AQA A level Biology Topic 5 – Energy transfers in and between organisms notes (A* achieved)

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

2