Navigating through the newly revised CBSE Class 9 Science curriculum (Exploration) requires a thorough understanding of biological organization, division of labor in multicellular organisms, plant tissue systems (meristematic and permanent), animal tissue specialization (epithelial, connective, muscular, and nervous), skeletal joint mechanics, and plant micropropagation. Chapter 3, “Tissues in Action”, explores how groups of specialized cells coordinate to perform vital physiological functions. It investigates how localized meristematic zones (apical, lateral, and intercalary) drive plant elongation and secondary thickening; explains the structural differences between protective dermal tissues, supportive ground tissues (parenchyma, collenchyma, sclerenchyma), and complex vascular conduits (xylem and phloem); details the four foundational animal tissue types; and explores how the musculoskeletal system coordinates locomotion and movement under neural control. To help students master every aspect of this high-weightage chapter, this comprehensive solutions guide offers textbook-accurate, highly structured, and pedagogically sound responses strictly aligned with the latest CBSE Class 9 evaluation standards.
Every question presented in the official NCERT textbook—ranging from all introductory “Think It Over” sections and in-text “Pause and Ponder” prompts (Pages 28, 33, 34, and 40) to the complete end-of-chapter “Revise, Reflect, Refine” exercises (Questions 1 to 15 on Pages 44–46)—has been solved with exhaustive detail. Short-answer conceptual responses adhere to standard examination word limits, while multi-step physiological deductions, tissue culture evaluations, and joint biomechanics use structured comparison tables and step-by-step text blocks. Key scoring terms, official CBSE exam tags, and an expanded set of 15 high-yield FAQs have been integrated to ensure students secure top marks in their examinations.
Master Concept & Comparative Summary Tables
1. Classification of Plant Tissues
| Major Tissue Group | Sub-Types / Locations | Cell Characteristics | Primary Biological Functions |
|---|---|---|---|
| Meristematic Tissue (Actively dividing) | • Apical Meristem: Root and shoot tips. • Lateral Meristem (Cambium): Radial sides of stem/root. • Intercalary Meristem: Base of leaves / nodes. | Living, thin-walled, dense cytoplasm, prominent nucleus, lack vacuoles, divide continuously. | • Apical: Elongation (Primary growth in length). • Lateral: Increase in girth/thickness. • Intercalary: Regeneration of grass blades and nodal elongation. |
| Simple Permanent Tissue (One cell type) | • Parenchyma: Pith, cortex, mesophyll. • Collenchyma: Leaf stalks (petioles), stem corners. • Sclerenchyma: Coconut husk, walnut shells, seed coats. | • Parenchyma: Living, thin cellulose walls, intercellular spaces. • Collenchyma: Living, uneven pectin thickening at corners. • Sclerenchyma: Dead cells, heavily lignified thick walls, no lumen/space. | • Parenchyma: Food storage, photosynthesis (Chlorenchyma), floating buoyancy (Aerenchyma). • Collenchyma: Tensile flexibility without breaking. • Sclerenchyma: Hardness, rigidity, mechanical protection. |
| Complex Permanent Tissue (Vascular Conduits) | • Xylem: Tracheids, Vessels, Xylem Fibres, Xylem Parenchyma. • Phloem: Sieve Tubes, Companion Cells, Phloem Parenchyma, Phloem Fibres. | • Xylem: Mostly dead tubular cells (except living xylem parenchyma); lignified walls. • Phloem: Mostly living cells (except dead phloem fibres); perforated sieve plates. | • Xylem: Unidirectional upward transport of water and dissolved minerals from roots to leaves; structural support. • Phloem: Bidirectional translocation of organic food (sucrose) from leaves to storage/growing organs. |
2. Overview of the Four Fundamental Animal Tissue Types
| Animal Tissue Type | Key Sub-Types / Structural Examples | Distinct Structural Features | Primary Physiological Roles |
|---|---|---|---|
| Epithelial Tissue (Covering & Lining) | Squamous, Cuboidal, Columnar, Ciliated, Glandular. | Tightly packed continuous cellular sheets; almost no intercellular space; rests on a basement membrane. | Protection against mechanical injury, selective barrier for material exchange, secretion of enzymes, absorption of nutrients. |
