Components of Food — Class 6 Biological Science
'Food is fuel for the body — and different nutrients play different roles in keeping the engine running.'
1. Introduction
Food contains different components (nutrients) that our body needs. Each nutrient has a specific job — some give energy, some help growth, some protect from diseases.
The Six Main Nutrients
- Carbohydrates — Energy
- Proteins — Growth and repair
- Fats — Energy storage and warmth
- Vitamins — Protection from diseases
- Minerals — Body functions
- Dietary fibre and Water — Digestion and hydration
2. Carbohydrates
Carbohydrates are the body's main source of energy.
Sources
- Cereals: rice, wheat, maize, millets (ragi, jowar)
- Roots and tubers: potato, sweet potato, tapioca
- Fruits: banana, mango, grapes
- Sugars: sugar, honey, jaggery
Functions
- Provide energy for all activities (walking, running, studying)
- Excess carbohydrates are stored as fat
'In Andhra meals, rice provides the main carbohydrates — it is the energy source for the day.'
Test for Starch (Carbohydrate)
Iodine test: Add 2-3 drops of iodine solution to food.
- Blue-black colour → starch present
- No colour change → no starch
3. Proteins
Proteins are body-building nutrients. They help in growth and repair of body tissues.
Sources
- Animal: milk, eggs, meat, fish, chicken
- Plant: pulses (dal), beans, soyabean, groundnuts, legumes
- In AP: toor dal, moong dal, chana dal, fish from coast
Functions
- Build and repair body tissues
- Growth of muscles, bones, skin, hair
- Make enzymes and hormones
Test for Proteins
Copper sulphate + caustic soda test:
- Grind food, add water
- Add 10 drops of caustic soda solution
- Add 2 drops of copper sulphate solution
- Violet colour → protein present
4. Fats
Fats provide energy and help absorb certain vitamins. They also keep the body warm.
Sources
- Plant oils: groundnut oil, sunflower oil, coconut oil, mustard oil
- Animal fats: ghee, butter, cheese, meat fat
- Nuts and seeds: groundnuts, cashew, almonds, sesame seeds
- In AP: groundnut oil is widely used in cooking
Functions
- Provide concentrated energy (more than carbs)
- Store energy for later use
- Keep the body warm (insulation)
- Protect internal organs
- Help absorb vitamins A, D, E, K
Test for Fats
Paper test: Rub food on paper
- Greasy translucent spot → fat present
- No spot → no fat (or low fat)
| Food | Grease Spot | Fat Present? |
|---|---|---|
| Groundnut | Yes | Yes |
| Apple slice | No | No |
| Butter | Yes | Yes |
5. Vitamins
Vitamins protect the body from diseases and help various body functions. They are needed in small quantities.
Vitamin Types and Functions
| Vitamin | Source | Function | Deficiency Disease |
|---|---|---|---|
| Vitamin A | Carrot, papaya, mango, milk, egg yolk | Good eyesight, healthy skin | Night blindness |
| Vitamin B₁ (Thiamine) | Rice bran, wheat, pulses, nuts | Energy metabolism | Beriberi |
| Vitamin C | Citrus fruits (lemon, orange), amla, guava | Immunity, wound healing | Scurvy |
| Vitamin D | Sunlight, milk, egg, fish | Strong bones and teeth | Rickets |
| Vitamin K | Green leafy vegetables | Blood clotting | Bleeding disorders |
Key Points
- Vitamin D is called the 'sunshine vitamin' — our body makes it when exposed to sunlight
- Vitamin C is destroyed by heat — eat raw fruits for maximum benefit
- In AP: amla (usiri), guava, and leafy greens are excellent vitamin sources
6. Minerals
Minerals are needed for various body functions like building bones, making blood, and regulating body processes.
Important Minerals
| Mineral | Source | Function | Deficiency |
|---|---|---|---|
| Calcium | Milk, curd, cheese, leafy greens | Strong bones and teeth | Rickets, weak bones |
| Iron | Spinach, apple, meat, jaggery | Makes blood (haemoglobin) | Anaemia |
| Iodine | Iodised salt, seafood | Thyroid gland function | Goitre |
| Phosphorus | Milk, grains, nuts | Bones and teeth | Weakness |
AP Context
- Anaemia: Common in some parts of AP due to iron deficiency. Eating iron-rich foods like spinach (palakura) and jaggery (bellam) helps.
- Goitre: Seen in hilly regions where iodine in soil/water is low. Using iodised salt prevents this.
7. Dietary Fibre and Water
Dietary Fibre (Roughage)
Sources: Whole grains, green vegetables, fruits with skin, nuts, seeds Functions: Helps digestion, prevents constipation 'Roughage has no nutritive value but is ESSENTIAL for proper digestion.'
