Apples quickly turn brown when sliced because they contain an enzyme called polyphenol oxidase that reacts with oxygen. Slicing an apple breaks the surface apple cells and starts a chemical reaction called enzymatic browning, which turns the apple brown. Your year five student can perform different science fair experiments to test what slows down the chemical reaction that causes apples to turn brown and determine what keeps apples from turning brown the longest.
Using the scientific method
Your child should follow the scientific method for her science fair project. Before beginning the experiment, she needs to do some research on the browning of apples. Then she need to form a hypothesis, or educated guess, on which method she believes will keep the apple slices from turning brown the longest and why she believes her hypothesis is correct. Next, she conducts the experiments, analyses the results and draws a conclusion based on which experiment did prevent apples from turning brown the longest.
Apples in the refrigerator
For this experiment, your child need an apple, a knife, two plates and a refrigerator. You may need to help her cut two slices of the apple. She places one apple slice on a plate to be left on the counter and the other apple slice on a plate to be placed in the refrigerator. She needs to check the apple slices every hour for four hours. Your child should record which apple slice is the darkest at the end of four hours. Taking pictures of the process may be helpful and makes an informative visual presentation for a science project board.
Apples soaked in liquids
This experiment tests whether certain liquids prevent the browning of apples. Your child can try several liquids, such as soda, vinegar, water and lemon juice, or she can just try water and lemon juice. To do the experiment with just water and lemon juice, your child needs two small bowls, water, lemon juice, an apple, a baking tray, masking tape and a marker. Use the masking tape and marker to make labels for water, lemon juice and no liquid, and space the labels equally on the baking tray. Label the bowls. Pour lemon juice in one bowl. The lemon juice will need to be one inch deep in the bowl. Pour water in the other bowl, two inches deep. Cut three slices, 1 cm (0.4 inches) thick from the apple. Place one slice in each bowl for one minute and leave the other slice out on the baking tray. Remove the slices from the bowls and place on the baking tray above the corresponding label. Leave the slices for four hours, and report which slice turns darkest and which remains the lightest.
Apples in a brown paper bag
For the experiment, your child needs a brown paper bag, a plate and an apple. Cut two slices from the apple. Place one slice in the paper bag and roll the paper bag shut and place on the counter. Place the other slice on a plate on the counter. Check the apple slices every hour for four hours and note which apple slice is darkest. Your child can add other variables by using ziplock bags, white paper bags and waxed paper to wrap apple slices.