OCR Photosynthesis

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  • Created by: Yetunde
  • Created on: 08-11-11 19:02


  • C02 enters the leaves through the stomata
  • H20 enters from the roots moving up through the xylem
  • Light is the required energy source
  • Chlorophyll is required to absorb the light energy
  • Oxygen diffuses out of the stomata
  • Glucose is used in respiration

Photosynthesis - process whereby light energy from the sun is transformed into chemical energy and used to synthesise large organic molecules.

Define the term autotroph and heterotroph

Autotroph - able to synthesize complex organic molecules (carb/lipids/protein etc) using an energy source and inorganic molecules. They produce their own food. 2 types : Photoautotrophs (use light energy-photosynthesis) and chemoautotrophs (use energy from chemical reactions-respiation)

Heterotroph - digest organic complex molecules into simpler molecules to then resynthesize to make other complex molecules.

state that light energy is used during photosynthesis to produce complex organic molecules.

explain how respiration in plants and animals depend upon the products of photosynthesis

the Glucose produced is used in respiration 

C6H12016 + 02 -----> H20 + C02

Structure of chloroplast


  • Stroma - fluid filled matrix, the light independent stage takes place here.
  • Grana - Stacks of tylakoids, the light dependent stage takes place here (thylakoid membranes).

Adaptations of chloroplast 

  • chloroplasts have their own DNA and ribosome, so they are able to produce the proteins needed during photosynthesis.
  • stroma surrounds the grana so the products of the LDR can pass easily from the grana to the stroma to be used in the LIR.
  • Photosynthetic pigments arranged in special funnel shape clusters called photosystems allowing maximum light absorption 
  • many grana(stacks of thylakoids) provide a large surface area for the reactions to take place. (photosystems,atp synthase etc)
  • inner membrane consists of transport proteins controlling entrance of substances inside and outside the chloroplast.

Adaptations of Palisade cells/leaves for photosynthesis

  • Thin allowing gases to diffuse in and out quickly ( C02 in/02 out)
  • Large SA, maximising light absorption
  • Thin layer of waxy cuticle reducing the loss of water (evapouration) 
  • Stomata: open during the day(sunlight) allowing C02 to diffuse in and close at night reducing water loss.
  • spongy mesophyll : create air space making gaseous exchange more efficient and trap C02 allowing photosynthesis even when stomata close.


  • photo-system is a light-harvesting funnel consisting of photosynthetic pigments. They absorb certain light-waves and reflect others.
  • The primary reaction centre consists of Chlorophyll A in both photosystem 1 and 2
  • Accessory pigments are clusters around the photo-system (Chlorophyll B and Carotenoids) 


  • Consist of long phytol chain (hydrocarbon) chain and porphyin ring (Mg in the middle)
  • when light hits the chlorophyll, electrons associated with the Mg become excited 
  • 2 forms of chlorophyll a - P700 (PS1) and P680 (PS2)
  • accessory pigments - pass energy down to the primary reaction centre.


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