Class 9 Science Chapter 1 Nutrition in Plants Previous Year Questions (2020–2025)

Reading textbook explanations trains passive recognition. Solving past papers trains active recall and exam technique—the skills that actually score marks. When you work a PYQ, three things happen: (1) You see the exact wording and command words ('state', 'explain', 'distinguish') examiners use, so you know what depth to write. (2) You discover which concepts are heavily tested. In Nutrition in Plants, photosynthesis and the types of nutrition appear in almost every paper; symbiosis appears less often but in high-value questions. (3) You build speed and confidence. A student who has solved 5 variations of 'Distinguish between autotrophic and heterotrophic nutrition' can answer it in 90 seconds on exam day. A student who only read the chapter might take 5 minutes and still miss a point. CBSE Class 9 Science examiners follow predictable patterns—they test the same concepts repeatedly but rephrase them. By working PYQs, you decode these patterns and avoid surprises. This landing page compiles the most-repeated questions from 2020–2025 papers, grouped by mark value, so you see at a glance what to prioritize.

1-mark questions test quick recall and definition accuracy. They often follow these patterns: (a) 'Define [term]' or 'State the meaning of [term]'. (b) 'Name the process by which…'. (c) 'Give one word for [description]'. Here are 5 of the most commonly repeated 1-mark questions: **Q1. Define photosynthesis.** Answer: Photosynthesis is the process by which green plants manufacture their own food (glucose) from carbon dioxide and water in the presence of sunlight and chlorophyll, releasing oxygen as a byproduct. In symbols: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂. **Q2. What do you call an organism that makes its own food?** Answer: An autotroph (or autotrophic organism). Green plants are examples because they use photosynthesis to convert inorganic matter into organic food. **Q3. Name the process by which a saprotroph obtains its food.** Answer: Saprophagy (or saprotrophic nutrition). Saprotrophs secrete enzymes onto dead organic matter, breaking it down externally before absorption. **Q4. Define parasitism.** Answer: Parasitism is a symbiotic relationship in which one organism (the parasite) lives on or inside another organism (the host) and feeds on its body or body fluids, usually harming the host. **Q5. What is a mycorrhizal association?** Answer: A mycorrhizal association is a mutualistic symbiotic relationship between a fungus and the roots of a green plant. The fungus absorbs water and minerals for the plant; the plant supplies sugars to the fungus.

3-mark questions expect definition + explanation + one or two points of elaboration. They commonly ask you to 'Explain', 'Distinguish between', or 'Describe a process'. Here are 5 high-frequency 3-mark questions: **Q1. Explain the difference between autotrophic nutrition and heterotrophic nutrition.** Answer: Autotrophic nutrition is a mode of feeding in which organisms manufacture their own organic food from simple inorganic substances (CO₂, H₂O, mineral salts) using energy from light (photosynthesis) or chemical reactions (chemosynthesis). Examples: green plants, photosynthetic bacteria. Heterotrophic nutrition is a mode in which organisms cannot produce their own food and must consume other organisms or organic matter. Examples: animals, fungi, non-photosynthetic bacteria. The key distinction: autotrophs are self-feeders; heterotrophs depend on pre-made food. **Q2. Describe the main steps of photosynthesis.** Answer: Photosynthesis occurs in two stages: (a) Light-dependent reactions (in thylakoids): Light energy splits water molecules (photolysis), releasing O₂, H⁺ ions, and electrons. These electrons are energized and used to form ATP and NADPH. (b) Light-independent reactions or Calvin Cycle (in stroma): ATP and NADPH from stage 1 power the reduction of CO₂ to form glucose (C₆H₁₂O₆). Overall equation: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂. Green plants use glucose for energy and growth. **Q3. Distinguish between a parasite and a saprotroph.** Answer: A parasite is a heterotroph that lives on or inside a host organism and feeds on its living cells or body fluids, usually harming the host (parasitism is an antagonistic symbiosis). Examples: tapeworm, mosquito. A saprotroph is a heterotroph that feeds on dead or decaying organic matter by secreting powerful enzymes externally and absorbing the digested products. Examples: mushrooms, bread mould. Key difference: parasites feed on living hosts and cause harm; saprotrophs feed on dead matter and aid decomposition. **Q4. What do you understand by symbiosis? Give two examples.** Answer: Symbiosis is a close and prolonged relationship between two organisms of different species living together. The relationship may benefit one or both partners. Types: (a) Mutualism—both organisms benefit. Example: mycorrhizal association (fungus and plant roots); nitrogen-fixing bacteria in legume root nodules. (b) Parasitism—one benefits, one is harmed. Example: tapeworm in human intestine. (c) Commensalism—one benefits, the other is unaffected (rare in nature). **Q5. Explain why the rate of photosynthesis varies with light intensity.** Answer: Light is one of the limiting factors of photosynthesis. At low light intensity, fewer photons reach chlorophyll, so fewer water molecules are split and less ATP/NADPH is produced. This slows the Calvin Cycle, reducing glucose synthesis. As light intensity increases, the rate of photosynthesis increases proportionally up to a saturation point. Beyond saturation, other factors (like CO₂ concentration or enzyme availability) become limiting, and increasing light produces no further increase in rate.

