u
Autotrophs  are  organisms  that  create  their   own  energy  molecules  from  inorganic   molecules
–   Plants  are  autotrophs  since  they  convert  sunlight   into  sugar  molecules   u
Heterotrophs  are  organisms  that  consume   other  organisms  (dead  or  alive)  to  meet  their   energy  needs

•   photosynthesis  –  uses  the  energy  in  sunlight  to  convert   carbon  dioxide  to  sugars
•   provides  usable  chemical  energy  for  life  on  earth,  carbon   building  blocks,  and  oxygen
•   food,  clothing,  and  shelter

u
For  most  organisms,  adenosine  triphosphate
(ATP)  is  the  principle  energy  molecule
–   Contains  one  adenine  molecule,  one  ribose
(sugar)  molecule  and  three  phosphate  groups   u
Adenosine  diphosphate  (ADP)  has  one  less   phosphate  group  than  ATP  and  is  the   breakdown  product  of  ATP

u
ATP  is  the  basic  energy  source  for  most  cells
–   AcDve  transport  across  membranes
–   Movement  within  the  cell   u
ATP  has  a  very  short  life  span  in  cells  and  thus  is  not   ideal  for  energy  storage   u
Cells  store  energy  in  the  form  of  carbohydrates,   lipids  or  protein
–   One  glucose  molecules  contains  90  Dmes  the  stored   energy  in  a  molecule  of  ATP

u   u
Historical investigations of photosynthesis
–   Van Helmont (1600 ’ s) determined that plant growth was not due to soil…he thought it was due to water
–   Joseph Priestly (1700 ’ s) determined that a substance in the atmosphere was required for combustion and that plants produce this substance
–   Jan Ingenhousz (1700 ’ s) determined the substance produced by plants only occurred when sunlight was present
These investigations indicated that plants utilize CO2 &
H2O to grow and produce O2 as a by-product

•   At  first  it  is  thought  that  only  heterotrophs   existed  (heterotroph  hypothesis)  that  fed  on  an   organic  soup.    As  the  soup  was  depleted  so  did   the  heterotroph  organisms.    However,  some  of   the  heterotrophs  were  now  capable  of  using   light  energy,  they  used  the  light  energy  and   began  to  provide  food  for  themselves  and   others.    These  were  simple  bacteria.
•   Today  similar  bacteria  exist,  and  it  is  thought   that  those  simple  bacteria  became  a  part  of  the   eukaryoDc  cell

u
To  carry  out  PS  plants  need  chlorophyll
–   Chlorophyll  is  a  pigment  that  absorbs  light
–   Chlorophyll  a  and  chlorophyll  b  are  the  two   principle  types  found  in  plants

u
Chlorophyll  a  absorbs  light  in  the  red  and   violet  region  of  the  light  spectrum   u
Chlorophyll  b  absorbs  light  in  the  red  and  blue   region  of  the  light  spectrum   u
In  both  forms  of  chlorophyll,  light  energy   raises  the  energy  levels  in  electrons…these   high-­‐energy  electrons  make  PS  work

u   u   u   u
In photosynthetic eukaryotes, PS takes place in chloroplasts
–   Outer membrane – regulates substances into and out of organelle
–   Thylakoids: saclike membranes that are stacked into grana which increase membrane surface area u
Contain pigments and proteins that capture the energy in sunlight
Stroma: region outside the grana– surrounds the thylakoids, contains enzymes as well as its own DNA and RNA, and ribosomes
–   evidence of bacterial origin for chloroplasts
Light dependent reactions take place in the thylakoids
–   Energy fixing reactions
Light independent reactions (Calvin cycle) take place in the stroma
–   Carbon fixing reactions

•   Thylakoids
•   Grana  –  stacked  thylakoids  oriented  to  have  maximum   sunlight  absorpDon
•   Light  absorbing  pigments  are  embedded  in  the   thylakoids
•   Chlorophyll  a  &  Chlorophyll  b
•   Both  absorb  light  in  the  violet/blue  and  orange/red   regions  and  reflect  green
•   accessory    pigments  are  available,  their  absorbed  energy   is  given  to  special  chlorophyll  a
•   cartenoids

Chloroplast Anatomy
Chloroplast  >
~  contains  chlorophyll;    makes  plants  green
~  performs  Photosynthesis
~  makes  Glucose  to  harness  Energy
~  found  only  in  plant  cells

