Chapter 2 — Components Of Food

Food is essential for all living beings. It provides energy to carry out daily activities, raw materials for growth and repair of tissues, and substances that regulate body processes. Without adequate and appropriate food, organisms cannot grow, stay healthy, move, or repair damage.

Main reasons why we need food

• Energy: Food supplies energy required for walking, running, thinking, playing, and keeping the body warm. Energy comes mainly from carbohydrates and fats.
• Growth and repair: Proteins and minerals (like calcium) give the building blocks to grow new cells and repair tissues (for example, muscles, bones, and skin).
• Protection and defence: Vitamins and minerals help the body fight infections and keep the immune system working properly (for example, vitamin C and iron).
• Regulation: Water, vitamins and minerals help regulate body temperature, chemical reactions and transport of substances in the body.
• Digestion and cellular processes: Food is broken down by digestion into smaller molecules. Cells then use these molecules in respiration to release energy.

Important types of nutrients

• Carbohydrates: Main source of energy (e.g., rice, bread, potatoes).
• Proteins: For growth and repair (e.g., pulses, eggs, meat, milk).
• Fats: Concentrated energy source and insulation (e.g., ghee, oils, nuts).
• Vitamins and minerals: Small quantities but vital for health (e.g., vitamin C in citrus fruits, calcium in milk).
• Roughage (fibre): Keeps the digestive system healthy (e.g., vegetables, whole grains).
• Water: Needed for most body processes and to maintain body temperature.

How food becomes useful: After eating, food is digested into simple molecules (glucose, amino acids, fatty acids). Cells use these molecules in cellular respiration to release energy that the body stores or uses for work.

Key point: A balanced diet (right proportions of carbohydrates, proteins, fats, vitamins, minerals, water and fibre) keeps us healthy and active.

What are major nutrients?

Major nutrients are the food components our body needs in relatively large amounts to grow, get energy, build and repair tissues, and keep body functions normal. The main (major) nutrients are carbohydrates, proteins, fats, vitamins, minerals, water and dietary fibre (roughage). A balanced diet contains all of these in the right amounts.

Brief description of each major nutrient

• Carbohydrates: Main source of energy. Found as sugars, starches and cellulose. Examples: rice, wheat, potatoes, fruits. Simple test: iodine turns blue-black in presence of starch.
• Proteins: Used for growth and repair of body tissues and for making enzymes and hormones. Made of amino acids. Examples: pulses, eggs, meat, milk. Deficiency causes stunted growth and weakness. Protein test (class experiment): biuret or simple heat/coagulation of milk/egg protein.
• Fats (lipids): Concentrated source of energy, provide insulation and protect organs; help absorb fat‑soluble vitamins (A, D, E, K). Examples: butter, oil, ghee, nuts. Too much fat leads to obesity; too little causes energy shortage.
• Vitamins: Organic compounds needed in small amounts for body processes (vision, immunity, blood clotting, etc.). Examples: vitamin A (carrots, liver), vitamin C (citrus fruits), vitamin D (sunlight, fish). Deficiency causes specific diseases (e.g., scurvy for vitamin C, night blindness for vitamin A).
• Minerals: Inorganic elements like calcium, iron, iodine and sodium needed for bones, blood, thyroid function and fluid balance. Examples: milk (calcium), green leafy vegetables (iron), iodised salt (iodine). Deficiency may lead to anaemia, weak bones, goitre.
• Water: Essential for all life processes — transport of substances, digestion, temperature regulation and chemical reactions. Most of the body is made up of water; dehydration is harmful.
• Dietary fibre (Roughage): Indigestible plant material (cellulose) that helps in bowel movement and prevents constipation. Examples: whole grains, vegetables, fruits.

Balanced diet and approximate composition

A healthy balanced diet for most children contains roughly: 50–60% of energy from carbohydrates, 10–15% from proteins, and 20–30% from fats, plus sufficient vitamins, minerals, water and fibre. Quantities vary with age, activity and health.

