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BIOLOGY  
 
F214:  Communication,  Homeostasis  and  Energy      
1) Respiration  
a) Outline   why   plants,   animals   and   microorganisms   need   to   respire,   with   reference   to   active  
transport  and  metabolic  reactions  
i) Respiration   –   process   whereby   energy   stored   in   complex   organic   molecules  
(carbohydrates,  fats  and  proteins)  is  used  to  make  ATP  
(1) Respiration  takes  place  in  all  living  cells  
ii) Metabolic  reactions  –  biochemical  reactions  that  take  place  within  organisms  
iii) Anabolic  reactions  –  metabolic  reactions  that  build  large  molecules  
iv) Catabolic  reactions  –  metabolic  reactions  that  break  large  molecules  into  smaller  ones  
v) Reasons  why  we  need  energy  
(1) Active   transport   –   moving   ions   and   molecules   across   a   membrane   against   a  
concentration  gradient  
(2) Secretion  –  large  molecules  made  in  some  cells  are  exported  by  exocytosis  
(3) Endocytosis  –  bulk  movement  of  large  molecules  into  cells  
(4) Synthesis   –   of   large   molecules   from   small   ones   eg
...
 flagella  in  bacteria  and  undulipodia  in  eukaryotic  
cells  
(7) Activation  of  chemicals  –  glucose  is  phosphorylated  at  the  beginning  of  respiration  so  
that  it  is  unstable  and  can  be  broken  down  to  release  energy  
 
b) Describe,  with  the  aid  of  diagrams,  the  structure  of  ATP  
i) ATP  =  phosphorylated  nucleotide  –  a  high-­‐energy  intermediate  compound  
ii) Each  molecule  consists  of:  
(1) Adenosine  –  adenine  and  ribose  sugar  
(2) Three  phosphate  groups  

iii) ATP  cycle  

(1) ATP   is   hydrolysed   to   ADP   +   Pi   –   releasing   30
...
 Nicotinamide  adenine  dinucleotide  
(d) Made  of  two  linked  nucleotides  
(e) One  nucleotide  contains  adenine,  the  other   contains  a  
nicotinamide  ring  that  can  accept  up  to  two  hydrogen  
atoms   (is   reduced)   or   loses   hydrogen   atoms   (is  
oxidised)  
(2) Function  
(a) During  glycolysis,  the  link  reaction  and  Krebs  cycle  
–   hydrogen   atoms   are   removed   from   substrate  
molecules  (oxidation  reactions)  
(b) NAD   helps   dehydrogenase   enzymes   carry   out   these  
reactions  
(c) NAD  carries  the  hydrogen  atoms  to  the  inner  mitochondrial  membranes  
(d) Hydrogen  atoms  can  be  split  into  hydrogen  ions  and  electrons  
(e) Hydrogen  ions  then  involved  in  oxidative  phosphorylation  –  producing  lots  of  ATP  
(f) Delivery   of   hydrogens   to   the   cristae   reoxidises   the   coenzymes   so   they   can  
combine  with  more  hydrogen  atoms  from  the  first  three  stages  of  respiration  
ii) Coenzyme  A  (CoA)  
(1) Made  from  pantothenic  acid  (B  group  vitamin),  adenosine  (ribose  +  adenine),  three  
phosphate  (phosphoryl)  groups  and  a  cysteine  (amino  acid)  group  
(2) Carries  acetate  groups  made  from  pyruvate  (during  Link  Reaction)  onto  Krebs  cycle  

(3) Can   also   carry   acetate   groups   that   have   been   made   from   fatty   acids   or   from   some  
amino  acids  onto  Krebs  cycle  

