Complete question-answer bank for Class 9 Science Chapter 3: Tissues in Action. Covers 1-mark, 2-mark, 3-mark, and 5-mark questions with detailed answers, along with competency-based questions and case studies. Topics include meristematic tissue, permanent tissue, epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Aligned with CBSE and NCERT Exploration syllabus 2026–27.
Complete Question Bank | 1-Mark to 5-Mark Questions | Competency-Based | Case Studies | Reading Time: 25 minutes
Master the Tissues in Action chapter with this comprehensive question bank covering all important topics from NCERT Class 9 Science Chapter 3. Each answer includes detailed explanations with links to concept pages for deeper understanding. Questions are organised by marks for effective exam preparation. For practice with objective questions, visit the Tissues MCQ page.
Each question carries 1 mark. Answer in one word or one sentence.
Answer: A tissue is a group of cells that are similar in structure, origin, and function, working together to perform a specific task. Read more on the Tissues in Action notes page.
Answer: Meristematic tissue is responsible for growth in plants. Its cells actively divide to produce new cells.
Answer: Differentiation is the process by which meristematic cells lose their ability to divide, mature, and take on a specific structure and function to become permanent tissue.
Answer: The three types of meristematic tissue based on location are: (i) Apical meristem, (ii) Lateral meristem, and (iii) Intercalary meristem.
Answer: Collenchyma is the simple permanent tissue with living cells and unevenly thickened (at corners) cell walls, providing mechanical support and flexibility. Learn more about simple permanent tissues.
Answer: Stomata are tiny pores in the epidermis of leaves that regulate gaseous exchange (CO2 and O2) and transpiration (loss of water vapour). They are surrounded by guard cells that control their opening and closing.
Answer: Tracheids and vessel elements (tracheae) are the water-conducting elements of xylem that are dead at maturity.
Answer: Companion cells assist sieve tube elements in phloem. They are living cells connected to sieve tubes and help in loading and unloading of food materials.
Answer: The four types of animal tissue are: (i) Epithelial tissue, (ii) Connective tissue, (iii) Muscular tissue, and (iv) Nervous tissue.
Answer: Ciliated epithelium (columnar epithelium with cilia) lines the respiratory tract and moves mucus and debris upward towards the throat by the wave-like motion of cilia. See epithelial tissue types.
Answer: Smooth (unstriated) muscle tissue is involuntary and found in the walls of blood vessels, digestive tract, urinary bladder, and other internal organs. Learn more on the muscular tissue page.
Answer: The neuron (nerve cell) is the structural and functional unit of the nervous system. It is a highly specialised cell that receives and transmits electrical impulses. Read about nervous tissue.
Answer: Tendon is the fibrous connective tissue that connects a muscle to a bone. It is made of white fibrous tissue and is very strong and inelastic. See connective tissue types.
Answer: Collenchyma provides flexibility to the petiole of a leaf. Its living cells with unevenly thickened walls allow the tissue to stretch and bend without breaking, making it ideal for this function.
Answer: The axon carries nerve impulses away from the cell body of the neuron towards the next neuron or an effector organ (muscle or gland). It is usually a single long fibre. Read more on nervous tissue.
Each question carries 2 marks. Answer in 2–4 sentences.
Answer:
Meristematic Tissue: Cells are actively dividing; they are small, have dense cytoplasm, and lack vacuoles. Found at growing tips of roots and shoots.
Permanent Tissue: Cells have lost the ability to divide; they are mature, often have a large vacuole, and are specialised for specific functions. Formed by differentiation of meristematic cells.
Answer: Parenchyma is the most common simple permanent tissue with the following functions: (i) It stores food materials such as starch and oil. (ii) In leaves, chlorenchyma (parenchyma with chloroplasts) performs photosynthesis. (iii) In aquatic plants, aerenchyma (parenchyma with large air spaces) helps the plant float by providing buoyancy.
Answer: Both are simple permanent tissues that provide mechanical support, but they differ in structure: Collenchyma has living cells with cellulose deposited unevenly at cell corners, allowing flexibility. Sclerenchyma has dead cells with uniformly thickened walls heavily lignified (containing lignin), making them rigid and hard. Sclerenchyma provides much stronger support and forms structures like seed coats, nut shells, and the husk of coconut.
