Part 1: Plain puffed rice cakes are composed primarily of starch, but may also contain small amounts of reducing sugars such as maltose.

Describe the chemical tests that a student could perform to demonstrate the presence of both starch and reducing sugars in a sample of rice cake.

Your description should include details of the reagents used, the expected positive results, and a suitable risk assessment with precautions.

Part 2: A student designed an experiment to compare three different brands of plain rice cakes.

For each brand, the student:

• placed a 1.5 g fragment of the rice cake directly onto the center of their tongue
• held their mouth closed without chewing or swallowing
• used a stopwatch to record the time taken (in seconds) until a distinct sweet taste was first perceived.

The results of the investigation are shown below:

Answer the following questions based on this investigation:

State the dependent variable in this investigation.

Give one control variable that was kept constant, or should have been kept constant, to ensure a fair comparison.

Explain, in terms of enzymes and chemical digestion, why the rice cake began to taste sweet.

Suggest one reason why the results of this investigation may lack validity. Do not refer to control variables in your answer.