Class 9 Science Chapter 10 Living Creatures: Exploring their Characteristics — Important Questions with Complete Answers

Chapter 10 carries significant weightage in CBSE Class 9 Science term papers. The recent rationalized syllabus emphasises observational learning and functional understanding of living systems rather than rote memorization. Board examiners test two key competencies: (1) Structural knowledge—identifying and naming plant and animal parts, and understanding their functions (roots absorb water, leaves manufacture food). (2) Process understanding—explaining how photosynthesis and respiration occur, and how organisms are classified based on feeding habits. In the 2026-27 pattern, expect 1–2 questions from this chapter in Section A (MCQ/1-mark), 2–3 questions in Section B (2-mark short answer), and 1–2 in Section C (3–5 mark long answer). Case-study and diagram-based questions are increasingly common; you may be asked to label a leaf cross-section, identify an organism's diet from its teeth structure, or explain energy flow during photosynthesis. Mastering these 18 questions ensures you recognize common question patterns, practice time management, and develop the ability to construct complete, marking-scheme-aligned answers. CBSETUTOR.ai's AI tutor drills exactly these question types daily, with personalized feedback on answer structure and scientific terminology.

Multiple-choice questions in CBSE Class 9 Science test single-concept recall and are designed to be answered in 30–45 seconds. These five questions cover plant parts, photosynthesis, animal classification, and respiration. **Q1: Which of the following is the primary site of photosynthesis in a plant leaf?** A) Epidermis B) Palisade mesophyll C) Spongy mesophyll D) Xylem **Answer: B) Palisade mesophyll** Explanation: The palisade mesophyll layer contains abundant chloroplasts arranged in neat columns perpendicular to the upper epidermis, maximizing light capture for photosynthesis. The spongy mesophyll aids gas exchange but is not the primary photosynthetic site. **Q2: An organism that feeds on both plants and animals is called a/an:** A) Herbivore B) Carnivore C) Omnivore D) Detritivore **Answer: C) Omnivore** Explanation: Omnivores (humans, bears, crows) consume both plant and animal material. Herbivores eat only plants; carnivores eat only meat; detritivores feed on dead organic matter. **Q3: In plants, respiration occurs in:** A) Roots only B) Leaves only C) All living cells D) Flowers only **Answer: C) All living cells** Explanation: Every living plant cell undergoes cellular respiration to release energy from glucose. Although photosynthesis occurs only in green tissues, respiration is a universal process in all cells (roots, stems, leaves, flowers, fruits). **Q4: The vascular bundle in a stem consists of:** A) Xylem and phloem B) Xylem and epidermis C) Phloem and cortex D) Epidermis and cortex **Answer: A) Xylem and phloem** Explanation: Xylem transports water and minerals upward; phloem transports sugars and other organic compounds throughout the plant. Together they form the vascular bundle. **Q5: Which organ system is responsible for gas exchange in animals?** A) Digestive system B) Respiratory system C) Circulatory system D) Excretory system **Answer: B) Respiratory system** Explanation: The respiratory system (lungs, trachea, diaphragm in mammals; gills in fish) facilitates the exchange of oxygen and carbon dioxide between the organism and the environment.

