Welcome to Food and Diet!
Have you ever wondered why you feel sluggish after skipping breakfast, or why athletes eat huge bowls of pasta before a big race? Your body is an incredible biological machine, and just like a car needs fuel and oil to run smoothly, your body needs the right balance of nutrients from food to keep you active, healthy, and growing.
In this chapter for CCEA GCSE Single Award Science (Unit 1: Biology), we will explore:
• The seven essential nutrients your body needs and what happens if you do not get enough of them.
• The chemical food tests used in the laboratory to detect nutrients.
• How to measure the energy content of food using a simple calorimeter.
• Why maintaining an energy balance is vital for long-term health.
Don't worry if some of the scientific terms feel new or tricky at first. We will break every concept down step by step with easy-to-remember tips and real-world examples!
---Part 1: The Seven Components of a Balanced Diet
A balanced diet means eating the correct proportions of seven key food groups so that your body gets all the energy and materials it needs without taking in too much or too little.
1. Carbohydrates (Your Body's Fuel)
Carbohydrates are the body's main source of energy. They come in two main forms:
• Simple sugars (e.g., glucose): Provide fast-release energy. Your body breaks them down almost instantly for a quick boost. Found in fruits, sweets, and fizzy drinks.
• Complex carbohydrates (e.g., starch, glycogen): Provide slow-release energy. These are long chains of sugar units joined together that take longer to digest, giving you steady energy throughout the day. Found in bread, pasta, rice, and potatoes.
2. Proteins (The Building Blocks)
• Function: Essential for the growth and repair of body cells and tissues (like building muscle or healing cuts), and for producing enzymes.
• Good sources: Meat, fish, eggs, beans, and pulses.
3. Fats / Lipids (Energy Storage & Warmth)
• Function: Used for long-term energy storage, thermal insulation (keeping you warm), and protecting vital organs (like a protective cushion around your kidneys).
• Energy Density: Fats are extremely concentrated stores of energy. One gram of fat releases about \(9\text{ kcal/g} \approx 37\text{ kJ/g}\), which is more than double the energy released by carbohydrates or proteins (about \(4\text{ kcal/g} \approx 17\text{ kJ/g}\)).
• Good sources: Butter, cooking oils, cheese, and nuts.
4. Vitamins (Vital in Tiny Amounts)
You only need small amounts of vitamins, but missing them causes specific deficiency diseases:
• Vitamin C: Needed for healthy skin, strong gums, and repairing connective tissues.
Deficiency: Scurvy (leads to bleeding gums, loose teeth, and delayed wound healing).
Sources: Citrus fruits (oranges, lemons) and blackcurrants.
• Vitamin D: Needed to help your body absorb calcium to build strong bones and teeth.
Deficiency: Rickets (causes soft, weakened, and bent bones in growing children).
Sources: Oily fish, eggs, and sunshine on the skin.
5. Minerals (Essential Elements)
Just like vitamins, minerals are needed in small amounts for specific body functions:
• Calcium: Needed for strong bones and teeth, and for healthy blood clotting.
Sources: Milk, cheese, yoghurt, and green leafy vegetables.
• Iron: An essential component of haemoglobin, the red pigment inside red blood cells that transports oxygen around your body.
Deficiency: Anaemia (causes extreme tiredness, fatigue, and lack of energy because your cells cannot get enough oxygen for respiration).
Sources: Red meat, spinach, and liver.
6. Dietary Fibre / Roughage (Keeping Things Moving)
• Function: Fibre cannot be digested by human enzymes. Instead, it adds bulk to the food in your intestines. This bulk gives the muscular walls of your gut something to grip and push against during peristalsis (the wave-like muscle contractions that move food along). Fibre prevents constipation and keeps your digestive tract healthy.
• Good sources: Wholemeal bread, oats, bran cereals, vegetables, and fruit skins.
7. Water (The Essential Solvent)
• Function: Acts as a solvent for chemical reactions in cells, forms the main part of blood plasma to transport nutrients and waste, and helps regulate body temperature through sweating.
• Sources: Drinking water, fruit juices, and moisture in solid food.
Quick Memory Trick: "Can Pigs Fly Very Much Down Waterways?"
Use this sentence to recall the 7 components: Carbohydrates, Proteins, Fats, Vitamins, Minerals, Dietary fibre, Water.
