Food — Sources, Components and Food Preservation

Sources of Food

All food ultimately comes from plants and animals. Plants are the primary producers because they make their own food through photosynthesis; everything else in the food chain depends on them. Common plant sources include cereals (wheat, rice, maize), pulses (dal, soybean), vegetables, fruits, nuts and seeds, and vegetable oils. Common animal sources include milk and dairy products, meat, fish, eggs, and honey.

Some foods are obtained from both plant and animal origins. Sugar is produced from sugarcane (plant) but also from sugar beet. Cooking oils come from sunflower, mustard, or groundnuts (plant) as well as from fish liver oil (animal). Soybean is particularly important as a plant source of protein — it contains roughly 36–40 g of protein per 100 g, comparable to animal protein in quality.

CTET frequently tests the concept that some organisms do not prepare their own food. Cuscuta (amarbel) is a parasitic plant that twines around a host plant and absorbs nutrients from it — it lacks chlorophyll and is therefore dependent. This is a standard Class 6 NCERT concept that appears in CTET Science questions.

Major Nutrient Groups

Nutrients are the chemical substances in food that the body uses for energy, growth, and repair. NCERT Class 6 identifies the following groups:

• Carbohydrates — primary source of energy. Present in rice, wheat, potatoes, sugars. Starch and sugar are the two forms tested in CTET.
• Proteins — needed for growth and repair of body tissues. Rich sources: pulses, eggs, fish, meat, milk, soybean. Proteins are called 'body-building foods'.
• Fats — concentrated energy source (9 kcal/g, more than double carbohydrates). Present in butter, ghee, oil, nuts, meat. Also called energy-giving foods.
• Vitamins — needed in very small amounts; do not provide energy but regulate body processes. Fat-soluble: A, D, E, K. Water-soluble: B group and C.
• Minerals — inorganic elements needed in small amounts. Calcium (bones/teeth), Iron (haemoglobin), Iodine (thyroid function).
• Water — transports nutrients, regulates temperature, removes waste. Constitutes about 60–70% of body mass.
• Roughage / Dietary Fibre — cellulose from plant cell walls. Does NOT provide energy, but aids digestion and prevents constipation.

A balanced diet contains all nutrients in appropriate amounts. NCERT stresses that no single food gives all nutrients; variety is essential.

Vitamins and Their Roles

Vitamins are organic compounds required in tiny amounts. CTET tests vitamins A, B1, B2, B12, C, and D most frequently.

Important: Vitamin D is unique — it is synthesised in the skin when exposed to sunlight (UV rays). It is therefore both a vitamin and a hormone precursor.

Minerals and Their Importance

Minerals are inorganic elements required for structural and regulatory functions. The most tested minerals in CTET are:

• Calcium — essential for strong bones and teeth, muscle contraction, blood clotting. Deficiency leads to weak bones (osteoporosis in adults, rickets along with Vitamin D deficiency in children). Sources: milk, curd, paneer, leafy vegetables, ragi.
• Iron — component of haemoglobin in red blood cells, which carries oxygen. Deficiency causes anaemia (paleness, fatigue, breathlessness). Sources: green leafy vegetables (spinach), jaggery, meat, pulses.
• Iodine — essential for thyroid hormone production, which regulates metabolism. Deficiency causes goitre (enlarged thyroid gland) and cretinism in children if maternal iodine is deficient. Sources: iodised salt, seafood.
• Phosphorus — works with calcium for bone and tooth formation; also important in DNA, energy molecules (ATP). Sources: milk, eggs, meat, nuts.

A common exam question pairs minerals with deficiency diseases. Remember: Iron → Anaemia, Iodine → Goitre, Calcium → Rickets/Osteoporosis.

Tests for Nutrients

NCERT Class 6 Chapter 2 describes simple chemical tests for detecting nutrients. These are high-priority CTET topics:

The iodine test for starch is the single most-tested food content test in CTET. When iodine solution is added to a starch-containing sample, the starch-iodine complex forms, giving an intense blue-black colour. This is NOT seen with glucose, proteins, or fats.

Methods of Food Preservation

Food spoils because of microbial growth (bacteria, fungi, yeast). Preservation slows or prevents microbial activity. NCERT and CTET test these methods:

• Sun-drying / Dehydration — removes moisture that microbes need. Used for fish, vegetables, fruits (raisins, dried figs).
• Salting — creates a hypertonic environment; microbes lose water by osmosis and die. Used for pickles, preserved fish, meat.
• Adding sugar — same osmotic principle as salting. Used in jams, jellies, marmalade.
• Oil and vinegar — vinegar (acetic acid) lowers pH; oil excludes oxygen. Used in pickles.
• Pasteurisation — heating milk to 72°C for 15 seconds (HTST) then cooling rapidly. Kills pathogenic bacteria without significantly changing taste or nutrition.
• Refrigeration and freezing — low temperature slows microbial growth and enzyme activity.
• Canning — food sealed in airtight cans and heat-treated; excludes oxygen and sterilises.
• Chemical preservatives — sodium benzoate, sodium metabisulphite used in jams, squashes, and packaged foods.

The concept of osmosis as the mechanism behind salting and sugaring is conceptually rich and appears in both food and biology questions. CTET Paper 2 teachers should be ready to explain this linkage.

Balanced Diet and Malnutrition

A balanced diet is one that provides all nutrients in correct proportions according to a person's age, sex, and level of physical activity. It must include:

• Carbohydrates and fats — for energy
• Proteins — for growth and repair
• Vitamins and minerals — for regulation and protection
• Water and roughage — for digestion and waste removal

Malnutrition results when the diet lacks one or more nutrients or when total intake is inadequate. Types:

• Undernutrition — total caloric deficit. Causes kwashiorkor (protein deficiency in children — pot belly, discoloured hair) and marasmus (severe calorie + protein deficiency — wasting).
• Overnutrition — excess caloric intake leading to obesity, diabetes, cardiovascular disease.
• Specific deficiency — vitamin or mineral deficiency diseases (listed above).

CTET pedagogy questions ask how teachers can use students' prior knowledge about home cooking and local foods to build understanding of balanced diets. A contextualised approach — using regional food habits, local crops — is preferred over rote definitions.

Pedagogical Approaches for Food Topics

CTET Paper 2 Science has a dedicated pedagogy component (SCI-08, SCI-09). Food-related pedagogy questions focus on:

• Activity-based learning — students perform the iodine, Biuret, or fat tests on common foods. This develops process skills: observing, inferring, predicting, recording.
• Constructivist approach — start with students' existing knowledge about what they eat at home, then introduce scientific concepts. Avoid starting with definitions of carbohydrates or proteins in isolation.
• Socio-scientific dimension — food security, organic farming, GM food are examples of socio-scientific issues that can be incorporated. Q84 of CTET Aug 2023 directly tested this understanding.
• Concept mapping — helping students connect food sources → nutrients → body functions → deficiency diseases as a linked concept network.
• Common misconceptions — students often believe that roughage (dietary fibre) provides energy, or that all fats are harmful. A good teacher addresses these alternate conceptions explicitly through guided inquiry.

Jan 2024 Q77 asked about the best strategy to introduce deficiency diseases: the preferred answer was to arrange a doctor's prescription pertaining to a deficiency disease and discuss it — a contextualised, real-world approach over simply listing nutrients or definitions.