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Biology  Alternative  to  Practical  
Buiret  Test  for  Proteins  
This  test  is  used  for  the  presence  of  proteins  by  seeing  if  the  blue  reagent  turns  purple
...
 If  protein  is  present,  a  mauve/purple  color  appears
...
   
In  order  to  test  for  the  presence  of  fats,  add  a  food  sample  in  a  tube
...
 Wait  a  bit
...
 Then  add  2cm  of  water
...
 If  fats  is  not  present,  the  liquid  remains  clear
...
 Water  caused  droplets  to  develop  once  the  lipids  are  dissolved  in  ethanol  and  the  white  color  
comes  from  light  scattered  through  the  water
...
 In  one  minute  period,  count  oxygen  bubbles  given  off  by  the  plant  which  
indicates  the  rate  of  Photosynthesis
...
   
Repeat  the  experiment  at  different  lower  CO₂  concentrations  by  using  different  dilutions  of  saturated  
solution
...
 
 
On  the  graph,  the  line  (Rate  of  Photosynthesis)  steadily  increases  because  of  the  increasing  CO₂  
concentration
...
 
 
Photosynthesis  investigations  –  Chlorophyll,  CO₂  ,  light  tests  
 
Is  chlorophyll  needed  for  photosynthesis?  
Take  a  plant  with  green/white  leaves
...
 Expose  plant  
in  sunlight  for  few  days
...
 If  the  colour  turns  from  
brown  to  blue/black,  chlorophyll  patches  are  present  and  green  patches  means  Chorophyll  is  
present
...
   
 
Is  light  essential  for  photosynthesis?  
Take  a  potted  plant
...
 Check  if  starch  is  present  in  
one  of  the  leaves  by  boiling  the  leaf  in  hot  ethanol  in  a  hot  beaker  of  water  (breaks  down  cell  
membranes  &  softens  cell  walls)  and  add  drop  of  iodine  solution  to  see  if  the  colour  brown  turns  into  
purple/black
...
 Remove  cover  and  do  starch  test  (iodine  solution)
...
 Cover  them  with  bell  jars  &  label  them  A  and  B
...
 Keep  both  
set-­‐ups  in  sunlight  for  6  hours
...
 The  result  will  be  plant  A  gives  a  
positive  test  because  it  gets  CO₂  while  the  plant  B  gives  a  negative  test  because  it  doesn’t  get  CO₂  
while  it’s  a  obligatory  source  for  photosynthesis
...
 Put  the  test  tube  in  beaker  of  fresh  water  at  25◦C  
(maintains  constant  temperature  around  pond  weed)
...
 Place  lamp  at  a  distance  from  the  plant
...
 Check  if  its  oxygen  showing  a  glowing  splint
...
 Graph  the  results  with  light  intensity  on  the  X-­‐axis  and  number  of  
bubbles  on  the  Y-­‐axis
...
 Low  light  intensity  causes  plants  to  respire,  and  even  if  the  light  
intensity  increases  further,  the  rate  remains  constant
...
 
 
Effect  of  Temperature  on  the  Rate  of  Photosynthesis  
 
Temperature  rises  =  rate  of  photosynthesis  rises
...
 
 
In  order  to  test  the  effect  of  Carbon  Dioxide,  we  place  a  tube  of  a  pond  weed  in  a  tube  containing  
water  at  25◦C  ,  then  put  it  in  a  beaker  of  fresh  water  with  Sodium  Bicarbonate  (Gives  constant  
saturated  solution  of  CO₂)  Then  put  a  lamp  at  a  fixed  distance  away  from  the  plant  at  room  
temperature  of  20◦C
...
 Check  if  its  oxygen  showing  a  glowing  splint
...
,)  by  using  a  hot  plate
...
 
 
Results  indicate  that  at  low  temperatures  the  enzymes  don’t  have  enough  energy  to  meet  substrate  
molecules  so  the  reactions  slows  down
...
 Optimum  temperature  is  where  the  
rate  and  enzyme  are  most  effective
...
 
Variables  are  things  that  you  change  for  different  parts  of  the  experiment
...
 (breaks  down  cell  walls,  denatures  enzymes  &  easier  
penetration  by  ethanol)  Then  warm  it  in  ethanol  till  its  colorless  (chlorophyll  is  soluble  in  ethanol,  
NOT  in  water)
...
 Then  place  a  leaf  on  a  white  tile  and  add  a  drop  of  
iodine
...
 If  starch  is  not  present,  orangebrown  
remains  and  shows  on  the  white  tile
...
   
Then,  if  you  insert  the  leaf  in  bag  with  soda  lime  (absorbs  CO₂)  and  another  leaf  in  a  bag  with  
hydrogencarbonate  solution  (  provides  CO₂)  it  shows  carbon  dioxide  is  needed
...
 
 
Carbon  dioxide:  Take  two  potted  plants
...
 Place  plants  on  
these  glass  sheets
...
 On  the  other  glass  sheet,  
place  a  dish  containing  caustic  soda
...
 Leave  them  alone  for  few  
hours
...
 Petroleum  
jelly  makes  bell  jars  airtight
...
 
 
Light  intensity:  Place  a  lamp  as  close  as  possible  to  the  apparatus  (device)
...
 
Placing  a  clear  glass  sheet  between  the  lamp  and  the  device  will  prevent  the  heat  from  the  bulb  
affecting  the  results  and  the  pond  weed  that  is  used  is  left  for  a  couple  of  minutes  in  each  new  light  
intensity
...
 
 
Temperature:  Set  up  the  device  in  several  different-­‐temperature  environments  (each  experiment  
you  measure  the  volume  of  oxygen  produced  per  amount  of  time/how  long  it  takes  to  create  certain  
amount  of  oxygen)  Limiting  factor  :  Something  present  in  the  environment  in  short  supply  that  it  
restricts  life  processes
...
g
...
 
Coloured  solution  has  been  carried  up  the  xylem
...
 
 
Testing  food  samples  for  the  presence  of  sugar  (Benedicts  test)  
 
 
 
 
 
 



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