5-mark questions demand depth: a definition, multiple sub-points, explanation of mechanisms, or comparative analysis. Examiners test whether you can connect ideas and show understanding beyond rote learning. Here are 3 commonly appearing 5-mark questions with full solutions: **Q1. Explain the role of chlorophyll in photosynthesis. Describe the structure of a chloroplast and explain why photosynthesis is essential for life on Earth.** Answer: (a) Role of chlorophyll: Chlorophyll is the green pigment found in thylakoids within chloroplasts. It absorbs light energy, particularly in blue and red wavelengths, exciting electrons to a higher energy state. This light absorption is the first step of the light-dependent reactions. Without chlorophyll, light energy cannot be converted into chemical energy (ATP and NADPH), and photosynthesis cannot proceed. (b) Structure of a chloroplast: A chloroplast is bounded by a double membrane (outer and inner envelope) and contains two main regions. The stroma is a fluid-filled space where light-independent reactions (Calvin Cycle) occur. Thylakoids are flattened sac-like structures stacked into grana, suspended in the stroma; they are the site of light-dependent reactions. Chlorophyll and other photosynthetic pigments are embedded in thylakoid membranes. (c) Why essential for life: Photosynthesis produces glucose (energy-rich organic food) and oxygen. Heterotrophs (animals, fungi) depend on glucose either directly (herbivores eat plants) or indirectly (carnivores eat herbivores). Without photosynthesis, no organic matter and no oxygen—most aerobic life cannot exist. Plants are the primary producers in all ecosystems. Thus photosynthesis is the foundation of food chains and oxygen cycling. **Q2. Compare and contrast autotrophic, heterotrophic, and saprophytic nutrition. For each type, give two examples and explain how each organism obtains its food.** Answer: (a) Autotrophic nutrition: Organisms synthesize organic food from inorganic substances (CO₂, H₂O, minerals) using energy from light (photosynthesis) or chemical bonds (chemosynthesis). Examples: Spinacia oleracea (spinach plant)—uses photosynthesis; Bacillus firmus—a chemotrophic bacterium. Method: Green plants capture light in chlorophyll, split water, fix CO₂ via the Calvin Cycle, and produce glucose. (b) Heterotrophic nutrition: Organisms consume pre-made organic food produced by others. Examples: Homo sapiens (human)—ingests plants and meat; Panthera leo (lion)—hunts and eats prey. Method: Heterotrophs ingest food, digest it mechanically and chemically, and absorb nutrients. (c) Saprophytic nutrition: Organisms feed on dead or decaying organic matter by external digestion. Examples: Agaricus bisporus (cultivated mushroom); Rhizopus (bread mould). Method: Saprophs secrete hydrolytic enzymes (amylase, protease, lipase) onto dead substrates, breaking polymers into monomers, then absorb soluble products. Key contrast: Autotrophs require only inorganic input; heterotrophs and saprotrophs require organic input. Heterotrophs and saprophs both absorb through a digestive system, but heterotrophs prey on living organisms, saprotrophs feed on dead matter. **Q3. Discuss the nutritional relationships (symbiosis) between a legume plant (e.g., pea) and nitrogen-fixing bacteria in root nodules. Explain the structure of a root nodule, the benefits to each partner, and why this relationship is classified as mutualistic symbiosis.** Answer: (a) What happens: Nitrogen-fixing bacteria (e.g., Rhizobium leguminosarum) enter root hairs of legume plants and proliferate in root cortex cells, inducing the formation of root nodules—specialized organs housing bacterial colonies. (b) Structure of a root nodule: A nodule is a swollen outgrowth of the root containing infected root cortex cells. Inside, bacteria live in plant-derived membrane sacs called symbiosomes. The nodule is vascularized (has xylem and phloem) for nutrient exchange. A colourless pigment called leghaemoglobin (similar to haemoglobin) maintains a low-oxygen environment suitable for the nitrogen-fixing enzyme nitrogenase. (c) Benefits to the bacterium: The plant provides a protected habitat, a steady supply of sugars (from photosynthesis) for respiratory energy, and minerals. (d) Benefits to the plant: Nitrogen-fixing bacteria reduce atmospheric N₂ to NH₃ (ammonia) using nitrogenase enzyme. This ammonia is assimilated into amino acids and proteins, which the plant uses for growth. Without nitrogen fixation, the plant would depend on soil nitrates, often scarce in agricultural fields. (e) Why mutualistic: Both organisms gain: bacteria receive organic nutrients; plants receive usable nitrogen. Neither is harmed. Hence it is a mutualistic symbiotic relationship, and is ecologically important in agriculture—farmers rotate legume crops to naturally enrich soil nitrogen.

