Leave an apple slice on a table. Why will it slowly turn brown?

Question

The apple becomes heavier.

Water enters the apple.

The air causes a physical change.

The air causes a chemical change.

Answer 1

The apple slice will slowly turn brown because of a chemical change caused by the exposure to oxygen in the air. When the cells of the apple are damaged (such as by cutting it), enzymes in the apple react with oxygen in the air to form compounds called polyphenols. These polyphenols then react with other substances in the apple to create brown pigments known as melanin, causing the apple slice to change color over time.