These questions require 3–5 sentence answers that explain structure-function relationships or simple processes. Mark distribution: typically 1 mark for correct identification/definition, 1 mark for reason or example. **Q1: Name the three types of root systems in plants and state one function of roots.** **Answer:** The three types of root systems are: (1) Taproot system (one main root with lateral branches, found in dicots like beans), (2) Fibrous root system (many fine roots of equal size, found in monocots like grasses), (3) Adventitious roots (roots that arise from stems or leaves, as in ivy or maize). Function: Roots absorb water and minerals from the soil, anchor the plant firmly in the ground, and in some plants (carrots, turnips), store food. **Q2: Explain why leaves are flat and broad. What advantage does this shape provide?** **Answer:** Leaves are flat and broad to maximize the surface area exposed to sunlight. This large surface area increases the amount of light captured for photosynthesis, which improves the rate of food manufacture. The flattened structure also facilitates gas exchange (CO₂ enters, O₂ exits) through stomata on the lower epidermis. In some plants (lotus, water lily), leaves float to ensure optimal light exposure. **Q3: Distinguish between a herbivore and a carnivore. Give one example of each.** **Answer:** A herbivore is an animal that feeds exclusively on plants (leaves, fruits, seeds, flowers). Example: cow, deer, grasshopper. A carnivore is an animal that feeds exclusively on the flesh (meat) of other animals. Example: lion, eagle, crocodile. The teeth and digestive systems of herbivores are adapted for grinding plant material, while carnivores possess sharp, pointed teeth (canines) for tearing flesh and shorter digestive tracts optimized for protein digestion. **Q4: What is the main difference between aerobic and anaerobic respiration?** **Answer:** Aerobic respiration occurs in the presence of oxygen and produces more energy (approximately 38 ATP molecules per glucose molecule). It occurs in mitochondria and is the primary respiration type in most organisms. Anaerobic respiration occurs without oxygen and produces much less energy (2 ATP molecules per glucose). It occurs in the cytoplasm and produces lactic acid (in animals) or ethanol and CO₂ (in yeast) as by-products. Anaerobic respiration is used by bacteria in oxygen-free environments or briefly by muscle cells during intense exercise. **Q5: Draw a simple diagram of a flower and label its male and female reproductive organs.** **Answer:** [Conceptual description, as diagrams render in text format: A typical flower diagram shows: (1) Stamen (male organ)—consisting of filament (stalk) and anther (pollen-producing structure at the tip). (2) Pistil/Carpel (female organ)—consisting of stigma (topmost, sticky part), style (middle tube), and ovary (base, containing ovules). (3) Sepals and petals surrounding these organs.] The anther produces pollen grains containing male gametes. The ovary contains ovules with female gametes. Pollination occurs when pollen reaches the stigma, leading to fertilization and seed formation.

These questions demand deeper understanding—you must explain processes, compare concepts, or apply knowledge to new situations. Answers typically require 6–10 sentences and logical organization. **Q1: Explain the process of photosynthesis in plants. Write the word equation and state where in the leaf this process occurs.** **Answer:** Photosynthesis is the process by which green plants manufacture their own food using light energy, water, and carbon dioxide. Word equation: Carbon dioxide + Water + Light energy → Glucose + Oxygen Or, in chemical notation: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ Photosynthesis occurs primarily in the leaves, specifically in the palisade mesophyll layer where chloroplasts are densely packed. The chloroplasts contain chlorophyll pigment which absorbs light energy. The process has two stages: (1) Light-dependent reactions (in thylakoid membranes), which split water molecules, release oxygen, and produce ATP and NADPH. (2) Light-independent reactions or Calvin cycle (in the stroma), which uses ATP and NADPH to fix CO₂ into glucose. Plants use this glucose for energy and growth, and release oxygen as a by-product essential for animal respiration. The rate of photosynthesis depends on light intensity, temperature, and CO₂ concentration. **Q2: Compare the structure and function of xylem and phloem tissues in plants.** **Answer:** Xylem and phloem are the two types of vascular tissues in plants, each with distinct structure and function. Xylem: Composed of dead cells including tracheids and vessel elements (long tubes), plus supporting fibres. Functions: Transport water and dissolved minerals (nitrates, phosphates) from roots to leaves and other parts via root pressure and capillary action. Also provides mechanical support to the stem. Phloem: Composed of living cells including sieve tubes and companion cells. Functions: Transport dissolved organic compounds, especially glucose and amino acids, from leaves (source) to roots and growing regions (sinks) via active transport (requiring ATP). Phloem transport is bidirectional; it moves sugars downward to roots and upward to developing fruits. Key difference: Xylem is dead and transports water upward only; phloem is living and transports organic solutes in both directions. Both are necessary for plant survival and growth. **Q3: A student observes that a potted plant kept in complete darkness for one week becomes pale and weak. Explain why this happens and what role chlorophyll plays.