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Life Processes in Animals – Class 7 Science Chapter 9 Notes & NCERT PDF

Class 7ScienceChapter 9NCERT book: Curiosity - Science Class 7

Notes and a simple summary of Chapter 9 of the NCERT Class 7 Science book, with the official chapter PDF, flashcards, an MCQ quiz and an AI tutor for your doubts.

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Chapter 9: Life Processes in Animals

Introduction

"If your food is fully digested before you eat again, you won't need medicine for pain." — Thirukkural 942

In Grade 6 we learnt that nutrition, respiration, excretion and reproduction are life processes — processes essential for the survival of living beings. This chapter looks closely at two of them in animals: nutrition (how food is broken down and used) and respiration (how energy is released from food).

Animals eat very different foods: bees and sunbirds suck nectar, infants feed on mother's milk, pythons swallow their prey whole, and some aquatic animals filter tiny floating particles. But all food contains complex components — carbohydrate, protein and fat — which must be broken into simpler forms before the body can use them.

Key Concepts

9.1 Nutrition in animals — the alimentary canal

The breakdown of food happens in a long tube called the alimentary canal, which starts at the mouth and ends at the anus. Digestive juices released along the way break food into simpler forms, which are then absorbed and carried to all parts of the body.

Digestion is the process of breaking complex food components into simpler forms in the body.

Journey of food in humans:

  • Mouth: Teeth crush and chew food into fine pieces — mechanical digestion. Saliva contains a digestive juice that breaks starch into sugar (that is why chapati or rice tastes sweet if you chew it for 30–60 seconds). Saliva also moistens food so it is easy to swallow; the tongue mixes food with saliva and pushes it back.
  • Food pipe (oesophagus): A long, flexible tube from mouth to stomach. Its walls contract and relax in a wave-like motion to push food down. This movement happens throughout the alimentary canal.
  • Stomach: Walls churn the food. The stomach lining releases digestive juice, acid and mucus. The juice breaks down proteins; the acid helps break proteins and kills many harmful bacteria; the mucus protects the stomach lining from the acid. Food becomes a semi-liquid mass.
  • Small intestine: About 6 metres long — the longest part of the alimentary canal. It receives juices from three sources:

    • - its own inner lining (further breaks fats, proteins and carbohydrates),

    - the liver, which secretes bile (mildly basic) — bile neutralises acid from the stomach and breaks fats into tiny droplets,

    - the pancreas, which secretes pancreatic juice (also basic) — it neutralises acid and breaks down carbohydrates, proteins and fats.

  • Absorption: Digested nutrients pass from the small intestine into blood vessels in its walls. The inner lining is thin and has thousands of finger-like projections that increase surface area for efficient absorption.
  • Large intestine: About 1.5 metres long — shorter but wider than the small intestine (hence "large"). It absorbs water and some salts, making waste semi-solid (stool), which is stored in the rectum and expelled through the anus — egestion. Fibre-rich food helps it work well, and helpful bacteria here break down fibre.

    • Do all animals digest food the same way?

  • Ruminants (cows, buffaloes, goats) partially chew grass and swallow it; after partial digestion in the stomach (rumen) the food comes back to the mouth for slow chewing — rumination. A cow spends about 8 hours a day chewing!
  • Birds have no teeth. A muscular chamber called the gizzard grinds food, often with the help of grit (small stones) they swallow.

    • 9.2 Respiration in animals

    Breathing is taking air in (inhalation) and pushing it out (exhalation). The respiratory system:

  • Nostrils → nasal passages (tiny hair and mucus trap dust — so breathe through the nose) → windpipe → two branches entering the two lungs → finer branches ending in balloon-like sacs called alveoli. The rib cage protects the lungs.
  • Inhalation: ribs move up and outwards, the diaphragm (dome-shaped muscle below the lungs) moves down, chest space increases, air enters.
  • Exhalation: ribs move down and inwards, diaphragm moves up, air is pushed out.

    • Gas exchange: Alveoli have thin walls surrounded by fine blood tubes. Blood gives carbon dioxide to the alveoli and takes oxygen from them, carrying it to all parts of the body.

    Respiration is the process by which nutrients are converted into usable energy.
    Glucose + Oxygen → Carbon dioxide + Water + Energy

    Inhaled air has nearly 21% oxygen and 0.04% carbon dioxide; exhaled air has nearly 16–17% oxygen and 4–5% carbon dioxide — not all oxygen is used up.

    Breathing is a physical process; respiration is a chemical process. The circulatory system (heart, blood, blood vessels) carries nutrients and oxygen to all parts and takes wastes away.

    Breathing in other animals

  • Birds, elephants, lions, cows, lizards and snakes breathe with lungs (of different structures).
  • Fish use gills, richly supplied with blood vessels, to exchange gases dissolved in water.
  • Frogs: tadpoles use gills; adult frogs use lungs on land and skin in water.
  • Earthworms exchange gases through their moist skin.

    • Activities in the Chapter

  • Activity 9.1 — Action of saliva on starch: Tube A has boiled rice, Tube B has rice chewed for 30–60 seconds; add water and 3–4 drops of iodine. A turns blue-black (starch present); B shows no or very light colour — saliva has broken starch into sugar.
  • Activity 9.2 — Breathing model: Bottle with a Y-tube, two balloons and a rubber sheet at the base. Pulling the sheet down inflates the balloons; releasing it up deflates them. Balloons = lungs, rubber sheet = diaphragm.
  • Activity 9.3 — What we breathe out (teacher demo): Air from a pichkari/syringe (inhaled air) does not change lime water; air blown through a straw (exhaled air) turns lime water milky — exhaled air has more carbon dioxide.

