Jennifer Demmon, age 9, of Merrillville, Ind., for her question:

HOW DOES WATER PROVIDE BREATHABLE OXYGEN FOR THE FISHES?

Water is made from oxygen and hydrogen. So it’s natural to think that fishes take their oxygen from water molecules. However, this is impossible. Fishes can breathe only free molecules of oxygen that happen to be dissolved in the water. Some of their breathable oxygen is added by seaweeds and waterweeds. Some is added by dashing streams and tossing waves, as    they take oxygen from the air and mix it with the water.