** **Answer:** When a plant is kept in darkness for an extended period, it cannot perform photosynthesis because photosynthesis requires light energy. Without photosynthesis, the plant cannot manufacture glucose (its food source), so stored energy reserves (starches) deplete rapidly. The plant becomes pale because chlorophyll (green pigment) is degraded in the absence of photosynthesis or light-dependent chlorophyll regeneration; in some plants, other pigments (carotenoids, xanthophyll) become visible, causing yellowing. The plant becomes weak due to energy depletion, reduced growth, and inability to synthesize new proteins and cell structures. Chlorophyll is the light-absorbing pigment that captures photon energy from sunlight and initiates electron excitation in the thylakoid membrane. Without light, chlorophyll cannot function; thus, no light energy is converted to chemical energy in ATP and NADPH. This is why plants require adequate light for healthy, vigorous growth. If returned to light, the plant can resume photosynthesis and recover, re-synthesizing chlorophyll and regaining colour and strength. **Q4: Describe the life cycle of a frog from egg to adult (metamorphosis). How does this differ from the life cycle of a bird?** **Answer:** Frogs undergo complete metamorphosis, a dramatic change in body form as they mature. Frog life cycle: (1) Adult frogs lay eggs in ponds or water bodies; eggs are covered in jelly-like substance. (2) Eggs hatch into tadpoles (aquatic larval stage), which resemble fish with a tail and gills for breathing underwater. Tadpoles feed on aquatic plants and algae. (3) Over weeks to months, tadpoles undergo metamorphosis: hind limbs develop first, then front limbs, lungs replace gills, eyes develop, and the tail shortens. (4) Metamorphosed tadpoles (froglets) emerge onto land and breathe air. (5) They mature into adult frogs. Birds, by contrast, undergo no metamorphosis. A newly hatched bird (chick from egg) is a miniature adult (in precocial birds) or is born featherless and helpless (in altricial birds), but its body shape does not fundamentally change. The chick grows larger and develops feathers, but remains fundamentally a bird throughout. This difference reflects ecological niches: frogs exploit both aquatic (tadpole) and terrestrial (adult) environments, whereas birds remain terrestrial/aerial throughout their lives.

Long-answer questions require detailed, well-structured responses (12–15 sentences) demonstrating deep conceptual understanding. These often combine multiple sub-topics or require interpretation of diagrams. **Q1: Explain the structure of a leaf cross-section and relate each tissue layer to its specific function in photosynthesis and gas exchange.** **Full Solution:** A leaf is a specialized organ for photosynthesis and gas exchange. Its internal structure consists of several tissue layers, each with distinct functions: (1) **Upper Epidermis**: A single layer of colourless, transparent cells covered by a waxy cuticle. Functions: Protects inner tissues, reduces water loss, and allows light penetration to reach chloroplasts below. The cuticle is impermeable, preventing entry of pathogens. (2) **Palisade Mesophyll**: 1–3 layers of tall, columnar cells packed with chloroplasts, arranged perpendicular to the upper surface. Functions: Primary site of photosynthesis; the vertical arrangement maximizes light capture as light passes through. Chloroplasts contain chlorophyll and perform both light-dependent and light-independent reactions. (3) **Spongy Mesophyll**: Loosely arranged, irregular cells with intercellular air spaces. Contains fewer chloroplasts than palisade mesophyll. Functions: (a) Secondary photosynthesis site; (b) Facilitates gas exchange—CO₂ diffuses into these air spaces and reaches palisade cells; O₂ produced during photosynthesis exits via these spaces. The irregular packing provides maximum surface area for gas diffusion. (4) **Lower Epidermis**: Similar to upper epidermis but contains stomata (pores) and guard cells. Functions: Main site of gas exchange; stomata open and close to regulate CO₂ entry and water vapour loss. Guard cells control opening via turgor pressure changes. (5) **Veins (Vascular Bundles)**: Contain xylem (transporting water and minerals) and phloem (transporting sugars). Functions: Xylem supplies water to mesophyll cells for photosynthesis and to maintain turgor pressure. Phloem exports glucose manufactured in photosynthesis to other plant parts. **Integrated Function**: The leaf structure is perfectly adapted for photosynthesis. Light passes through the transparent epidermis and is captured by palisade chloroplasts. Water from xylem and CO₂ from stomata/spongy mesophyll meet in chloroplasts, where photosynthesis occurs. Glucose is produced and transported by phloem; oxygen is released through stomata. This structure maximizes light absorption while minimizing water loss through the waxy cuticle. **Q2: Compare aerobic respiration in animals and plants. Explain why both organisms rely on respiration despite plants producing glucose through photosynthesis.