Carbohydrates
Carbohydrates are sugars and starches in food that living things break down for energy.
Sugar cubes and flour bags in your kitchen are both carbohydrates. Your body breaks them down like a jar of sugar dissolving in warm water. Simple sugars dissolve fast and give quick energy right away. Starches are like stacked sugar cubes that must be pulled apart one by one first.
Explaining carbohydrates by grade level
When you mix yeast with sugar water, bubbles start to form. The yeast eats the sugar and makes gas. Sugar is a type of food that gives energy. Bread, fruit, and rice all have this kind of food in them.
Projects that explore carbohydrates
Bananas contain sugars that yeast — a fungus that feeds on organic matter — can break down for energy. When you sprinkle dry yeast on a banana slice and seal it in a bag, the yeast uses the fruit's carbohydrates as fuel. As a result, the yeast-covered slice breaks down noticeably faster than the plain control slice.
Not all sugars have the same structure, so yeast breaks them down for energy at different rates. You dissolve different carbohydrates in water, adjust the pH to 6.5, add yeast, and warm the mixture to 37.5 degrees Celsius. An upside-down water-filled cylinder collects the carbon dioxide so you can measure its volume. Sugars like sucrose and glucose produce lots of gas. Others like galactose and lactose produce almost none.