Why these nutrients matter (summary)

• Carbohydrates and fats = main energy providers.
• Proteins = builders and repairers.
• Vitamins and minerals = regulators of body functions.
• Water = medium for life processes.
• Fibre = keeps digestive system healthy.

Common deficiency signs (quick list)

• Protein — stunted growth, weak muscles.
• Iron — pale skin, tiredness (anaemia).
• Vitamin A — night blindness.
• Vitamin C — bleeding gums, slow healing (scurvy).
• Calcium/Vitamin D — weak bones, rickets in children.

Understanding major nutrients helps choose foods that give energy, growth and protection against disease. Use food from different groups (grains, pulses, milk, vegetables, fruits, fats) every day to get all nutrients.

This practical shows simple tests to identify the main components of food: starch (a carbohydrate), sugar (reducing sugars like glucose), proteins and fats. Each test uses a specific reagent and a clear visible change (colour or spot) as evidence. These tests are qualitative and commonly done in school labs.

• Materials commonly used: food samples (potato, rice, apple, milk, egg white, butter, dal, bread), iodine solution, Benedict's reagent, Biuret reagent (or sodium hydroxide + dilute copper sulphate), brown paper or Sudan III stain, test tubes, dropper, water bath, glass rod, spatula.
• Test for starch (Iodine test)
  • Procedure: Put a small piece or paste of the food in a clean spot or test tube. Add 2–3 drops of iodine solution.
  • Observation: If starch is present the sample turns blue-black. If not, it remains brownish-yellow.
  • Interpretation: Blue-black colour = starch present.
• Test for reducing sugar (Benedict's test)
  • Procedure: Put about 1 ml of aqueous extract of the food in a test tube. Add equal volume of Benedict's reagent. Heat the mixture in a boiling water bath for 2–5 minutes.
  • Observation: Colour changes from blue → green → yellow → orange → brick-red depending on amount of reducing sugar; brick-red precipitate (Cu2O) indicates high reducing sugar.
  • Interpretation: Any change from blue indicates presence of reducing sugar. No change (remains blue) = no reducing sugar.
• Test for protein (Biuret test)
  • Procedure: Take sample extract in a test tube. Add few drops of 10% sodium hydroxide solution. Then add 1–2 drops of 1% copper sulphate solution (or a ready Biuret reagent).
  • Observation: Formation of a violet or purple colour indicates protein.
  • Interpretation: Violet colour = protein present; no colour change = protein absent.
• Test for fats (Grease spot test or Sudan III staining)
  • Grease spot: Rub a bit of sample on a piece of brown paper and let it dry. A translucent grease spot that does not disappear when dry indicates fat.
  • Sudan III: Mix extract with Sudan III stain; if fat is present a red-stained oil layer separates or red droplets appear.
  • Interpretation: Translucent spot or red-stained oil = fat present.
• Precautions
  • Use clean, dry test tubes and fresh reagents. Carry out Benedict's test with care and heat only in a water bath. Handle copper sulphate and strong alkali carefully and use gloves/eye protection if available. Do small-scale tests only.
• Summary
  • These simple colour/spot tests let you identify major food components quickly. They are qualitative—useful for classroom experiments and understanding what different foods contain.

Introduction
Food is made of different components — carbohydrates, proteins, fats, vitamins, minerals, water and roughage (fibre). Each component has specific functions that keep the body healthy, give energy, help growth and protect against disease.

1. Carbohydrates

Function: Main source of energy for the body. They are broken down to release glucose used by cells for work and heat.

• Sources: Rice, wheat, potatoes, sugar, fruits.
• Deficiency/too much: Low energy if deficient; weight gain and dental problems if excess.

2. Proteins

Function: Building and repair of body tissues (muscles, skin, organs); important for growth, and making enzymes and some hormones.

• Sources: Milk, eggs, pulses (dal), meat, fish, soy, nuts.
• Deficiency: Poor growth in children, muscle wasting, slow healing.

