Class 9 Science Chapter 1: Nutrition in Plants MCQ Quiz with Detailed Answers

The revised CBSE Class 9 assessment framework emphasizes objective testing to evaluate conceptual depth in shorter timeframes. MCQs in the Science exam (particularly in Section A) require students to rapidly distinguish between similar-sounding distractors, making them an ideal diagnostic tool for identifying knowledge gaps. For Chapter 1 (Nutrition in Plants), examiners craft questions that blend straightforward recall (e.g., 'Which organelle performs photosynthesis?') with higher-order thinking (e.g., 'Why do parasitic plants lack chlorophyll?'). Unlike lengthy descriptive answers, MCQs force precision: a single misread word can flip the correct option. The new pattern allocates approximately 40–50% of marks to objective questions, meaning mastery of MCQ strategies directly impacts your final score. Students who practise MCQs systematically develop pattern recognition skills—they learn which keywords signal photosynthesis questions, which phrases indicate heterotrophic nutrition, and which statement pairs form valid assertion-reason combos. Timed MCQ practice also simulates exam pressure, reducing anxiety and improving decision-making speed. This section-by-section approach ensures you build confidence progressively.

**Question 1:** Which of the following is an autotrophic organism? (A) Fungus (B) Green plant (C) Tapeworm (D) Lion **Answer:** (B) Green plant **Reason:** Autotrophs synthesize organic food from inorganic substances using light or chemicals; green plants use photosynthesis. **Question 2:** Photosynthesis primarily occurs in which organelle? (A) Mitochondrion (B) Ribosome (C) Chloroplast (D) Nucleus **Answer:** (C) Chloroplast **Reason:** Chloroplasts contain chlorophyll and are the site of light and dark reactions. **Question 3:** Which gas is absorbed by plants during photosynthesis? (A) Oxygen (B) Nitrogen (C) Carbon dioxide (D) Hydrogen **Answer:** (C) Carbon dioxide **Reason:** CO₂ from the atmosphere is fixed into glucose during the Calvin cycle. **Question 4:** A saprotroph obtains nutrition by: (A) Photosynthesis (B) Feeding on living organisms (C) Decomposing dead organic matter (D) Parasitizing host cells **Answer:** (C) Decomposing dead organic matter **Reason:** Saprotrophs secrete enzymes onto dead material and absorb digested nutrients. **Question 5:** Which is a parasitic plant? (A) Neem (B) Cuscuta (dodder) (C) Wheat (D) Rice **Answer:** (B) Cuscuta (dodder) **Reason:** Cuscuta lacks roots and chlorophyll, extracting nutrients from host plants. **Question 6:** The products of photosynthesis are: (A) Carbon dioxide and water (B) Glucose and oxygen (C) Starch and hydrogen (D) Cellulose and nitrogen **Answer:** (B) Glucose and oxygen **Reason:** The overall equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ under light. **Question 7:** Heterotrophic nutrition is found in: (A) All plants (B) Chlorophyll-containing organisms (C) Animals and fungi (D) Only photosynthetic bacteria **Answer:** (C) Animals and fungi **Reason:** Heterotrophs cannot produce their own food; they depend on other organisms. **Question 8:** Which of these is NOT a heterotrophic mode of nutrition? (A) Parasitism (B) Saprophagy (C) Photosynthesis (D) Holozoic nutrition **Answer:** (C) Photosynthesis **Reason:** Photosynthesis is autotrophic; all others are heterotrophic modes. **Question 9:** The site of light-dependent reactions in photosynthesis is: (A) Stroma (B) Thylakoid membrane (C) Mitochondrial matrix (D) Cytoplasm **Answer:** (B) Thylakoid membrane **Reason:** Light-dependent reactions occur on thylakoid membranes where photosystem complexes are embedded. **Question 10:** A symbiotic relationship where both organisms benefit is called: (A) Parasitism (B) Mutualism (C) Commensalism (D) Predation **Answer:** (B) Mutualism **Reason:** Mutualism involves two-way benefit; examples include nitrogen-fixing bacteria in legume roots and mycorrhizal fungi.

