Potato Osmosis(…and some other ideas)

9-12.L.1.1. Students are able to relate cellular functions processes to specialized structures within cells.

Concepts:

• Osmosis• Hypertonic/hypotonic/isotonic• Problem solving• Graphing and analyzing graphs

http://www.youtube.com/watch?v=2Th0PuORsWY

If the cell had a concentration of 0.2M sucrose, what might be the concentration of the surrounding solutions in A, B and C?

Challenge Question

Can you determine the concentration of sucrose

in a potato?

Sucrose Solutions Before After difference

0.1 0.29 0.36 0.07

0.2 0.29 0.31 0.02

0.3 0.24 0.3 0.06

0.4 0.32 0.29 -0.03

0.5 0.31 0.25 -0.06

0.6 0.32 0.25 -0.07

0.7 0.36 0.25 -0.11

0.8 0.33 0.23 -0.1

Data collected:

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Difference in Mass vs. Concentration of solution

Before After

Concentration of sucrose (M)

Diff

ere

nce in m

ass (

g)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

f(x) = − 0.269047619047619 x + 0.0935714285714286R² = 0.885076592500173

Difference of mass due to hypotonic vs. hypertonic so-lutions

Concentration of Sucrose (M)

Diff

ere

nce

of

Ma

ss (

g)

0.35 M

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

-40.00%

-30.00%

-20.00%

-10.00%

0.00%

10.00%

20.00%

30.00%

f(x) = − 0.855895362465163 x + 0.31586673584727R² = 0.839701172939611

Percent difference in mass vs. concentration

Concentration of Sucrose

Pe

rce

nt

diff

ere

nce

of

ma

ss b

efo

re a

nd

a

fte

r

0.37 M

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.90.2

0.22

0.24

0.26

0.28

0.3

0.32

0.34

0.36

0.38

f(x) = − 0.166666666666667 x + 0.355R² = 0.897435897435897

f(x) = 0.102380952380952 x + 0.261428571428571R² = 0.50312925170068

Mass of potato vs. concentration of sucrose

Before Linear (Before )AfterLinear (After)

Concentration of sucrose (M)

Ma

ss o

f p

ota

to (

g)

• Students make their own solutions, cut their own potatoes, etc.

• Allow procedural mistakes

• Student-directed graphs

• Solutions are made ahead of time by teacher, divided up by the class, or only dilutions are required.

• Make sure procedures are correct before allowing experimentation

• Potatoes cut into equal sized pieces ahead of time

• Require certain graphs at the end of the experiment

Easier: Challenging:

Potato nutritional value

Is this experiment really measuring the

sucrose concentration?

Molality NaCl Sucrose Glucose

0 11.02% 9.57% 11.92%

0.1 4.88% 7.23% 6.54%

0.2 -4.81% 1.66% 4.44%

0.3 -14.16% -4.13% -0.74%

0.4 -20.86% -10.82% -8.29%

0.5 -25.16% -15.98% -15.66%

http://biology.clemson.edu/bpc/bp/lab/110/osmosis.htm

Average percent change in mass of white potato cores during a 1.5-hour incubation in several NaCl, sucrose, and glucose solutions.

0 0.1 0.2 0.3 0.4 0.5 0.6

-30.00%

-25.00%

-20.00%

-15.00%

-10.00%

-5.00%

0.00%

5.00%

10.00%

15.00%

f(x) = − 0.535914285714286 x + 0.130995238095238R² = 0.969264626865587f(x) = − 0.536257142857143 x + 0.113280952380952R² = 0.986405421224318f(x) = − 0.7642 x + 0.109233333333333R² = 0.987038336528939

NaClLinear (NaCl)SucroseLinear (Sucrose)Glucose

Other ideas:

• Grape lab – Middle School

• Discussion/writing probes

Show what you know…

Salting the earth refers to the practice of spreading salt on fields to make them incapable of being used for crop-growing. This was done in ancient times at the end of some wars as an extremely harsh tactic designed to hurt an entire population of people. (The lack of crops would lead to food shortages.)Based on your knowledge of cells and cell transport, explain why salting the earth was an effective way to destroy plants.