| Connective Tissue (Binding & Support) | Blood, Bone, Cartilage, Tendons, Ligaments, Areolar, Adipose. | Cells are loosely spaced and embedded in an intercellular matrix (fluid, jelly-like, or hard rigid calcified matrix). | • Bone/Cartilage: Skeletal framework. • Ligaments: Connect Bone to Bone. • Tendons: Connect Muscle to Bone. • Blood: Transport of oxygen, nutrients, and hormones. |
| Muscular Tissue (Contractile Movement) | Striated (Skeletal / Voluntary), Smooth (Visceral / Involuntary), Cardiac (Heart). | Composed of elongated muscle fibers containing contractile proteins (actin and myosin) that contract and relax. | Generates mechanical force for locomotion, heart pumping, peristalsis in food pipe, and blood pressure regulation. |
| Nervous Tissue (Signaling & Coordination) | Neurons (Nerve cells) and supporting Neuroglial cells. | Star-shaped cyton (cell body), branched receptive Dendrites, and a long conducting Axon. | Rapid reception of sensory stimuli, generation of electrochemical nerve impulses, and coordination of body responses. |
NCERT In-Text Questions: “Think It Over” (Page No. 28)
Question 1 How is the study of cells and tissues significant for understanding the life processes and human welfare? [Exam Favorite]
Answer: The study of cells and tissues (Histology) is vital for science and human welfare because:
- Understanding Physiological Mechanisms: It reveals how specialized cellular groups perform essential life processes such as respiration, nerve transmission, muscular contraction, and nutrient transport.
- Medical Diagnosis and Pathology: Biopsies of diseased tissues allow doctors to diagnose cancers, infectious diseases, and inflammatory disorders at the microscopic level.
- Agricultural and Industrial Applications: Tissue culture (micropropagation) enables the rapid clonal multiplication of high-yielding, disease-free crop varieties, boosting food security.
Question 2 How are tissues in plants and animals different, and why? [Exam Favorite]
Answer: Plant and animal tissues differ fundamentally due to their distinct modes of life, mobility, and nutritional requirements:
- Plant Tissues: Plants are stationary (sessile) and autotrophic. They require mechanical support and rigidity, so a large proportion of plant tissues are dead, thick-walled, and supportive (e.g., sclerenchyma, cork, xylem vessels). Plant growth is localized to specific regions called meristems throughout life.
- Animal Tissues: Animals are mobile (motile) and heterotrophic. They require high energy for locomotion and rapid physiological adjustments. Hence, almost all animal tissues are living, highly specialized, and metabolically active (e.g., muscular, nervous, connective), with uniform growth throughout the body.
Question 3 How is the division of labour at various levels of organisation in multicellular organisms correlated with their structure and function? [Exam Favorite]
Answer: In multicellular organisms, division of labor ensures efficiency by assigning specialized functions to structurally tailored cellular assemblies:
- Cellular Level: A neuron is elongated with dendrites and an axon to transmit electrical impulses across distances.
- Tissue Level: Muscle cells contain contractile proteins arranged in parallel bundles to generate force and body movement.
- Organ Level: In the stomach, epithelial tissue secretes digestive juices, muscular tissue churns food, and nervous tissue coordinates gastric motility.
- Organ System Level: The circulatory system integrates blood, vessels, and the heart to transport oxygen and nutrients throughout the body.
Question 4 Why do you think that the cells of meristematic tissue lack vacuoles? [Exam Favorite]
Answer: Meristematic cells lack large permanent vacuoles because:
- Active Cell Division: Their primary function is rapid and continuous mitotic division. They require a high ratio of active dense cytoplasm and a large, prominent nucleus without physical obstruction.
- No Storage Function: Vacuoles function primarily to store nutrients, water, and metabolic wastes. Meristematic cells rapidly consume all synthesized nutrients to fuel cell division and maintain high metabolic rates, producing no stored waste.
- Maintaining Structural Rigidity: Large vacuoles contain cell sap that exerts turgor pressure; actively dividing embryonic cells require flexible, thin cellulose walls rather than rigid, turgid states.