THE  PROCESS  OF  PHOTOSYNTHESIS
An  Overview
•   major  steps  in  energy  conversion
•   absorpDon  of  light  energy
•   conversion    of  light  energy  into  chemical  energy
•   storage  of  chemical  energy  in  sugars
•   light  reacDons  and  the  Calvin  cycle                      (Calvin-­‐
Benson  cycle  or  photosyntheDc  carbon  reducDon   cycle)
•   EquaDon:    3  CO
2
+    3  H
2
O   à    C
3
H
6
O
3
+    3  O
2

Photosynthetic Pigment Absorptions

Photosynthesis
Two Phases of Photosynthesis
1.) Light-Dependent Reactions (Light reactions)
~ occurs in thylakoid membrane of chloroplast
~ needs light to start process
~ chlorophyll absorbs light, and water is split into O
2
gas and H +
~ photolysis - process of water being split by light
~ H + ions have a positive charge that powers the formation of ATP
~ final products = Oxygen, NADPH, and ATP
~ Light Reactions provide the ENERGY for next step (Calvin Cycle)
Light-Dependent Reactions
Photosynthetic ET and ATP synthase

•   Light  reac+ons  convert  visible  light  into   chemical  energy  that  powers  sugar  produc+on
•   Chlorophyll  absorbs  light,  water  molecules  split,   chemical  energy  stored
•   Photosystem  I
•   connected  by  electron  transport  system
•   work  together  to  absorb,  concentrate,  and   transfer  light  energy  to  special  chlorophyll  a
•   Photosystem  II

•   chlorophyll  a    -­‐  reacDon  center
•   in  each  photosystem  the  reacDon  center  loses   energy–rich  electrons  which  are  carried  on  the   electron  transport
•   PSI  –  loses  electrons  but  they  are  replaced  by   electrons  from  PSII
•   PSII  –  loses  electrons  but  they  are  replaced  by   electrons  removed  from  water
•   EquaDon  –  H
2
O   à    2  H +    +    2e +    +    ½  O
2

•   at  end  of  flow  the  electrons  from  water  combine  with  a   hydrogen  carrier,  NADP+  -­‐  nicoDnamide  adenine   dinucleoDde  phosphate
•   forms  NADPH  –  which  transports  the  electrons  needed   for  the  Calvin  cycle  and  other  biosyntheDc  reacDons  in   the  chloroplast
•   as  they  flow  some  of  the  energy  is  used  in  acDve   transport  of  protons  across  the  thylakoid  membrane
•   high  []  of  protons
•   high  []  of  protons  now  diffuse  down  steep  []  gradient   through  ATP  synthtase  forming  ATP  +  P

•   The  first  two  events  of  photosynthesis  occur
•   AbsorpDon  of  light
•   Conversion  of  light  energy  into  chemical  energy
•   Three  products  formed:    oxygen  gas,  ATP,  and  NADPH

•   powered  by  the  light  reac+ons
•   Series  of  reacDons  in  which  carbon  dioxide  is   combined  with  the  hydrogen  split  from  water  in   the  light  reacDons
•   Takes  place  in  the  stroma  `
•   Products  of  the  Calvin  Cycle  (G3P)
•   The  3  carbon  sugar  produced  can  be  used  in  many   biosynthesis  reacDons
•   sucrose  made  in  cytosol,  and  starch  made  in   chloroplasts

The Calvin Cycle (continued)
For each fixed carbon atom, 9 ATP equivalents are required; thus 54 ATP are needed to make one glucose molecule and to complete the cycle
Even though there is an expenditure of energy in the Calvin Cycle, recall that one glucose molecule contains 90 times the stored energy contained in a molecule of ATP

Photosynthesis
2.) Light-Independent Reactions (Dark Reactions AKA Calvin Cycle)
~ occurs in stroma of the chloroplast
~ happens with and without light
~ Uses energy, ATP and NADPH, from light reactions to make Glucose
Calvin cycle
Photosynthesis Song

Do Now
I Need a Little Light (Photosynthesis Song) by Ross Durand
Use your notes on Photosynthesis to explain the following lyrics. Please write in complete sentences.
1.
“ I need a little light so I can store energy. I need a light like so I can make
ATP ”
2.
“ I ’ m sitting here in this chloroplast feeling green the whole day through.
”
3.
“ The ATP and NADPH are going to make a cycle go round.
”
Photosynthesis Song

I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I ’ m gunna make some food.
It ’ s out of sight, and I need a little light.
I ’ m sitting here in this chloroplast feeling green the whole day through.
You add a little thylakoid just a-waiting for something to do.
I ’ m going to move some electrons through a chain
And pump some Hydrogen in
But its been dark all night, and you can see the state I ’ m in.
So I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I ’ m gunna make some food.
It ’ s out of sight, and I need a little light.