 
e) State  that  glycolysis  takes  place  in  the  cytoplasm  
i) Hydrolysis  –  breaking  down  of  large  molecules  to  smaller  molecules  by  adding  water  
ii) Glycolysis   –   metabolic   pathway   where   each   glucose   molecules   is   broken   down   to   two  
molecules  of  pyruvate  (the  oxidation  of  glucose  to  pyruvate)  
iii) Takes  place  in  the  cell  cytoplasm  in  both  prokaryotic  and  eukaryotic  cells  
iv) First  stage  of  respiration  common  to  both  aerobic  and  anaerobic  respiration  
v) 2  ATP  molecules  are  consumed  in  initial  phosphorylation  (adding  phosphate)  reactions  
vi) 4  ATP  molecules  are  produced  by  substrate  level  phosphorylation  
vii) Therefore,  products…  
(1) Net  gain  of  2  ATP  molecules  per  glucose  molecule  
(2) 4  hydrogen  atoms  transported  to  electron  transfer  chain  (as  2  molecules  of  reduced  
NAD  (NADH2)  form  
(3) 2  molecules  of  pyruvate  (pyruvic  acid)  produced  for  every  glucose  molecule  
 

f) Outline  the  process  of  glycolysis  
beginning  with  the  
phosphorylation  of  glucose  to  
hexose  bisphosphate,  splitting  
of  hexose  bisphosphate  into  two  
triose  phosphate  molecules  and  
further  oxidation  to  pyruvate,  
producing  a  small  yield  of  ATP  
and  reduced  NAD  
i) Glucose  (hexose  6-­‐Carbon  
sugar)  needs  to  be  activated  
ii) ATP  hydrolysed  to  ADP  +  Pi  
iii) Pi  attaches  to  the  carbon-­‐6  
iv) Glucose  6-­‐phosphate  produced  
v) Another  ATP  is  hydrolysed  
vi) Phosphate  attached  to  the  
carbon-­‐1  
vii) Fructose  1,6-­‐bisphosphate  produced    
viii) Molecule  is  symmetrical  so  it  
has  a  high  activation  energy  
(activated)  and  so  is  more  
reactive  
ix) Energy  from  the  hydrolysed  
ATP  molecules  activates  the  
hexose  sugar  
x) Hexose  1,6  bisphosphate  
splits  into  two  x  3-­‐carbon  
sugars  –  2  x  triose  
phosphates  
xi) Dehydrogenase  enzymes  are  used  to  remove  two  hydrogen  atoms  from  each  triose  
phosphate  –  oxidising  it  as  electrons  are  lost  with  the  hydrogen  (anaerobic  process)  
xii) The  hydrogen  atoms  are  carried  away  by  NAD  (hydrogen  acceptor)  
xiii) NAD  becomes  reduced  NAD  (or  NADH2)  as  it  combines  with  hydrogen  atoms  
xiv) The  rearrangement  of  the  molecule  makes  new  bonds  
xv) Substrate   level   phosphorylation   –   energy   released   from   making   the   new   bonds   makes  
ATP  from  ADP  +  Pi  (the  Pi  is  free  floating  in  the  cytoplasm)  
xvi) Another  isomerisation  means  another  ATP  molecule  is  formed  from  ADP  +  Pi  (this  time  
the  Pi  is  from  the  triosphosphate)  
xvii) Final  products  
(1) 2  x  3-­‐carbon  pyruvates  –  normally  actively  transported  into  the  mitochondrial  matrix  
for  the  next  stage  of  aerobic  respiration  (or  lactate/ethanol  in  anaerobic  conditions)  

(2) 2  molecules  of  reduced  NAD  (to  carry  the  hydrogen  atoms  to  the  inner  mitochondrial  
membranes  to  generate  more  ATP  during  oxidative  phosphorylation)  
(3) …  Including  4  hydrogen  atoms  
(4) 4  ATPs  –  but  a  net  gain  of  2  ATPs  
 
g) State   that,   during   aerobic   respiration   in   animals,   pyruvate   is   actively   transported   into  
mitochondria  
i) During   aerobic   respiration   in   animals,   each   pyruvate   is   actively   transported   into   a  
mitochondrion  
ii) Glucose   itself   cannot   enter   directly   as   there   are   no   protein   channels   in   the   inner   and  
outer  cell  surface  membranes  of  the  mitochondria  for  it  to  enter  through  
 
