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The  Variety  of  Life  
 

The  Variety  of  
Life  
 

 
 
 
 
 
 
 
 
 
 
 
 

 

•  Haemoglobin  
•  Oxygen  dissociation  curves  
•  Starch,  glycogen  and  cellulose  
•  Plant  cell  structure  

The  Variety  of  Life  
 

Haemoglobin  
 

Haemoglobin  molecules  

Haemoglobins  are  a  group  of  chemically  similar  molecules
...
 Each  chain  is  associated  with  a  haem  group  
which  contains  an  Fe2+  ion
...
 
•  
•  
•  
•  

 

The  role  of  haemoglobin  
•   To  transport  oxygen
...
 
-­‐   Readily  dissociating  with  oxygen  where  tissues  need  it
...
 
•   Shape  changes  in  presence  of  other  substances,  e
...
 CO2
...
 
Region  of  
body  
Gas  exchange  
surface  
Respiring  
tissues  
 
 
 
 

Oxygen  
concentration  
High  
Low  

Carbon  
Affinity  of  
dioxide  
haemoglobin  
concentration   for  oxygen  
Low  
High  
High  

Low  

Result  

Oxygen  is  
attached  
Oxygen  is  
released  

The  Variety  of  Life  
 

Why  have  different  haemoglobins?  
•   Haemoglobin  with  high  affinity  for  oxygen:  Take  up  oxygen  easily  by  
release  it  less  readily
...
 
•   Organism  in  environment  with  little  oxygen  needs  haemoglobin  with  a  
high  affinity  to  absorb  enough  of  it
...
 
Why  do  different  haemoglobins  have  different  affinities  for  oxygen?  
•   Due  to  the  shape  of  the  molecule
...
 
•   Their  shape  determines  whether  they  have  a  high  or  low  affinity  for  
oxygen
...
 
•   In  humans  it  occurs  in  the  lungs
...
 
•   In  humans  this  occurs  in  the  tissues
...
 
•   At  low  conc
...
 
•   Once  it  is  loaded,  it  causes  the  polypeptides  to  load  the  remaining  oxygen  
molecules  easily
...
 
•   A  very  small  decrease  in  the  partial  pressure  of  oxygen  leads  to  a  lot  of  
oxygen  being  dissociated  from  the  haemoglobin
...
 
•   The  further  to  the  left  the  curve,  the  greater  the  affinity  for  oxygen  the  
haemoglobin  has
...
 
 

Effects  of  carbon  dioxide  concentration  
•   Behaviour  of  haemoglobin  changes  in  different  regions  of  the  body
...
g
...
 
•   Here,  the  affinity  for  oxygen  has  increased  which,  along  with  high  levels  of  
oxygen  in  the  lungs,  means  that  the  oxygen  is  readily  loaded
...
 
•   In  rapidly  respiring  tissues  (e
...
 muscles),  the  level  of  CO2  is  high
...
 The  increased  CO2  has  shifted  
High  CO2  
conc
...
 All  this  is  because  dissolved  CO2  
Low  CO2  
is  acidic  and  the  low  pH  causes  the  
conc
...
   

 

 

Loading,  transport  and  unloading  of  oxygen  
•   At  the  gas-­‐exchange  surface  CO2  is  constantly  being  removed
...
 
•   The  shape  also  increases  the  affinity  for  oxygen  so  it  is  not  released  during  
transport
...
 
•   CO2  is  acidic  in  solution  so  the  pH  of  the  blood  in  the  tissues  is  lowered
...
 
•   Haemoglobin  releases  oxygen  into  the  respiring  tissues
...
 
 
The  higher  the  rate  of  respiration  à  the  more  CO2  the  tissues  produce  à  the  
lower  the  pH  à  the  greater  the  haemoglobin  shape  change  à  the  more  
readily  oxygen  is  unloaded  à  the  more  oxygen  there  is  available  for  
respiration  
 
•   In  humans,  once  a  haemoglobin  molecule  is  saturated  with  oxygen,  it  will  
only  unload  one  oxygen  molecule  to  resting  tissues,  returning  to  the  lungs  
with  three  molecules  still  attached  before  becoming  saturated  again
...
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 
 
 
 
 
 
 
 
 
 
 
 

The  Variety  of  Life  
 

Starch,  glycogen  and  cellulose  
 

Starch  
•   A  polysaccharide  found  in  many  parts  of  a  plant  in  the  form  of  small  
grains
...
 
•   Forms  and  important  component  of  food  and  is  a  major  energy  source
...
 
•   The  unbranched  chain  in  wound  into  a  coil  which  makes  the  molecule  very  
compact
...
 
-­‐   As  it  is  insoluble,  doesn’t  easily  diffuse  out  of  cells  
-­‐   When  hydrolysed,  forms  α-­‐glucose,  which  is  easily  transported  and  
used  in  respiration
...
 
•   Never  found  in  an  animal  cell
...
 
•   Major  carbohydrate  storage  product  and  is  stored  in  small  granules  in  the  
liver  and  muscles
...
 
•   Good  for  energy  storage  for  same  reasons  as  starch
...
 
•   This  creates  fundamental  differences  between  cellulose  and  the  other  
molecules
...
 
•   This  means  that  rather  than  forming  coiled  chains  like  starch,  cellulose  has  
straight,  unbranched  chains
...
 
•   Each  individual  bond  adds  little  to  the  overall  strength  of  the  molecule,  the  
sheer  number  of  them  makes  cellulose  much  stronger
...
 
•   Cellulose  grouped  together  to  form  microfibrils  which,  in  turn,  make  
fibres
...
 
•   Prevents  cell  from  bursting  as  water  enters  it  via  osmosis  by  exerting  an  
inward  pressure,  stopping  further  water  entering  the  cell
...
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

Hydrogen  
bonds  

 

 

The  Variety  of  Life  
 

Leaf  palisade  cell  

Plant  cell  structure  
 

•   Function  is  to  carry  out  photosynthesis
...
 
•   Number  of  chloroplasts  which  arrange  themselves  in  the  best  position  to  
absorb  maximum  sunlight
...
 
 

Chloroplasts  
•   The  chloroplast  envelope:  double  plasma  membrane  that  surrounds  the  
organelle
...
 
•   The  grana:  stacks  of  up  to  100  disc-­‐like  structures  called  thylakoids
...
 The  grana  
is  where  the  first  stage  of  photosynthesis  happens
...
 Within  the  grana  are  a  number  of  structures  (e
...
 starch)
...
 Attached  to  membrane  in  a  highly  ordered  
fashion
...
 
-­‐   Chloroplasts  contain  both  DNA  and  ribosomes  and  so  they  can  
quickly  and  easily  create  the  proteins  needed  for  photosynthesis
...
 
•   Thin  layer  (middle  lamella)  which  marks  the  boundary  between  adjacent  
cell  walls  and  cements  them  together
...
 
•   Gives  strength  to  plant  as  a  whole
...
 
 

Difference  between  plant  and  animal  cells  
 
 
Plant  cells  
Cellulose  cell  wall  surrounds  the  plant  
cell  as  well  as  a  cell-­‐surface  
membrane
...
 
Normally  have  large,  single,  central  
vacuole  filled  with  cell  sap
...
 

 
 
 

Animal  cells  
Only  a  cell-­‐surface  membrane  
surrounds  the  cell
...
 
If  vacuoles  are  present,  they  are  small  
and  scattered  throughout  the  cell
...
 



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