This MCQ module is based on: Nutrition and Digestion in Humans
TOPIC 31 OF 46
Nutrition and Digestion in Humans
🎓 Class 7
Science
CBSE
Theory
Ch 9 — Life Processes in Animals
⏱ ~14 min
🌐 Language: [gtranslate]
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Why Do We Need Food?
Imagine skipping breakfast, lunch and dinner for a whole day. By evening, you would feel tired, dizzy and unable to think clearly. Food is the fuel that our body burns to stay active, grow taller, repair an injured knee, and even fight off a cold. But food in the form we eat — a chapati, a banana, a bowl of dal — is much too large and complex for our cells to use directly. Before the body can absorb its goodness, the food must be broken down into tiny, simple pieces. This whole journey — from the first bite to the waste leaving the body — is called nutrition.
Think first: When you chew a piece of bread for a long time, it starts to taste slightly sweet. What could be changing inside your mouth to cause this taste?
9.1 The Five Stages of Nutrition in Animals
All animals — from a tiny ant to an elephant — follow the same five steps when they eat. The body does not skip any of them; each step prepares the food for the next.
1IngestionTaking food into the body through the mouth.
2DigestionBreaking large food pieces into simple, tiny molecules.
3AbsorptionDigested food passes into the blood through the intestine wall.
4AssimilationCells use the absorbed food for energy, growth and repair.
5EgestionUndigested waste is thrown out of the body.
9.2 The Human Digestive System
The human digestive system is a long, muscular tube called the alimentary canal, along with helper organs like the liver, gall bladder and pancreas. Food travels through the canal in one direction — from mouth to anus — and at each stop, something new is added or absorbed.
Step-by-step through the alimentary canal
- Mouth (buccal cavity): Teeth cut, tear and grind the food. The tongue rolls it into a soft ball. Saliva from three pairs of salivary glands wets the food. A special substance in saliva — the enzyme salivary amylase — starts breaking starch into sugar, which is why rice or bread starts tasting sweet if you chew it for long.
- Oesophagus (food-pipe): A muscular tube about 25 cm long. Wave-like muscle movements, called peristalsis, push the food-ball down into the stomach. That is why astronauts can swallow food even in zero gravity.
- Stomach: A J-shaped muscular bag that churns food with gastric juice. Gastric juice contains hydrochloric acid (which kills germs and softens food), mucus (which protects the stomach wall from its own acid), and the enzyme pepsin (which starts breaking down proteins).
- Small intestine: A long coiled tube (about 7 m). Here, bile from the liver (stored in the gall bladder) breaks fat into tiny droplets, and pancreatic juice from the pancreas finishes digesting proteins, carbohydrates and fats. The inner wall has millions of finger-like projections called villi that absorb the digested nutrients into the blood.
- Large intestine: Shorter but wider (about 1.5 m). It absorbs most of the remaining water and some salts, leaving behind a semi-solid waste called faeces.
- Rectum and anus: Faeces are stored briefly in the rectum and egested through the anus.
Enzyme recap:
• Saliva (mouth) → salivary amylase → starts starch digestion.
• Gastric juice (stomach) → pepsin + HCl → starts protein digestion.
• Bile (liver) → no enzyme, but emulsifies fats into tiny drops.
• Pancreatic juice (pancreas) → completes digestion of starch, protein and fat.
• Intestinal juice (small intestine) → finishes the job.
• Saliva (mouth) → salivary amylase → starts starch digestion.
• Gastric juice (stomach) → pepsin + HCl → starts protein digestion.
• Bile (liver) → no enzyme, but emulsifies fats into tiny drops.
• Pancreatic juice (pancreas) → completes digestion of starch, protein and fat.
• Intestinal juice (small intestine) → finishes the job.
9.3 Types of Teeth
A healthy adult has 32 teeth. A child has 20 milk teeth, which start falling out by about 6–7 years of age and are replaced by permanent teeth. Each tooth has a shape that matches its job.
| Tooth | Shape | Job | Number (adult) |
|---|---|---|---|
| Incisors | Chisel-like, sharp edge | Cutting, biting | 8 (4 upper + 4 lower) |
| Canines | Pointed, cone-shaped | Tearing, piercing | 4 |
| Premolars | Broad with small bumps | Crushing, grinding | 8 |
| Molars | Broad with many bumps | Grinding food finely | 12 (includes wisdom teeth) |
Taking care of your teeth: Brush twice a day, rinse after every meal, and avoid too many sticky sweets. Sugar sticks to teeth and feeds bacteria, which produce acid. The acid eats into the enamel and causes dental caries (cavities).
Activity 9.1 — The Sweet Taste of Starch L3 Apply
Take a small piece of plain boiled rice or white bread. Chew it slowly for one full minute without swallowing. Pay close attention to the taste every 15 seconds.
- At the start the food feels starchy and bland.
- After about 30 seconds, it begins to feel slightly sweet.
- After 60 seconds, the sweetness becomes more noticeable.
Predict: Why did the food turn sweet without adding sugar? Which part of your mouth is responsible?
Rice and bread contain starch, which is tasteless. Saliva contains the enzyme salivary amylase, which breaks starch into maltose, a simple sugar that tastes sweet. The longer you chew, the more starch gets converted — so the sweeter it tastes. This proves digestion of starch begins right in the mouth.
Competency-Based Questions
Apply & Reason — Nutrition & Human Digestion
Rohan ate a plate of dal-chawal with vegetables. His mother reminds him to chew thoroughly. Later, he feels a slight burning near his chest — his teacher explains it is acid from the stomach splashing upwards.
Q1. Which stage of nutrition is happening when Rohan's teeth and tongue break his food into smaller pieces? L1
(b) Digestion. Physical breakdown by chewing is the first part of digestion, which begins in the mouth.
