BIOL  1208  

Lab  Report  

Cover  Sheet    

 

 

 

I  certify  that  the  writing  in  this  assignment  is  my  individual  work  and  is  my  sole  intellectual  property.    It  does  not  contain  the  ideas  or  writing  of  other  individuals/authors.  

Matthew  Landry______________________                                                                _______11/18/11______________  Author                 Date  

 

_____20_____  Lab  Section  #  

 

 

 

 

 

 

 

 

 

 

 

 

 

The  Effect  of  Sucrose  Concentration  on  the  Relative  Osmotic  Concentration  in  Potato  Tubers    

 Abstract    

This  lab  was  conducted  in  order  to  determine  the  molarity  of  sucrose  concentration  

where  the  mass  of  potato  tuber  segments  does  not  change,  indicating  an  isosmotic  

concentration.  By  calculating  the  change  of  mass  of  the  potato  tuber  cells  prior  to  

incubation  against  the  mass  after  incubation  in  the  sucrose  solution,  our  goal  was  to  

determine  what  type  of  osmotic  concentration  was  created  as  compared  to  the  

potato  tissues.  The  results  of  our  lab  indicated  three  different  osmotic  

concentrations.  According  to  our  data,  the  isosmotic  concentration,  of  a  potato  tuber  

disk  is  around  0.175M.  At  this  sucrose  concentration  the  sucrose  solution  is  isotonic  

relative  to  the  potato  tissues.  Anything  lower  than  the  isosmotic  concentration  

resulted  in  a  hypertonic  concentration.  Additionally,  anything  higher  than  the  

isosmotic  concentration  resulted  in  a  hypotonic  solution.    

Introduction    

The  purpose  of  a  biological  membrane  is  to  control  the  internal  environment  of  a  

cell.  A  cell  can  be  surrounded  by  millions  of  molecules  at  any  given  time,  and  it  is  up  

to  the  membrane  to  control  what  enters  and  what  leaves  a  cell.  Water  is  the  single  

most  important  molecule  in  any  living  system.    Due  to  water’s  small  size,  it  passes  

through  biological  membranes  with  ease  even  though  water  is  a  polar  molecule.  

Water  molecules  are  moving  across  the  cell  membrane  at  all  times,  and  the  when  

more  water  molecules  are  traveling  in  one  direction  than  the  other  an  osmotic  

situation  occurs.  The  significance  of  this  lab  is  to  determine  the  relative  osmotic  

concentration  of  disk  of  potato  tubers  that  are  incubated  in  different  sucrose  

solutions  and  to  determine  at  which  concentration  the  mass  of  the  tissues  does  not  

change.  This  will  allow  us  to  better  understand  of  osmotic  responses  and  water  

balance  in  biological  systems.  Our  null  hypothesis  for  the  lab  was  that  our  treatment  

in  varying  sucrose  solutions  would  have  no  effect  on  the  potato  tuber’s  osmotic  

concentration.  Our  alternative  hypothesis  was  that  our  treatment  in  varying  sucrose  

solutions  would  have  an  effect  on  the  potato  tuber’s  osmotic  concentration.    

Materials  and  Methods      

To  begin  our  lab  we  gathered  six  potato  tuber  segments  and  used  a  razor  blade  to  

cut  all  of  the  segments,  each  approximately  4cm  in  length.  Next,  we  cut  one  of  the  

segments  into  thin  disks  approximately  2mm  in  thickness.  We  placed  the  other  

segments  in  a  moist  paper  towel  to  prevent  them  from  drying  out.  We  then  placed  

the  disks  from  the  first  segment  into  a  beaker  and  washed  off  any  surface  starch.  We  

then  blotted  off  the  surface  water  with  a  dry  paper  towel.  Next,  we  calculated  the  

mass  of  an  empty  weight  boat.  We  then  transferred  the  potato  disks  into  the  boat  

and  determined  the  mass  to  the  nearest  0.1g.  We  then  placed  the  disks  into  a  beaker  

with  100mL  of  deionized  water.  We  then  repeated  the  steps  with  the  remaining  five  

