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AQA AL Biology notes Topic 5 – Energy transfers in and between organisms
Topic 5 – Energy transfers in and between organisms
Table of Content
5.1 Photosynthesis.............................................................................2
5.2 Respiration...................................................................................6
5.3 Energy and Ecosystems...............................................................10
5.4 Nutrient cycles............................................................................12
1
, AQA AL Biology notes Topic 5 – Energy transfers in and between organisms
5.1 Photosynthesis
Light-dependent reaction (LDR)
Where does LDR occur?
Thylakoid membranes of chloroplast or grana
Stages of LDR
1. Photoionisation of chlorophyll
Chlorophyll absorbs light energy
Light excites e-, leaving chlorophyll
2. Chemiosmotic theory
e- move along electron transport chain, releasing energy
o Energy used to actively transport H+ from stroma into thylakoid via chloroplast membranes
o Electrochemical gradient created across thylakoid membrane
+
3. H move by facilitated diffusion down concentration gradient into stroma via ATP synthase
o Energy used to join ADP+Pi(+H+)to produce ATP (photophosphorylation)
o H+ also combine with co-enzyme NADP & reduced by e- to form NADPH
4. Photolysis of water produces protons, electrons (to replace those lost from chlorophyll) & oxygen
Products of light dependent reaction
ATP & reduced NADP → light independent reaction
O2 → leaves cell as by-product / used in respiration
Light-independent reaction (Calvin cycle)
Where does LIR occur?
Stroma
Stages of LIR
CO2 combines with RuBP to form 2 molecules of GP catalysed
by rubisco (carboxylation/fixation)
GP reduced to TP using energy from ATP & NADPH from LDR
provides H+ to produce NADP
Some TP converted into useful organic substances eg hexose
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