Class 9 Science Chapter 2: Nutrition in Animals Previous Year Questions (2020–2025)

Solving previous year questions is the single most effective revision tool for CBSE Class 9 Science. Here's why: (1) Exposure to real exam language – CBSE uses consistent terminology and phrasings across years. Familiarity reduces reading anxiety during the actual test. (2) Pattern recognition – you'll notice that certain topics (e.g., peristalsis, ruminant digestion) appear repeatedly in 3-mark questions, while tooth structure dominates 1-mark slots. This helps you allocate study time wisely. (3) Accuracy in answers – textbook definitions are often too verbose for exam answers. PYQs show you the right level of detail: complete but concise. (4) Confidence – when you've seen and solved a variant of a question before, your response is faster and more assured. (5) Marking criteria – model answers reveal which points examiners reward. For instance, describing peristalsis in human oesophagus requires mentioning muscle contraction direction and wave motion—omit this and you lose marks. Start a 3-day free trial at cbsetutor.ai to access video solutions for every question on this page.

One-mark questions test direct recall and single-sentence understanding. These five are prototypical and frequently reworded: **Q1. Name the type of teeth that are used for cutting and grinding food.** A: Incisors cut; molars and premolars grind. (Or: Incisors and canines cut; molars and premolars grind.) Examiners accept 'incisors' alone as incomplete but acceptable. Ideal answer names both processes and teeth. **Q2. What is the role of saliva in the mouth?** A: Saliva contains amylase enzyme that begins chemical digestion of carbohydrates (starch → maltose). It also lubricates food for swallowing. Do not just say 'makes food wet'—mention the enzyme or carbohydrate digestion. **Q3. In which part of the digestive system is protein digestion initiated?** A: Stomach. The enzyme pepsin breaks proteins into peptides in acidic medium. Avoid 'mouth' (carbohydrate digestion only) or 'small intestine' (protein is further digested there, but initiation is in stomach). **Q4. What is the scientific name for the throat?** A: Pharynx. Often paired with 'which part does the oesophagus connect to?'—answer is stomach. **Q5. Define rumination.** A: The process of re-chewing food regurgitated from the rumen. Or: Bringing partially digested food back to the mouth for further chewing in ruminants. Avoid vague definitions like 'chewing twice'—emphasise the regurgitation and re-chewing cycle.

Three-mark questions demand structured answers with multiple linked facts. Model answers below show the expected depth: **Q1. Describe the structure and function of the human stomach.** A: The stomach is a J-shaped muscular organ located below the diaphragm. Its wall has three muscle layers (longitudinal, circular, transverse) that contract to churn food into a semi-liquid mass called chyme. It secretes gastric juice containing hydrochloric acid (HCl) and pepsin enzyme. HCl provides the acidic medium for pepsin to break proteins into peptides. The stomach also stores food temporarily and releases it gradually into the small intestine via the pyloric sphincter. (Structure + muscle layers, Function + churning + chemical digestion of proteins + storage + regulated release.) **Q2. Explain peristalsis in the human oesophagus.** A: Peristalsis is a wave-like muscular contraction. In the oesophagus, the circular muscles contract above the food bolus while relaxing below it, pushing the bolus downward toward the stomach. This occurs involuntarily and does not require gravity (food can travel down even if you are upside down). Peristalsis enables smooth passage of food and occurs throughout the digestive tract. (Mechanism: contraction above + relaxation below, Direction: downward, Properties: involuntary + gravity-independent.) **Q3. Compare the digestive system of ruminants and humans. (Any three points.)** A: Ruminants have a four-chambered stomach (rumen, reticulum, omasum, abomasum) while humans have a simple, single-chambered stomach. Ruminants regurgitate and re-chew food (rumination) for thorough breakdown; humans do not. Ruminants digest plant cellulose using symbiotic bacteria in the rumen; humans lack this ability and cannot digest cellulose. Ruminants (cows, sheep) are herbivorous; humans are omnivorous. (Any three comparative points earn full marks.) **Q4. What are the functions of the small intestine?** A: The small intestine is the main site of digestion and absorption. Its wall secretes enzymes (pancreatic amylase, trypsin, lipase) and intestinal juices that break down carbohydrates, proteins, and fats into simple sugars, amino acids, and fatty acids respectively. Its inner lining is covered with villi and microvilli that maximise surface area for absorption of these nutrients into the bloodstream. The small intestine also receives bile from the liver (emulsifies fats) and pancreatic juice. (Functions: completion of digestion, absorption, large surface area via villi.) **Q5. Describe the structure of a molar tooth.** A: A molar tooth has a crown (visible part above the gum), root (embedded in the jaw), and neck (junction between crown and root). The crown is covered with hard enamel for protection and grinding surfaces. Below enamel is dentine, a softer bone-like tissue. The central pulp cavity contains blood vessels and nerves that supply the tooth. Molars have broad, flat surfaces with cusps for grinding tough food. (Parts: crown, root, neck; Materials: enamel, dentine, pulp; Function: grinding.)

