Photosynthesis
Photosynthesis Overview
• What goes into photosynthesis?
• What comes out of photosynthesis?
• https://www.youtube.com/watch?v=xt0sGyjfto (photosynthesis rap)
• https://www.youtube.com/watch?v=yrQzEw9
xY5k (song)
Photosynthesis Overview
• 6 CO2 + 6 H2O + Sunlight  C6H12O6 + 6 O2
– With chlorophyll
• 6 Carbon dioxide + 6 Water + Sunlight  1 Glucose
+ 6 Oxygen
+
+

• Put energy in to make food
+
Photosynthesis Overview
• Endergonic Reactions (put energy in):
– Water is split (hydrogen and oxygen)

+
– Carbon dioxide is used to build sugar

• Exergonic reaction (get energy out)
– Oxygen moves to mitochondria or into atmosphere after
– Glucose used to make energy
• http://www.youtube.com/watch?v=AcX2n1rC4W4 (strange
photosynthetic organisms)
• http://www.youtube.com/watch?v=eo5XndJaz-Y (intro to
photosynthesis – TED- ED)
Photosynthesis Overview
• Light Reactions: (Thylakoid) – What do you think
happens?
– Step 1: Chlorophyll absorbs sunlight
– Step 2: Converts light into chemical energy; releases O2 (light
reactions)
• Calvin Cycle/Dark Reactions: (Stroma) – What do you
think happens?
– Step 3: Uses products of the light reactions to turn CO2 into
sugars (dark reactions)
https://www.you
tube.com/watch?
v=uixA8ZXx0KU
(Amoeba Sisters
– Photosynthesis)
Types of Molecules
• Energy – Which molecule
is it?
– ATP
– ADP (Broken ATP; recycled)
• Electron carriers – What
are they?
– NADP+/NADPH
– NAD+/NADH
– FAD/FADH2
– Move electrons stored in a
bond
Light Reactions
• Called Light Dependent reactions
• Broken into parts:
– 2 Photosystems
– 2 Electron Transport Chains (ETCs)/Chemiosmosis
Order of Reactions
1.
2.
3.
4.
Photosystem II
ETC 1
Photosystem I
ETC 2
General – Light Reactions
• Light energy is absorbed by
chlorophyll
• H2O is broken down
– O2 gas released as waste
– Electrons moved along ETC
 stored in NADPH
– H+ ions used to make ADP
into ATP
• Products: ATP (energy),
NADPH (electron carrier),
O2 (waste)
Photosystem II (PS II)
• Chlorophyll absorbs UV light
energy – What does it then
do?
– Energy used to split water (H+
ions, O2, electrons)
– Hydrogen ions stay inside
– Electrons are excited and gain
energy from the sunlight
• Holding onto that energy
– Oxygen released out of the
chloroplast
ETC 1
• Electron transport chain – What
does this mean?
– Electrons go through a few proteins
– Energy from them used to move H+
ions
• Stroma into thylakoid
• Creates H+ ion concentration
gradient – What does this mean?
– Higher concentration inside
thylakoid
– ATP synthase creates ATP from ADP
• Uses concentration gradient
Photosystem I (PS I) and ETC II
• Photosystem I
– Light energy hits chlorophyll
• Electrons come in from ETC I
• Electrons gain energy
• ETC II
– Electron is passed to an
acceptor
– Reduces NADP+ to NADPH
• Stores those electrons/energy
for Calvin Cycle
Light Reaction Products
• Products:
– ATP, NADPH, O2
• Cannot stop with these –
Why?
– No food has been made
• Provides Calvin Cycle with
some of its reactants
– To produce sugars
• https://www.youtube.com
/watch?v=GHesqcpl09s
(explaining light reactions)
Light Reactions
http://www.youtube.com/watch?v=BK_cjd6Evcw
Calvin Cycle
• Called the Light Independent reactions or Dark
Reactions
• Uses an enzyme called rubisco
– Recycled
– Why does it need to be recycled?
• Is the process of carbon fixation
– What does this mean?
Calvin Cycle
• Carbon Fixation reaction
– Rubisco combines CO2 with a 5-C sugar (RuBP)
• Makes a 6-C compound that is unstable
• Splits into 2 3-C molecules
• For every 3 CO2 used  6 3-C compounds are made.
Calvin Cycle
• 6 ATP and 6 NADPH are used
– Changes 6 3-PGAs (3 carbons each) into 6 G3Ps (3
carbons each)
• 5 remain in the cycle
• 1 released as a product
• 2 are needed to make 1 glucose molecule
Calvin Cycle
• Regeneration of RuBP
– ATP is used to rearrange
5 3-C compounds into 3
RuBP
– 15 carbons total: 5 3C
compounds into 3 5C
compounds
• The cycle then
continues
http://www.youtube.com/watch?v=E_XQR800
AgM
Photosynthetic Reaction Equations
• Light Reactions:
– H2O + Light + ADP + NADP+  O2 + ATP + NADPH
• Dark Reactions:
– CO2 + ATP + NADPH  Glucose + ADP + NADP+
• Net equation:
– CO2 + H2O + Sunlight  Glucose + O2
– https://www.youtube.com/watch?v=0UzMaoaXKaM
(TED-Ed = Calvin Cycle)
Both Cycles
• How are they related?
– Light reactions power the dark reactions
• Why are they called the “light reactions” and
“dark reactions”?
– Requires light vs. not needing light
Photorespiration
• Addition of O2 instead of CO2 by rubisco
• Reduces efficiency of photosynthesis
– Plants can’t use the oxygen very well
• Makes CO2 but no glucose – When would this be
helpful for plants?
– Helps plants in extremely hot conditions
Khan Academy videos
• http://www.youtube.com/watch?v=rsYk4eCKnA#t=11 (overview)
• http://www.youtube.com/watch?v=yfR36PM
Wegg (light reactions)
• http://www.youtube.com/watch?v=slm6D2VE
XYs (dark reactions)
Glucose
• Why is glucose (or any sugar) so important to the
plant’s survival?
• What does it allow for the plant to do?
• What other sugars can be made? Why would they be
made?
•
•
•
•
Fuel for cellular respiration
Building cellulose for sturdiness
Stored as starch for energy
Used in fruit production
Photosynthesis videos
• http://www.youtube.com/watch?v=aupr9qT2qgc (Photosynthesis
Song – Mr. Edmonds)
• http://www.youtube.com/watch?v=C1_uez5WX1o (The
photosynthesis song)
• http://www.youtube.com/watch?v=6GugfL45XHE (call me maybe
photosynthesis parody)
• http://www.youtube.com/watch?v=BeUmj8d6Mag (Summarizing
lecture video)
• http://www.youtube.com/watch?v=sQK3Yr4Sc_k (crash course
photosynthesis)
• https://www.youtube.com/watch?v=joZ1EsA5_NY (animation)
• https://www.youtube.com/watch?v=Q_1mxZdF2TY
(sciencemusicvideos)
• https://www.youtube.com/watch?v=ww33L0lD37I (song –
“Trouble” parody)
Factors that Effect Photosynthesis
• What factors affect photosynthesis? How so?
– Light Intensity
– Temperature
– Carbon dioxide concentration
– Oxygen concentration
– Water concentration
• There is an optimal level