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C12 Energy and Respiration Cheat Sheet by

CIE ALevel A2 bio summary 2022


Use of energy in organism?
photos­ynt­hesis, anabolic reacti­ons(DNA replic­ation, protein synthe­sis), active transport, homeos­tasis, muscle contra­ction, exocyt­osis, biolum­ine­cence
Why ATP is universal energy currency?
stable­,re­cyc­lable, small, water-­sol­uble, quick hydrol­ysi­s(3­0.5­kJm­ol-1), energy wastage low,
Synthesis of ATP?
transfer of phosphate in substr­ate­-linked reaction, chemio­smosis in crista­e/grana membrane
Compare relative energy values...
highest to lowest, carb, lipid, protein, more hydrogen atoms, more H atom transp­orted by NAD/FAD, greater proton gradient, more ATP formed via chemio­smosis
Define Respir­atory Quotient (RQ)
ratio of carbon dioxide released over oxygen used
RQ of different substrates
Carb=1, Lipid=0.7, Protei­n=0.9

Link reaction

Krebs cycle

Oxidative phosph­ory­lation


Adapta­tions of mitoch­ondria
large surface area -able to hold many ETC and ATP synthase,
Outline lactate fermen­tation
one step process, after glycol­ysis, pyruvate is the hydrogen acceptor to form lactate. Lactate can be oxidized back to pyruvate or stored as glycogen in liver.
Outline ethanol fermen­tation
2 step process, after glycol­ysis, pyruvate is decarb­oxy­lated to ethanal, then reduced by alcohol dehydr­ogenase to form ethano­l.E­thanol cannot be further metabo­lised, it is toxic.
Energy yield comparison between aerobic and anaerobic
oxidation of glucose in anaerobic is incomp­lete. Only 2 ATP formed in glycol­ysis. Large amount of ATP form in stages in mitoch­ondria.
Rice adaptation to grow under water
Ethanol stimulates production of gibber­ellin, growth regulator. Rice has high tolerance to ethanol as they produce ethanol dehydr­oge­nase. Develo­pment of aerenchyma which is a specia­lised plant tissue that has lots of air spaces that allow storing of gas even underwater

Respir­ometer (inves­tigate RQ)


4 stages of aerobic respir­ation
glycol­ysi­s-c­yto­plasm, link reaction and Krebs cycle-­mit­och­ondrial matrix, oxidative phosph­ory­lat­ion­-cr­istae
Outline glycolysis
phosph­ory­lation of glucose, splitting of fructose 1,6-bi­sph­osphate into 2 triose phosphate, oxidation of triose phosphate and dephos­pho­ryl­ation of interm­ediate substrates into pyruvate
Product of glycolysis
used 2 ATP in phosph­ory­lation, form 2NADH and 4 ATP during oxidation (nett 2 ATP, 2 NADH, 2 pyruvate)
When does pyruvate enter mitoch­ondrial matrix
when oxygen is available to take part in link reaction
Outline Link reaction
decarb­oxy­lation and dehydr­oge­nation of pyruvate
Product of Link reaction
acetate, CO2 and NADH
Role of Coenzyme A
carrie­r,binds to acetate to form acetyl coA, transport and supply acetate to Krebs cycle
Outline Krebs cycle
enzyme controlled reactions, oxoloa­cetate accepts acetate from acetyl coA-forms citrate, oxaloa­cetate reformed by decarb­oxy­lation, dehydr­oge­nation and reduction of NAD and FAD
Role of NAD and FAD
coenzymes to dehydr­oge­nase, transports hydrogen to electron transport chain for oxidative phosph­ory­lation (NADH=­3ATP, FADH2=­3ATP)
Outline oxidative phosph­ory­lation
NADH/FADH2 oxidise at electron carriers, H atom splits into proton and energetic electron. Electron travels through electron transport chain which supplies energy for proton pumps. Proton pumped from matrix to interm­embrane space and proton gradient formed. Proton facili­tated diffusion by ATP synthase, moves down gradient into matrix, energy for ATP synthesis.
Role of oxygen in oxidative phosph­ory­lation
final electron acceptor to form water. if no oxygen, electrons and hydrogen have nowhere to go, ETC stops and NAD/FAD unable to regene­rate.

Lactate fermen­tation

Ethanol fermen­tation

Methylene blue (measure rate of respir­ation)



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