Summary - IAL Edexcel Biology Unit 4: Photosynthesis

Week 1: Lead Lessons

Photosynthesis I



Adenosine triphosphate

 Universal energy currency
 Interference with production is fatal




 ENERGY NEEDED by cell ATP HYDROLYSED
 Forms ADP and INORGANIC PHOSPHATE (Pi)
 Releases energy = 34kJ mol^-1




How is it used?

 Some energy transferred to environment but most used in biology activity
 Reverse reaction also possible (requires same energy input) => PHOPHORYLATION)
 ATP can’t be stored in large amounts so is manufactured when needed from raw ingredients
 Once raw ingredients used up = no more ATP made [rigor mortis sets in post death]

, Making ATP
 ELECTRON TRANSPORT CHAIN (ETC)
 Also made by energy released in catabolic reactions



 Removal of hydrogen atoms from intermediate compounds in metabolic pathway

 Hydrogen atoms collected by carrier (REDUCED) and when hydrogen atoms given up
(OXIDISED)

 High energy e- from hydrogen atoms passed along ETC

 As e- passed along = small quantity of energy which drives synthesis of ATP




Photosynthesis

 Split in light dependent reactions (LDRs) and light independent reactions (LIRs or Calvin
Cycle)

1. Light energy used to break O-H bonds in water molecules
2. Hydrogen reacts with CO2 to form glucose
3. Oxygen released as waste product




Chloroplast structure