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Tamil Nadu (TNBSE)Class 5 Science★ 5-6 marks in TN Class 5 Term 2 exams — choose the correct answer, fill in the blanks, match the following, true/false, short and detailed answers

Food

Samacheer Kalvi (TN State Board) Class 5 Science — Chapter 5, Food. Food preservation and balanced nutrition. Study notes, key concepts, worked examples, practice questions and quick revision for exam preparation.

⏱ 12 min readMedium difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Identify biotic factors that spoil food: microorganisms (bacteria, fungi/mould), insects, rodents
2Identify abiotic factors that spoil food: temperature (warmth speeds up spoilage), humidity (moisture encourages mould), air (oxygen causes rancidity in oily foods)
3List and explain food preservation methods: drying (removes water — vathal, dry fish), refrigeration/freezing (slows microbial growth), pickling (salt/oil/vinegar prevents microbial growth), canning (sealed, heated to kill microbes), adding sugar (jam, murabba), adding chemical preservatives (sodium benzoate in packaged foods)
4Define deficiency diseases and match: Vitamin A → night blindness, Vitamin B1 → beriberi, Vitamin C → scurvy, Vitamin D → rickets, Iron → anaemia, Iodine → goitre, Calcium → weak bones/osteoporosis
5Define a balanced diet as one containing all nutrients — carbohydrates, proteins, fats, vitamins, minerals, fibre, and water — in the right proportions
6Define BMI (Body Mass Index) as a measure of body fat based on weight and height: BMI = weight (kg) ÷ height² (m²); understand that BMI categories indicate underweight, normal, overweight, or obese

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Why this chapter matters

Food in Class 5 addresses one of the most practical science topics: why does food spoil, and how do we prevent it? Children learn that microorganisms (bacteria, fungi) are the main biotic factors that spoil food — the same invisible life they studied in earlier chapters. They explore preservation methods used for centuries in Tamil households (drying vathal, pickling, fermenting) alongside modern methods (refrigeration, vacuum packing). The chapter also covers deficiency diseases with specific nutrient-disease connections and introduces Body Mass Index (BMI) — a simple health metric. This chapter turns every child into an informed eater and a food-safety conscious individual.

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Food — Class 5 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 5 Science, Chapter 5. Food preservation and balanced nutrition.

1. About this chapter

This chapter covers Food as part of the Class 5 Samacheer Kalvi Science curriculum. It deals with food preservation and balanced nutrition and builds conceptual understanding essential for the TN School Term Exam.

By the end of this chapter, students will be able to:

Explain methods of food preservation
State importance of a balanced diet

2. Key concepts

Concept 1: Explain methods of food preservation.
Concept 2: State importance of a balanced diet.

3. Important terms and formulas

Term / Formula	Description
Explain methods of food…	Explain methods of food preservation
State importance of a…	State importance of a balanced diet

4. Worked examples

Example 1. Applying a key concept from this chapter.

Solution: Identify the relevant principle → apply the formula or rule → state the answer with correct units.

Example 2. A typical exam-style question on food.

Solution: Break the problem into steps, use the appropriate formula and verify the answer.

5. Common mistakes

Mistake: Skipping units or forgetting to state them. Fix: Always write units alongside every quantity and answer.
Mistake: Confusing similar terms or concepts in this chapter. Fix: Make a comparison table of the terms during revision.

6. Practice (exam-style)

Define the main term or principle covered in Chapter 5.
Give two real-life examples related to food.
Solve a short numerical or descriptive question from this chapter.
State one important formula and explain each symbol.

7. Answer key (hints)

Refer to section 2 (Key concepts) above for the definition.
Examples should be drawn from daily experience and local context.
Apply the formula from section 3, show all steps clearly.
Formula with units — refer to the textbook glossary for symbol meanings.