3. Fats (Lipids)

Function: Concentrated energy store, insulation to keep the body warm, protection of organs, and help absorb fat‑soluble vitamins (A, D, E, K).

• Sources: Ghee, butter, oil, nuts, oily fish.
• Deficiency/too much: Too little causes low energy; excess causes obesity and heart problems.

4. Vitamins

Function: Small amounts needed for growth, repair and regulation of body processes (vision, immunity, blood clotting, etc.). Each vitamin has a special role.

• Examples: Vitamin A (vision, growth), Vitamin C (wound healing, immunity), Vitamin D (calcium absorption).
• Deficiency: Night blindness (A), scurvy (C), rickets (D).

5. Minerals

Function: Elements like calcium and iron are needed for strong bones and teeth, blood formation and nerve function.

• Sources and roles: Calcium (milk, bones), Iron (green leafy vegetables, meat) — iron prevents anaemia.

6. Water

Function: Makes up a large part of the body, helps in transport of nutrients and waste, keeps temperature stable and supports chemical reactions.

7. Roughage (Dietary Fibre)

Function: Helps digestion and prevents constipation by adding bulk to stool; helps a healthy gut.

• Sources: Whole grains, vegetables, fruits, dals.

Balanced Diet (brief)

A balanced diet contains the right proportion of all food components so the body gets energy, growth materials and protection. For children, this typically means a mix of cereals, pulses, milk, vegetables, fruits and fats in appropriate amounts.

Summary: Carbohydrates and fats provide energy; proteins build and repair; vitamins and minerals regulate body processes; water sustains life activities; fibre aids digestion.

What are food groups? Foods are grouped according to the main nutrients they provide and the functions they perform in the body. The major food groups are:

• Carbohydrates: Main source of energy. Found in rice, wheat, maize, potatoes, bread, sugar.
• Proteins: Needed for growth and repair of body tissues. Found in pulses (dal), legumes, eggs, meat, fish, milk and dairy products, soy.
• Fats (lipids): Concentrated energy source and needed for warmth, cushioning organs and absorption of fat‑soluble vitamins. Found in oils, ghee, butter, nuts, seeds, fatty fish.
• Vitamins: Small amounts needed for specific body functions (immunity, vision, blood clotting). Fruits and vegetables, milk, eggs, liver are common sources (e.g., vitamin C in citrus, vitamin A in carrots).
• Minerals: Elements like calcium and iron. Calcium for bones and teeth (milk, cheese, leafy greens); iron for blood (green leafy vegetables, jaggery, meat).
• Dietary fibre (roughage): Helps digestion and prevents constipation. Found in whole grains, fruits, vegetables, pulses.
• Water: Essential for all body processes, transport of nutrients and removal of wastes.

Balanced diet — meaning and importance

A balanced diet supplies all the nutrients in the right amounts to keep the body healthy, growing and active. It should include foods from all groups in proper proportions. A balanced diet helps: healthy growth, good immunity, energy for study and play, proper digestion and prevention of deficiency diseases (such as scurvy, rickets, anemia).

Simple guideline for proportions

• Carbohydrates: largest portion (staple foods like rice/roti/potatoes)
• Proteins: moderate portion (pulses, milk, eggs, meat as available)
• Fats: small to moderate portion (use small amount of cooking oil/ghee)
• Fruits & vegetables: include daily for vitamins, minerals and fiber
• Water: drink adequate plain water throughout the day

Practical tips for children (Class 6 level)

• Have a variety of colored fruits and vegetables every day.
• Combine cereals with pulses (e.g., roti + dal or rice + dal) to get better protein quality.
• Avoid too many sweets and fried foods; treat them occasionally.
• Include a glass of milk or a dairy serving daily for calcium.
• Eat regular meals and healthy snacks (fruit, nuts, yogurt) rather than skipping meals.