    • Key Terms

  • Life processes (जीवन प्रक्रियाएँ) — nutrition, respiration, excretion, reproduction etc.
  • Alimentary canal (आहार नाल) — tube from mouth to anus
  • Mechanical digestion (यांत्रिक पाचन) — breaking food into pieces by teeth
  • Digestion (पाचन) — breaking complex food into simple forms
  • Saliva (लार) — breaks starch into sugar
  • Oesophagus (ग्रासनली) — food pipe
  • Bile (पित्त) — basic juice from the liver
  • Pancreas (अग्न्याशय) — gland secreting pancreatic juice
  • Absorption (अवशोषण) — nutrients passing into blood
  • Egestion (मल-त्याग) — removal of stool through the anus
  • Rumination (जुगाली) — re-chewing partly digested food
  • Gizzard (पेषणी) — grinding chamber in birds
  • Diaphragm (डायाफ्राम / मध्यपट) — dome-shaped muscle below the lungs
  • Alveoli (कूपिकाएँ) — tiny air sacs in lungs
  • Gills (गलफड़े / क्लोम) — breathing organs of fish
  • Respiration (श्वसन) — releasing energy from food using oxygen

    • Real-life Connections

  • Brush teeth and clean the tongue twice a day; rinse after meals to prevent decay.
  • Celiac disease: the body reacts to gluten (in wheat, barley, rye), damaging the small intestine lining; millets like jowar, bajra and ragi are gluten-free alternatives.
  • Fermented foods (curd, buttermilk, kanji, gundruk, poita bhat) support healthy gut bacteria; the Charaka Samhita praises easily digestible food and spices like ginger, black pepper and cumin.
  • Pranayama and Ladakh's Tummo breathing improve lung health; smoking and passive smoking damage the lungs.
  • In 1822 Dr William Beaumont studied digestion through a permanent hole in Alexis St. Martin's stomach after a gunshot wound.

    • Common Misconceptions

  • "The small intestine is small." — It is the longest part (about 6 m); the large intestine is shorter but wider.
  • "We inhale pure oxygen." — We inhale air that contains about 21% oxygen.
  • "Breathing and respiration are the same." — Breathing moves air in and out (physical); respiration breaks down glucose to release energy (chemical).
  • "We exhale only carbon dioxide." — Exhaled air still has about 16–17% oxygen.
  • "Digestion happens only in the stomach." — It starts in the mouth and is completed in the small intestine.

    • Keep the Curiosity Alive (exercise hints)

  • Food journey: Mouth → Food pipe → Stomach → Small intestine → Large intestine → Anus.
  • Chapati test (Sahil/Neha/Santushti): unchewed chapati and mashed potato give blue-black (starch); well-chewed chapati shows little or no colour.
  • Anu/Shanu/Tanu: the most accurate is "we inhale air rich in oxygen" (Tanu) — air is a mixture, not pure oxygen.
  • Sneezing pushes out dust that irritates the nasal passages.
  • Faster breathing after running: more energy was used, so more oxygen is needed; fitness and effort differ between people.

    • 💡 Key Learning Points

    • ✓Digestion breaks carbohydrate, protein and fat into simpler forms along the alimentary canal, from mouth to anus.
    • ✓Saliva breaks starch into sugar; the stomach's juice, acid and mucus digest protein, kill germs and protect the lining; bile and pancreatic juice work in the small intestine.
    • ✓Digested food is absorbed through finger-like projections of the small intestine; the large intestine absorbs water and salts.
    • ✓Breathing (inhalation/exhalation by ribs and diaphragm) is physical; respiration (glucose + oxygen → carbon dioxide + water + energy) is chemical.
    • ✓Animals differ: ruminants chew the cud, birds grind food in a gizzard, fish use gills, frogs use lungs and skin, earthworms use moist skin.

    👨‍🏫 Teaching Tips

    • →Start with the 'sweet chapati' experience: let students chew a small piece for 30–60 seconds and describe the taste change before explaining salivary digestion.
    • →Run Activity 9.1 with iodine and chewed vs unchewed rice in pairs; have students record colours in the table and reason about the difference.
    • →Build the bell-jar/bottle breathing model (Activity 9.2) in groups and ask them to map each part to the lungs and diaphragm.
    • →Use a long rope marked at 6 m and 1.5 m to show the lengths of the small and large intestines.
    • →Let students place a hand on their ribs while breathing deeply to feel them move up-outwards and down-inwards.
    • →Demonstrate the lime water test with a pichkari vs exhaled air; ask students to predict before observing.
    • →Link to health: discuss oral hygiene, fibre, fermented foods, celiac disease and the harm of smoking/passive smoking.

    📋 Assessment Questions

    1. Can the student trace the path of food and name the role of each organ and digestive juice?
    2. Can the student explain the result of the iodine test on chewed and unchewed rice?
    3. Can the student describe rib and diaphragm movement in inhalation and exhalation?
    4. Can the student distinguish breathing from respiration and write the word equation of respiration?
    5. Can the student give examples of different digestive and breathing adaptations in animals?

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    Keep learning

    All chapters in Curiosity - Science Class 7

    1. 1. The Ever-Evolving World of Science
    2. 2. Exploring Substances: Acidic, Basic, and Neutral
    3. 3. Electricity: Circuits and their Components
    4. 4. The World of Metals and Non-metals
    5. 5. Changes Around Us: Physical and Chemical
    6. 6. Adolescence: A Stage of Growth and Change
    7. 7. Heat Transfer in Nature
    8. 8. Measurement of Time and Motion
    9. 9. Life Processes in Animals
    10. 10. Life Processes in Plants
    11. 11. Light: Shadows and Reflections
    12. 12. Earth, Moon, and the Sun