h) Explain,   with   the   aid   of   diagrams   and   electron   micrographs,   how   the   structure   of  
mitochondria  enables  them  to  
carry  out  their  functions  
i) Structure  of  mitochondria  
–  organelles  found  in  
eukaryote  cells  that  are  
the  sites  of  the  Link  
Reaction,  Krebs  cycle  and  
oxidative  phosphorylation  
(aerobic  stages  of  
respiration)  
(1) Envelope  –  inner  and  
outer  phospholipid  
membranes  
(2) Smooth  outer  phospholipid  membrane  
(3) Inner   phospholipid   membrane   folded   into   cristae   –   giving   the   inner   membrane   a  
large  surface  area  
(4) Intermembrane  space  –  between  the  inner  and  outer  membrane  
(5) Matrix  –  semi-­‐rigid  and  gel-­‐like  section  enclosed  by  inner  membrane  consisting  of  a  
mixture   of   proteins   and   lipids   (also   contains   a   looped   mitochondrial   DNA,  
mitochondrial  ribosomes  and  enzymes)  
ii) Shape,  size  and  distribution  
(1) Changeable  rod-­‐shaped  (can  also  be  thread-­‐like)  
(2) Range   between   0
...
0   micrometres   in   diameter,   and   2-­‐5   micrometres   long   (some  
can  be  10  micrometres  long)  
(3) Can  be  moved  around  cells  by  the  cytoskeleton  (microtubules)  
(4) Mitochondria   can   be   permanently   positioned   near   a   site   of   high   ATP   demand   eg
...
 Mammalian  liver  cell  may  contain  up  to  2500  mitochondria  (20%  of  cell  volume)  
iii) Outer  membrane  
(1) Phospholipid  composition  (similar  to  membranes  around  other  organelles)  
(2) Can  include  channels  or  carries  that  allow  the  passage  of  molecules  eg
...
 stalked  particles  
(a) Large  and  protrude  from  the  inner  membrane  into  the  matrix  
(b) Allows  protons  to  pass  through  them  via  the  channel  part  of  the  enzyme  
(6) FAD  (flavine  adenine  dinucleotide)  dehydrogenase  enzyme  
(a) FAD  is  bound  to  a  dehydrogenase  enzyme  embedded  in  the  inner  membrane  
(b) Hydrogen   atoms   accepted   by   FAD   do   not   get   pumped   into   the   intermembrane  
space  –  they  stay  back  in  the  mitochondrial  matrix  
v) Matrix  –  site  of  the  Link  Reaction  and  Krebs  cycle  containing…  
(1) Enzymes  that  catalyse  stages  in  the  Link  Reaction  and  Krebs  cycle  
(2) Molecules  of  coenzyme  NAD  
(3) Oxaloacetic  –  4  carbon  compound  that  accepts  acetate  from  the  Link  Reaction  
(4) Mitochondrial  DNA  –  some  codes  for  mitochondrial  enzymes  and  other  proteins  
(5) Mitochondrial  ribosomes  –  where  proteins  are  assembled  
 
i) State  that  the  link  reaction  takes  place  in  the  mitochondrial  matrix  
j) Outline  the  link  reaction,  with  reference  to  decarboxylation  of  pyruvate  to  acetate  and  the  
reduction  of  NAD  
k) Explain  that  acetate  is  combined  with  coenzyme  A  to  be  carried  to  the  next  stage  

i) Link  Reaction  –  converts  pyruvate  to  acetate,  NAD  is  reduced    
(NB:  no  ATP  is  produced)  
ii) Link  Reaction  occurs  in  the  mitochondrial  matrix  
iii) Pyruvate   is   actively   transported   into   the   matrix   of  
the   mitochondria,   across   the   inner   and   outer  
mitochondrial  membranes  
iv) Decarboxylation   of   pyruvate   occurs   with   the   aid   of  
pyruvate   decarboxylase   enzymes   (removing   a  
carboxyl  group  which  eventually  becomes  CO2)  
v) Dehydrogenation   occurs   with   the   aid   of   pyruvate  
dehydrogenase  enzymes  
vi) NAD   is   reduced   to   form   reduced   NAD   –   accepting  
the   hydrogen   atoms,   taking   them   to   the   inner   mitochondrial   membrane   to   make   ATP  
during  oxidative  phosphorylation  
vii) Coenzyme  A  (CoA)  accepts  acetate…  
viii) Product  –  acetyl  coenzyme  A  (2-­‐carbon)  to  be  carried  to  the  next  stage  (Krebs  Cycle)  
ix) 2  Pyruvate  +  2NAD+  +  2CoA  à  2CO2  +  2  reduced  NAD  +  2  acetyl  CoA  
 