Key Takeaway:
A healthy diet requires all seven food groups in the correct balance. Missing a vitamin or mineral leads to deficiency diseases: lack of Vitamin C causes scurvy, lack of Vitamin D causes rickets, and lack of iron causes anaemia.
---Part 2: Food Tests (Prescribed Practical Skills)
In your practical assessments and written exams, you are expected to know the exact reagents, methods, starting colours, and positive results for four key food tests.
1. Testing for Starch (Iodine Test)
• Reagent: Iodine solution.
• Initial colour: Yellow-brown (or orange-brown).
• Method: Add a few drops of iodine solution directly onto the food sample at room temperature.
• Positive result: Turns blue-black.
• Negative result: Stays yellow-brown.
2. Testing for Reducing Sugars, e.g., Glucose (Benedict's Test)
• Reagent: Benedict's reagent.
• Initial colour: Blue.
• Method: Add Benedict's reagent to the food solution and heat in a hot water bath (\(>75\text{ }^\circ\text{C}\) or boiling) for several minutes.
• Positive result: Colour changes from blue \(\rightarrow\) green \(\rightarrow\) yellow \(\rightarrow\) brick-red precipitate (the more sugar present, the closer it gets to brick-red).
• Negative result: Stays blue.
3. Testing for Protein (Biuret Test)
• Reagent: Biuret reagent (or dilute sodium hydroxide followed by copper sulfate solution).
• Initial colour: Blue.
• Method: Add Biuret reagent directly to the food sample solution at room temperature and shake gently.
• Positive result: Turns lilac / purple / violet.
• Negative result: Stays blue.
4. Testing for Fats / Lipids (Ethanol Emulsion Test or Sudan III)
• Method (Ethanol Emulsion): Dissolve the sample in ethanol, shake thoroughly, then pour the liquid into a tube of cold water.
• Initial appearance: Clear / colourless.
• Positive result: A cloudy-white emulsion forms.
• Alternative test: Adding Sudan III stain gives a red-stained oily layer floating on top.
Top Exam Pitfalls to Avoid:
• Forgetting the Water Bath: Benedict's test is the only standard food test that requires heating! If you do not state "heat in a hot water bath", you will lose marks.
• Confusing Reagent Colours: Iodine starts yellow-brown and turns blue-black. Biuret starts blue and turns lilac/purple. Do not mix them up!
Key Takeaway:
• Starch: Iodine \(\rightarrow\) Yellow-brown to blue-black.
• Glucose / Sugar: Benedict's + HEAT \(\rightarrow\) Blue to brick-red precipitate.
• Protein: Biuret \(\rightarrow\) Blue to lilac / purple.
• Lipids: Ethanol + Water \(\rightarrow\) Colourless to cloudy-white emulsion.
Part 3: Measuring Energy in Food (Calorimetry)
We can find out how much energy is stored inside a piece of food by burning it underneath a known volume of water and measuring how much the water heats up.
Step-by-Step Laboratory Method:
1. Measure a set volume of water (for example, \(10\text{ cm}^3\) or \(20\text{ cm}^3\)) into a boiling tube held by a clamp and stand.
2. Record the starting temperature of the water with a thermometer.
3. Weigh the starting mass of the dry food sample (e.g., a piece of pasta or peanut) using an electronic balance.
4. Mount the food on a mounted needle, set it alight in a Bunsen burner flame, and immediately hold it directly underneath the boiling tube of water.
5. If the flame goes out and the food is not fully burnt, relight it immediately until the food is completely burnt to ash.
6. Measure the final maximum temperature of the water to find the temperature rise (\(\Delta T\)).
7. Re-weigh any unburnt residue to find the exact mass of food that burned.
Calculations:
Remember that \(1\text{ cm}^3\) of water has a mass of \(1\text{ g}\). Therefore, \(20\text{ cm}^3\) of water \(= 20\text{ g}\).
Step 1: Calculate Energy Transferred to the Water:
\(\text{Energy Transferred (Joules, J)} = \text{Mass of water (g)} \times 4.2\text{ J/g}^\circ\text{C} \times \text{Temperature Rise }(^\circ\text{C})\)
Note: The value \(4.2\text{ J/g}^\circ\text{C}\) is the specific heat capacity of water (the energy required to heat \(1\text{ g}\) of water by \(1\text{ }^\circ\text{C}\)).
