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ATP  
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Adenosine  triphosphate  
Light  energy  from  the  sun  is  converted  by  plants  into  chemical  energy  
during  photosynthesis
...
 The  ATP  is  then  used  where  needed
...
 The  bonds  between  them  are  unstable  so  have  a  low  
activation  energy-­‐  they  can  be  easily  broken,  when  they  do  they  release  
a  large  amount  of  energy
...
 The  condensation  reaction  
(synthesis  of  ATP)  can  occur  in:  
• Photophosphorylation  (photosynthesis)  
• Oxidative  phosphorylation  (respiration)  
• Substrate  level  phosphorylation  (when  phosphate  groups  are  
transferred  from  donor  molecules  e
...
 in  the  formation  of  pyruvate  
at  the  end  of  glycolysis)    

 
Not  a  good  long  term  energy  store  (due  to  instability  of  phosphate  bonds)  
so  converted  to  fats/  glycogen  for  this
...
   
Roles  of  ATP  
• Metabolic  processes-­‐  e
...
 the  synthesis  of  polypeptides  from  amino  acids  
• Movement-­‐  energy  for  muscle  contraction  
• Active  transport-­‐  energy  to  change  the  shape  of  carrier  proteins  so  
molecules  can  move  against  their  gradient  through  plasma  membranes  
• Activation  of  molecules-­‐  can  lower  activation  enthalpy  of  molecules-­‐  
allow  enzyme  catalysed  reactions  to  occur  more  readily
...
   
Does  not  require  light  but  requires  the  products  from  the  LDR  
Carbon  dioxide  diffuses  through  the  stomata  and  dissolves  in  water  around  the  
walls  of  the  mesophyll  cells  
It  then  diffuses  through  the  plasma  membrane,  cytoplasm  and  chloroplast  
membranes  into  the  stroma  of  the  chloroplast    
It  combines  with  ribulose  bisphosphate  RuBp  using  an  enzyme  
GP-­‐  glycerate  3-­‐phosphate-­‐  and  TP-­‐  triose  phosphate-­‐  are  then  produce  
leading  to  the  regeneration  of  RuBp  (detailed  above)    

 
The  stroma  of  the  chloroplast  contains  DNA  and  ribosomes  to  quickly  manufacture  
some  of  the  proteins  needed  for  the  LIR
...
   

 
 

Factors  affecting  photosynthesis    

Limiting  factors  
• A  limiting  factor  is  one  which  limits  the  rate  of  a  process-­‐  is  at  the  least  
favorable  level
...
   
Light  intensity    
• When  light  is  the  limiting  
factor,  the  rate  of  
photosynthesis  is  directly  
proportional  to  light  
intensity
...
   
• At  this  point  there  will  be  no  
net  exchange  of  gasses  in  
and  out  of  the  plant-­‐  the  light  
compensation  point
...
   
Carbon  dioxide  concentration    
• Carbon  dioxide  needed  in  respiration  but  affects  enzyme  activity-­‐  e
...
 
enzyme  that  catalyses  the  joining  of  carbon  dioxide  and  RuBP  so  can  be  a  
limiting  factor  at  too  high  concentrations  
Temperature  
• Rate  of  photosynthesis  increases  in  direct  proportion  to  the  
temperature  up  to  about  25  degrees  
• After  this  rate  declines  due  to  enzyme  denaturation  (proves  that  the  
process  is  not  entirely  photochemical)  
• So  temperature  a  limiting  factor  
 
 
 
 
 
 
 
 

1
...
 
1) Glucose  is  activated  by  phosphorylation
...
 This  provides  the  
energy  to  activate  glucose  and  lowers  the  activation  energy  for  the  
enzyme-­‐controlled  reactions  to  follow  
2) Phosphorylated  glucose  is  split  into  2  3-­‐carbon  molecules  of  triose  
phosphate
...
 
4)  Enzyme-­‐controlled  reactions  then  convert  the  triose  phosphate  
molecules  into  pyruvate-­‐  as  they  loose  their  Pi  molecules,  ATP  can  be  
regenerated  from  ADP
...
   
 
 
 
 

The  link  reaction  
• The  pyruvate  molecules  produced  during  glycolysis  possess  potential  
energy  which  can  only  be  released  using  oxygen  in  a  process  called  the  
Krebs  cycle  
• First  they  must  be  oxidised  in  a  procedure  known  as  the  link  reaction
...
Pyruvate  molecules  produced  in  the  cytoplasm  during  glycolysis  are  
actively  transported  into  the  matrix  of  mitochondria
...
The  pyruvate  undergoes  decarboxylation-­‐  a  molecule  of  carbon  dioxide  
is  removed  from  each  molecule  
3
...
The  two  carbon  molecule  formed  combines  with  a  molecule  called  
acetylcoenzyme  A  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

The  Krebs  cycle  
• Acetylcoenzyme  A  (from  link  reaction)  combines  with  a  four-­‐
carbon  molecule  (oxaloacetate)  to  produce  the  6  carbon  citrate
...
 
 
1
...
The  reduced  NAD  and  FAD  are  oxidised  and  donate  electrons  to  
the  electron  carriers  which  pass  along  the  chain  loosing  energy  as  
they  go  in  a  series  of  redox  reactions  
3
...
The  protons  diffuse  back  across  the  membrane  along  the  
electrochemical  gradient  which  triggers  ATP  synthase  to  
produce  ATP  from  ADP  and  Pi  
5
...
 This  is  catalysed  by  cytochrome  
oxidase  (the  final  electron  carrier  in  the  chain)
...
   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Anaerobic  Respiration    
• In  the  absence  of  oxygen,  neither  the  Krebs  cycle  nor  the  electron  
transport  chain  can  take  place,  leaving  only  the  anaerobic  process  of  
glycolysis  as  a  potential  source  of  ATP

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