potato  segments;  however,  we  placed  the  disks  from  the  each  new  segment  into  

different  sucrose  concentrations,  0.1M,  0.2M,  0.3M,  0.4M,  and  0.5M.  We  then  

incubated  all  the  disks,  in  their  various  concentrations  for  one  hour,  swirling  the  

beakers  every  ten  minutes.  At  then  end  of  the  one-­‐hour  period,  we  removed  the  

disks  from  their  concentration.  Next,  we  blotted  off  any  surface  water  with  a  dry  

paper  towel.  We  placed  the  disks  into  the  weight  boat  and  measured  the  mass  on  a  

scale.    Finally,  we  calculated  the  percent  change  in  mass  by  diving  the  change  in  

mass  by  the  initial  mass  then  multiplying  by  one  hundred.    

Results    

Based  on  the  data  from  the  six  treatments  a  regression  line  was  formed.  The  percent  

change  in  mass  of  the  potato  cells  is  positive  when  incubated  in  concentrations  of  

0.0,  0.1,  and  0.2  M  of  sucrose.    At  these  three  concentrations,  a  hypertonic  

environment  was  observed  within  the  cell.  The  percent  change  in  mass  of  the  potato  

cells  is  negative  when  incubated  in  concentrations  of  0.3,  0.4,  and  0.5M  of  sucrose.    

At  these  three  concentrations,  a  hypotonic  environment  was  observed  within  the  

cell.  According  to  the  data,  a  line  of  best  fit  crosses  the  x-­‐axis  where  an  isotonic  

relative  osmotic  concentration  is  achieved.  An  isotonic  solution  was  achieved  when  

the  sucrose  solution  is  around  0.175  M.  Based  on  the  results  from  the  experiment,  

our  alternative  hypothesis  was  correct.  

 

Based  on  the  data,  the  concentration  of  sucrose  at  approximately  0.175  M  shows  no  change  in  the  weight  of  the  potato  tuber  disks  indicating  an  isotonic  relationship  

between  the  disks  and  solution.    

 

Discussion      

According  to  our  data,  the  relative  isosmotic  concentration  of  a  potato  tuber  disk  is  

around  0.175M,  which  is  where  the  sucrose  concentration  surrounding  the  cells  

creates  neither  a  hypotonic  or  hypertonic  environment.  If  the  concentration  of  

sucrose  is  greater  on  the  outside  of  the  cell,  then  the  net  movement  of  water  is  out  of  

the  potato  cells.  A  hypertonic  situation  occurs,  and  the  tuber  cells  experience  a  loss  

in  mass  .In  plant  cells,  the  loss  of  water  from  a  cell  causes  the  cell  to  shrivel  or  

-30.00%

-25.00%

-20.00%

-15.00%

-10.00%

-5.00%

0.00%

5.00%

10.00%

15.00%

0 0.1 0.2 0.3 0.4 0.5 0.6

Percent Δ∆ in Mass (g)

Concentration of Sucrose Solution (M)

The Effect of Sucrose Concentration on the Relative Osmotic Concenctration in

Potato Tubers

undergo  plasmolysis.    This  trend  can  be  viewed  when  the  sucrose  concentration  was  

raised  over  0.3M.  If  the  concentration  of  sucrose  is  greater  on  the  inside  of  the  cell,  

then  the  water  enters  the  potato  disks.  A  hypotonic  situation  occurs  outside  of  the  

cells,  and  the  tuber  cells  experience  a  gain  in  mass,  as  the  net  movement  of  water  is  

into  the  cells.  In  plant  cells,  this  trend  is  known  as  turgid  pressure.  This  trend  can  be  

viewed  when  the  sucrose  concentration  is  lowered  from  0.2M  to  0.0M  of  sucrose.  

For  this  experiment  the  expected  isosmotic  concentration  is  0.3  molar;  however,  our  

data  does  not  support  this.  Some  possible  sources  of  error  in  our  experiment  include  

missteps  during  setup  and  preparation  for  the  experiment,  inaccurately  measuring  

the  mass,  or  other  factors.