Carbohydrates are one of the main nutrients in food, and they are a major source of energy for the human body. They are found in foods such as fruits, grains, beans, vegetables, milk, and sweets. Understanding carbohydrates helps students connect chemistry to digestion, blood sugar, exercise, and long-term health.
Carbohydrates also matter in food science because they affect taste, texture, cooking, and storage.
Key Facts
- Carbohydrates contain carbon, hydrogen, and oxygen, often in a ratio close to 1:2:1.
- Glucose has the formula C6H12O6 and is a key fuel molecule for cells.
- 1 gram of carbohydrate provides about 4 Calories of energy.
- Photosynthesis stores energy in glucose: 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2.
- Cellular respiration releases energy from glucose: C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy.
- Simple carbohydrates digest quickly, while fiber and many complex carbohydrates usually slow digestion.
Vocabulary
- Carbohydrate
- A nutrient made mainly of carbon, hydrogen, and oxygen that provides energy and sometimes structural support.
- Glucose
- A simple sugar with the formula C6H12O6 that cells use as a major source of energy.
- Starch
- A complex carbohydrate made of many glucose units that plants use to store energy.
- Fiber
- A type of carbohydrate from plants that humans cannot fully digest but that supports healthy digestion.
- Glycogen
- A stored form of glucose found mainly in the liver and muscles of animals.
Common Mistakes to Avoid
- Calling all carbohydrates unhealthy is wrong because many carbohydrate-rich foods, such as fruits, beans, oats, and vegetables, also provide fiber, vitamins, and minerals.
- Confusing sugar with all carbohydrates is wrong because sugars are simple carbohydrates, while starches and fibers are larger carbohydrate molecules with different effects on digestion.
- Ignoring serving size is wrong because the total grams of carbohydrate depend on how much food is eaten, not just the type of food.
- Assuming fiber gives the same usable energy as sugar is wrong because humans cannot fully break down most fiber for energy.
Practice Questions
- 1 A snack contains 32 grams of carbohydrate. Using 4 Calories per gram, how many Calories come from carbohydrate?
- 2 A cereal serving has 45 grams of total carbohydrate, including 6 grams of fiber and 12 grams of sugar. How many grams of carbohydrate are neither fiber nor sugar?
- 3 A student eats white bread before exercise on one day and oatmeal with fruit before exercise on another day. Explain how the different types of carbohydrates might affect digestion speed, blood glucose, and usable energy.