Tissues – Case-based Questions with Answers
Class 9 • Biology
Chapter 6: Tissues — Case-Based Questions & Answers
Instructions: Each case below describes a short scenario followed by questions. Answers are concise and NCERT-focused to help build conceptual clarity and exam readiness. Use these for understanding application of concepts and practicing answer-writing.
Topic: Meristematic Tissue & Growth
Case 1
A gardener trims off the tips of growing shoots to shape a hedge. Soon, many new shoots emerge below the cut surface.
Q1: Explain which meristematic regions are activated and why pruning leads to bushier growth.
A1: Pruning removes apical dominance — the apical meristem normally secretes auxin that suppresses axillary buds. When the tip is cut, auxin levels fall and axillary (lateral) meristems activate, dividing to form new shoots; intercalary meristems may also contribute in grasses. This results in bushier growth.
Note: Apical meristem promotes length growth, lateral meristem (cambium) contributes to thickness; removal of apical influence allows lateral buds to grow.
Case 2
A lawn recovers quickly after mowing compared to a tree after heavy pruning.
Q1: Which type of meristem allows grasses to regrow quickly and why trees recover slower?
A1: Grasses have intercalary meristems at the base of internodes and leaf bases; these remain active after mowing and enable quick regrowth. Trees rely on apical and lateral meristems and may require longer to regenerate because large woody stems involve extensive secondary growth and cambial activity.
Intercalary meristems are an adaptation in monocots (grasses) for rapid regrowth after cutting.
Topic: Simple Permanent Tissues
Case 3
A student examines cross-sections of celery stalk and notices thickened, angular cells under the epidermis.
Q1: Identify the tissue and explain how its structure supports its function.
A1: The tissue is collenchyma. Its cells have unevenly thickened primary cell walls (thicker at corners) that provide flexible mechanical support to young stems and petioles, allowing bending without breaking while the plant grows.
Collenchyma often forms strands under the epidermis, visible in celery as crunchy strands.
Case 4
A mango seed feels hard due to stone-like cells when a student squeezes it.
Q1: Which tissue causes the hardness and what are its characteristics?
A1: Sclereids (sclerenchyma) in the seed coat (endocarp) make it hard. Sclerenchyma cells have thick, lignified secondary walls and are typically dead at maturity, providing protection.
Sclereids give hardness to seed coats and gritty texture to pear fruit flesh.
Topic: Xylem & Phloem
Case 5
A cut stem placed in coloured water shows dye moving up the stem and appearing in leaves after a few hours.
Q1: Explain which tissue transports the dye and the mechanism involved.
A1: Xylem transports the coloured water upward. Transpiration from leaves creates a negative pressure (transpiration pull), and cohesion between water molecules and adhesion to xylem walls allow a continuous water column to move upward through vessels and tracheids, carrying the dye.
If stomata are closed or humidity high, transpiration reduces and dye movement slows.
Case 6
During a study, sugar produced in leaves was later detected in roots and developing fruits.
Q1: Which tissue is responsible for this distribution and how does the direction of flow get determined?
A1: Phloem transports sugars from source (leaves) to sinks (roots, fruits). Direction depends on source–sink relationships; active loading at sources and unloading at sinks creates pressure differences (pressure-flow hypothesis) that drive bulk flow through sieve tubes, mediated by companion cells.
Phloem transport can be bidirectional depending on changing sink demands.
Topic: Tissue Adaptations
Case 7
A cactus stem is thick and fleshy while a water lily leaf floats on the surface of water.
Q1: Explain tissue-level adaptations in these two plants for their habitats.
A1: Cactus stems have parenchyma modified for water storage (succulent parenchyma) with reduced leaves to reduce transpiration; sclerenchyma/fibres provide support. Water lily leaves have extensive aerenchyma (parenchyma with air spaces) facilitating buoyancy and internal gas exchange. Both show tissue specialisations for habitat adaptation.
Aerenchyma is common in hydrophytes; succulence is an adaptation to xerophytes.
Case 8
A farmer notices that older stems of a tree are much thicker than younger branches.
Q1: Which meristem is responsible for this thickening and what tissues does it produce?
A1: Vascular cambium (lateral meristem) causes secondary growth (thickening). It produces secondary xylem (wood) inward and secondary phloem outward; cork cambium forms protective cork contributing to bark.
Repeated seasonal activity of cambium increases girth and forms growth rings in temperate trees.
Topic: Animal Tissues — Epithelial & Protective Roles
Case 9
A researcher examines lung tissue and finds very thin, single-layered cells forming the alveoli walls.
Q1: Identify this epithelial type and explain why it is suited for its function.
A1: Simple squamous epithelium forms alveoli walls. Its thin, flat cells provide minimal diffusion distance for rapid gas exchange (oxygen and carbon dioxide) between air and blood capillaries.
Thin cytoplasm and extensive capillary networks aid efficient diffusion.
Case 10
An individual with chronic smoking has thickened, irregular epithelium in their airways and increased mucus-secreting goblet cells.
Q1: Explain how epithelial changes affect respiratory function.
A1: Thickened, dysplastic epithelium and excess mucus reduce airway clearance and increase diffusion distance, impairing gas exchange and predisposing to infections and chronic bronchitis. Loss of ciliated epithelium reduces mucociliary clearance.
Epithelial alterations due to irritants compromise protective functions and gas exchange efficiency.
