Final answer:
Sodium bicarbonate, or baking soda, is used to weigh down leaf disks. It reacts with an acid to produce carbon dioxide gas, causing the dough or batter to rise. This process can be used in an experiment to study photosynthesis.
Step-by-step explanation:
Sodium bicarbonate, also known as baking soda, is used in baking as a leavening agent. When sodium bicarbonate is mixed with an acid, such as vinegar or lemon juice, it undergoes a chemical reaction that produces carbon dioxide gas. This gas creates bubbles in the dough or batter, causing it to rise and become lighter. In the context of weighing down leaf disks, sodium bicarbonate can be used to sink the disks in water so that they can be used in an experiment to study photosynthesis.