NCERT In-Text Questions: “Pause and Ponder”
Page No. 33: Pause and Ponder (Question 1)
Question 1 You may have noticed that fibres of coconut husk are hard and brittle, whereas the leaf stalks of coriander are soft and flexible. Find out the reason. [Exam Favorite]
Answer: The difference is due to the distinct types of simple permanent plant tissues present in each:
- Coconut Husk Fibres: Composed of Sclerenchyma tissue. Sclerenchyma cells are dead at maturity with cell walls heavily thickened by lignin (a natural cement-like chemical). This structural composition provides extreme mechanical strength, hardness, and brittleness.
- Coriander Leaf Stalks (Petioles): Composed of Collenchyma (and Parenchyma) tissue. Collenchyma cells are living with cell walls unevenly thickened by pectin and cellulose at the corners. This gives the stalks tensile elasticity and mechanical flexibility, allowing them to bend in the wind without breaking.
Page No. 34: Pause and Ponder (Questions 2 to 4)
Question 2 Why do you think that a thick cuticle on the outer wall of epidermis is advantageous for a plant living in the desert but disadvantageous for a plant living underwater? [Exam Favorite]
Answer:
- Advantage in Desert Plants (Xerophytes): Desert plants face intense solar heat and arid winds. A thick, waxy cuticle (made of cutin) on the epidermal surface acts as an impermeable waterproof barrier that minimizes transpirational water loss, helping the plant conserve vital water.
- Disadvantage in Submerged Aquatic Plants (Hydrophytes): Submerged plants do not face the risk of desiccation. Instead, they absorb dissolved carbon dioxide, oxygen, and mineral nutrients directly through their general epidermal surface from the surrounding water. A thick, waterproof cuticle would block gaseous diffusion and nutrient uptake, suffocating the plant.
Question 3 Once water is absorbed by plant roots, it has to travel against gravity through xylem. How do the ‘dead’ cells of the xylem work together with the living cells of leaves at the top to keep the water moving? [Exam Favorite]
Answer: The upward movement of water occurs through the coordination of dead vascular conduits and living leaf cells via the Transpiration Pull Mechanism:
================================================================================ STEP-BY-STEP WATER CONDUCTION MECHANISM (TRANSPIRATION PULL): -------------------------------------------------------------------------------- 1. Path Formation: Dead, hollow xylem tracheids and vessels join end-to-end to form a continuous, non-collapsible pipeline from roots to leaf veins. 2. Evaporative Pull: Living mesophyll cells in the leaves lose water vapor into the atmosphere through stomatal pores during TRANSPIRATION. 3. Suction Pressure: This water loss creates a strong negative suction pressure (Transpiration Pull) in the leaf xylem. 4. Cohesive Column: Due to high cohesive forces between water molecules and adhesive forces to xylem walls, water is drawn upward as an unbroken column from the roots to the tallest branches of the tree. ================================================================================
Question 4 What do you think will happen if there were no stomata in the epidermis of the stem or leaves? [Exam Favorite]
Answer: If stomatal pores were absent from the epidermis of leaves and young stems:
- Halting of Photosynthesis: Carbon dioxide (CO_2) could not enter the leaf interior, shutting down photosynthetic carbohydrate synthesis.
- Impairment of Respiration: Gaseous exchange of oxygen (O_2) and carbon dioxide would cease, causing respiratory failure and cell suffocation.
- Collapse of Water and Mineral Transport: Transpiration would stop, destroying the transpirational pull required to lift water and dissolved minerals through the xylem.
- Thermal Stress: Plants would lose their evaporative cooling mechanism, leading to overheating and thermal tissue death under direct sunlight.
Page No. 40: Pause and Ponder (Question 5)
Question 5 Look at the movements of joints during dancing or sports (Neck, Shoulder, Elbow, Wrist, Hip, Knee, Ankle). What kind of joints allow these movements? [Exam Favorite]
Answer: The human musculoskeletal system utilizes specialized synovial joints to enable diverse movement patterns:
| Anatomical Joint Location | Type of Synovial Joint | Nature of Movement Permitted |
|---|---|---|
| Shoulder & Hip Joints | Ball-and-Socket Joint | Rotational movement in all planes (360° circumduction, flexion, extension, abduction, adduction). |
| Elbow & Knee Joints | Hinge Joint | Unidirectional movement in a single plane (flexion and extension, like a door hinge). |
| Neck Joint (Atlanto-axial) | Pivot Joint | Rotational and side-to-side turning of the head on the spinal axis. |
| Wrist & Ankle Joints | Gliding / Condyloid Joint | Multi-directional sliding and fine angular adjustments for balance and gestures. |
NCERT Chapter-End Exercises: “Revise, Reflect, Refine” (Pages 44–46)
Question 1 Meristematic tissues divide repeatedly. What property of their cells allows them to do this? (i) They have thick walls for protection. (ii) They contain large vacuoles that store nutrients. (iii) They have thin walls, dense cytoplasm, and large, prominent nucleus. (iv) They are functionally differentiated cells.