Water
- Makes up about 70% of our body weight
- Functions: digestion, transport, temperature regulation, waste removal
- Need 6-8 glasses of water daily
- More water needed in hot climates (like Andhra Pradesh summers)
8. Balanced Diet
A balanced diet contains all nutrients in the right proportions.
Components of a Balanced Meal
| Food Group | Examples | Portion |
|---|---|---|
| Cereals/Grains | Rice, chapati, ragi | Largest portion |
| Pulses/Meat | Dal, fish, egg, chicken | Moderate |
| Vegetables | Leafy greens, other veggies | Moderate |
| Fruits | Seasonal fruits | Moderate |
| Milk/Curd | Glass of milk, bowl of curd | Daily |
| Fats/Oils | Ghee, oil in cooking | Small |
Thali Concept (AP Style)
A traditional Andhra meal (thali) includes:
- Rice (carbohydrates)
- Toor dal / sambar (proteins)
- Vegetable curry (vitamins, minerals)
- Gongura / chutney (vitamins)
- Curd / buttermilk (calcium, probiotics)
- Ghee (fats)
'You don't need expensive food for a balanced diet — traditional Andhra meals are naturally balanced!'
9. Deficiency Diseases
When a nutrient is consistently missing from the diet, it causes a deficiency disease.
| Disease | Deficient Nutrient | Symptoms |
|---|---|---|
| Night blindness | Vitamin A | Poor vision in dim light |
| Beriberi | Vitamin B₁ | Weakness, nerve damage |
| Scurvy | Vitamin C | Bleeding gums, slow wound healing |
| Rickets | Vitamin D | Soft, bent bones (in children) |
| Anaemia | Iron | Weakness, pale skin, tiredness |
| Goitre | Iodine | Swollen thyroid gland (neck) |
| Kwashiorkor | Protein | Swollen belly, stunted growth |
| Marasmus | Protein + Calories | Severe thinness, weakness |
Kwashiorkor vs Marasmus
| Feature | Kwashiorkor | Marasmus |
|---|---|---|
| Cause | Protein deficiency | Protein + calorie deficiency |
| Age | Usually after weaning (1-3 yrs) | Infants (<1 year) |
| Appearance | Swollen belly | Very thin, 'skin and bones' |
| Main symptom | Retained fluid (oedema) | Wasting of muscles |
10. Common Mistakes — Fix Them Now
| # | Mistake | Correction |
|---|---|---|
| 1 | Thinking all fats are bad | Fats are essential for energy and vitamin absorption. Only EXCESS fat is harmful. |
| 2 | Calling fibre a nutrient with energy value | Fibre (roughage) has NO nutritive value but is essential for digestion. |
| 3 | Confusing night blindness with complete blindness | Night blindness is difficulty seeing in dim light, not total blindness. |
| 4 | Thinking only medicine can cure deficiency | Many deficiencies are cured by including the right foods in diet. |
| 5 | Believing all vitamins come from food | Vitamin D is obtained from SUNLIGHT (plus some foods). |
11. Exam Focus
Marks Blueprint
| Question Type | Marks | Topic |
|---|---|---|
| MCQ | 1 | Nutrient function / deficiency disease |
| Fill in blank | 1 | Vitamin/mineral source |
| Short answer | 2 | Nutrient test / deficiency |
| Long answer | 3 | Balanced diet / deficiency diseases |
| Long answer | 4 | Nutrients and their functions detailed |
Quick Self-Test (5 Questions)
Q1: Which nutrient gives the most energy per gram?
<details><summary>Answer</summary>Fats (9 cal/g, compared to 4 cal/g for carbs and proteins).</details>Q2: Name the vitamin obtained from sunlight.
<details><summary>Answer</summary>Vitamin D.</details>Q3: What disease is caused by iron deficiency?
<details><summary>Answer</summary>Anaemia.</details>Q4: Which test shows the presence of starch in food?
<details><summary>Answer</summary>Iodine test — blue-black colour indicates starch.</details>Q5: What is a balanced diet?
<details><summary>Answer</summary>A diet containing all nutrients (carbs, proteins, fats, vitamins, minerals, fibre, water) in the right proportions.</details>12. Chapter Summary
- Six nutrients: carbohydrates (energy), proteins (growth), fats (energy+warmth), vitamins (protection), minerals (functions), fibre+water (digestion)
- Tests: Iodine (starch), Copper sulphate+NaOH (protein), Paper (fat)
- Balanced diet: right mix of all nutrients; traditional meals are naturally balanced
- Deficiency diseases: caused by lack of specific nutrients (scurvy, rickets, anaemia, goitre, etc.)
- AP context: rice provides carbs, dal provides protein, leafy greens provide vitamins and iron
'You are what you eat — a balanced diet keeps you healthy, active, and ready to learn!'