Topic: Animal Tissues — Connective & Muscular
Case 11
A patient has a sprained ankle where the ligament fibres are torn.
Q1: Explain the tissue involved and why ligaments are prone to such injuries.
A1: Ligaments are dense fibrous connective tissues made of parallel collagen fibres providing tensile strength between bones. Sudden overstretching can exceed collagen fibre tensile limits causing tears. Poor blood supply slows healing, requiring immobilisation for recovery.
Tendons and ligaments have abundant collagen making them strong but less elastic than muscle, hence prone to injury under rapid strain.
Case 12
Athletes doing endurance training show increased capillary density and mitochondrial content in muscle cells.
Q1: Which tissue adaptations enable improved endurance and why?
A1: Skeletal muscle undergoes physiological adaptation: increased capillary density (better blood supply) and mitochondrial biogenesis (more mitochondria) in muscle fibres improve oxygen delivery and aerobic ATP production, enhancing endurance and fatigue resistance.
These changes reflect plasticity of muscle tissue in response to training stimuli.
Topic: Nervous Tissue & Signal Transmission
Case 13
A patient with multiple sclerosis (MS) has episodes of muscle weakness and sensory disturbances.
Q1: Explain how demyelination affects nerve impulse conduction and leads to symptoms seen in MS.
A1: Myelin sheath insulates axons and enables saltatory conduction — impulses jump between nodes of Ranvier. Demyelination reduces insulation, slows conduction or causes conduction block, leading to muscle weakness, sensory deficits and coordination problems seen in MS.
Loss of myelin disrupts rapid, coordinated signalling in CNS pathways.
Case 14
A biology student notices a neuron with many dendrites and a single long axon.
Q1: Explain how the neuron's structure suits its function.
A1: Multiple dendrites increase surface area to receive signals from many neurons; a single long axon transmits impulses to distant targets. This arrangement facilitates integration of inputs and long-distance communication — ideal for sensory/interneurons and motor neurons.
Neuronal polarity (dendrites vs axon) underlies directionality of signal flow.
Topic: Practical Skills & Tissue Identification
Case 15
In a practical exam, a student stains onion peel and cheek cells and compares them under the microscope.
Q1: Which features help distinguish plant epidermal (onion) cells from animal (cheek) cells?
A1: Plant epidermal cells show a regular brick-like shape, prominent cell wall, large central vacuole, and often chloroplasts absent in onion epidermis; animal cheek cells are irregular in shape, lack cell walls, and show a prominent nucleus with cytoplasm. Staining highlights nucleus in cheek cells (methylene blue) and cell walls in plant cells (iodine/safranin).
Cell wall presence and regular packing are key distinguishing features.
Case 16
A student measures the thickness of xylem vessels using calibrated ocular and stage micrometers.
Q1: Why is calibration necessary and how does it improve measurement accuracy?
A1: Calibration aligns ocular micrometer units with a known scale (stage micrometer), converting arbitrary divisions into actual length units (µm). This ensures accurate size measurements of microscopic structures and comparability across observations.
Without calibration, ocular divisions are meaningless for quantitative analysis.
Topic: Applications — Agriculture & Medicine
Case 17
A crop breeder selects plants with stronger stems to resist lodging in windy regions.
Q1: Which tissues should be targeted and what traits would confer stem strength?
A1: Increase sclerenchyma fibres and lignified xylem (secondary xylem) for tensile strength and rigidity. Traits include thicker cell walls, more fibre bundles, and higher lignin content in vascular tissues, which reduce lodging.
Breeding or management practices that enhance secondary growth and fibre content improve stem strength.
Case 18
A plant pathologist notices wilt in crops and suggests checking xylem function.
Q1: How can xylem dysfunction lead to wilting and what might cause such dysfunction?
A1: Xylem dysfunction (blockage, cavitation) impairs water transport to leaves, lowering turgor and causing wilting. Causes include pathogen clogging (e.g., bacterial wilt), air embolisms (cavitation) due to drought/stress, or physical damage to vascular bundles.
Restoring water supply or controlling pathogens can help recovery if damage is not severe.
Topic: Comparative & Higher-Order Questions
Case 19
A student compares seedless (parthenocarpic) fruits with seeded fruits and finds more sclereids in seeded varieties.
Q1: Suggest why seed-bearing fruits might have more sclereids and how this relates to seed protection and dispersal.
A1: Sclereids provide hardness and protection; seeded fruits may have evolved more sclereids to protect developing seeds from herbivores and mechanical damage, aiding seed survival and effective dispersal. Harder fruit tissues can also influence dispersal mechanisms (e.g., surviving gut passage in animals).
Sclereid abundance contributes to texture (apple/pear gritty cells) and mechanical protection.
Case 20
A biotech firm engineers faster-growing trees by modifying cambial activity.
Q1: Explain the role of cambium in secondary growth and potential ecological concerns of modifying cambial rates.
A1: Vascular cambium produces secondary xylem and phloem, increasing stem girth. Enhancing cambial activity can increase wood production and biomass. Ecological concerns include altered wood density and mechanical properties, changes in habitat structure, potential impacts on water and nutrient allocation, and unforeseen effects on ecosystem interactions and biodiversity. Responsible assessment is necessary before deployment.
Genetic or hormonal modifications should be evaluated for long-term ecological consequences.