Answer: (iii) They have thin walls, dense cytoplasm, and large, prominent nucleus. Explanation: Active mitotic division requires unhindered cytoplasmic metabolism, flexible primary cellulose walls, and a prominent nucleus containing active chromatin. Large vacuoles and thick walls hinder rapid cytokinesis.
Question 2 If a plant is unable to transport food from leaves to roots, which tissue is malfunctioning? [Exam Favorite]
Answer: The Phloem tissue (specifically Sieve Tubes and Companion Cells) is malfunctioning. Phloem is the complex vascular tissue responsible for the translocation of soluble photosynthetic organic food (sucrose) from the leaves (source) downward to the roots and storage organs (sink).
Question 3 Why are the epithelial tissues that line an animal’s internal organs usually only one or a few cells thick? (i) To store food efficiently. (ii) To provide maximum strength. (iii) To allow quick exchange of materials across them. (iv) To reduce friction.
Answer: (iii) To allow quick exchange of materials across them. Explanation: Simple epithelial linings (like squamous epithelium in lung alveoli and capillary walls) are extremely thin to minimize the diffusion distance, enabling the rapid exchange of gases (O_2/CO_2), nutrients, and wastes across biological membranes.
Question 4 You can perform these two jumps: • Straight-leg jump — Keep knees and ankles stiff. • Normal jump — Bend knees and ankles naturally. How did your ankle, knee, and hip positions differ between the two jumps? [Exam Favorite]
Answer:
- In the Straight-Leg Jump: The ankle, knee, and hip joints remain locked in rigid extension. This restricts the shock-absorbing flexion of leg muscles, producing a low jump height and delivering a jarring mechanical impact directly to the spine and joints upon landing.
- In the Normal Jump:
- Before Take-off (Preparation): The hips flex backward, the knees bend deeply (flexion), and the ankles dorsiflex, stretching the quadriceps and calf muscles to store elastic potential energy.
- Take-off (Propulsion): The hip, knee, and ankle joints extend forcefully simultaneously, converting stored muscular energy into maximum upward kinetic momentum.
- Landing (Shock Absorption): The joints bend smoothly upon impact, dissipating ground reaction forces safely over time via muscular elasticity.
Question 5 Which type of muscle tissue is responsible for involuntary movements like peristalsis in the alimentary canal and contraction of blood vessels? [Exam Favorite]
Answer: Smooth Muscle Tissue (also known as Non-Striated, Involuntary, or Visceral Muscle Tissue).
- Structural Characteristics: Smooth muscle cells are spindle-shaped (fusiform) with pointed ends, uninucleated, and lack transverse cross-striations. Their contraction is regulated automatically by the autonomic nervous system without conscious voluntary control.
Question 6 In each of the following cases (A, B, C, and D), choose the correct option as given below: (a) Both (A) and (R) are true, and (R) is the correct explanation of (A). (b) Both (A) and (R) are true, but (R) is not the correct explanation of (A). (c) (A) is true, but (R) is false. (d) (A) is false, but (R) is true.
Case 1: Assertion (A): Tendons connect muscles to bones. Reason (R): Ligaments connect bones to bones and provide joint stability. Answer: (b) Both (A) and (R) are true, but (R) is not the correct explanation of (A). (Both statements are scientifically accurate descriptions of dense regular connective tissues, but R does not explain why tendons connect muscle to bone).
Case 2: Assertion (A): In a hinge joint, movement occurs primarily in one plane. Reason (R): The bone ends are shaped to allow sliding in all directions. Answer: (c) (A) is true, but (R) is false. (Hinge joints restrict motion to a single back-and-forth plane, such as at the elbow; bone ends that slide in all directions characterize gliding or ball-and-socket joints).
