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Chapter 9 of Class 7 science is full of names: oesophagus, villi, diaphragm, alveoli. Students who try to memorise them as a list tend to mix them up. Students who learn them as two journeys, one for food and one for air, usually do not. This guide gives you both journeys, the experiments behind them, worked examples with the chapter's numbers, and the confusion that trips up most students: breathing versus respiration.
What does Chapter 9 of Class 7 Curiosity cover?
Life Processes in Animals is Chapter 9 of NCERT's *Curiosity* for Grade 7 (first edition April 2025, reprint 2026-27). It covers:
Digestion in humans, from the mouth to the anus, with the liver and pancreas.
The saliva and starch test with iodine.
Digestion in other animals: rumination in cows and the gizzard in birds.
Breathing: the path of air, the diaphragm and rib cage, and a balloon model of the lungs.
Respiration: what it is and how it differs from breathing.
Breathing in other animals: gills in fish, lungs and skin in frogs, and skin in earthworms.
What is the journey of food?
Learn it as a sequence with one job at each stop:
Mouth: teeth crush and chew (mechanical digestion); saliva starts breaking starch into sugar.
Food pipe (oesophagus): walls contract and relax in a wave to push food down.
Stomach: churns food and adds digestive juice, acid and mucus. The juice breaks down proteins, the acid kills many harmful bacteria, and the mucus protects the stomach lining.
Small intestine: receives bile from the liver and pancreatic juice from the pancreas, finishes digestion, and absorbs nutrients into the blood through finger-like projections.
Large intestine: absorbs water and some salts, leaving semi-solid waste.
Rectum and anus: store and then remove the waste (egestion).
Worked examples
Example 1: the starch test. Test tube A has boiled rice. Test tube B has boiled rice chewed for 30 to 60 seconds. Both get water and a few drops of iodine. A turns blue-black; B stays almost unchanged. Why? Iodine turns blue-black with starch. In B, saliva has broken most of the starch into sugar, so little starch is left to react. If B still shows some colour, the chapter suggests chewing for longer and repeating.
Example 2: the two intestines. The chapter gives the small intestine as about 6 m long and the large intestine as about 1.5 m. So the small intestine is 6 ÷ 1.5 = 4 times longer. Then why is the other one called "large"? Because it is wider, not longer.
Example 3: what your lungs take in. The chapter's figure gives inhaled air as nearly 21% oxygen and 0.04% carbon dioxide, and exhaled air as nearly 16 to 17% oxygen and 4 to 5% carbon dioxide.
Oxygen used: 21 − 17 = 4 to 21 − 16 = 5 percentage points. That is 4 ÷ 21 ≈ 0.19 to 5 ÷ 21 ≈ 0.24, so your body takes roughly a fifth to a quarter of the oxygen in each breath.
Carbon dioxide: 4 ÷ 0.04 = 100 and 5 ÷ 0.04 = 125. Exhaled air has about 100 to 125 times as much carbon dioxide as inhaled air.
This is why lime water turns milky when you blow into it but not when you pump ordinary air through it.
Why do students confuse breathing and respiration?
Because everyday English uses "respiration" for breathing. Researchers have tracked this for a long time. Seymour and Longden (1991), whose paper is titled "Respiration—that's breathing isn't it?", used questionnaires, diagnostic tests and interviews in schools and found that pupils poorly understood the cellular basis of respiration and respiration in plants. The chapter's own exercise asks how Sanvi could convince Anil that the two are different. A good answer: "If respiration were just breathing, how would a fish or an earthworm respire?"
Other mistakes to avoid:
"We inhale oxygen." We inhale air, which is rich in oxygen. The chapter's question about Anu, Shanu and Tanu tests exactly this.
"All digestion happens in the stomach." It starts in the mouth and finishes in the small intestine.
"The large intestine digests most food." Its main job is absorbing water and some salts.
"Air goes into the lungs and pushes the ribs out." It is the other way round: the ribs move out and the diaphragm moves down, which makes space, and air comes in.
"Bile digests fat by itself." Bile from the liver breaks fat into tiny droplets and neutralises stomach acid, which makes digestion easier; pancreatic juice and the juice from the intestine wall do the breaking down.
A one-week practice plan
Day 1: Draw the food journey from memory as six boxes with one job each. Check against the chapter.
Day 2: Chew a piece of chapati for a minute and notice the sweet taste. Write why it happens.
Day 3: Build the bottle-and-balloon lung model with an adult and label what each part represents.
Day 4: Redo Example 3 with your own words, then answer the chapter questions from memory.
Day 5: Explain to a parent the difference between breathing and respiration in two sentences.
Food and nutrients come up again in our Class 6 guide to mindful eating and a balanced diet, and the companion chapter on life processes in plants shows respiration happening in seeds too. If one step in the chain still does not make sense, the Fermi Concept Library has every concept in biology with its own lesson, so you can fill that gap and return to the chapter.
Tonight, close the book and write both journeys, food and air, as numbered steps.