8. Quick revision

Class 5 Science — Chapter 5: Food.
Core idea: Food preservation and balanced nutrition.
Key outcomes: Explain methods of food preservation; State importance of a balanced diet.
Always revise diagrams / tables from the Samacheer Kalvi textbook before the exam.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Why food spoils

Biotic factors → bacteria, fungi (mould), yeast — microscopic organisms that grow on food, breaking it down and producing waste that makes food smell, taste, and look bad. Insects and rodents also spoil stored grains. Abiotic factors → temperature (warm, humid conditions = ideal for microbial growth), moisture (damp food spoils faster), air (oxygen reacts with fats in fried foods making them rancid).

Food left at room temperature in Chennai's humid climate can spoil within hours. That is why traditional Tamil cuisine developed preservation methods suited to the tropical climate — sun-drying, fermentation, and pickling.

Food preservation methods

Drying → removes water; microorganisms cannot grow without moisture. Sun-drying (vathal, vadagam, dry fish, papad). Refrigeration → 4°C slows microbial growth (does NOT kill all). Freezing → −18°C stops growth almost completely. Pickling → salt draws out water through osmosis; oil/vinegar creates acidic environment — microbes cannot survive. Examples: mango pickle (oorugai), lime pickle, onion pickle. Canning → food sealed in airtight containers and heated to kill all microbes. Adding sugar → high concentration preserves fruits as jam/jelly/murabba. Chemical preservatives → sodium benzoate, potassium metabisulphite added to packaged foods, sauces, and jams.

Tamil tradition: during the summer, raw mangoes are salted and sun-dried to make maavadu and vatha moolagai. This preserves seasonal produce for the entire year.

Deficiency diseases (key matches)

Vitamin A → Night blindness (cannot see in dim light). Sources: carrot, papaya, mango, greens, fish liver oil. Vitamin B1 → Beriberi (muscle weakness, nerve damage). Sources: whole grains, pulses, nuts. Vitamin C → Scurvy (bleeding gums, poor wound healing). Sources: amla (richest!), citrus fruits, guava. Vitamin D → Rickets (soft, bent bones in children). Sources: sunlight (body makes it), milk, egg yolk, fish. Iron → Anaemia (tiredness, pale skin, weakness). Sources: keerai (spinach/greens), dates, jaggery, liver. Iodine → Goitre (swollen thyroid gland in neck). Sources: iodised salt, seafood. Calcium → Weak bones, tooth decay. Sources: milk, curd, ragi (finger millet), sesame seeds.

Amla (Indian gooseberry/nellikkai) has 20× the Vitamin C of an orange. It grows widely in Tamil Nadu and is used in pickles, chutneys, and Ayurvedic medicine.

Balanced diet and BMI

A balanced diet includes: Carbohydrates (rice, chapati — ~50-60%), Proteins (dal, milk, egg, fish — ~15-20%), Fats (oil, ghee, nuts — ~20-25%), Vitamins & Minerals (fruits, vegetables), Fibre (whole grains, greens), Water (6-8 glasses). BMI = weight (kg) ÷ height² (m²). BMI < 18.5 = Underweight. 18.5-24.9 = Normal/Healthy. 25-29.9 = Overweight. ≥ 30 = Obese.

BMI is a simple screening tool, not a diagnostic. A very muscular athlete may have a high BMI but low body fat. For children, BMI is interpreted differently using age and gender-specific growth charts.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Thinking refrigeration KILLS bacteria (it only slows them)

✓ Refrigeration at 4°C SLOWS bacterial growth but does NOT kill all bacteria. Food in the fridge still spoils eventually. Only cooking at high temperature (above 70°C) or freezing at −18°C reliably stops bacterial activity.

WATCH OUT

✗ Confusing 'Best Before' and 'Expiry Date'

✓ 'Best Before' means the food is at its best quality before this date but is still safe to eat afterwards (dry foods, biscuits, chips). 'Expiry Date' means the food should NOT be consumed after this date (milk, medicines, baby food) — it may be unsafe.

WATCH OUT

✗ Eating only 'filling' foods (rice, potatoes) and ignoring vegetables and protein

✓ A plate full of rice fills the stomach but lacks protein and vitamins. This leads to 'hidden hunger' — you feel full but your body is starving for nutrients. Always include dal, vegetables, and curd in every meal.

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