Question 7 Plot a graph between the age of a tree (in years) on the x-axis and the diameter of the tree (in cm) along with the number of annual rings formed over time on the y-axis, using the data given in textbook Table 3.7. (i) Analyse the graph in terms of the diameter of the stem over time and share the interpretation. (ii) What is the relation between the diameter of the teak tree to the annual rings formed? (iii) Which specialised tissue is responsible for the girth of the stem, and where is it located? [Exam Favorite]
Answer:
================================================================================ GRAPHICAL & DENDROCHRONOLOGICAL ANALYSIS: -------------------------------------------------------------------------------- (i) Interpretation of Stem Diameter Over Time: • The stem diameter increases steadily as tree age advances. • The growth curve shows positive progression: early growth is rapid due to vigorous active tissue formation, followed by steady secondary thickening. (ii) Relationship Between Diameter and Annual Rings: • There is a DIRECT PROPORTIONAL RELATIONSHIP. • Each annual ring represents one year of secondary growth (Spring wood + Autumn wood). • As the number of annual rings increases, the cumulative radial thickness and total stem diameter increase proportionally. (iii) Specialized Tissue Responsible for Girth: • Tissue Name: LATERAL MERISTEM (specifically VASCULAR CAMBIUM and CORK CAMBIUM). • Location: Arranged as a cylindrical ring between the xylem and phloem inside the stem, and beneath the bark (cork cambium). It divides outward to form secondary phloem and inward to form secondary xylem (wood). ================================================================================
Question 8 In a forest, it was observed that one of the trees was severely debarked by an elephant to meet its food requirements, as the bark is a rich source of nutrients (Fig. 3.22). Based on your learning, answer the following: (i) Which function(s) of the tree is/are hampered by debarking? (ii) Which plant tissue would be affected by further damage to the tree trunk even after debarking? (iii) Which function of the tree would be hampered if the tissues beneath the bark were severely damaged? (iv) What assumptions are you making to answer the questions above? How would the answer change if your assumptions are also changed? [Exam Favorite]
Answer:
- (i) Functions Hampered by Debarking:
- Loss of Protective Barrier: The dead cork layer containing suberin is stripped away, exposing inner living tissues to desiccation, fungal infections, and pest infestations.
- Interruption of Food Translocation: The outer phloem layer attached to the inner bark is damaged, disrupting the downward transport of food to the roots.
- (ii) Tissues Affected by Further Deep Damage: If elephant stripping cuts deeper, the Vascular Cambium (Lateral Meristem) and the inner Xylem vessels will be lacerated.
- (iii) Impact if Sub-Bark Tissues are Destroyed (Complete Girdling): If the phloem and xylem are severed around the trunk circumference, downward food transport to roots halts completely, starving the root cells. Subsequently, root death stops water absorption, drying out the leaves and killing the entire tree.
- (iv) Assumptions Made:
- Assumption: The debarking is partial (only one side of the trunk), leaving residual intact vascular strands on the other side.
- Effect of Changing Assumption: If the debarking is a complete circumferential ring (girdling), the tree cannot recover and will die within weeks. If xylem is damaged along with phloem, water transport fails immediately, causing rapid leaf wilting and death within days.
Question 9 Aamrapali observed that a young mango sapling’s stem bends flexibly during monsoon winds and does not break. Which tissue is responsible for this flexibility? Predict and provide your explanation of the impact if the existing tissue was replaced by sclerenchyma. [Exam Favorite]
Answer:
- Tissue Responsible for Flexibility: Collenchyma tissue (located in the hypodermis of dicot stems and leaf petioles).
- Impact of Replacement by Sclerenchyma:
- If collenchyma were replaced by rigid sclerenchyma, the young stem would lose its tensile elasticity and bending capacity.
- Sclerenchyma cells have thick, hard, non-elastic lignified walls. When high-velocity monsoon winds blow, the inflexible stem would snap and break off completely under mechanical stress instead of swaying and bending safely.