Five-mark questions require detailed, multi-step explanations or complete pathways. Below are three representative problems with full solutions: **Q1. Trace the path of food from the mouth to its absorption in the small intestine. Describe the digestion that occurs at each major stage.** A (Full Solution): (i) Mouth: Food is ingested and mixed with saliva secreted by salivary glands. Salivary amylase begins chemical digestion of starch into maltose. Teeth mechanically break food into smaller pieces. The bolus is formed and pushed by the tongue. (ii) Oesophagus: The bolus travels down via peristalsis (wave-like muscle contractions). No digestion occurs here; it is purely a passage. (iii) Stomach: The bolus enters and is churned by muscular contractions. Gastric juice (HCl + pepsin) is secreted. Pepsin breaks proteins into peptides in the acidic medium. The semi-liquid mass (chyme) is formed. (iv) Small Intestine: Chyme is released gradually. Pancreatic enzymes (amylase, trypsin, lipase) and bile (from liver) enter. Complete digestion occurs: carbohydrates → glucose, proteins → amino acids, fats → fatty acids and glycerol. Villi and microvilli absorb these nutrients into the bloodstream. Undigested food (fibre) passes to the large intestine. (Structure: 5 stages, Digestion at each, Absorption final step. Award marks for each correctly described stage.) **Q2. Explain how a ruminant's stomach is adapted for digestion of plant material. How does this differ from the human digestive system?** A (Full Solution): Ruminant Stomach Adaptations: The ruminant stomach has four chambers: (a) Rumen: A large fermentation vat containing symbiotic bacteria that produce cellulase enzyme. These bacteria break down cellulose (the main structural component of plant cell walls) into soluble sugars. Humans lack these bacteria, so cannot digest cellulose. (b) Reticulum: Stores partially digested food and enables regurgitation for rumination (re-chewing). (c) Omasum: Absorbs water and minerals from the semi-digested food. (d) Abomasum: Similar to the human stomach; secretes HCl and pepsin for protein digestion. Rumination Process: After initial chewing and swallowing, the cow brings food back to the mouth (regurgitation) for thorough re-chewing, further reducing particle size and increasing surface area for bacterial action. Difference from Humans: Humans have a simple, single-chambered stomach. We lack rumen and cellulase-producing bacteria. We digest plant cell contents (proteins, sugars) but not cellulose. Humans are omnivorous and lack the extended fermentation process. Ruminants are herbivorous with highly specialised multi-chambered stomachs. (Explanation of 4 chambers + bacterial role + rumination process + comparison with humans. Award 5 marks for comprehensive coverage.) **Q3. Draw and label a diagram of the human alimentary canal. Identify the organs involved in digestion and name the main enzyme(s) secreted at each site.** A (Full Solution – Text-based): The human alimentary canal includes (in order): 1. Mouth: Salivary glands secrete saliva containing amylase. Digestion: Starch → maltose (carbohydrate digestion begins). 2. Pharynx: No digestion; passage only. 3. Oesophagus: No digestion; passage by peristalsis. 4. Stomach: Gastric glands secrete pepsin and HCl. Digestion: Proteins → peptides (protein digestion begins). 5. Small Intestine (Duodenum, Jejunum, Ileum): – Pancreas secretes pancreatic amylase (carbohydrate), trypsin (protein), and lipase (fat). – Liver secretes bile (emulsifies fat, not an enzyme). – Intestinal glands secrete peptidase, maltase, sucrase, lipase. Digestion: Complete breakdown of all macronutrients; Absorption: Nutrients absorbed via villi. 6. Large Intestine: No digestive enzymes; water absorption. 7. Rectum & Anus: Storage and elimination of faeces. (Labelled diagram + enzyme names + substrates. Award marks for accurate identification of all organs and enzymes.)