l) State  that  the  Krebs  cycle  takes  place  in  the  mitochondrial  matrix  
m) Outline   the   Krebs   cycle,   with   reference   to   the   formation   of   citrate   from   acetate   and  
oxaloacetate   and   the   reconversion   of   citrate   to   oxaloacetate   (names   of   intermediate  
compounds  are  not  required)  
n) Explain   that   during   the   Krebs   cycle,   decarboxylation   and   dehydrogenation   occur,   NAD   and  
FAD  are  reduced  and  substrate  level  phosphorylation  occurs  
i) Krebs  Cycle  –  series  of  small  steps  catalysed  by  enzymes,  oxidising  acetate  to  CO2,  NAD  
and  FAD  are  reduced  and  ATP  is  made  by  substrate  level  phosphorylation  
ii) The  Krebs  Cycle  takes  place  in  the  mitochondrial  matrix  
iii) Acetate  is  offloaded  from  coenzyme  A  (then  free  to  collect  more  acetate)  
iv) Citrate  (6-­‐C)  is  the  first  intermediate  formed  from  the  4-­‐carbon  oxaloacetate  (acceptor  
molecule)  and  the  2-­‐carbon  acetate  
v) Decarboxylation   –   2   molecules   of   carbon   dioxide   are   released   per   turn   of   the   cycle,  
catalysed  by  decarboxylase  enzymes  
vi) Dehydrogenation   –   4   pairs   of   hydrogen   atoms   are   released   per   turn   of   the   cycle,  
catalysed  by  dehydrogenase  enzymes  
vii) This   leaves   a   4   carbon   compound   which   is   changed   into   another   4   carbon   compound  
during  which  ATP  is  formed  by  substrate  level  phosphorylation  
viii) The  second  4  carbon  compound  is  changed  into  another  4  carbon  compound  –  a  pair  of  
hydrogen  atoms  is  removed  and  accepted  by  FAD  (to  produce  reduced  FAD)  
ix) The  third  4  carbon  compound  is  further  dehydrogenated  and  regenerates  oxaloacetate  –  
another  molecule  of  NAD  is  reduced    
x) 4   pairs   of   hydrogen   atoms   are   picked   up   by   NAD   and   FAD   (hydrogen   acceptors)   –  
resulting  in  6  NAD  and  2  FAD  both  becoming  reduced  per  glucose  molecule  (two  turns)  

xi) Amino  acids  and  fatty  acids  can  also  be  fed  into  the  cycle  

 
Product  per  molecule  of  glucose   Link  Reaction   Krebs  Cycle  (2  turns  of  the  cycle)  
Reduced  NAD  
2  
6  
Reduced  FAD  
0  
2  
Carbon  Dioxide  
2  
4  
ATP  
0  
2  
 
o) Outline   the   process   of   oxidative   phosphorylation,   with   reference   to   the   roles   of   electron  
carriers,  oxygen  and  the  mitochondrial  cristae  
p) Outline  the  process  of  chemiosmosis,  with  reference  to  the  electron  transport  chain,  proton  
gradients  and  ATPsynthase  (HSW7a)  
q) State  that  oxygen  is  the  final  electron  acceptor  in  aerobic  respiration  
i) Oxidative   Phosphorylation   takes   place   on   the   cristae   –   on   and   within   the   inner  
membrane  of  the  mitochondrion    
ii) Key  Definitions  
(1) Oxidative  phosphorylation  –  formation  of  ATP  by  adding  a  phosphate  group  to  ADP  
in  the  presence  of  oxygen  (the  final  electron  acceptor)  
(2) Chemiosmosis   –   the   diffusion   of   ions   through   a   partially   permeable   membrane   –  
specifically   the   flow   of   protons   through   channels   of   ATP   synthase   enzymes   and  
across   the   inner   mitochondrial   membrane,   down   the   proton   gradient   from   the  
intermembrane  space  to  the  mitochondrial  matrix  