**Question 11:** A plant is kept in a dark room for 24 hours. What will happen to its glucose production? (A) Increase due to dark reactions (B) Decrease to zero (C) Remain constant (D) Increase only if water is available **Answer:** (B) Decrease to zero **Reason:** Light is essential for the light-dependent reaction, which generates ATP and NADPH needed for the Calvin cycle; without light, glucose synthesis halts. **Question 12:** Identify the correct sequence in photosynthesis: (A) Light reactions → Calvin cycle → CO₂ fixation (B) CO₂ fixation → Light reactions → Calvin cycle (C) Light reactions → CO₂ fixation → Calvin cycle (D) Calvin cycle → Light reactions → CO₂ fixation **Answer:** (C) Light reactions → CO₂ fixation → Calvin cycle **Reason:** Light reactions generate energy carriers (ATP, NADPH); these drive CO₂ fixation and the Calvin cycle. **Question 13:** Why do parasitic plants like Cuscuta lack leaves? (A) Environmental stress (B) They obtain ready-made food from hosts, so photosynthesis is unnecessary (C) Mutations prevent leaf formation (D) Cold climate adaptations **Answer:** (B) They obtain ready-made food from hosts, so photosynthesis is unnecessary **Reason:** Structural reduction (loss of roots, leaves, chlorophyll) is an evolutionary adaptation to parasitic lifestyle. **Question 14:** A fungus breaking down a fallen tree obtains energy. This is an example of: (A) Autotrophic nutrition (B) Holozoic nutrition (C) Saprophytic nutrition (D) Chemosynthesis **Answer:** (C) Saprophytic nutrition **Reason:** Fungi are saprophytes; they secrete extracellular enzymes and absorb organic compounds from decomposing matter. **Question 15:** In the equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂, where does the oxygen in O₂ originate? (A) From CO₂ (B) From H₂O (C) From glucose (D) From the air **Answer:** (B) From H₂O **Reason:** Isotope studies confirm that O₂ released during photosynthesis comes from water molecules split during the light reactions. **Question 16:** A plant grows well when provided with nitrogen-fixing bacteria in its root nodules. This relationship is: (A) Parasitism (B) Predation (C) Mutualism (D) Commensalism **Answer:** (C) Mutualism **Reason:** The plant receives fixed nitrogen; bacteria gain carbohydrates from the plant's photosynthesis—mutual benefit. **Question 17:** Chloroplasts are absent in: (A) All photosynthetic plants (B) Fungi, animals, and non-photosynthetic bacteria (C) Only the roots of plants (D) Aquatic organisms **Answer:** (B) Fungi, animals, and non-photosynthetic bacteria **Reason:** Chloroplasts are found only in autotrophs and certain algae; heterotrophs lack them entirely. **Question 18:** The dark reactions of photosynthesis can occur: (A) Only during the day (B) Only during the night (C) Both day and night, as long as ATP and NADPH are available (D) Only in the presence of chlorophyll **Answer:** (C) Both day and night, as long as ATP and NADPH are available **Reason:** The Calvin cycle (dark reactions) uses products from light reactions; it doesn't require light directly but runs continuously if energy carriers are supplied. **Question 19:** Which statement correctly compares autotrophs and heterotrophs? (A) Both produce their own food (B) Both depend on other organisms (C) Autotrophs are self-sufficient; heterotrophs depend on organic sources (D) Heterotrophs can perform photosynthesis in the dark **Answer:** (C) Autotrophs are self-sufficient; heterotrophs depend on organic sources **Reason:** By definition, autotrophs synthesize food from inorganic matter; heterotrophs ingest or absorb pre-formed organic compounds. **Question 20:** A plant loses 95% of the water it absorbs through transpiration. This water loss is offset by: (A) The 5% used in photosynthesis and growth (B) Osmotic uptake from soil (C) Recycling of water from respiration (D) Absorption of dew at night **Answer:** (A) The 5% used in photosynthesis and growth **Reason:** The small fraction retained supports metabolic reactions including photosynthesis and cellular processes.