How to recognize imbalance

• Too little protein — poor growth, weak muscles.
• Too little iron — tiredness, pale skin (anemia).
• Too little vitamin C — easy bruising and infections (scurvy is rare now but vitamin C prevents it).
• Excess fats and sugar — weight gain and reduced fitness.

Definition: Deficiency diseases are illnesses caused by the lack of one or more essential nutrients (vitamins, minerals, proteins, or calories) in the diet. When the body does not get enough of a nutrient it needs to function properly, specific symptoms and disorders develop.

Causes

• Poor or unbalanced diet (not eating foods that contain required nutrients)
• Poverty or lack of access to varied foods
• Poor absorption of nutrients by the body (due to illness)
• Increased need for nutrients during growth, pregnancy or illness

Common deficiency diseases, their missing nutrient, symptoms and prevention

• Scurvy — Lack of vitamin C. Symptoms: bleeding gums, swollen joints, tiredness. Prevention: eat citrus fruits, tomatoes, guava, green leafy vegetables.
• Rickets — Lack of vitamin D (and sometimes calcium). Symptoms: weak, bowed legs, delayed growth. Prevention: sunlight exposure, milk, eggs, fish, fortified foods.
• Night blindness — Lack of vitamin A. Symptoms: difficulty seeing in dim light, dry eyes. Prevention: carrots, sweet potatoes, spinach, milk, liver.
• Beriberi — Lack of vitamin B1 (thiamine). Symptoms: weakness, nerve problems, swelling. Prevention: whole grains, pulses, meat, nuts.
• Pellagra — Lack of vitamin B3 (niacin). Symptoms: diarrhea, dermatitis, mental confusion. Prevention: pulses, meat, dairy, green vegetables.
• Iron deficiency anemia — Lack of iron. Symptoms: tiredness, pale skin, shortness of breath. Prevention: green leafy vegetables, meat, jaggery, iron-fortified cereals; vitamin C helps iron absorption.
• Goitre — Lack of iodine. Symptoms: swelling in the neck (thyroid enlargement). Prevention: iodised salt, seafood.
• Kwashiorkor and Marasmus — Protein-energy malnutrition. Symptoms: stunted growth, thinness (marasmus), swollen belly and skin changes (kwashiorkor). Prevention: adequate caloric intake and good-quality proteins (milk, pulses, eggs, meat).

How to detect and when to see a doctor

• Look for persistent symptoms such as constant tiredness, pale skin, slow growth, dental and gum problems, frequent infections, or changes in vision.
• Simple checks: weight and height compared to standard charts for age, and in older children/adults, Body Mass Index (BMI) can be calculated.
• See a doctor if symptoms persist; blood tests can confirm deficiencies (for example, haemoglobin for iron, blood levels for vitamins).

Prevention and treatment

• Eat a balanced diet containing fruits, vegetables, cereals, pulses, milk, eggs and meat (if not vegetarian).
• Use fortified foods where available (e.g., iodised salt, fortified flour).
• Sunlight exposure for vitamin D production.
• Medical treatment: supplements or medicines prescribed by a healthcare provider when deficiency is confirmed.

Summary: Deficiency diseases are avoidable with a varied, balanced diet and simple public-health measures (fortification, supplements and awareness). Recognising early signs and correcting diet quickly prevents long-term harm.

What is food? Food is any substance eaten to provide energy and materials for growth, repair and maintenance of the body. Food contains different nutrients — carbohydrates, proteins, fats, vitamins, minerals, fibre and water — each with specific functions.

Nutrients and their functions

• Carbohydrates: Main source of energy (found in rice, wheat, potatoes, sugar).
• Proteins: Build and repair body tissues (found in pulses, eggs, meat, milk).
• Fats: Provide concentrated energy and help absorb some vitamins (found in oil, ghee, nuts).
• Vitamins: Help chemical reactions and keep body healthy (vitamin C in citrus; vitamin D from sunlight and milk).
• Minerals: Important for body structure and function (iron for blood, calcium for bones).
• Fibre (roughage): Helps digestion and prevents constipation (vegetables, whole grains).
• Water: Required for almost all body processes and to maintain temperature.