The 2024–25 CBSE rationalised syllabus (and preview of 2026–27) shows subtle but important shifts in question patterns for Nutrition in Animals: (1) Decreased focus on purely anatomical labelling – examiners now expect functional integration. For example, 'Name the parts of the tooth' (outdated) has shifted to 'Explain how tooth structure is adapted to its function' (current). (2) Increased emphasis on ruminant digestion and symbiosis – questions are moving away from simple 'describe the rumen' toward 'why do ruminants need a rumen that humans do not?' This tests deeper conceptual understanding. (3) Greater integration with other chapters – digestion links to nutrition (carbohydrates, proteins, fats), absorption to the circulatory system, and fibre to the excretory system. Expect 5-mark questions that span multiple chapters. (4) Emphasis on enzyme specificity – examiners reward answers that name not just 'enzymes' but specific enzymes (pepsin, amylase, trypsin, lipase) and their substrates. (5) Case-study or scenario-based questions – instead of 'what is the function of HCl?', expect 'A patient has low stomach acid. Predict the effect on protein digestion and explain why.' (6) Practical/observational questions gaining weight – expect questions on observing digestion of starch by saliva or testing enzyme activity, rather than pure theory. Revision strategy: focus on mechanisms and adaptations, not isolated facts.

Exam psychology: You have ~40 minutes for a 20-mark section on digestive system and nutrition. Here's a time-efficient strategy: (1) Read all questions first (2 min) – identify 1-mark, 3-mark, and 5-mark questions. Prioritise the 5-mark question as it carries weight. (2) Start with 1-mark questions (5 min total) – these are quick confidence-boosters. Recall-based; no lengthy explanation needed. Typical trap: students over-explain and waste time. (3) Attempt 3-mark questions (12 min, ~4 min each) – structure your answer with bullet points or short sentences. Do not write paragraphs. Example structure: 'The stomach has three functions: (a) mechanical digestion via muscle churning, (b) chemical digestion via pepsin and HCl breaking proteins into peptides, (c) temporary storage and gradual release into small intestine.' (4) Tackle the 5-mark question last (15 min) – usually a pathway, comparison, or explanation with diagram. Plan your answer for 1 minute (list key points), then write. If a diagram is requested, sketch it clearly with labels; examiners reward neat, labelled diagrams highly. (5) Reserve 6 minutes for review – re-read answers for completeness and correct any spelling of organ names or enzyme names. Final tip: Memorise the enzyme names and their substrates as a table (Enzyme | Substrate | Product | Site). This is the backbone of 70% of questions in this chapter.

Before your exam, self-test against this checklist. Tick each only if you can explain it in under 3 minutes without notes: (☐) Name all parts of a tooth (incisors, canines, premolars, molars) and state one function of each. (☐) Describe the structure of a molar tooth (crown, root, neck, enamel, dentine, pulp) and relate each part to its function. (☐) Trace the path of a glucose molecule from the mouth to its absorption in the small intestine. (☐) Explain why amylase works in the mouth (neutral/slightly acidic pH) but stops in the stomach (HCl denatures it). (☐) Describe peristalsis: the muscular wave, direction, and why it is involuntary and gravity-independent. (☐) Draw a labelled diagram of the human digestive system with all major organs and glands. (☐) State the role of HCl in the stomach (provides acidic medium for pepsin, kills bacteria, helps denature proteins). (☐) List the main enzymes secreted by pancreas and intestinal glands and their substrates. (☐) Explain why bile is not an enzyme but essential for fat digestion (emulsifies, increases surface area). (☐) Describe the ruminant stomach: all four chambers, function of each, and the rumination process. (☐) Compare ruminant and human digestive systems: enzyme production, ability to digest cellulose, symbiotic bacteria, tooth structure. (☐) Explain the role of villi and microvilli in the small intestine (increase surface area for nutrient absorption). (☐) State what happens to undigested food in the large intestine (water reabsorption, faeces formation). If you can confidently explain 11 or more of these, you are well-prepared for this chapter.