A2 Biology - Photosynthesis

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PHOTOSYNTHESIS

  1. the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a by-product.



  2. THE LEAF IS THE MAIN PHOTOSYNTHETIC STRUCTURE 
  3. CHLOROPLASTS ARE THE ORGANELLES WITHIN THE LEAF WHERE PHOTOSYNTHEISS OCCURS 

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STRUCTURE OF THE LEAF

LEAVES ARE ADAPTED- TO BRING TOGETHER 3 MAIN RAW MATERIALS OF PHTOSYNTHESIS (WATER, CO2 AND LIGHT) 

  • LARGE SURFACE AREA - MAXIMISES LIGHT INTAKE 
  • ARRANGEMENT OF LEAFS TO AVOID SHADOWING 
  • THIN - SO DIFFUSION DISTANCE IS SHORT FOR LIGHT 
  • TRANSPARENT CUTICLE AND EPIDERMIS - LET LIGHT THROUGH TO MESPHYLL PHOTOSYNTHETIC CELLS 
  • LOTS OF STOMATA FOR GAS EXCHANGE 
  • STOMATA OPEN AND CLOSE TO CHNAGES IN LIGHT INTESNISTY 
  • NETWORK OF XYLEM THAT BRINGS WATEER TO LEAF AND PHLOEM WHICH CARRIES SUGARS 

EQUATION FOR PHOTOSYNTHESIS 

CO2 + WATER = GLUCOSE + OXYGEN 

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STRUCTURE AND ROLE OF CHLOROPLASTS

GRANUM - stacks of thykaloids

THYKALOID - where photosynthetic pigment chlorophyll is and where light dependent takes place 

STROMA - fluid filled matrix where light independent takes place 

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LIGHT DEPENDENT

LIGHT DEPENDENT REACTION INVOLVES THE CAPTURE OF LIGHT WHOSE ENERGY IS USED FOR 2 PURPOSES; 

  • ADD AN INORGANIC PHOSPHATE TO ADP - MAKING ATP 
  • TO SPIT WATER INTO IONS THROUGH PHOTOLYSIS 
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OXIDATION AND REDUCTION

OXIDATION - LOSS OF ELECTRONS, LOSS OF HYDROGEN OR GAIN OF OXGEN 

REDUCTION - GAIN OF ELECTRONS, GAIN OF HYDROGEN OR LOSS OF OXYGEN 

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PROCESS OF LDR

  1. PHOTON OF LIGHT HITS CHLOROPHYLL
  2. ENERGY FROM LIGHT TRANSFERRED TO 2 ELECTRONS - THEY BECOME EXITED 
  3. THEY LEAVE CHLOROPHYLL MOLECULES AND PASS ALONG ELECTRON CARRIERS EMBEDDED IN THYKALOID MEMBRANE 
  4. UNDERGO A SERIES OF REDOX REACTIONS 
  5. AS REACTIONS TAKE PLACE THEY LOSE ENERGY 
  6. ENERGY IS USED FOR SYNTHESIS OF ATP - PHOTOPHOSPHORYLATION 
  7. ELECTRONS LOST FROM CHLOROPHYLL MUST BE REPLACED 
  8. IN THYKALOID SPACE AN ENZYME CATALYSES THE PHOTOLYSIS OF WATER - SPLITS INTO OXYGEN, ELECTRONS AND HYDROGEN 
  9. ELECTRONS GO BACK TO CHLOROPHYLL
  10. ELECTRONS THAT PASSED ALONG ETC COMBIN ITH COENZYME NADP TO MAKE NADPH 
  11. OXYGEN FROM WATER - RELEASED AS WASTE PRODUCT OR USED IN RESPIRATION 
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SITE OF THE LDR

TAKES PLACE IN THYKALOIDS OF CHLOROPLASTS 

CHLOROPLASTS ARE ADAPTED TO CAPTURE LIGHT 

  • THYKALOIDS PROVIDE LARGE SURFACE AREA FOR ATTATCHMENT OF CHLOROPHYLL , ELECTRON CARRIERS AND ENZYMES THAT ARE INVOLVED IN LDR 
  • NETWORK OF PROTEINS NEAR GRANA HOLD CHLOROPHYLL IN A PRECIES MANNER TO MAXIMISE LIGHT ABSORBTION 
  • CHLOROPLASTS CONTAIN DNA AND RIBSOMES - THEY CAN QUICKLY MANAFACTURE PROTEINS NEEDED FOR LDR 
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LIGHT INDEPENDENT

