Osmosis, Food Tests, and Enzyme Practical Instructions

This section covers the Potato osmosis experiment and other biochemical tests crucial for GCSE Biology practicals.

Osmosis Experiment

The osmosis practical uses potato cylinders to demonstrate water movement across cell membranes. Key steps include:

1. Preparing uniform potato cylinders
2. Measuring initial mass and length
3. Immersing cylinders in various sugar/salt concentrations
4. Measuring final mass and length after a set time
5. Calculating percentage changes

Highlight: Controlled variables in osmosis potato experiment include cylinder size, solution volume, and immersion time.

Example: The Potato osmosis experiment observations might include changes in cylinder firmness or flexibility.

Food Tests

The food tests practical covers four main biochemical tests:

1. Iodine test for starch
2. Emulsion test for lipids
3. Biuret test for proteins
4. Benedict's test for reducing sugars

Vocabulary: Positive results include blue-black for starch, cloudy emulsion for lipids, purple for proteins, and brick-red for reducing sugars.

Enzyme Practical

The enzyme practical investigates the effect of pH on amylase activity. Key steps include:

1. Preparing buffered solutions of different pH
2. Setting up starch and amylase solutions
3. Maintaining temperature at 35°C using a water bath
4. Testing for starch breakdown using iodine

Definition: Amylase is an enzyme that breaks down starch into simpler sugars.

Example: The Microbiology practical gcse might ask students to explain how pH affects enzyme activity based on their results.