Step 2: Calculate Energy Content per Gram of Food:
Because different food samples have different starting masses, you must calculate the energy per gram to make a fair comparison:
\(\text{Energy content per gram of food (J/g)} = \frac{\text{Energy Transferred (J)}}{\text{Mass of food burned (g)}}\)
Worked Example:
A student burns \(0.5\text{ g}\) of crisp underneath a boiling tube containing \(20\text{ cm}^3\) of water. The water temperature rises from \(18\text{ }^\circ\text{C}\) to \(38\text{ }^\circ\text{C}\).
• Temperature rise \(= 38 - 18 = 20\text{ }^\circ\text{C}\)
• Mass of water \(= 20\text{ g}\)
• \(\text{Energy transferred} = 20\text{ g} \times 4.2 \times 20\text{ }^\circ\text{C} = 1680\text{ J}\)
• \(\text{Energy per gram} = \frac{1680\text{ J}}{0.5\text{ g}} = 3360\text{ J/g}\)
Sources of Error & How to Improve the Experiment:
Simple classroom experiments always give an energy value much lower than the real nutritional value printed on the food packaging. In an exam, you may be asked why this happens:
• Heat loss to the surroundings: Heat escapes into the surrounding air and heats the glass boiling tube instead of the water. Improvement: Put a heat shield (draught shield) around the apparatus.
• Incomplete burning: Some food does not burn completely. Improvement: Supply pure oxygen using a professional bomb calorimeter.
• Heat lost during transfer: Heat is lost while moving the burning food from the Bunsen burner to the boiling tube. Improvement: Ignite the food electronically inside an enclosed container.
Key Takeaway:
Food energy is calculated using \(\text{Energy (J)} = \text{Mass of water (g)} \times 4.2 \times \text{Temperature Rise }(^\circ\text{C})\). Simple test-tube experiments underestimate energy mainly due to heat loss to the surroundings and incomplete combustion.
---Part 4: Energy Balance, Diet, and Health
The Energy Balance Equation
Your body takes in energy from food and expends energy through everyday metabolic processes (like keeping your heart beating) and physical activity:
• Energy Intake = Energy Output: Body mass stays constant (healthy balance).
• Energy Intake > Energy Output: Excess energy is converted and stored as fat. Over time, this leads to weight gain and obesity.
• Energy Intake < Energy Output: The body breaks down fat and muscle stores to supply energy, resulting in weight loss, weakness, and muscle wasting.
Health Risks Associated with Obesity
Eating too much sugar and saturated fat while not exercising can lead to obesity. Obesity is a major risk factor for:
• Type 2 diabetes: The body becomes resistant to insulin, making it hard to control blood glucose levels.
• High blood pressure: Puts strain on blood vessels and organs.
• Coronary heart disease: Fatty deposits build up in the coronary arteries, reducing oxygen delivery to the heart muscle and increasing the risk of a heart attack.
Factors Affecting Daily Energy Requirements
Not everyone needs the exact same amount of energy each day. Requirements vary depending on:
• Age: Growing children and teenagers require more energy per kilogram of body weight to support rapid growth and high metabolic rates.
• Activity level: Athletes and manual labourers need significantly more energy than people with sedentary (desk-based) lifestyles.
• Biological sex: Males generally have a higher proportion of muscle mass and larger body size on average, requiring more energy.
• Pregnancy: Pregnant and breastfeeding women need extra energy and nutrients to support the growing baby and produce milk.
Key Takeaway:
Energy balance means matching calorie intake to energy output. Excess intake leads to fat storage and obesity, increasing the risk of Type 2 diabetes and coronary heart disease.
---Chapter Quick Review Checklist
Before sitting your Unit 1 Biology exam, make sure you can answer YES to each of these points:
✔ Can you name the 7 food groups and state the main function of each?
✔ Do you know that Scurvy comes from lack of Vitamin C, Rickets from lack of Vitamin D, and Anaemia from lack of Iron?
✔ Can you describe the color changes for Iodine (blue-black), Biuret (lilac/purple), Benedict's (brick-red precipitate + heat), and Ethanol (cloudy emulsion)?
✔ Can you calculate energy transferred using \(\text{Mass of water} \times 4.2 \times \text{Temp Rise}\)?
✔ Can you explain why simple calorimetry results are lower than true values (heat loss to air, incomplete burning)?
✔ Can you name three health risks linked to obesity (Type 2 diabetes, high blood pressure, coronary heart disease)?