When the electrons leave that chain
They ’ re going to join NADP
And that high concentration of hydrogen
Is gunna walk outside of me
It ’ s gunna go through a special protein,
It ’ s gunna kick some ATP out
But that ’ s what moving these elections is really all a-bout
So I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I ’ m gunna make some food.
It ’ s out of sight, and I need a little light.
The ATP and NADPH are going to make a cycle go round.
At the end of the Calvin cycle, glucose can be found.
You gotta put in 6 pieces of CO2 to make that precious food.
And use up the products of the thylakoid - darn this systems good

So I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I ’ m gunna make some food.
It ’ s out of sight, and I need a little light.
There ’ s one other thing I need besides light – it ’ s good old water.
And see that chlorophyll, that loses its electrons, needs to get some back - and that ’ s what the water does
But the whole reason that electron moved is because of the light
So I need a little light so I can store energy.
I need a little light so I can make ATP.
I need a little light; I ’ m gunna make some food.
It ’ s out of sight, and I need a little light.

u
PS  is  the  process  plants  use  to  turn  the  energy   in  sunlight  into  chemical  energy   u
Plants  are  autotrophs   u
There  are  two  major  steps  in  PS:
–   Light  reacDons  =  fix  energy
–   Light  Independent  ReacDons  (Dark  reacDons)  =  fix   carbon  into  G3P

u
The  light  reacDons  have  two  parts:
–   PS  system  II:  occurs  in  thylakoids,  absorbs  light
(P680),  creates  high  energy  electrons  and  H+,   forms  ATP,  splits  water  and  releases  O2
–   PS  I:  occurs  in  thylakoids,  absorbs  light  (P700),   makes  the  electron  carrier  NADPH

u
The  dark  reacDons  occur  as  the  Calvin  Cycle
–   CO2  is  removed  from  the  air
–   One  of  every  three  carbon  atoms  fixed  in  the
Calvin  cycle  is  used  to  make  glucose…the  rest  are   used  to  replenish  chemicals  used  in  the  cycle
–   Nine  ATP  equivalents  are  required  to  fix  each   carbon  to  complete  the  cycle

•   environment  effects  photosynthesis
•   rate  –  acDvity  per  unit  of  Dme
•   measure  CO
2
absorbed,  or  O
2
given  off
•   four  environmental  factors
•   light  intensity   -­‐  levels  off  at  certain  point,  can  determine  what   plant  grows  there  and  then  what  ecosystem  can  exist
•   Temperature   -­‐  opDmum  temperature  is  necessary,  or  freezing  or   denaturing  of  Calvin  cycle  enzymes  may  occur
•   []  of  CO
2
-­‐  as  CO a  certain  point  before  leveling  off
•   []  of  O
2
increases  so  does  the  rate  of  photosynthesis,  to
2
-­‐  an  increase  of  O
2
reduces  the  rate  of  photosynthesis
•   the  environmental  factors  play  together,  some  are  opDmum   while  others  are  minimum  so  they  have  a  combined  effect
•   limiDng  factors

•   PhotorespiraDon  –  light-­‐dependent  process   involving  the  uptake  of  oxygen  and  release  of   carbon  dioxide  that  occurs  along  with   photosynthesis  in  all  plants
•   CounterproducDve  to  photosynthesis
•   Prevents  incorporaDon  of  CO  in  the  Calvin  cycle   and  results  in  the  loss  of  previously  incorporated
CO
2
•   When  rubisco  binds  with  oxygen  in  the
chloroplast,  no  new  carbon  dioxide  is  fixed,  and
RuBP  is  converted  to  Carbon  dioxide
•   Photosynthesis  slows,  photorespiraDon   interferes  with  Calvin  cycle

•   C-­‐4      plants,  carbon  dioxide  is  first  incorporated   in  a  4-­‐carbon  acid  (that ’ s  where  the  name   comes  from)
•   Low  CO2,  high  light  and  temp
•   sugarcane,  corn,  crabgrass
•   special  features  keep  CO
2
low  in  an  area  so  it   diffuses  quickly  keeping  photosynthesis  running
•   And  CAM  plants  (crassulacean  acid  metabolism)
–  open  stomates  at  night,  desert  plants  –  cactus   and  jade  plants