Answer: Two differences between xylem and phloem:
1. Xylem conducts water and dissolved minerals from roots to leaves in an upward direction; Phloem transports prepared food (sucrose) from leaves to all parts of the plant in both directions.
2. The main conducting cells of xylem (tracheids and vessels) are dead at maturity; the main conducting cells of phloem (sieve tube elements) are living.
Answer: Plants need less maintenance energy because a large proportion of their body is made up of dead cells (e.g., sclerenchyma, xylem vessels) which require no energy for metabolic activities. Dead cells can still provide structural support, water conduction, and mechanical strength. Animals, on the other hand, have mostly living cells that constantly require energy for their activities.
Answer: Two types of simple epithelial tissue:
1. Squamous (Pavement) Epithelium: Flat, tile-like cells forming a smooth surface. Function: Forms protective lining of the mouth cavity and oesophagus; also forms the walls of alveoli in lungs facilitating gas exchange.
2. Columnar (Cuboidal) Epithelium: Tall, column-shaped cells. Function: Lines the intestine and is involved in absorption of digested food; in the kidney tubules, it is involved in reabsorption.
Answer: Both ligament and tendon are types of connective tissue, but differ as follows:
Ligament: Connects bone to bone at a joint; made of yellow elastic fibres with some collagen; elastic and stretchy, allowing joint movement while providing stability.
Tendon: Connects muscle to bone; made of white collagen fibres; very strong but inelastic, transmitting the force of muscle contraction to the bone.
Answer: Cardiac muscle is the specialised muscular tissue found exclusively in the wall of the heart. It is unique because: (i) It has faint striations (stripes) like striated muscle, making it appear striated under a microscope. (ii) It contracts involuntarily and rhythmically throughout life without fatigue. (iii) Its cells are branched and interconnected, allowing electrical impulses to spread rapidly across the entire heart muscle.
Answer: Two components of xylem and their functions:
1. Tracheids: Elongated, spindle-shaped dead cells with lignified walls and bordered pits. They conduct water and dissolved minerals and also provide mechanical support.
2. Xylem fibres: Dead cells with thick lignified walls. They provide mechanical strength to the plant body but do not conduct water.
Answer: Adipose tissue is a type of loose connective tissue found beneath the skin (subcutaneous layer), around kidneys, in the bone marrow, and between internal organs. Functions: (i) It stores energy in the form of fat. (ii) It acts as an insulator, preventing heat loss from the body. (iii) It cushions and protects internal organs from mechanical shock.
Answer: Both are types of meristematic tissue:
Apical Meristem: Located at the tips (apices) of roots and shoots. It is responsible for the primary growth of the plant — increase in length. It produces new cells at the growing tips.
Intercalary Meristem: Located at the base of leaves or at internodes (between nodes). It is responsible for the elongation of internodes, as seen in grasses and monocots, allowing rapid regrowth after grazing.
Answer: Blood is considered a connective tissue because it connects different parts of the body by transporting materials between them. It has a fluid matrix (plasma) in which cells (RBCs, WBCs, platelets) are suspended — this is characteristic of connective tissue (cells surrounded by non-living matrix). Blood connects the digestive system, respiratory system, and all other organs by transporting oxygen, nutrients, hormones, and waste products.
Each question carries 3 marks. Answer in 5–8 sentences or with a labelled diagram.
Answer: The three types of simple permanent plant tissues are:
1. Parenchyma: Living cells with thin cellulose walls and large central vacuoles; loosely packed with intercellular spaces. Functions include food storage, photosynthesis (chlorenchyma), and buoyancy (aerenchyma).
2. Collenchyma: Living cells with unevenly thickened (at corners) cellulose walls; provide mechanical support with flexibility. Found at the periphery of stems and in petioles of leaves.
3. Sclerenchyma: Dead cells with uniformly and heavily thickened lignified walls; no living contents at maturity. Provides maximum mechanical strength and rigidity. Found as fibres in jute, hemp, and as stone cells (sclereids) in seed coats and the husk of coconut.
Answer: A neuron consists of three main parts:
1. Cell Body (Cyton/Soma): Contains the nucleus, cytoplasm, and other organelles. It is the metabolic centre of the neuron and maintains the entire cell.
2. Dendrites: Short, branched extensions of the cell body that receive nerve impulses from other neurons or from sensory receptors and bring them towards the cell body.
