Homework: Question from Past Paper Half Yearly Exam 2008

Name: ______Class: ______

Homework: Question from Past Paper Half Yearly Exam 2008.

Two strips of uncooked potato were prepared and labelled A and B. One strip was placed in a strong sugar solution. The other strip was placed in distilled water. After 30 minutes, strip A had grown longer, while strip B had shrunk.

a. Which strip was placed in the sugar solution, strip A or strip B? Explain what happened in the potato cells. (2 marks)

b. Which strip was placed in distilled water, strip A or strip B? Explain what happened in the potato cells. (2 marks)

c. If red blood cells were placed in the same conditions as strip A, the consequences would have been totally different. What would have happened to them? (1 mark)

d. Give a reason for your answer in part c. (2 marks)

e. The experiment was repeated using strips that were covered with plastic cling film. The strips did not change in length. Suggest a reason why this might have happened. (1 mark)

f. In a separate experiment, a student placed a spot of dye (colour) at one end of a potato strip. After 1 hour the student observed that the dye had moved from its original position. By which process did the dye move? (1 mark)

g. Mention one substance that enters the cell by this process. (1 mark)

h. Mention one factor which the student could have changed to increase the rate of movement of the dye. (1 mark)

i. Explain what happens when a plant cell is plasmolysed. (2 marks)

j. Sometimes roots take up mineral salts from the soil when the outside concentration of the salts is lower than the salt concentration inside the roots. By which process does this occur? (1mark)

k. Give one important difference between this process and the process described in part (f). (1 mark)

2. An experiment was carried out to investigate the effect of different concentrations of sucrose solution on the length of potato strips. 5 test-tubes were set up, each containing a different concentration of sucrose solution. Another test-tube was set up, containing distilled water. A strip of potato tissue was placed in each tube. The strips were of equal size; they were all 70mm long and of the same width and thickness. The strips of potato were completely covered by the solutions and were left in the test-tubes for 30 minutes. The potato strips were removed and measured. The results are shown in the following table :

(a) Plot the changes in length against the concentration of sucrose solution on a graph paper. Join the dots using straight lines. (4 marks)

(b) What conclusions can be drawn from these results ? (4 marks)

(c) Using the graph, suggest the concentration of the sucrose solution which is the most similar to the solution inside the potato cells. Explain your answer. (2 marks)

3. Give a biological explanation for each of the following with the aid of diagrams:

(a) A red blood cell bursts when placed in water. (3 marks)

(b) A plant cell does not burst when placed in water. (3 marks)

(c) Root cells take up salts into the cells when, their concentration outside the cells, is lower than that inside the cells (3 marks)

Mrs. J. Ebejer Grech B.Ed.(Hons.)