Balanced diet
A balanced diet contains the right amount of all nutrients in proper proportion. A simple school-level plate example: a cereal (roti/rice), a pulse (dal), vegetables, a source of protein (egg/curd/tofu), fruit and water. Balanced diet supports growth, active life and resistance to disease.

Deficiency diseases (short examples)

• Scurvy: Vitamin C deficiency — bleeding gums, poor wound healing.
• Rickets: Vitamin D/calcium deficiency — weak or deformed bones in children.
• Anaemia: Iron deficiency — tiredness, pale skin.
• Kwashiorkor/Marasmus: Severe protein-energy malnutrition — stunted growth, swelling.

Health and hygiene
Good health is the result of proper food habits plus hygiene. Hygiene includes personal cleanliness, food safety and safe water. Key practices: regular handwashing with soap (especially before eating and after using toilet), cleaning fruits/vegetables, cooking food thoroughly, storing food safely (cover and refrigerate where possible), and drinking boiled/filtered water.

How food and hygiene are connected
Poor hygiene (unclean hands, contaminated water or food) can cause infections like diarrhoea, which reduces nutrient absorption and leads to weakness and malnutrition. Good hygiene protects the nutritional benefits of food.

Practical tips for children/families

• Eat a variety of foods every day: cereals, pulses, vegetables, fruits, milk and limited sweets.
• Wash hands with soap before meals and after the toilet.
• Clean and store food properly; reheat leftovers thoroughly.
• Drink safe water — boil or filter if unsure.
• Play and exercise daily to stay active and maintain appetite.

This topic describes the hands-on practical skills and classroom activities used to identify the main components of food (carbohydrates, fats, proteins and sugars) and how to assess students' practical performance. Emphasis is on careful observation, following safe procedures, accurate recording of results and drawing correct conclusions.

Common practical skills taught

• Making and following step-by-step experimental procedures.
• Careful observation of colour or physical change during tests.
• Using simple apparatus correctly (dropper, test tubes, heating gently with adult supervision).
• Recording results in tables, drawing clear diagrams and writing conclusions.
• Working safely: wearing gloves/goggles where needed, handling reagents carefully and disposing waste properly.

Typical classroom activities (with expected results)

• Starch test (iodine solution): Put a drop of iodine on a sample of food (or food extract). A blue-black or dark blue colour shows presence of starch.
• Fat test (brown paper/surface grease test): Rub a small amount of the food on a piece of brown (blotting) paper. A translucent grease spot that does not disappear on drying indicates fats/oils.
• Sugar test (Benedict's test for reducing sugars) — teacher demonstration or with supervision: Mix food extract with Benedict's solution and heat. Colour change from blue → green → yellow → orange → brick-red depends on sugar amount (green = small, red = large).
• Protein test (Biuret test) — optional/advanced: Add Biuret reagent (alkaline copper sulfate). A violet/lilac colour indicates protein.

Safety and supervision

• Carry out chemical tests under teacher supervision. Use small quantities of reagents. Wear protective gear when instructed.
• Never taste reagents or unknown mixtures. Follow disposal instructions for chemical waste.

Assessment of practical work

• Assess planning and understanding: Can the student explain the purpose and procedure?
• Assess practical performance: correct use of materials/apparatus, following steps, and safety.
• Assess observation & recording: clarity of notes, accuracy of recorded colours/changes, labelled diagrams or tables.
• Assess interpretation & conclusions: correct identification of nutrient and reasoning.
• Use a simple rubric (for example out of 10): Procedure & safety (3), Observation & recording (3), Interpretation & conclusion (3), Neatness/teamwork (1).

Tips for teachers and students

• Demonstrate reagent colours before students perform tests so comparisons are clear.
• Use control samples (known starch, sugar, fat) alongside unknown foods for reliable comparison.
• Encourage students to write one-sentence conclusions like: “Iodine turned blue-black → sample contains starch.”