3. Axon: A single, long fibre that carries impulses away from the cell body towards the next neuron or effector. It may be covered by a myelin sheath (in myelinated neurons) that acts as an insulator and speeds up impulse transmission. The terminal end of the axon branches into axon terminals, which form synapses with dendrites of the next neuron.
Answer: The three types of muscular tissue are:
1. Striated (Skeletal/Voluntary) Muscle: Has alternating dark and light bands (striations); cylindrical, multi-nucleate fibres; under voluntary control. Found attached to bones, forming the muscles of limbs, face, and trunk. Responsible for body movements.
2. Smooth (Unstriated/Involuntary) Muscle: No striations; spindle-shaped cells, each with a single central nucleus; under involuntary control (controlled by autonomic nervous system). Found in walls of internal organs — digestive tract, blood vessels, urinary bladder, uterus.
3. Cardiac Muscle: Has faint striations; branched, cylindrical cells with a single nucleus; involuntary and contracts rhythmically without fatigue. Found only in the wall of the heart (myocardium). Responsible for the heartbeat.
Answer: Complex permanent tissues are groups of more than one type of cell that work together as a unit to perform a common function. They are called "complex" because they consist of multiple different cell types (unlike simple tissues which have only one cell type).
The two types are:
1. Xylem (wood): Composed of tracheids, vessel elements, xylem parenchyma, and xylem fibres. It conducts water and dissolved minerals upward from roots to leaves and provides mechanical support.
2. Phloem (bast): Composed of sieve tube elements, companion cells, phloem parenchyma, and phloem fibres. It transports prepared food (mainly sucrose) from leaves to all parts of the plant (translocation).
Answer: Types of epithelial tissue and their locations:
1. Squamous Epithelium: Flat, scale-like cells. Location: lining of mouth, oesophagus, and walls of alveoli (air sacs in lungs).
2. Cuboidal Epithelium: Cube-shaped cells with central nuclei. Location: kidney tubules, salivary glands, thyroid follicles.
3. Columnar Epithelium: Tall, column-like cells. Location: lining of the stomach, intestine, and gall bladder; also forms ciliated epithelium in the respiratory tract.
4. Stratified Squamous Epithelium: Multiple layers of flat cells. Location: outer layer of skin (epidermis). Provides protection against wear and tear.
5. Glandular Epithelium: Modified columnar cells that form glands and secrete substances. Location: gastric glands, intestinal glands.
Answer: Tissue organisation in plants and animals differs in three major ways:
1. Dead vs. Living cells: Plants have a large proportion of dead cells (e.g., sclerenchyma, xylem vessels), which still perform essential functions. Animals are mostly made of living cells that constantly require energy.
2. Growth pattern: In plants, growth occurs only in specific regions (meristems); most of the plant body is permanent tissue. In animals, growth occurs in all parts of the body; most cells can divide for repair.
3. Maintenance energy: Since a large part of a plant body is dead, plants need much less maintenance energy than animals. Animals' living cells require continuous energy supply for metabolism.
Answer: Epidermis is the outermost protective layer of a plant body, part of the dermal tissue system. It has the following adaptations for protection:
1. Waxy cuticle: The outer surface of epidermal cells in aerial parts secretes a waxy, waterproof substance called cutin that forms the cuticle. This prevents excessive water loss by evaporation.
2. Stomata: Pores in the leaf epidermis surrounded by guard cells that regulate gaseous exchange and control transpiration. Their opening and closing is regulated according to environmental conditions.
3. Trichomes (hairs): Epidermal cells may produce hair-like outgrowths called trichomes that reduce water loss, reflect sunlight (in desert plants), and protect against insects.
4. Root hairs: In roots, epidermal cells produce long root hairs that increase the surface area for absorption of water and minerals from the soil.
Answer: The three plant tissue systems are:
1. Dermal (Epidermal) Tissue System: Forms the outermost covering of the plant body. Main tissue: Epidermis (simple squamous permanent tissue). In older woody stems, it is replaced by cork (periderm).
2. Vascular (Conducting) Tissue System: Responsible for transport of water, minerals, and food. Main tissues: Xylem (water conduction) and Phloem (food conduction) — both are complex permanent tissues.
3. Ground (Fundamental) Tissue System: Makes up the bulk of the plant body (cortex, pith, mesophyll). Main tissues: Parenchyma, collenchyma, and sclerenchyma — all simple permanent tissues. Functions include photosynthesis, storage, and support.
