Paper 3 Question 2

QUESTION 2.
The cell sap concentration in a plant tissue depends on the water content of its cell sap. When in a hypertonic solution, the cell sap loses water and become flaccid. In a hypotonic solution, the water content of the cell sap will increase causing the cell to expand and become turgid. In an isotonic solution, the plant cell maintains its shape because the cell sap concentration is equal to the concentration of the solution outside the cell.

Plan a laboratory experiment to determine the isotonic concentration of a potato cell.

The planning of the experiment should cover the following aspect:

(i) Objective of study
(ii) Statement of hypothesis
(iii) Variables
(iv) List of apparatus and materials
(v) Experimental procedure
(vi) Presentation of results
(vii) Conclusion

Step 1:

...IDENTIFY

i. Manipulated Variable

ii. Responding Variable

iii. Fixed/constant variable

SUGGESTED ANSWER:

Aim: To Investigate what concentration of sucrose solution is isotonic to potato cell sap.

Problem statement : How to determine the concentration of an isotonic solution to potato cell sap ?

Hypothesis: The sucrose solution which is isotonic to potato cell sap is the solution that shows no change of mass of the potato strip.

Variables:
Manipulated variable: Different concentration of sucrose
Responding variable: Mass of the strips
Fixed variables: Length of the strips, volume of the solutions, time of immersion.

List of apparatus and materials:
Potato, sucrose solution of different concentrations of solutions of sucrose; Core borer, glass beakers,forcep,electronic balance, ruler,string, filter paper,white tile, knife, tissue paper

Technique: Measure and RECORD the mass or length of strips using electronic balance/ ruler

Procedure:
1. Pour 100ml of the assigned sucrose solutions into their 250ml beakers ,labeled A,B,C,D, and E
2. Obtain a large potato. Using a core borer, take 20 samples out of the potato.
3 Measure each in centimeters so that they are all equal in length (use the knife to slice off ends). Make sure not to leave any skin with the samples.
4.Place these cores in a covered beaker until an electronic balance can be obtained.
5.Determine the mass of four cores at a time, placing the four in their sucrose solutions.
6.Record this data for each of the six beakers.
7.Allow these potato samples to sit immersed in the solutions 8 hours, covered.
8.Remove the cores, blot off excess solution, and weigh the samples, recording the mass in the data table.
9.Determine the mass difference and the percent change in mass
10.Graph the increase and decrease in mass of the potato cores according to the molarity of the solutions they were placed in on graph .

Results: (Table with UNITS..)

Plot graph Sucrose concentrations against the percent changes.

From the graph, select the point that cross the x-axis to get the value of isotonic point.

Conclusion:

The sucrose solution which is isotonic to potato cell sap is the point on the plotted graph that cross the x-axis. Hypothesis accepted