Required Practicals

RP1: Microscopy (B1)

What stain is used for plant cells?

Iodine solution

What is a main risk and corresponding safety step in the microscopy practical?

• Risk: Glass slides breaking.
• Safety step: Handle carefully and wear eye protection.

RP2: Osmosis in Potato Cylinders (B1)

What is the independent variable?

The concentration of the sugar or salt solution.

What is the dependent variable in the potato osmosis experiment?

The change in mass of the potato cylinders.

Why should you blot potato cylinders dry before weighing them?

To remove excess surface solution to ensure an accurate mass measurement.

What does it mean if there is no change in the mass of the potato cylinder?

The solution is isotonic, meaning it has the same concentration as the cell sap.

Why must all potato cylinders be cut to the same size?

To control the surface area and volume as control variables.

RP3: Food Tests (B2)

What is the test for starch and the positive result?

Iodine solution; result is a color change to blue-black.

What is the test for reducing sugars and the potential results?

Benedict’s solution + heat; results range from green/yellow to orange/red depending on concentration.

What is the test for protein and the positive result?

Biuret reagent; result is a color change to lilac/purple.

What is the test for lipids and the positive result?

Ethanol emulsion test; result is a cloudy white emulsion.

Why is the Benedict’s test reagent heated?

The chemical reaction requires heat to occur.

RP4: Enzymes (B2)

Which enzyme is typically used to study the effect of pH?

Amylase

What reaction does amylase catalyze?

Starch \xrightarrow{\text{Amylase}} \text{Sugars}

How is the presence of starch detected during the enzyme practical?

Using iodine; it turns blue-black if starch is still present.

Why is a buffer solution used in the enzyme practical?

To keep the pH constant for each trial.

Why does a very high or very low pH slow the enzyme reaction?

The enzyme denatures, meaning the active site changes shape and the substrate can no longer fit.

RP5: Culturing Microorganisms (B3)

What is 'aseptic technique'?

Procedures used to prevent contamination from unwanted microorganisms.

Why are agar plates taped but not fully sealed?

To prevent the growth of harmful anaerobic bacteria by allowing some oxygen in.

Why are bacterial cultures in schools incubated at a maximum of 25^{\circ}C?

To reduce the risk of growing pathogens that are harmful to humans.

What does a 'clear zone' (zone of inhibition) around an antibiotic disc indicate?

It shows that the antibiotic has killed or inhibited the growth of the bacteria in that area.