Answer: Types of connective tissue and their locations:
1. Areolar (Loose Connective) Tissue: Between organs and beneath skin; fills spaces between organs and supports them.
2. Adipose Tissue: Beneath skin and around kidneys; stores fat and insulates the body.
3. Fibrous Connective Tissue: Forms tendons (muscle to bone) and ligaments (bone to bone).
4. Cartilage: Tip of the nose, ear pinna, trachea rings, ends of long bones (joints); provides flexible support.
5. Bone: Skeleton; provides rigid structural support and protects internal organs.
6. Blood: Blood vessels and heart; transports materials throughout the body.
Answer: In a unicellular organism like Amoeba, a single cell performs all life processes. As organisms became multicellular during evolution, the body grew more complex and different regions specialised for different functions. This is called division of labour.
Tissues are essential for division of labour because:
1. Similar cells group together to form a tissue that is structurally specialised for a particular function (e.g., muscle cells group to form muscular tissue for contraction).
2. Each tissue can perform its function more efficiently because all its cells are adapted for that purpose.
3. Tissues combine to form organs, which combine to form organ systems — a hierarchy that allows complex functions like digestion, circulation, and reproduction to occur simultaneously.
Thus, tissues increase efficiency, reduce energy waste, and allow complex body functions in multicellular organisms. Visit the Tissues in Action notes page for more.
Each question carries 5 marks. Answer in detail with diagrams where required.
Answer:
(i) Types of Tissue:
Plant tissues: Meristematic tissue and Permanent tissue (simple: parenchyma, collenchyma, sclerenchyma; complex: xylem, phloem).
Animal tissues: Epithelial tissue, Connective tissue, Muscular tissue, Nervous tissue.
(ii) Ability to Divide:
In plants, only meristematic cells divide actively. Once differentiated, permanent tissue cells generally cannot divide. A few parenchyma cells can de-differentiate and resume division under injury.
In animals, most cells retain the ability to divide for growth and repair throughout life, though nervous tissue has very limited ability to regenerate.
(iii) Proportion of Dead Cells:
Plants have a large proportion of dead cells — sclerenchyma, xylem vessels, and tracheids are all dead at maturity yet functional. This is a unique feature of plant permanent tissues.
Animals have very few dead cells. Most animal tissues (epithelial, muscular, nervous) consist almost entirely of living cells. Exceptions include the outermost cornified layer of the skin.
(iv) Maintenance Energy:
Plants require much less maintenance energy because their large proportion of dead cells does not need metabolic energy for their own upkeep — they still perform structural and conduction functions without consuming ATP.
Animals require high maintenance energy because their mostly living cells constantly need energy for metabolic activities, ion pumping, protein synthesis, and other cellular functions.
Answer: Xylem is a complex permanent tissue composed of four different cell types:
1. Tracheids: Elongated, spindle-shaped dead cells with lignified walls. They have bordered pits through which water moves from cell to cell. They conduct water and provide mechanical support. Present in all vascular plants.
2. Vessel Elements (Tracheae): Wide, short, barrel-shaped dead cells joined end-to-end to form long continuous tubes called vessels. Water moves more efficiently through vessels than tracheids. Present mainly in angiosperms (flowering plants).
3. Xylem Parenchyma: The only living cells in xylem. Store food (starch and fats) and assist in lateral (sideways) transport of water from one vessel to another. They also help in loading minerals into the xylem stream.
4. Xylem Fibres: Dead, elongated cells with thick lignified walls. They do not conduct water but provide mechanical strength and rigidity to the plant body.
Xylem is called a complex tissue because it is composed of more than one type of cell (four different cell types) that work together as a single functional unit to transport water and provide mechanical support — unlike simple tissues which have only one cell type.
Answer:
(a) Meristematic Tissue — Types and Characteristics:
Characteristics: Meristematic cells are small, roughly isodiametric (equal dimensions in all directions), with dense cytoplasm, prominent nuclei, thin cellulose cell walls, and no vacuoles (or very small ones). They divide actively and continuously, producing new cells for growth.
Types based on location:
1. Apical Meristem: Located at root tips and shoot tips (apices). Responsible for the primary growth — increase in length of roots and shoots. Also called primary meristem. Example: root apical meristem, shoot apical meristem.
2. Intercalary Meristem: Located at internodes (regions between nodes) or at the base of leaves. Responsible for elongation of internodes. Common in monocots like grasses, allowing rapid regrowth after grazing or mowing.