(3) Proton   Motive   Force   –   force   generated   by   the   flow   of   protons   which   changes   the  
configuration  of  parts  of  ATP  synthase  and  causes  ADP  and  Pi  to  join  to  make  ATP  
(4) Oxido-­‐reductase   enzyme   –   enzyme   that   catalyses   a   reduction   reaction   that   is  
coupled  with  an  oxidation  reaction  
iii) Hydrogens   are   brought   to   the   Electron   Transport   Chain   (ETC)   on   the   cristae   of   the  
mitochondrion  by  the  coenzymes  NAD  and  FAD  (reduced  in  the  mitochondrial  matrix)  
iv) Hydrogens  split  forming  H+  ions  (protons)  and  electrons  using  dehydrogenase  enzymes  
v) The  electrons  pass  along  a  series  of  electron  carriers/cytochromes  (protein  complexes),  
at  three  places  in  the  chain  the  electrons  drop  to  a  lower  energy  level  
vi) The   first   electron   carrier   is   complex   I   (aka
...
 
NADH  dehydrogenase)  
vii) The  last  electron  carrier  is  called  cytochrome  oxidase  
viii) Each   protein   complex   is   associated   with   a   co-­‐factor   –   the   iron   ion   which   accepts  
electrons  to  form  Fe2+  but  is  oxidised  to  Fe3+  (alternately  reduced  and  oxidised)  
ix) As   the   electrons   are   transferred   from   one   complex   to   the   next   along   the   series   of  
electron  carriers,  a  small  yet  sufficient  amount  of  energy  is  released  
x) The   coenzymes   associated   with   complexes   I,   III   and   IV   pump   H+   ions   through   to   the  
intermembrane  space  
xi) The  inner  and  outer  membranes  are  impermeable  to  small  ions  so  the  proton  gradient  
(also  a  pH  and  electrochemical  gradient)  builds  up  as  hydrogens  ions  accumulate  in  the  
intermembrane  space,  creating  a  potential  source  of  energy  
xii) Chemiosmosis   –   protons   pass   back   through   the   ion   channels   of   the   ATP   synthase  
enzymes,   flowing   down   the   proton   gradient   from  
the  intermembrane  space  to  the  matrix  
xiii) A  proton  motive  force  is  created  
xiv) This  drives  the  rotation  of  the  headpiece  on  the  ATP  
synthase  enzyme  
xv) The  force  allows  the  phosphorylation  of  ADP  to  ATP  
xvi) The   electrons   are   passed   from   the   last   electron  
carrier  in  the  chain  to  molecular  oxygen  
xvii) Oxygen   is   the   final   electron   and   proton   acceptor  
(essential   for   aerobic   respiration   only   as   it   is  
required  for  oxidative  phosphorylation)  
xviii) Oxygen   accepts   an   electron   and   a   hydrogen   joins  
the  electron  –  oxygen  is  reduced  to  water  
xix) 4H+  +  4e-­‐  +  O2  à  2H2O  
xx) The  next  electron  can  then  move  along  the  ETC  
 
 
 
 
 

