIGHT  Sugar + Oxygen  CO 2 + H 2 O + SUN  C 6 H 12 O 6 + O 2

Photosynthesis occurs in the chloroplasts

Photosynthesis animation

Thylakoids – Structures inside chloroplasts where process of photosynthesis takes place

There are 2 basic steps for photosynthesis  1) Light reactions  2) Dark reactions (light independent reactions) Calvin cycle

MAIN FUNCTIONS of the 2 reactions  Light reactions convert light energy to temporary chemical energy (ATP & NADPH)  Dark reactions (Calvin Cycle) turn these chemical energy molecules into Sugars

Light reactions Occur in the Thylakoid membrane  Have two parts Photosystem II (PSII) Photosystem I (PSI)

Photosystem II (comes first) 3 STEPS 1) Sunlight hits Chlorophyll A and transfers energy to the reaction center (another Chlorophyll molecule) This releases electrons to the primary electron acceptor

Photosystem II 2) Electrons then travel through proein molecules in the electron transport chain (ETC) to PSI PS II PS I

Photosystem II 3) An enzyme splits water into protons, electrons and oxygen. This provides more electrons to travel to PSI

PSII

Water reaction in PSII 2H 2 0  4 H e - + O 2 Protons (H + ) Will be used later in PSI Electrons (e - ) – Move along ETC to PSI Oxygen (O 2 ) – Released as a gas, NOT needed

Animation of photosystem II  temII/light.htm temII/light.htm temII/light.htm

Photosystem I (comes 2 nd ) 1)Electrons from ETC reach PSI reaction center in a second molecule of Chlorophyll A

Photosystem I 2) Sun helps electrons go through a 2 nd Electron transport chain (ETC) in membrane and turns NADP+ into NADPH

Photosystem I 3) ATP synthase pushes protons (H + ) out of membrane to make ATP H+

Overview

Reduction of NADPH  NADP + is reduced by electrons and protons that were produced by the water splitting  NADP + + e - + H +  NADPH

Formation of ATP The enzyme ATP synthase uses H + energy to produce ATP ADP + P + Energy  ATP

Animation – light dependant reaction  ary/source/61a.swf ary/source/61a.swf ary/source/61a.swf

Summary of light reactions  H sunlight + NADP + + ADP  O 2 + NADPH + ATP  The energy molecules NADPH and ATP can not be stored for long.  They will be used in Dark reactions to make sugar

Dark reactions (Calvin Cycle)  Occurs in Stroma  Called Light independent reactions  They do not need light, but they need the ATP and NADPH from the light reactions

Calvin Cycle in Dark  If there is no light, The Calvin Cycle soon uses up its ATP and NADPH and stops working.  LIKE a car, will drive for a while, but must fill up sometime

Calvin cycle = dark reactions = light independent reactions

Calvin Cycle overview  The process of using ATP and NADPH energy to join CO 2 into sugars

Calvin Cycle Steps 1) Carbon Fixation A molecule of CO 2 combines with RuBP (enzyme = Rubisco) then splits into 2 PGA molecules

Calvin Cycle Steps (C 3 ) 2) Reduction - ATP and NADPH used to form GP3, 3 carbon sugar

Calvin Cycle Steps (C 3 ) 3) Regeneration of RuBP - 5 of the 6 Carbons reform into RuBP

Production of sugar (C 3 Plants) Three turns of the cycle produce one 3 carbon sugar. 6 turns forms 1 glucose

What happens to the 3 carbon sugar?  Forms Glucose  Forms Sucrose  Forms Starches  Forms amino acids using Nitrogen

Summary of Dark Reactions  CO 2 + NADPH + ATP  Sugar + NADP + + ADP + P

 Why Light dependant?  The dark reactions are called the light dependant reactions because they depend on the ATP and NADPH produced in the light reactions