3. Lateral Meristem: Located along the sides of stems and roots (runs parallel to the long axis). Responsible for secondary growth — increase in girth (thickness) of stems. Includes vascular cambium (produces secondary xylem and phloem) and cork cambium (produces cork/bark).
(b) From Meristematic to Permanent Tissue — Differentiation:
When meristematic cells stop dividing, they undergo a process called differentiation. During differentiation:
1. Cells enlarge and develop a large central vacuole.
2. Cell walls thicken and may become lignified (in sclerenchyma and xylem).
3. Cells develop specialised structures — chloroplasts (parenchyma in leaves), unevenly thickened walls (collenchyma), or heavily lignified walls with no living contents (sclerenchyma, xylem).
4. Cells become incapable of further division.
The result is the formation of permanent tissue — mature, specialised cells that perform specific functions for the rest of the plant's life.
Answer: Connective tissue is characterised by cells embedded in a non-living matrix (ground substance + fibres). Types and structure-function relationships:
1. Areolar Tissue: A loose connective tissue with a gel-like matrix, collagen and elastic fibres, and various cell types (fibroblasts, macrophages, mast cells). It fills spaces between organs, supports them, and is the site of immune responses (macrophages engulf pathogens).
2. Adipose Tissue: Cells (adipocytes) packed with fat droplets. The fat acts as an energy store, an insulating layer preventing heat loss, and a cushion protecting organs from mechanical shock.
3. Dense Fibrous Connective Tissue: Packed with collagen fibres arranged parallel to each other, making it extremely strong and resistant to pulling forces. Forms tendons (muscle-to-bone, transmit muscular force) and ligaments (bone-to-bone, stabilise joints; contains elastic fibres for some stretch).
4. Cartilage: Semi-rigid matrix of chondroitin sulphate with embedded chondrocytes. Flexible yet firm — provides smooth surface at joints (hyaline cartilage), shape to the ear and nose (elastic cartilage), and support to trachea and bronchi rings to prevent collapse.
5. Bone: Hard matrix of calcium phosphate and collagen (ossein). Rigid structure — forms the skeleton that supports the body, protects internal organs (e.g., skull protects brain, ribs protect heart and lungs), acts as levers for muscles, and stores calcium.
6. Blood: Fluid matrix (plasma) with RBCs, WBCs, and platelets. The fluid matrix allows blood to flow through vessels, enabling transport of oxygen (RBCs), immune responses (WBCs), and clotting (platelets) throughout the body.
Answer: Phloem is a complex permanent tissue that transports prepared food (mainly sucrose) from the leaves (source) to all other parts of the plant (sink).
Four components of Phloem:
1. Sieve Tube Elements: The main conducting cells of phloem. They are living cells, joined end-to-end to form long sieve tubes. The end walls between adjacent cells have sieve plates — porous regions through which food (sucrose solution) flows. Sieve tube cells lack a nucleus and most organelles at maturity; their cytoplasm is connected to the next cell through sieve pores.
2. Companion Cells: Living cells closely associated with sieve tube elements. They retain their nucleus and all organelles and carry out the metabolic activities needed by the sieve tubes. They actively load sucrose into sieve tubes at source (leaves) using energy (ATP).
3. Phloem Parenchyma: Living parenchyma cells associated with phloem. Store food materials and assist in lateral transport of food.
4. Phloem Fibres (Bast Fibres): Dead elongated cells with thickened walls. Provide mechanical support to phloem but do not conduct food. Commercial fibres like jute and flax are phloem fibres.
How phloem transports food (Pressure Flow / Mass Flow):
1. In leaves (source), companion cells actively load sucrose into sieve tubes using ATP energy.
2. This raises the solute concentration in the sieve tube, causing water to enter from adjacent xylem by osmosis, building up pressure (turgor pressure).
3. At the sink (roots, fruits, growing buds), sucrose is unloaded from the sieve tubes, the solute concentration falls, water leaves, and pressure drops.
4. The pressure difference between source and sink drives the flow of sucrose solution along sieve tubes from high pressure (source) to low pressure (sink) — this is called mass flow or pressure flow.
Answer: Epithelial tissue is the covering and lining tissue of the body surfaces, cavities, and organs. It forms a protective boundary between the internal body and the external environment. Characteristics: cells tightly packed with almost no intercellular matrix; rest on a basement membrane; capable of cell division for repair.