**Question 21:** Assertion: Photosynthesis is the reverse of cellular respiration. Reason: Both involve carbon and hydrogen compounds and energy transfer. (A) Both A and R are true; R explains A (B) Both A and R are true; R does NOT explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (B) Both A and R are true; R does NOT explain A **Reason:** While both involve carbon-hydrogen bonds and energy, photosynthesis and respiration differ fundamentally in direction, reactants, and purpose; similarity alone doesn't make respiration the 'reverse'. **Question 22:** Assertion: Saprotrophs cannot be autotrophs. Reason: Saprotrophs lack chlorophyll and cannot synthesize glucose from CO₂. (A) Both A and R are true; R explains A (B) Both A and R are true; R does NOT explain A (C) A is true; R is false (D) Both A and R are false **Answer:** (A) Both A and R are true; R explains A **Reason:** Saprotrophs are obligately heterotrophic; the absence of photosynthetic capacity directly explains why they cannot be autotrophs. **Question 23:** A plant exhibits symptoms of nitrogen deficiency despite adequate soil nitrogen. The most likely reason is: (A) Nitrogen is insoluble in water (B) The plant lacks symbiotic nitrogen-fixing bacteria in its roots (C) Photosynthesis is blocked (D) Nitrogen cannot enter through leaves **Answer:** (B) The plant lacks symbiotic nitrogen-fixing bacteria in its roots **Reason:** Many plants rely on mutualistic bacteria to convert atmospheric N₂ into usable forms; without them, soil nitrogen remains inaccessible. **Question 24:** Assertion: Cuscuta is a parasite that does not harm its host plant. Reason: Cuscuta absorbs only excess nutrients the host plant produces. (A) Both A and R are true; R explains A (B) Both A and R are true; R does NOT explain A (C) A is false; R is false (D) A is true; R is false **Answer:** (C) A is false; R is false **Reason:** Cuscuta parasites significantly reduce host photosynthetic capacity and nutrient availability; they extract nutrients for their own growth, harming the host. **Question 25:** In a sealed greenhouse, a plant is exposed to light but CO₂ levels drop to near-zero. Photosynthesis will: (A) Accelerate due to excess light (B) Slow dramatically because CO₂ is a raw material (C) Continue normally using stored CO₂ in cells (D) Switch to heterotrophic mode **Answer:** (B) Slow dramatically because CO₂ is a raw material **Reason:** CO₂ is a critical substrate for the Calvin cycle; without it, glucose synthesis ceases even if light and water are abundant. **Question 26:** Assertion: Mutualism and commensalism are functionally identical. Reason: In both relationships, one or both organisms benefit. (A) Both A and R are true; R explains A (B) Both A and R are true; R does NOT explain A (C) A is false; R is false (D) A is false; R is true **Answer:** (D) A is false; R is true **Reason:** Mutualism requires both organisms to benefit; commensalism benefits only one. The difference is fundamental, not functional. **Question 27:** A researcher observes that in a mycorrhizal association, the fungus receives glucose from the plant's photosynthesis, while the plant obtains phosphate ions from the fungus. This relationship is best classified as: (A) Parasitism (B) Mutualism (C) Commensalism (D) Predation **Answer:** (B) Mutualism **Reason:** Both partners gain essential resources (glucose and minerals); the direct exchange of benefits defines mutualistic symbiosis. **Question 28:** Assertion: During the light-dependent reactions, electrons from water are excited by photons and transferred through electron transport chains. Reason: This energy is used to pump protons into the thylakoid lumen, creating a gradient for ATP synthesis. (A) Both A and R are true; R explains A (B) Both A and R are true; R does NOT explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Reason:** The assertion describes photolysis and electron transport; the reason explains the immediate consequence—proton gradient formation—which drives chemiosmosis and ATP production. **Question 29:** If a heterotrophic organism consumes an autotroph that has been exposed to ¹⁴C-labeled CO₂, the heterotroph's glucose molecules will eventually become labeled. This demonstrates: (A) Heterotrophs can photosynthesize (B) Energy transfer within food chains preserves carbon from photosynthesis (C) Heterotrophs produce their own glucose (D) Carbon dioxide is created in the heterotroph's cells **Answer:** (B) Energy transfer within food chains preserves carbon from photosynthesis **Reason:** The labeled carbon fixed during autotrophic photosynthesis passes into consumer tissues, showing the linkage between primary production and heterotrophic nutrition. **Question 30:** Assertion: Without photosynthesis, cellular respiration would eventually cease globally. Reason: Photosynthesis replenishes atmospheric oxygen and produces glucose, which are used in respiration. (A) Both A and R are true; R explains A (B) Both A and R are true; R does NOT explain A (C) A is true; R is false (D) A is false; R is true **Answer:** (A) Both A and R are true; R explains A **Reason:** Photosynthesis is the primary source of O₂ and organic carbon; without it, respiratory pathways would exhaust available substrates and gas, collapsing aerobic metabolism.

CBSE MCQ writers craft distractors that exploit common misconceptions. Recognizing these patterns boosts your accuracy significantly. **Trap 1: Reversing Definitions** Example: "Photosynthesis is the reverse of cellular respiration." Why it's tempting: Both involve C, H, O compounds and energy; students assume symmetry. Reality: The processes differ in direction, location, purpose, and enzyme requirements; similarity ≠ reversal. **Trap 2: Partial Truths** Example: "Dark reactions can occur only at night." Why it's tempting: The word 'dark' suggests darkness. Reality: Dark reactions require ATP and NADPH from light reactions; they occur continuously during daylight as long as energy carriers are supplied. **Trap 3: Confusing Related Organisms** Example: Mixing up saprotrophs (bacteria, fungi decomposing dead matter) with parasites (feeding on living hosts). Why it's tempting: Both are heterotrophs. Reality: Saprotrophs digest externally; parasites extract from living tissues. **Trap 4: Oversimplified Symbiosis** Example: "All symbiotic relationships benefit both organisms equally." Why it's tempting: Introductory chapters emphasize mutualism. Reality: Commensalism (one benefits, one unaffected) and parasitism (one benefits, one harmed) are also symbiotic. **Trap 5: Location Confusion** Example: "Light reactions occur in the stroma; dark reactions occur in thylakoids." Why it's tempting: 'Light' and 'dark' seem to suggest locations. Reality: It's the opposite—light reactions occur on thylakoid membranes; dark reactions in stroma. **Trap 6: Mixing Raw Materials and Products** Example: "Oxygen is a raw material for photosynthesis." Why it's tempting: Oxygen is involved in photosynthesis. Reality: O₂ is a byproduct; water is the source of O₂ atoms. **Trap 7: Absolute vs. Conditional Statements** Example: "Heterotrophs never perform photosynthesis." Why it's tempting: Definitions seem absolute. Reality: Most heterotrophs cannot; a few protists and bacteria do both (mixotrophs)—but for CBSE Class 9, treat heterotrophs as non-photosynthetic. **Strategy to Avoid Traps:** Read each option twice—once for its literal meaning, once for its assumption. If an option sounds 'too simple' or repeats a textbook phrase, re-examine it against experimental evidence or the diagram in your NCERT text.