Question 10 Sohan designed an experiment to study vegetative propagation in sugarcane using two types of stem cuttings: • Type A: Stem cuttings taken from the middle of an internode (having no nodes/buds). • Type B: Stem cuttings having at least one intact node with an axillary bud. He planted both in moist soil under identical environmental conditions. After three weeks, Type B sprouted into healthy sugarcane plants, whereas Type A decayed without any growth. (i) Why were the type ‘B’ cuttings able to grow into sugarcane plants but type ‘A’ could not? (ii) What structural difference was present in type ‘B’ compared to type ‘A’? (iii) What observation or measurement was made to determine whether this change had an effect? (iv) What parameters should be kept the same for both types of cuttings to ensure a fair comparison? [Exam Favorite]
Answer:
================================================================================ EXPERIMENT ANALYSIS (VEGETATIVE REGENERATION IN SUGARCANE): -------------------------------------------------------------------------------- (i) Why Type B Sprouted and Type A Decayed: • Type B cuttings contained NODES possessing active INTERCALARY MERISTEM and dormant axillary buds. Meristematic cells divide rapidly to produce new shoots and adventitious roots. • Type A cuttings lacked nodes entirely; internodal regions consist only of differentiated, non-dividing permanent tissues that cannot generate new buds. (ii) Structural Difference: • Type B had intact NODES with meristematic axillary buds. • Type A consisted purely of an INTERNODAL stem segment without meristems. (iii) Observations & Measurements Recorded: • Sprouting percentage of buds, appearance of green shoot leaves, and length of newly formed adventitious roots over 3 weeks. (iv) Controlled Parameters for Fair Testing: • Length and diameter of stem cuttings, planting depth, soil composition, daily water volume, sunlight exposure, and ambient temperature. ================================================================================
Question 11 In an experiment on carrot phloem tissue culture: Small pieces of phloem tissue were excised from a carrot root and placed in nutrient culture media under different combinations of physical factors (liquid nutrient medium, solid agar, varying light, aeration, and hormone concentrations). (a) What conclusion can be drawn about the characteristics of carrot phloem cells? (b) Under which condition would the highest and lowest biomass be obtained? (c) Would the same regeneration results be obtained if mature animal cells were used? (d) State two commercial applications of plant tissue culture. [Exam Favorite]
Answer:
- (a) Conclusion Regarding Carrot Phloem Cells: Mature, differentiated plant phloem parenchyma cells retain the genetic potential of Cellular Totipotency—the ability to dedifferentiate back into actively dividing meristematic cells (callus) and regenerate into an entire plant under sterile nutrient conditions.
- (b) Biomass Optimization:
- Highest Biomass: Obtained in a liquid nutrient medium supplied with essential macronutrients, micronutrients, sucrose, balanced auxin/cytokinin plant hormones, continuous aeration, and controlled light/temperature cycles.
- Lowest Biomass: Obtained where aeration is absent (anaerobic conditions) or where plant growth regulators (hormones) are omitted, causing cellular starvation and growth arrest.
- (c) Animal Cell Comparison: No, mature animal cells would not regenerate a complete organism. Mature animal cells undergo irreversible terminal differentiation and lack totipotency (only early embryonic stem cells exhibit pluripotency).
- (d) Two Commercial Applications:
- Micropropagation: Rapid mass cloning of millions of identical, disease-free commercial crops (such as banana, potato, sugarcane, and orchids) in a small space regardless of season.
- Production of Secondary Metabolites: In vitro cultivation of plant cells in bioreactors to extract valuable medicinal alkaloids, pharmaceuticals, and natural food colors.
Question 12 Coconut husk fibres are used for making mats, ropes, and brushes which are tough and fibrous. Which tissue has structural features suitable for providing this strength? Explain why living parenchyma couldn’t serve the same purpose. [Exam Favorite]
Answer:
- Tissue Responsible for Strength:Sclerenchyma (Sclerenchymatous Fibres).
- Structural Features: Long, narrow, spindle-shaped cells with thick, lignified secondary cell walls and narrow lumens. At functional maturity, the cells are dead and empty of cytoplasm, forming a dense, rigid structural mesh that withstands high tensile pulling, friction, and environmental wear without tearing.
- Why Living Parenchyma Cannot Serve This Purpose:
- Parenchyma consists of living, thin-walled cells made of soft cellulose with large intercellular spaces.
- Parenchyma cells are specialized for food storage and photosynthesis, lacking lignin deposition. If ropes or mats were made of parenchyma, the thin cellulose walls would crush under minimal pressure, tear under tensile strain, and rot rapidly upon contact with moisture.