** **Full Solution:** Aerobic respiration is the oxidative breakdown of glucose to release energy stored in chemical bonds. Although both animals and plants perform aerobic respiration, the contexts differ: **Aerobic Respiration in Animals:** - Occurs in all living cells, primarily in mitochondria. - Animals obtain glucose by consuming food (other organisms). - Glucose + oxygen → carbon dioxide + water + energy (ATP). - ATP is used for muscle contraction, nerve impulses, active transport, biosynthesis, and maintaining body temperature. - Respiration rate increases with physical activity and metabolic demands. - In humans, the respiratory system (lungs, diaphragm) supplies oxygen; the circulatory system transports glucose and oxygen to cells. **Aerobic Respiration in Plants:** - Occurs in all living cells (roots, stems, leaves, flowers), primarily in mitochondria. - Plants manufacture glucose through photosynthesis in leaves. - Glucose + oxygen → carbon dioxide + water + energy (ATP). - ATP is used for root growth, soil nutrient absorption (active transport), moving substances through phloem, cell division, and maintenance of cell turgor. - Unlike animals, plants respire at relatively constant rates regardless of external activity, as they are sessile. - CO₂ produced by respiration in roots diffuses out; CO₂ in leaves is partially recycled into photosynthesis. **Why Both Rely on Respiration:** Although plants produce glucose via photosynthesis, they cannot directly use the chemical energy in glucose molecules. Respiration breaks C-C bonds in glucose, releasing energy in controlled steps and capturing it in ATP (adenosine triphosphate) bonds. ATP is the universal energy currency—all cellular processes (biosynthesis, active transport, movement, replication) require ATP. Photosynthesis stores solar energy into chemical bonds; respiration converts that chemical energy into ATP for use. Without respiration, even glucose-rich plants would not have usable energy. Additionally, plants respire 24 hours—during night, when photosynthesis ceases, respiration continues in roots and non-green tissues, sustaining growth and function. Thus, photosynthesis and respiration are complementary: photosynthesis captures and stores energy; respiration releases and utilizes it. **Q3: A student conducts an experiment to test which colour of light is most effective for photosynthesis. Design the experiment, predict the result, and explain your prediction.** **Full Solution:** **Experimental Design:** (1) **Objective**: Determine which wavelength of light (colour) supports the highest rate of photosynthesis. (2) **Materials**: Several identical potted plants (e.g., Elodea or spinach), transparent coloured filters (red, blue, green, yellow, white light), a light source (lamp), a gas collection apparatus or oxygen meter, a ruler, and a stopwatch. (3) **Procedure**: - Place each plant under a different coloured light filter at the same distance from a constant light source. - Maintain identical conditions: temperature, CO₂ concentration, water supply, light intensity (by adjusting lamp distance). - Measure the rate of oxygen production (using a gas syringe or oxygen sensor) over a fixed time period (e.g., 30 minutes), or count oxygen bubbles released by Elodea per minute. - Record data for each colour filter. - Repeat trials to ensure accuracy. (4) **Control**: Keep one plant in darkness (no photosynthesis control) and one in white light (maximum photosynthesis). **Predicted Result:** Red and blue light will show the highest photosynthetic rates; green light will show the lowest; yellow will be intermediate. **Explanation:** Chlorophyll absorbs light primarily in red (wavelength ~650–680 nm) and blue (wavelength ~400–450 nm) regions of the visible spectrum. These wavelengths provide energy to excite electrons in the thylakoid membrane's photosystem II and photosystem I, initiating the light reactions. Carotenoids and xanthophyll (accessory pigments) also absorb blue and red light, enhancing energy capture. Green light (wavelength ~500–550 nm) is poorly absorbed by chlorophyll, instead being mostly reflected (why plants appear green). Therefore, green light contributes minimally to photosynthesis. Yellow light (intermediate wavelength) is partially absorbed by accessory pigments, producing a moderate photosynthetic rate. White light, a mixture of all colours, provides the broadest spectrum and thus supports maximum photosynthesis. This experiment demonstrates the principle of the 'action spectrum of photosynthesis'—the efficiency of light in driving photosynthesis varies with wavelength. Knowledge of this principle is applied in agriculture, where grow lights are designed with high red and blue LED intensities to optimize crop growth in controlled environments.