CBSE Science papers allocate 1.5–2 minutes per MCQ on average. Strategic time use separates 90%-scorers from 70%-scorers. **Pre-Exam Prep (1 week before):** 1. Solve all 30 questions in this quiz untimed to identify weak topics. 2. Create a 'trap-prone' list: note which options you chose incorrectly and why. 3. Memorize these five facts verbatim from NCERT Chapter 1: (i) Photosynthesis equation, (ii) Location of light/dark reactions, (iii) Three heterotrophic modes, (iv) Parasite vs. saprotroph, (v) Mutualism example. **During the Exam:** 1. **Scan & Skip (0–60 seconds per question):** Read the question and all four options. If confident (>80%), mark and move. If unsure, mark for second pass. 2. **Elimination (First Pass, 1 min per Q):** Use process of elimination. Cross out options with glaring errors (e.g., 'photosynthesis produces CO₂'). Often, 2 of 4 options are immediately false. 3. **Keyword Match (30 sec):** Match question nouns/verbs to textbook diagrams. Example: If the Q asks about 'thylakoid,' light reactions must be involved. 4. **Assertion-Reason Logic (90 sec):** For AR questions, first judge if A is true, then if R is true, then if R explains A. Never assume A and R are true just because both sound plausible. 5. **Review (Last 3–5 min):** Return to marked questions. Avoid second-guessing correct answers; change only if you now see a clear logical error in your first choice. **Scoring Targets:** - Easy tier (Q1–10): 9–10/10 (allow ≤1 careless error). - Medium tier (Q11–20): 8–9/10 (application questions demand careful reading). - Hard tier (Q21–30): 7–8/10 (assertion-reason requires dual verification; one point missed per question is typical). **Example Walk-Through:** Q: "A plant is kept in a dark room for 24 hours. What will happen to its glucose production?" Step 1 (Scan): All four options reference glucose and light/reactions. Step 2 (Eliminate): Option (A) 'Increase due to dark reactions'—false; dark reactions need ATP from light reactions. Option (D) 'Increase only if water is available'—irrelevant; water alone doesn't drive glucose without light. Down to (B) and (C). Step 3 (Keyword): 'Dark room' + '24 hours' = no photosynthesis. Glucose production halts. Answer: (B) Decrease to zero. **Time: 75 seconds.** Start a 3-day free trial at cbsetutor.ai to access interactive timed MCQ drills, detailed solution videos, and performance analytics tailored to your weak topics.

**Autotrophy:** Self-feeding; organisms synthesize organic molecules from inorganic raw materials. Example: Green plants use light energy to convert CO₂ and H₂O into glucose (photosynthesis). Equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. **Heterotrophy:** Dependency; organisms ingest or absorb pre-formed organic food. Three modes: Holozoic (ingestion + digestion, e.g., animals), Saprophytic (external enzyme secretion + absorption, e.g., fungi), Parasitic (living on/in a host, e.g., tapeworm). **Photosynthesis—Two Stages:** 1. Light-dependent reactions (thylakoid membrane): Photons → electrons → proton gradient → ATP + NADPH. Also: 2H₂O → O₂ + 4H⁺ + 4e⁻. 2. Light-independent reactions/Calvin Cycle (stroma): ATP + NADPH + CO₂ → Glucose. **Symbiosis—Three Types:** 1. Mutualism: Both partners benefit. Example: Nitrogen-fixing bacteria in legume root nodules. 2. Commensalism: One benefits; other unaffected. Example: Orchids on tree branches. 3. Parasitism: One benefits; other harmed. Example: Cuscuta extracting nutrients from host stems. **Key Distinction:** Parasite vs. Saprotroph—Parasite feeds on *living* tissue (and reduces host fitness); saprotroph decomposes *dead* matter (and aids nutrient cycling). Both are heterotrophic. Practicingthe 30 MCQs above and reviewing these summaries will ensure you retain core facts and trap-awareness for your Class 9 exam. Consistency beats cramming.