Question 13 Vibha claims to her friend Neha that, “Meristematic cells are located only at the root and shoot apices”. What do you think about this statement? What question can Neha ask Vibha to help her understand further if the statement is incorrect? [Exam Favorite]
Answer:
- Evaluation of Statement: Vibha’s statement is incomplete and partially incorrect. While apical meristems are indeed located at root and shoot tips, meristematic tissues also exist in other vital growth zones of the plant body.
- Corrective Questions Neha Can Ask Vibha:
- “If meristems are located only at the tips, how does a slender tree sapling increase its stem thickness and trunk girth into a massive woody tree over years?” (Guides her to discover Lateral Meristem / Cambium).
- “When a lawnmower or grazing cow cuts off the top tips of grass blades, how do the grass leaves rapidly regrow from the base without shoot apices?” (Guides her to discover Intercalary Meristem at leaf bases and nodes).
Question 14 A plant cell and an animal cell are of the same size. (i) Which cell will have a larger vacuole? Give reasons. (ii) What assumptions are you making to answer the question above? [Exam Favorite]
Answer:
- (i) Cell with Larger Vacuole: The Plant Cell will have a substantially larger vacuole.
- Reasons: In a mature plant cell, a single large central permanent vacuole occupies 50% to 90% of the total cellular volume. It stores cell sap (amino acids, sugars, minerals) and maintains internal turgor pressure against the rigid cell wall, providing mechanical support and keeping non-woody plant structures upright. Animal cells do not rely on vacuoles for structural support and only possess small, temporary vacuoles for pinocytosis or waste excretion.
- (ii) Assumptions Made:
- The comparison is between a typical mature, fully differentiated plant cell (such as a leaf mesophyll or cortical cell) and a mature animal somatic cell.
- The plant cell is in a healthy, fully hydrated (turgid) state under normal physiological conditions.
- The plant cell is not an embryonic meristematic cell (which naturally lacks large vacuoles).
Question 15 A textbook states, “Each plant tissue performs only one specific function”. What questions would you ask to critically examine the correctness of this statement? What examples of tissues would you take to find out the answers to these questions? [Exam Favorite]
Answer:
- Critical Examination: The statement is scientifically incorrect and oversimplified. Many plant tissues are multifunctional, performing diverse physiological and structural roles simultaneously.
- Critical Questions to Ask:
- Can a supportive tissue also carry out metabolic food synthesis?
- Do conducting vascular tissues contribute to the mechanical stability of the plant body?
- Can storage tissues also provide internal buoyancy or defense?
- Supporting Examples of Multifunctional Plant Tissues:
- Parenchyma: Functions primarily for food storage, but when modified as Chlorenchyma (containing chloroplasts), it carries out photosynthesis; when modified as Aerenchyma, it provides buoyancy for aquatic plants.
- Collenchyma: Provides tensile mechanical strength while simultaneously allowing flexible bending of stems and petioles during storms.
- Xylem: Functions primarily in the upward transport of water and dissolved minerals, while its lignified tracheids, vessels, and xylem fibres provide the primary mechanical framework supporting tree trunks.
- Phloem: Translocates organic nutrients while phloem parenchyma stores tannins and resins, and phloem fibres provide structural support.
Frequently Asked Questions (FAQs) – Class 9 Science Chapter 3
Question 1: Define a biological tissue. [Exam Favorite] Answer: A tissue is defined as a cluster or group of similar cells having a common embryonic origin and specialized structural organization that work together to perform a specific biological function.
Question 2: What is the process of Cellular Differentiation? [Exam Favorite] Answer: Differentiation is the biological process by which unspecialized, actively dividing meristematic cells permanently stop dividing and undergo structural and biochemical specializations to take up a permanent shape, size, and specific physiological function.
Question 3: Name the three types of meristematic tissues and state their primary functions. [Exam Favorite] Answer:
- Apical Meristem: Located at the tips of roots and shoots; responsible for primary growth in length.
- Lateral Meristem (Cambium): Located radially along the sides of stems and roots; responsible for secondary growth in girth and diameter.
- Intercalary Meristem: Located at the base of leaves and internodes; responsible for nodal elongation and regrowth of grass blades.
