Transcript Photosynthesis and respiration

Photosynthesis
Overview video
3 mins
Photosynthesis over view
 Carbon Dioxide + Water + SUNLIGHT
 Sugar + Oxygen
 CO2 + H2O + SUN  C6H12O6 + O2
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
2H20

4 H+ + 4 e- + O2
Protons (H+ ) Will be used later in PSI
Electrons (e-) – Move along ETC to PSI
Oxygen (O2) – Released as a gas, NOT needed
Animation of photosystem II
 http://vcell.ndsu.edu/animations/photosys
temII/light.htm
Photosystem I (comes 2nd)
1) Electrons from ETC reach PSI reaction
center in a second molecule of
Chlorophyll A
Photosystem I
2) Sun helps electrons go through a 2nd
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
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
 http://www.biology4all.com/resources_libr
ary/source/61a.swf
Summary of light
reactions
 H20 + sunlight + NADP+ + ADP 
O2 + 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 CO2 into sugars
Calvin Cycle Steps
1) Carbon Fixation
A molecule of CO2 combines with RuBP
(enzyme = Rubisco) then splits into 2 PGA
molecules
Calvin Cycle Steps (C3)
2) Reduction - ATP and NADPH used to form
GP3, 3 carbon sugar
Calvin Cycle Steps (C3)
3) Regeneration of RuBP - 5 of the 6 Carbons
reform into RuBP
Production of sugar (C3
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
 CO2 + 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