Q2. The "burning" Rohan feels is caused by which substance? Why does the stomach not burn itself? L2
The burning is due to hydrochloric acid from the gastric juice. The stomach is protected from its own acid by a thick layer of mucus that lines its inner wall.
Q3. Match the organ with its main function: L2
Stomach → churns food and starts protein digestion. Liver → produces bile to emulsify fats. Small intestine → completes digestion and absorbs nutrients through villi. Large intestine → absorbs water and forms faeces.
Q4. True or False — "Bile is an enzyme that digests fat." Justify. L3
False. Bile is not an enzyme; it is a greenish-yellow juice made by the liver. It breaks large fat drops into tiny droplets (emulsification) so that fat-digesting enzymes from the pancreas can act on them quickly.
Q5. A patient's small intestine is surgically shortened. Which stage of nutrition will be most affected, and why? L4
Absorption will be most affected. The small intestine has millions of villi that greatly increase its inner surface area. A shorter intestine has fewer villi, so less digested food can pass into the blood, and the patient may lose weight even if he eats well.
Assertion–Reason Questions
Choose: (A) Both true, R explains A. (B) Both true, R does not explain A. (C) A true, R false. (D) A false, R true.
A: Chewing food properly is important for good digestion.
R: Chewing increases the surface area of food and mixes it with saliva, which contains digestive enzymes.
(A) — both true, and R correctly explains A.
A: The inner wall of the small intestine has villi.
R: Villi increase the surface area for absorption of digested food.
(A) — both true, and R explains A. Millions of villi make the absorbing surface many times larger.
A: Hydrochloric acid in the stomach kills harmful germs that enter with food.
R: The acid also helps the enzyme pepsin work best in an acidic medium.
(B) — both statements are true, but R describes a separate role of HCl and does not explain why germs die.
Frequently Asked Questions — Nutrition and Digestion in Humans
What does the topic 'Nutrition and Digestion in Humans' cover in Class 7 Science?
The topic 'Nutrition and Digestion in Humans' is part of NCERT Class 7 Science Chapter 9 — Life Processes in Animals. It covers the key ideas of nutrition, digestion, alimentary canal, teeth, stomach, small intestine, enzymes, absorption, explained through everyday examples, labelled diagrams and hands-on activities drawn from the NCERT Curiosity textbook. Students learn not just definitions but also the reasoning behind each concept so they can answer competency-based questions and assertion–reason items. The lesson helps Class 7 students build a strong base for higher classes by linking each idea to real observations at home, school and in nature, and by preparing them for CBSE school assessments and Olympiads.
Why is 'Nutrition and Digestion in Humans' important for Class 7 NCERT Science?
'Nutrition and Digestion in Humans' is important because it builds core scientific thinking that Class 7 students will use throughout middle and secondary school. NCERT Chapter 9 — Life Processes in Animals — introduces nutrition and related ideas that appear again in Class 8, 9 and 10 Science. Mastering this subtopic helps students read labels and safety signs, understand news about science and technology, and perform better in CBSE school exams. The chapter also encourages curiosity and evidence-based thinking — skills that support the National Education Policy (NEP) 2020 focus on conceptual understanding and competency-based learning.
What are the key concepts students should remember from Nutrition and Digestion in Humans?
The key concepts in 'Nutrition and Digestion in Humans' for Class 7 Science are: nutrition, digestion, alimentary canal, teeth, stomach, small intestine, enzymes, absorption. Students should be able to define each term in their own words, give at least one everyday example, and explain how the concept connects to other chapters in NCERT Class 7 Science. For example, linking the idea to daily life — in the kitchen, classroom or outdoors — makes revision easier. Writing short notes, drawing labelled diagrams and solving the NCERT in-text and exercise questions for Chapter 9 will help students retain these concepts for unit tests and the annual CBSE examination.
How is Nutrition and Digestion in Humans taught using activities in NCERT Curiosity Class 7?
NCERT Curiosity Class 7 Science teaches 'Nutrition and Digestion in Humans' using an inquiry-based approach with Predict–Observe–Explain activities. Students are asked to make a guess first, then perform a simple experiment with safe, easily available materials, and finally explain what they observed. This matches the NEP 2020 focus on learning by doing. For Chapter 9 — Life Processes in Animals — the textbook includes hands-on tasks, labelled diagrams and questions that build Bloom's Taxonomy skills from Remember (L1) to Create (L6). Teachers use these activities, along with competency-based questions (CBQs) and assertion–reason items, to check real understanding rather than rote memorisation.
What real-life examples of nutrition can Class 7 students observe at home?
Class 7 students can observe nutrition at home in many simple ways linked to 'Nutrition and Digestion in Humans'. Kitchens, school bags, playgrounds and the night sky are full of examples that connect to NCERT Chapter 9 — Life Processes in Animals. For instance, students can check labels on food and cleaning products, watch changes while cooking, or observe the Sun and Moon across a week. Keeping a small science diary — noting the date, what was observed and a quick sketch — turns everyday life into a science lab. These real-life connections make concepts stick and prepare students well for competency-based questions in CBSE Class 7 Science.
How does 'Nutrition and Digestion in Humans' connect to other chapters of Class 7 Science?
'Nutrition and Digestion in Humans' connects to many other chapters in NCERT Class 7 Science Curiosity. The ideas of nutrition appear again when students study related topics like heat, light, changes, life processes and Earth-Sun-Moon. For example, understanding this subtopic helps in building mental models for later chapters and for Class 8, 9 and 10 Science. Teachers often use cross-chapter questions in CBSE examinations to test whether students can apply what they learned in Chapter 9 — Life Processes in Animals — to new situations. This integrated approach matches the NEP 2020 and NCF 2023 focus on holistic, competency-based learning.
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