Question 4: What is the chemical composition of Sclerenchyma cell walls? [Exam Favorite] Answer: Sclerenchyma cell walls are heavily thickened with Lignin, a complex, waterproof, high-strength chemical polymer that acts as natural biological cement, making the tissue hard, rigid, and impervious to water.
Question 5: Differentiate between Chlorenchyma and Aerenchyma. [Exam Favorite] Answer:
- Chlorenchyma: Specialized parenchyma containing green chlorophyll that carries out photosynthesis in green leaves and stems.
- Aerenchyma: Specialized parenchyma containing large air cavities that provide buoyancy, enabling aquatic plants (hydrophytes) to float on water.
Question 6: Why is Xylem considered a complex permanent tissue? Name its four cellular components. [Exam Favorite] Answer: Xylem is called a complex tissue because it is composed of more than one type of cell working together as a functional unit. Its four components are: (i) Tracheids, (ii) Xylem Vessels, (iii) Xylem Fibres (all dead and supportive), and (iv) Xylem Parenchyma (the only living component, storing food).
Question 7: Name the living conducting cells of Phloem that lack a nucleus at maturity. [Exam Favorite] Answer: Sieve Tube Elements. They maintain living metabolic activity despite lacking a nucleus because their physiological functions are regulated by adjacent nucleated Companion Cells through plasmodesmatal connections.
Question 8: Differentiate between Tendons and Ligaments. [Exam Favorite] Answer:
- Tendons: Dense fibrous connective tissue with great strength and limited flexibility that connects Muscular Tissue to Bones.
- Ligaments: Highly elastic and flexible connective tissue containing yellow elastin fibers that connects Bone to Bone at joints.
Question 9: What is the primary function of Areolar Connective Tissue? [Exam Favorite] Answer: Areolar tissue is a loose packaging tissue found between the skin and muscles, around blood vessels and nerves, and in bone marrow. It fills internal spaces within organs, supports delicate internal structures, and assists in tissue repair after injury.
Question 10: Where is Adipose Tissue located, and what is its role? [Exam Favorite] Answer: Adipose tissue is located beneath the skin (subcutaneous layer) and around internal organs like the kidneys and heart. Its cells are filled with fat globules; it acts as a storage reservoir for fats and serves as a thermal insulator, preventing body heat loss.
Question 11: Describe the structure of a Neuron with the help of its three main parts. [Exam Favorite] Answer: A neuron consists of: (i) Cyton (Cell Body) containing the nucleus and cytoplasm, (ii) Dendrites, short branched fibers that receive incoming nerve stimuli, and (iii) Axon, a single long conducting fiber that transmits nerve impulses away from the cell body toward synaptic terminals.
Question 12: Differentiate between Skeletal (Striated) and Cardiac Muscle Tissues. [Exam Favorite] Answer:
- Skeletal Muscle: Cylindrical, unbranched, multinucleated, voluntary fibers attached to skeleton with dark and light alternating striations.
- Cardiac Muscle: Cylindrical, branched, uninucleated, involuntary fibers located strictly in the heart wall, possessing intercalated discs that contract rhythmically throughout life without fatigue.
Question 13: What is the role of Suberin in Cork (Bark) cells? [Exam Favorite] Answer: Suberin is an impervious, waxy chemical substance deposited in the walls of dead cork cells that makes the bark completely impermeable to water, air, and gases, protecting trees against dehydration, extreme temperatures, and mechanical injury.
Question 14: What is Dendrochronology? [Exam Favorite] Answer: Dendrochronology is the scientific method of calculating the exact age of a woody tree and reconstructing historical climate patterns by counting and analyzing the concentric annual growth rings (xylem rings) in a cross-section of its trunk.
Question 15: What type of epithelial tissue is found in the lining of kidney tubules and salivary gland ducts? [Exam Favorite] Answer: Cuboidal Epithelium (Simple Cuboidal Epithelial Tissue), which provides mechanical support and participates in secretory and absorptive processes.
Mastering the NCERT Solutions for Class 9 Science Chapter 3 (Exploration), “Tissues in Action”, equips students with the histological principles, vascular transport mechanics, and musculoskeletal concepts required for high performance in CBSE examinations. Review the plant and animal tissue comparative tables, the debarking and carrot tissue culture cases, and the 15 high-yield FAQs above to secure full marks in your biological evaluations.