PRODUCTS OF LIGHT DPENDENT REACTION - ATP AND NADPH ARE USED IN THE LIR

IT IS OTHERWISE KNOWN AS CALVIN CYCLE 

THEY CAN OCCUR IN LIGHT AND DARK 

TAKES PLACE IN THE STROMA 


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PROCESS OF LIR

  1. CO2 FROM THE ATMOSPHERE DIFFUSES IN THROUGH THE STOMATA AND COMBINES WITH A 5 CARBON COMPOUND CALLED RUBP
  2. THIS REACTION IS CATALYSED BY RUBISCO 
  3. FORMS A 6 CARBON COMPOUND SUGAR
  4. UNSTABLE SO IT BREAKS DOWN TO FORM 2 3 CARBON SUGARS CALLED TO GP 
  5. GP IS REDUCED TO TP USING THE HYDROGEN FROM NADPH AND ATP FOR ENERGY 
  6. SOME ATP IS USED TO CREATE CARBOHYDRATES
  7. MOST OF TP GOES BACK ROUND THE CYCLE AND FORMS RUBP
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SITE OF LIR

TAKES PLACE IN STROMA OF THE CHLOROPLASTS 

CHLROPLAST IS ADAPATED FOR LIR ....

  • FLUID OF STGROMA CONTAINS ENZYMES NEEDED TO CARRY OUT LIR 
  • STROMA FLUID SURROUNDS GRANA - SO PRODCUTS OF LDR CAN READILY DIFFUSE INTO STROMA 
  • IT CONTAINS BOTH DNA AND RIBOSOMES - IT CAN MAKE PROTEINS NEEDED FOR LIR. 
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FACTORS AFFECTING PHOTOSYNTHESIS

A LIMITING FACTOR - AT ANY GIVEN MOMENT, THE RATE OF PHYSIOLOGICAL PROCESS IS LIMITED BY THE FACTOR THAT IS AT ITS LEAST FAVORABLE VALUE

2 WAYS THAT PHOTOSYNTHESIS IS MEASURED 

  • VOLUME OF OXYGEN RELEASED 
  • VOLUME OF CO2 TAKEN UP 

THREE PROCESSES THAT ARE LIMITING FACTORS TO PHOTOSYNTHESIS

  • LIGHT INTENSITY 
  • CO2 CONCENTRATION
  • TEMPERATURE
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LIGHT INTENSITY ON PHOTOSYNTHESIS

WHEN LIGHT IS LIMITING FACTOR - RATE OF PHOTOSYNTHEISIS IS DIRECTLY PROPORTIONATE TO LIGHT INTENISITY

AS LIGHT INTENSITY INCREASE 

OXYGEN PRODUCED AND CO2 ABSORBTION WILL INCREASE 

POINT WILL BE REACHED WHERE FURTHER INCREASES WILL HAVE NO EFFECT ON PHOTOSYNTHESIS 

THEN ANOTHER LIMITING FACTOR WILL BE LIMITING THE REACTION 

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LIGHT INTENSITY ON PHOTOSYNTHESIS

WHEN LIGHT IS LIMITING FACTOR - RATE OF PHOTOSYNTHEISIS IS DIRECTLY PROPORTIONATE TO LIGHT INTENISITY

AS LIGHT INTENSITY INCREASE 

OXYGEN PRODUCED AND CO2 ABSORBTION WILL INCREASE 

POINT WILL BE REACHED WHERE FURTHER INCREASES WILL HAVE NO EFFECT ON PHOTOSYNTHESIS 

THEN ANOTHER LIMITING FACTOR WILL BE LIMITING THE REACTION 

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CO2 CONCENTRATION ON PHOTOSYNTHESIS

CO2 CONCENTRATION AFFECTS ENZYME ACTIVITY 

AN INCREASE IN THE CO2 AVALAIBLE GIVES AN INCREASE IN THE RATE OF PHOTOSYNTHESIS 

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TEMPERATURE AND PHOTOSYNTHESIS

RATE OF PHOTOSYNTHESIS INCREASES IN DIRECT PROPORTION TO THE TEMPERATURE 

REACHES AN OPTIMUM TEMP OF 25 DEGREES 

ABOVE 25 THE RATE LEVELS OFTEN DECREASE BECAUSE OF ENZYMES DENATURING 

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