  
r) Evaluate  the  experimental  evidence  for  the  theory  of  chemiosmosis  (HSW1)  
i) More  detailed  structure  of  the  mitochondria  was  only  discovered  in  the  1960s  
ii) 1978  –  Peter  Mitchell  received  the  Nobel  Prize  for  chemistry  and  chemiosmosis  theory  
iii) Modern  researchers  have  treated  isolated  mitochondria  by  placing  them  in  solutions  of  
very  low  water  potential  so  that  the  outer  membrane  is  ruptured  –  forming  mitoblasts    
iv) With   strong   detergent,   they   could   also   rupture   the   inner   membrane   and   release   the  
contents  of  the  mitochondrial  matrix  
v) Allowed   them   to   work   out   that   the   Link   Reaction   and   Krebs   Cycle   take   place   in   the  
mitochondrial  matrix  and  the  ETC  are  embedded  in  the  inner  membrane  
vi) Lower  pH  in  the  intermembrane  space  than  in  the  mitochondrial  matrix  
(1) High  acidity  is  caused  by  an  accumulation  of  H+  ions  
(2) Intermembrane  space  has  a  low  pH  due  to  an  accumulation  of  hydrogen  ions  here  
(3) This   fits   with   the   idea   that   hydrogen   ions   are   pumped   out   of   the   mitochondrial  
matrix  by  active  transport  into  the  intermembrane  space  
vii) The  more  negative  potential  on  the  matrix  side  of  the  inner  mitochondrial  membrane  
(1) A  negative  potential  on  the  matrix  side  of  the  inner  mitochondrial  membrane  proves  
the  existence  of  a  proton  gradient    
(2) Proton   gradient   must   have   a   high   concentration   of   protons   in   the   intermembrane  
space  and  a  lower  concentration  in  the  mitochondrial  matrix  
viii) No  ATP  made  in  mitoblasts  (mitochondria  stripped  of  their  outer  membrane)  
(1) Stripping   mitochondria   of   their   outer   membrane   releases   the   contents   of   the  
intermembrane  space  
(2) No  ATP  is  produced  as  the  intermembrane  space  is  involved  in  the  production  of  ATP  

(3) The   hydrogen   ions   cannot   accumulate   in   the   intermembrane   space,   producing   a  
proton  gradient    
ix) No  ATP  made  if  headpieces  are  removed  from  the  stalked  particles  
(1) Shows  that  the  headpieces  of  the  ATP  synthases  have  a  role  in  the  production  of  ATP  
(2) During   chemiosmosis,   the   headpieces   act   as   rotors   which   spin   due   to   the   proton  
motive  force  produced  
(3) This  force  is  produced  when  hydrogen  ions  pass  back  from  the  intermembrane  space  
into  the  mitochondrial  matrix,  allowing  the  phosphorylation  of  ADP  to  ATP  
x) No  ATP  made  in  the  presence  of  oligomycin  
(1) Oligomycin  is  an  antibiotic  that  blocks  the  flow  of  protons  through  the  ion  channel  
part  of  the  ATP  synthase  enzymes  
(2) If  the  ion  channel  is  blocked  by  oligomycin,  no  ATP  is  produced  
(3) Shows  that  the  ion  channel  has  a  role  in  the  production  of  ATP  during  chemiosmosis  
(4) The  ion  channel  is  required  in  chemiosmosis  to  allow  the  hydrogen  ions  to  pass  down  
the  proton  gradient    
(5) The  movement  of  hydrogen  ions  across  the  cristae  of  the  mitochondria,  moving  back  
into  the  mitochondrial  matrix,  produces  a  proton  motive  force  
(6) There  is  sufficient  energy  to  form  ATP  from  ADP  and  Pi  (phosphorylation  of  ADP)  
xi) Coenzymes  within  complexes  I,  III  and  IV  can   use  energy  released  from  the  transfer  of  
electrons   to   pump   hydrogen   ions   across   the   inner   mitochondrial   membrane   to   the  
intermembrane  spaces  
(1) Coenzymes   in   the   electron   transfer   chain   can   pump   protons   actively   using   energy  
released  from  the  inner  mitochondrial  membrane  to  the  intermembrane  space  
(2) Hydrogen  ions  are  able  to  accumulate  in  the  intermembrane  space  creating  a  proton  
gradient  
(3) This  proton  gradient  is  essential  for  the  protons  to  move  back  into  the  mitochondrial  
matrix  as  this  produces  the  proton  motive  force  that  allows  the  phosphorylation  of  
ADP  to  ATP  
 
s) Explain  why  the  theoretical  maximum  yield  of  ATP  per  molecule  of  glucose  is  rarely,  if  ever,  
achieved  in  aerobic  respiration  
i) Per  glucose  molecule…  
(1) Glycolysis  –  (net)  2  molecules  of  ATP  
(2) Krebs  Cycle  –  2  molecules  of  ATP  
(3) Reduced   NAD   =   10   molecules   can   theoretically   yield   26   molecules   of   ATP   during  
oxidative  phosphorylation  
(a) Glycolysis  –  2    
(b) Link  –  2    
(c) Krebs  Cycle  –  6  
(4) Reduced  FAD  =  2  
(a) Glycolysis  –  0    
(b) Link  –  0    