Higher-Order Thinking Skills (HOTS) questions present real-world scenarios and require students to analyze, synthesize, or evaluate information. **Case-Study Question:** **A biologist studying a forest ecosystem observes four organisms: a grass plant, a grasshopper, a frog, and a snake. The grass fixes 10,000 units of energy from sunlight. The grasshopper consumes grass and fixes 1,000 units. The frog eats grasshoppers and fixes 100 units. The snake eats frogs and fixes 10 units.** **Part A:** Identify the trophic level of each organism and classify them as producers, primary consumers, secondary consumers, or tertiary consumers. **Part B:** Explain why energy decreases at each trophic level (roughly 90% loss from one level to the next). **Part C:** If the grasshopper population was eliminated due to pesticide use, predict the impact on the frog and snake populations in the short and long term. Justify your answer. **Part D:** The biologist also notes that grass plants perform photosynthesis during the day but respire continuously. Why must grass respire if it already manufactures food? **Complete Solution with Steps:** **Part A — Trophic Level Classification:** - **Grass plant**: Trophic level 1 → **Producer** (manufactures food via photosynthesis from sunlight). - **Grasshopper**: Trophic level 2 → **Primary consumer** (herbivore; consumes producers). - **Frog**: Trophic level 3 → **Secondary consumer** (carnivore; consumes primary consumers). - **Snake**: Trophic level 4 → **Tertiary consumer** (carnivore; consumes secondary consumers). **Part B — Energy Loss Explanation (10% Rule):** At each trophic level, approximately 90% of energy is lost; only 10% is transferred to the next level. Reasons: (1) **Incomplete consumption**: Not all organisms at one level are eaten (some escape, die naturally, or are too old). (2) **Indigestible matter**: Some consumed biomass (bones, cellulose, chitin) cannot be digested. (3) **Metabolic respiration**: Organisms use energy for respiration (heat loss, movement, growth, biosynthesis) rather than storage. (4) **Excretion**: Waste products carry energy out of the food chain. Example: Grass fixes 10,000 units. A grasshopper must consume ~10,000 units of grass to accumulate 1,000 units of biomass (assuming 10% efficiency). Similarly, the frog consumes ~10,000 units of grasshopper biomass to gain 1,000 units net (but only gets 100 units shown, indicating actual efficiency varies). This cascading loss explains why long food chains are rare; energy becomes limiting. **Part C — Impact of Grasshopper Elimination:** **Short-term (weeks to months):** - Grasshoppers disappear due to pesticide toxicity. - Frogs lose their primary food source; frog population declines as starvation occurs and reproduction fails. - Snakes lose a secondary food source (frogs); snake population also declines but less dramatically if snakes can consume alternative prey. - Grass population increases (released from herbivory pressure). **Long-term (months to years):** - If frogs disappear, snakes may starvation further; snake population may collapse unless alternative prey (insects, birds) increase. - Grass becomes dominant, potentially outcompeting other plants (monoculture formation). - If snakes disappear, the entire food web is disrupted; ecosystem balance is lost. - Alternative herbivores may partially fill the grasshopper niche, slowly restoring the ecosystem. **Justification**: Food webs are interconnected; removing a key species (keystone species if grasshopper plays that role) causes cascading effects throughout the ecosystem. Energy transfer is severely disrupted, and predators are directly deprived of prey. Ecosystem recovery depends on ecological resilience and available alternative species. **Part D — Why Grass Respires Despite Photosynthesis:** Photosynthesis manufactures glucose (stores energy in chemical bonds), but glucose is not directly usable by cells. Respiration breaks glucose's C-C bonds via glycolysis and the citric acid cycle, releasing energy in manageable packets and capturing it in ATP molecules. ATP is the universal energy currency; all cellular processes (root nutrient uptake via active transport, synthesis of new cell wall cellulose, meristematic cell division, phloem transport of sugars) require ATP. Additionally, plants respire 24 hours—during night, photosynthesis stops, but respiration continues in roots and non-photosynthetic tissues, maintaining energy supply for survival. Furthermore, not all glucose is immediately used; some is converted to starch (stored energy); some to structural compounds (cellulose, hemicellulose); both processes require ATP. Without respiration, even a glucose-rich plant would lack usable energy and would not survive.

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