Class 7 Science Chapter 9: Life Processes in Animals | Complete NCERT Notes, Human Digestion, Respiration, Alimentary Canal, Activity 9.1 Solved
Complete Chapter 9 Guide: Human Digestive System (Mouth→Oesophagus→Stomach→Small Intestine→Large Intestine), Activity 9.1 Saliva on Starch Iodine Test, Respiration (Alveoli Gas Exchange), Breathing Mechanism (Diaphragm+Ribs), Ruminants (Cow Rumination), Birds Gizzard, Gills in Fish, Oral Hygiene, Lime Water CO2 Test, 25+ Practice Questions & Answers, CBSE Board Exams 2025
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Class 7 Science Chapter 9: Life Processes in Animals | Complete NCERT Notes, Activities, Questions & Answers 2025
Life Processes in Animals
Class 7 Science Chapter 9 | Complete NCERT Guide | Nutrition, Digestion, Respiration, Excretion in Animals 2025
Full Chapter Summary & Detailed Notes - Life Processes in Animals
Introduction & Life Processes
All animals (including humans) perform certain essential activities to stay alive. These are collectively called life processes. The four major life processes are:
Nutrition – taking in food and using it
Respiration – obtaining and using oxygen to release energy
Excretion – removal of waste
Reproduction – producing young ones
This chapter focuses mainly on Nutrition and begins the study of Respiration.
9.1 Nutrition in Animals
Animals cannot make their own food (except a few exceptions); they depend directly or indirectly on plants. Animals show great variety in their feeding habits:
Bees & sunbirds → suck nectar from flowers
Infants (humans & many mammals) → feed on mother’s milk
Snakes (e.g., python) → swallow the prey whole
Many aquatic animals (e.g., whales, some fish) → filter tiny floating food particles
Frogs → use sticky tongue to catch insects
Why do we need to digest food?
Food contains complex substances (carbohydrates, proteins, fats). These are large molecules that cannot pass through cell membranes. They must be broken down into simpler, soluble forms (glucose, amino acids, fatty acids) so that the body can absorb and use them for energy, growth and repair.
9.1.1 Digestion in Human Beings – The Alimentary Canal
Digestion takes place inside a long muscular tube called the alimentary canal (or digestive tract) that runs from mouth → anus. Length ≈ 8–10 metres when stretched.
Mouth
Mechanical digestion: Teeth cut, tear, crush and grind food into smaller pieces → increases surface area.
Chemical digestion: Saliva (secreted by salivary glands) contains the enzyme salivary amylase (ptyalin) that converts starch → maltose (sugar).
That is why chapati/rice tastes sweet after chewing for 30–60 seconds.
Tongue helps in mixing food with saliva and swallowing.
Oesophagus (Food pipe)
Food is pushed down by wave-like muscular contractions called peristalsis. No digestion occurs here.
Stomach
A J-shaped muscular bag.
Secretes gastric juice containing:
Hydrochloric acid (kills germs, makes medium acidic)
Pepsin (protein-digesting enzyme)
Mucus (protects stomach wall)
Food becomes a semi-liquid called chyme.
Small Intestine (≈ 6–7 m long)
Main site of complete digestion and absorption.
Receives pancreatic juice (from pancreas) → amylase, trypsin, lipase.
Receives bile juice (from liver, stored in gall bladder) → emulsifies fats, makes medium alkaline.
Intestinal juice (succus entericus) completes digestion of all nutrients.
Villi (finger-like projections) absorb simple nutrients into blood.
Large Intestine
Absorbs most of the water and some salts from undigested food. Remaining waste becomes solid faeces.
Rectum & Anus
Stores faeces temporarily. Faeces are expelled through anus (egestion).
Activity 9.1 – Action of Saliva on Starch (Iodine Test)
Test tube
Contents
Colour with iodine
Reason
A
Boiled rice (not chewed)
Blue-black
Starch present
B
Boiled rice chewed 30–60 s
No blue-black (remains brown)
Saliva converted starch → sugar
Science and Society – Oral Hygiene
Brush twice daily, clean tongue.
Rinse mouth after meals.
Traditional methods: neem twig (datun), charcoal, salt, etc.
Prevents tooth decay, gum disease and bad breath.
