Answers to Mid Year Biology Paper 3 – Question 1

1a. P – 7.5 cm
Q – 6.5 cm
R – 5.0 cm
S – 4.0 cm

bi)1.The final length of the potato strip immersed in 0% sucrose solution is 7.5 cm.
2.The final length of the potato strip immersed in 10% sucrose solution is 4.0 cm.

bii) 1. For the 0% sucrose solution, the increase in length is caused by the diffusion of water molecule into the cell sap by osmosis.
2. For the 10% sucrose solution, the decrease in length is caused by the diffusion of water molecule from the cell sap by osmosis.

c. Manipulated variable : Concentration of sucrose solution
Method to handle :Use different concentration of sucrose solutions:0%, 3%, 5%, 10%

Responding variable: Final length of potato strip/change in length of potato strips
Method to handle : Measure and record the final length of the potato strip using the given scale

Constant variable : Time of immersion/type of potato/size of potato strip/ volume of sucrose solution
Method to handle : Fix the time for the immersion of the potato strips at 30 min for all the expt/ Fix the type of potato to be the same / fix the diameter of the potato strips by using the same cork borer for all the strips/ Fix the same volume of sucrose solution at 20ml for all the expt.

d. The higher the concentration of sucrose solution, the shorter the length of the potato strips / inversely.

e. 1. Able to state all titles with units correctly
2. Able to record all the data correctly
3. Able to calculate and record % change correctly

f. Able to draw : 1. X – axis and Y – axis with correct scales and unit
2. correct transfer of points
3. correct shape of curve

g. Concentration of sucrose solution which is isotonic to the cell sap is 5%.
From the graph, the point where the graph cuts the X-axis indicates the concentration of sucrose solution that does not cause any change to the length of the potato strips.

h. The potato strip will be shorter than 4.0cm,maybe 3.5cm. This is because more water molecules diffuse out from the cell sap to the hypertonic solution outside.

i. Isotonic concentration is the concentration of sucrose solution that causes no change in the length of potato strips that are immersed in it.

j. 0% - Hypotonic solution
3% - Hypotonic solution
5% - Isotonic solution
10% - Hypertonic solution