Enhancement of Analytical Thinking through Scientific Investigations
Lesson 1-3 Osmosis (滲透作用)
Experiment︰Investigation of osmosis using potato and beet root strips
Remarks:
The students will first be allowed to design their own methods to investigate osmosis using potato and beet
root strips and then the teacher give comments on the students’ design.
Finally, the students agree on an
experimental design like this one through discussion and revising on the designs.
facilitate students to come up with a proper experimental design.
The teacher’s role is to
Students need to analyse own thinking
and other students’ viewpoints based on scientific knowledge.
Materials:
1. Cork borer
2. Fresh potatoes and beet root (Be careful! The beet root can make your hands and clothes red!)
3. Beaker
4. Sodium chloride
5. Petri dishes x 4
Procedures:
1. Cut the potatoes and beet root respectively using cork borer. Make 3 potato/beet root strips as a group,
and prepare 5 groups of potato/beet root strips in total (i.e. 15 potato / beet root strips).
2. Measure and record the length and diameter (of the cross section) of each potato/beet root strips in the
result table.
Diameter
3. Put the potato/beet root strips (3 in a group) into the following solutions respectively:
a.
Water
b.
Salt solution A
Length
(20 g sodium chloride in 1 L water = 0.02 g/mL)
c.
Salt solution B
(100 g sodium chloride in 1 L water = 0.1 g/mL)
d.
Glucose solution
(100 g glucose in 1 L water = 0.1 g/mL)
e.
Salt solution Y
(unknown concentration)
4. After 1 hour, measure and record the dimension of the potato/beet root strips in the following table.
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Result:
1. What sample did you choose to study in your investigation?
2.
Before soaking into the solution
Sample
1
2
3
After soaking into the solution
Mean
1
Length
Length
Diameter
Diameter
Length
Length
Diameter
Diameter
Length
Length
Diameter
Diameter
Length
Length
Diameter
Diameter
Length
Length
Diameter
Diameter
2
3
Change
Mean
(/)
Water
Salt solution A
Salt solution B
Glucose solution
Salt solution Y
3. Plot a graph using concentrations of salt solution as the x-axis and changes in length of potato/beet root
strips as y-axis, find out the concentration of the salt solution Y.
Concentration of salt solution Y:
4. How do you think the cells of the potato/beet root strips look like after soaking into different solutions?
Water
Before soaking
After soaking
Salt solution A
Before soaking
After soaking
Salt solution B
Before soaking
After soaking
Questions:
1. What happed to the cells of potato/beet root strips after they were soaked into different solutions?
2. Why did we choose potato and beet root as study models? (Any characteristics?)
3. Why did we use 3 strips in a group instead of using 1 strip only for each experiment?
4. After the experiment, do you understand how water moves in and out of a plant cell?
5. Is this experiment a qualitative or quantitative analysis?
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