(c) Krebs  Cycle  –  2  
(5) Therefore  the  total  yield  per  glucose  molecule  should  =  30  molecules  of  ATP  
ii) Roles  of  NAD  and  FAD  
(1) Both  provide  electrons  to  the  electron  transport  chain  for  oxidative  phosphorylation  
(2) Reduced   NAD   also   provides   hydrogen   ions   that   contribute   to   the   build   up   of   a  
protein  gradient  for  chemiosmosis  
(3) The  hydrogen  ions  from  reduced  FAD  stay  in  the  matrix  but  can  combine  with  oxygen  
to  form  water  
iii) Why  the  maximum  yield  per  molecule  of  glucose  is  theoretical  and  rarely  achieved  
(1) Some   protons   leak   across   the   mitochondrial   membrane,   reducing   the   number   of  
protons  to  generate  the  proton  motive  force  
(2) Some  ATP  is  used  to  actively  transport  the  pyruvate  into  the  mitochondria  
(3) Some  ATP  is  used  to  bring  hydrogen  from  reduced  NAD  made  during  glycolysis,  in  the  
cytoplasm,  into  the  mitochondria  
 
t) Explain   why   anaerobic   respiration   produces   a   much   lower   yield   of   ATP   than   aerobic  
respiration  
i) Anaerobic   respiration   –   release   of   energy   in   the   form   of   ATP   from   substrates,   eg
...
  when   running   where  
the  demand  for  oxygen  is  high  (muscle  contraction)  and  oxygen  deficit  is  the  result  
(2) Reduced  NAD  must  be  reoxidised  to  NAD+  
(3) Pyruvate  is  the  hydrogen  acceptor  –  accepting  hydrogen  atoms  from  reduced  NAD    
(4) NAD   is   now   reoxidised   and   is   available   to   accept   more   hydrogen   atoms   from   glucose  
during  glycolysis  
(5) This  is  catalysed  by  lactate  dehydrogenase  –  reducing  pyruvate  to  lactate  too  
(6) Glycolysis  can  continue,  generating  enough  ATP  to  sustain  muscle  contraction  
(7) Lactate  produced  is  carried  away  in  the  blood,  from  the  muscles,  to  the  liver  
(a) When  more  oxygen  is  available,  the  lactate  can  be  converted  back  to  pyruvate  
(b) The   pyruvate   may   then   enter   the   Krebs   Cycle   via   the   Link   Reaction   or   be   recycled  
to  glucose  and  glycogen  
(c) The   reduction   in   pH   due   to   the   build   of   lactate   will   cause   muscle   fatigue   as  
enzyme  activity  in  the  muscles  is  reduced  –  not  due  to  the  excess  lactate  itself  
(8) Cyanide  –  a  respiratory  poison  
(a) Has  no  effect  on  the  production  of  lactate  from  glucose  
(b) Binds  to  cytochrome  oxidase  (the  final  carrier  on  the  electron  transport  chain)  
(c) Electrons  cannot  pass  along  the  electron  transport  chain  and  NAD  isn’t  reoxidised  
(d) Aerobic  respiration  will  therefore  stop  
(e) Lactate  fermentation  pathway  will  be  used  instead  
ii) Ethanol  Fermentation  

(1) Facultative  anaerobe  eg
...
 In  a  1  minute  period,  or  
the  time  taken  for  the  liquid  to  travel  a  given  distance  eg
...
8kJg-­‐1  
(1) Highest  respiratory  quotient  =  1
...
0kJg-­‐1  (only  aerobic)  (protein  composition  varies  so  
energy  values  can  vary  depending  on  different  amino  acid  proportions)  
(1) Respiratory  quotient  =  0
...
4kJg-­‐1  (almost  double  the  energy  yield)  (only  aerobic)  
(1) Respiratory  quotient  =  0

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