Key Takeaways & Exam Points
Complex food → simple soluble form = digestion
Two types of digestion: mechanical (teeth) & chemical (enzymes)
Saliva → starch → sugar (sweet taste)
Stomach → proteins begin to digest
Small intestine → complete digestion + absorption
Bile → emulsifies fats; villi → increase absorption area
Large intestine → water absorption
Quick Revision One-liner:
Mouth (teeth + saliva) → Oesophagus → Stomach (acid + pepsin) → Small intestine (bile + pancreatic + intestinal juice + villi) → Large intestine (water) → Rectum → Anus
(i) The breakdown of complex food into simpler form is called
(c) digestion
(ii) The organ where maximum absorption of digested food takes place is
(b) small intestine
(iii) Saliva is secreted by
(a) salivary glands
(iv) The enzyme present in saliva is
(b) amylase
2. Fill in the blanks.
(i) The process of taking food into the body is called ingestion.
(ii) The tube that runs from mouth to anus is called alimentary canal.
(iii) The muscular movement that pushes food downwards is called peristalsis.
(iv) Bile juice is stored in the gall bladder.
(v) Undigested waste is removed through the anus.
3. Give one word for the following.
(i) Finger-like projections in small intestine → villi
(ii) Acid present in stomach → hydrochloric acid
(iii) Enzyme that digests proteins in stomach → pepsin
(iv) Juice that emulsifies fats → bile
(v) Removal of undigested food → egestion
4. State whether the following statements are True or False.
(i) Digestion of starch starts in the stomach. → False (starts in mouth)
(ii) Saliva contains an enzyme that converts starch into sugar. → True
(iii) Large intestine absorbs most of the water from undigested food. → True
(iv) Bile is produced by the pancreas. → False (produced by liver)
(v) Villi increase the surface area for absorption. → True
5. Short Answer Questions
(a) What is the role of saliva in digestion?
Saliva moistens the food, makes chewing and swallowing easy, and contains salivary amylase which converts starch into maltose (sugar). That is why chewed starchy food tastes sweet.
(b) Name the organs of the human digestive system in sequence.
Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus
(c) Why do we get a sweet taste when we chew chapati for a long time?
Salivary amylase present in saliva breaks down starch present in chapati into maltose (a sugar), so it tastes sweet.
(d) What is the function of villi?
Villi are tiny finger-like projections in the small intestine. They greatly increase the surface area for the absorption of digested nutrients into the blood.
6. Long Answer Questions
(a) Draw a labelled diagram of the human digestive system.
(Students should draw the standard diagram showing mouth, oesophagus, stomach, liver, pancreas, small intestine, large intestine, rectum and anus.)
(b) Describe the journey of food through the alimentary canal.
• Mouth: Teeth break food mechanically; saliva (amylase) starts starch digestion.
• Oesophagus: Peristalsis pushes food to stomach.
• Stomach: Gastric juice (HCl + pepsin) kills germs and digests proteins; food becomes chyme.
• Small intestine: Bile emulsifies fats; pancreatic juice digests carbohydrates, proteins and fats; intestinal juice completes digestion; villi absorb nutrients.
• Large intestine: Water and salts are absorbed; remaining waste becomes faeces.
• Rectum & Anus: Faeces stored and expelled.
(c) How is digestion different in humans and a python?
Humans chew food and digest gradually using many enzymes. Python swallows prey whole; digestion is very slow (may take many days) inside the stomach using powerful acids and enzymes.
7. Give reasons.
(i) We should chew food properly.
→ Proper chewing increases surface area, mixes food with saliva, and starts starch digestion.
(ii) We should brush our teeth twice a day.
→ To remove food particles and bacteria, prevent tooth decay, cavities and bad breath.
Key Concepts - In-Depth Exploration (Chapter 9)
Core ideas explained with examples, common confusions, and exam connections for "Life Processes in Animals".
Nutrition
Process: Food intake for energy Example: Bees suck nectar Exam Note: Varies by animal Confusion: Not same as digestion
Digestion
Types: Mechanical, chemical Example: Teeth crush, saliva breaks starch
Alimentary Canal
Parts: Mouth, stomach, intestines Key Point: Breaks and absorbs food
Saliva Action
Enzyme: Breaks starch to sugar Exam Must-Know: Iodine test confirms
Absorption
Site: Small intestine Example: Nutrients to blood
Oral Hygiene
Practices: Brush twice, rinse after meals Exam Point: Prevents decay
Exam Master Tips:
Mnemonics: "NRED" = Nutrition, Respiration, Excretion, Digestion wait no Reproduction
Digestion: Mouth (starch), Stomach (protein)
Activity: Iodine blue-black for starch
Most Asked: Human digestion process, activity results
Historical & Social Insights - Life Processes
Evolution of understanding life processes and societal aspects.
