Welcome to Nutrition and Energy!
Ever wondered why you are told to "eat your greens" or why athletes eat huge bowls of pasta before a race? Your body is like a high-performance machine, and the food you eat provides the fuel (energy) and the spare parts (building blocks) needed to keep it running smoothly. In this chapter, we will look at the specific molecules your body needs and what happens if you don't get enough of them.
The Building Blocks: Biological Molecules
Before we look at the food on your plate, we need to look at the chemistry inside it. All the main nutrients are made of chemical elements. Don't worry if chemistry isn't your favorite subject—you only need to know these four main elements: Carbon \( (C) \), Hydrogen \( (H) \), Oxygen \( (O) \), and Nitrogen \( (N) \).
1. Carbohydrates
Elements: \( C, H, O \)
Basic Units: Large carbohydrates like starch and glycogen are made by joining many simple sugars (like glucose) together.
Function: These are your body's main source of energy.
Sources: Bread, pasta, rice, and potatoes.
2. Proteins
Elements: \( C, H, O, N \)
Basic Units: Proteins are long chains made of amino acids.
Function: Essential for growth and repair of tissues.
Sources: Meat, fish, eggs, and beans.
3. Lipids (Fats and Oils)
Elements: \( C, H, O \)
Basic Units: One lipid molecule is made of three fatty acids joined to one glycerol molecule.
Function: They provide a long-term energy store and act as insulation to keep you warm.
Sources: Butter, oil, nuts, and oily fish.
Quick Review: Remember that starch is for plants and glycogen is for humans, but both are just "chains of sugar" used for energy!
The "Vital" Helpers: Vitamins and Minerals
We only need vitamins and minerals in tiny amounts, but without them, the body starts to break down. These are called micronutrients.
Vitamin A
Function: Keeps your skin healthy and helps you see in low light (night vision).
Sources: Carrots, liver, and butter.
Vitamin C
Function: Helps to stick cells together in tissues (like skin and gums) and aids in healing wounds.
Sources: Citrus fruits (lemons, oranges) and strawberries.
Vitamin D
Function: Helps the body absorb calcium to build strong bones and teeth.
Sources: Eggs, oily fish, and sunlight (your skin makes it when exposed to UV rays).
Calcium (Mineral)
Function: For strong bones and teeth.
Sources: Milk, cheese, and yogurt.
Iron (Mineral)
Function: Needed to make haemoglobin in red blood cells, which carries oxygen around your body.
Sources: Red meat, spinach, and liver.
Deficiency Diseases: What Happens When Nutrients are Missing?
If your diet is missing a specific nutrient for a long time, you may develop a deficiency disease. The Edexcel syllabus requires you to know these four specifically:
1. Blindness (Lack of Vitamin A): A severe lack of Vitamin A can lead to "night blindness," where it becomes impossible to see in the dark, eventually leading to total blindness.
2. Scurvy (Lack of Vitamin C): This was famous among sailors! Symptoms include bleeding gums, wounds that won't heal, and old scars opening up because the "cellular glue" in the body fails.
3. Anaemia (Lack of Iron): Without iron, you can't make enough haemoglobin. This means your blood carries less oxygen, making you feel very tired, weak, and pale.
4. Kwashiorkor (Lack of Protein): This often happens in areas of famine. Even if a person gets enough calories from carbs, a lack of protein causes stunted growth and a swollen abdomen (pot belly) due to fluid collecting in the tissues.
Note: For Bone health, also remember that a lack of Vitamin D or Calcium can lead to weak bones (Rickets), though the syllabus also links bone health to Osteoporosis in Chapter 4.
Dietary Fibre: The Body's Broom
Fibre is actually a carbohydrate (cellulose) from plant cell walls that we cannot digest. Because we can't digest it, it stays in the gut and provides "bulk." This gives the muscles of the gut something to push against, helping move food along via peristalsis. It prevents constipation and keeps the digestive system healthy.
Required Practicals: Investigating Food
In your exam, you might be asked how to test for these nutrients or how to measure their content.
Investigating Vitamin C Content
We use a blue liquid called DCPIP.
1. Measure a set volume of DCPIP into a test tube.
2. Add the food juice (e.g., orange juice) drop by drop using a pipette.
3. Shake gently after each drop.
4. The Vitamin C will turn the blue DCPIP colourless.
The fewer drops it takes to turn the liquid colourless, the more Vitamin C is in the food!
Investigating the Energy Content of Food
How do we know how many "calories" are in a crisp? We burn it!
1. Measure a volume of water into a boiling tube and record its initial temperature.
2. Weigh a small piece of food.
3. Set the food on fire using a Bunsen burner.
4. Immediately hold the burning food under the boiling tube until it is completely burnt out.
5. Record the final temperature of the water.
6. The rise in temperature tells us how much energy was released.
Common Mistake to Avoid: In a simple school lab, much of the heat energy escapes into the air rather than heating the water, so the result is always an underestimate of the true energy content.
Summary: Key Takeaways
- Carbohydrates: Energy (Starch/Glucose).
- Proteins: Growth/Repair (Amino Acids). Deficiency = Kwashiorkor.
- Lipids: Energy store/Insulation (Fatty acids/Glycerol).
- Vitamin A: Vision. Deficiency = Blindness.
- Vitamin C: Tissues/Healing. Deficiency = Scurvy.
- Iron: Haemoglobin. Deficiency = Anaemia.
- Fibre: Moves food through the gut (Peristalsis).