The 2024–25 rationalized CBSE Class 9 syllabus has already consolidated many topics, and trends suggest the 2026–27 exam pattern will emphasize: (1) Application and problem-solving over definition recall. Expect more questions asking 'Why does X happen in Y conditions?' or 'What would happen if Z were removed?' rather than pure definition questions. (2) Diagram-based questions. Chloroplast structure, root nodule cross-section, and the photosynthesis equation are likely to appear as fill-in-the-label or explain-the-role questions. Practice drawing and labelling these structures. (3) Real-world context. Questions linking photosynthesis to climate change, nitrogen fixation to sustainable agriculture, or parasitism to disease control will increase. (4) Integration with other chapters. Expect links between Nutrition in Plants and Chapter 5 (Fundamental Unit of Life—cell structure) and Chapter 6 (Tissues). For instance, 'Why are thylakoids stacked into grana?' requires knowledge of cell structure. (5) Reduced rote-learning emphasis. CBSE is moving away from 'Define photosynthesis' and toward 'Explain how changes in CO₂ concentration affect the rate of photosynthesis and why.' Prepare by solving application-style questions and understanding mechanisms, not just memorizing definitions. Start practising with CBSE sample papers released for 2025–26 and newer past papers to see these shifts in action.

On exam day, how you approach questions matters as much as what you know. Use this strategy: (1) Scan all questions first (2–3 minutes). Identify which are 1-mark, 3-mark, and 5-mark. Mark questions you can answer confidently. (2) Attempt 1-mark questions first (5 minutes total). These are quick wins and build confidence. Write one-line or one-sentence answers. Avoid over-explaining. (3) Move to 3-mark questions (30 minutes for five questions ≈ 6 min each). For 'Distinguish between' questions, use a two-row table: write the feature in the first column, then state the difference for each concept. This saves time and ensures you cover both sides. For 'Explain' questions, use the structure: Define → State cause/mechanism → Give example or effect. (4) Tackle 5-mark questions last (35 minutes for three questions ≈ 12 min each). These have time to lose, so ensure 1-mark and 3-mark questions are complete first. For 5-mark questions, outline your answer in point form on the margin (30 seconds), then write the full answer. This prevents rambling and ensures logical flow. (5) Use diagrams if asked or if helpful. A labelled chloroplast diagram or a root nodule cross-section can earn quick marks and clarify your understanding to the examiner. (6) Check keyword language. If the question says 'Explain', write an explanation (how and why). If it says 'State', one sentence suffices. If it says 'Distinguish', compare two things. (7) Time management: 1-mark (5 min) + 3-mark (30 min) + 5-mark (35 min) = 70 minutes, leaving 10 minutes for review. Practice this split with past papers to build speed. Start a 3-day free trial at cbsetutor.ai to access thousands of practice questions and personalized feedback on your answers.

Keep these definitions handy while revising: Autotroph—an organism that manufactures its own organic food from inorganic substances. Example: green plants. Heterotroph—an organism that consumes organic food produced by others. Examples: animals, fungi. Photosynthesis—the process by which green plants convert light energy, CO₂, and H₂O into glucose and O₂. Equation: 6CO₂ + 6H₂O + light energy (in chlorophyll) → C₆H₁₂O₆ + 6O₂. Chloroplast—the organelle in plant cells where photosynthesis occurs; contains thylakoids (site of light reactions) and stroma (site of Calvin Cycle). Chlorophyll—the green photosynthetic pigment that absorbs light energy. Saprotroph—a heterotroph that feeds on dead organic matter by external digestion (enzyme secretion and absorption). Examples: mushrooms, moulds. Parasite—a heterotroph that lives on or in a host and feeds on its living tissues, usually harming the host. Example: tapeworm. Host—the organism on which a parasite feeds. Symbiosis—a close, long-term relationship between two organisms of different species. Mutualism—symbiosis beneficial to both organisms. Example: flowering plants and pollinators. Commensalism—symbiosis beneficial to one, neutral to the other (rare). Nitrogen fixation—the process by which certain bacteria (e.g., Rhizobium) convert atmospheric N₂ into usable nitrogen compounds (NH₃, amino acids). Location: root nodules of legume plants. Mycorrhiza—a mutualistic association between a fungus and plant roots, where the fungus aids in water and mineral absorption, and the plant supplies sugars.