Required Practicals

Question 1

During RP3, why are the potatoes’ skin removed (1 mark)

Answer 1

• Different parts of the potato have different thicknesses of skin
• So this would affect the diffusion distance

Question 2

During RP3, why are the potato chips dried with a paper towel before weighing again (2 mark)

Answer 2

• To remove any excess liquid on the surface of the potato chips which may add to the mass
• The amount of water on the surface of each chip will vary

Question 3

State the independent variable in RP3 (1 mark)

Answer 3

Sucrose concentration

Question 4

State the dependent variable in RP3 (1 mark)

Answer 4

% change in mass

Question 5

State the control variables in RP3 (5 marks)

Answer 5

• Volume of solution
• Length and diameter of potato chip
• Time left in solution
• Temperature
• Type of potato

Question 6

Why should the potato chips not be squeezed after removing them from the sucrose solutions (3 marks)

Answer 6

• Squeezing would damage the cells and cause the cell membranes to break
• So water from inside the cells would come out
• This would give an inaccurate result

Question 7

State 3 aseptic techniques which must be used when doing RP6 (6 marks)

Answer 7

• Open lid of Petri dish as little as possible
• To prevent microorganisms from escaping and contaminating the air
• Use a sterile pipette / flame the loop
• To maintain a pure culture of bacteria
• Wash hands with soap
• To prevent contamination of bacteria on hands

Question 8

Why should the neck of the microorganism bottle be flamed (1 mark)

Answer 8

• To kill any other microorganisms that may contaminate the agar plate
• If they weren’t killed, they would compete with the microorganism being investigated for the nutrients and oxygen

Question 9

Why must the agar plates be incubated at 25 degrees in RP6 (1 mark)

Answer 9

• To prevent the excessive growth of bacteria and potential pathogens from growing