Types of Epithelial Tissue:
1. Squamous (Pavement) Epithelium:
Structure: Single layer of thin, flat, tile-like cells with a central nucleus.
Location: Mouth lining (buccal cavity), oesophagus, alveoli of lungs, walls of blood vessels (endothelium).
Function: Provides smooth surfaces for substances to pass across; allows gas exchange in alveoli; reduces friction in blood vessels.
2. Cuboidal Epithelium:
Structure: Single layer of cube-shaped cells with a central, round nucleus.
Location: Kidney tubules, ducts of salivary glands, thyroid follicles.
Function: Secretion and absorption — kidney tubules reabsorb useful substances; salivary gland ducts secrete saliva.
3. Columnar Epithelium:
Structure: Tall, column-like cells with nucleus near the base; may have microvilli (brush border) for absorption, or cilia for moving materials.
Location: Lining of stomach and intestine (with microvilli); respiratory tract (with cilia — ciliated columnar epithelium).
Function: Absorption of digested food in intestine; secretion of mucus; cilia move mucus and debris in respiratory tract.
4. Stratified Squamous Epithelium:
Structure: Multiple layers of flat squamous cells; outermost layers may be cornified (dead, filled with keratin).
Location: Skin (epidermis), lining of mouth, pharynx, vagina.
Function: Protection against mechanical abrasion, chemical damage, desiccation, and pathogens.
5. Glandular Epithelium:
Structure: Modified columnar or cuboidal cells that have the ability to secrete substances.
Location: Gastric glands, pancreatic glands, sweat glands, salivary glands.
Function: Produce and secrete digestive enzymes, hormones, saliva, sweat, and other substances.
Answer: The three types of muscular tissue compared:
| Feature | Skeletal (Striated) | Smooth (Unstriated) | Cardiac |
|---|---|---|---|
| Striations | Distinct dark and light bands | No striations | Faint striations |
| Cell shape | Long, cylindrical fibres | Spindle-shaped | Branched, cylindrical |
| Nuclei | Many (multinucleate) | One (central nucleus) | One (central nucleus) |
| Control | Voluntary | Involuntary | Involuntary |
| Location | Attached to bones | Internal organs (gut, blood vessels) | Wall of heart only |
| Fatigue | Fatigues easily | Slow to fatigue | Never fatigues |
Answer:
Structure of a Neuron:
A neuron has three main parts:
1. Cell Body (Cyton): Contains the nucleus (with nucleolus), cytoplasm, mitochondria, Golgi apparatus, and Nissl bodies (RER). It is the metabolic centre of the neuron.
2. Dendrites: Multiple short, branched extensions of the cell body that receive impulses from receptors or other neurons and bring them towards the cell body. The surface area is increased by branching.
3. Axon: A single long fibre (can be up to 1 metre in length). It carries the impulse away from the cell body. It may be covered by a myelin sheath (fatty insulating layer) produced by Schwann cells. The gaps between Schwann cells are called Nodes of Ranvier. The axon ends in axon terminals (synaptic knobs) that release neurotransmitters at synapses.
Six parts to label on a diagram: cell body, nucleus, dendrites, axon, myelin sheath, axon terminals (synaptic knobs).
How a nerve impulse travels:
1. A stimulus (e.g., touching a hot surface) is detected by a receptor (sensory receptor in the skin).
2. The receptor generates an electrical impulse (nerve impulse) that travels along the sensory (afferent) neuron towards the spinal cord / brain.
3. In the brain or spinal cord, interneurons (relay neurons) process the signal and generate a response.
4. The response impulse travels along a motor (efferent) neuron to an effector — a muscle (causes contraction) or a gland (causes secretion).
5. Impulses jump from one neuron to the next at a synapse: the axon terminal releases chemical neurotransmitters that cross the synaptic cleft and bind to receptors on the next neuron's dendrites, generating a new impulse.
These questions test application of tissue biology concepts to real-life situations. Answers require reasoning and analysis.
Answer: The intercalary meristem is responsible for the rapid regrowth of grass after mowing. It is located at the base of each internode (between nodes) and at the base of the leaf blade.
When grass is mowed, the top portions of the leaves are cut off, but the intercalary meristem at the base remains intact and undamaged. These actively dividing cells continue to produce new cells upward, regenerating the leaf blade. This is why grasses — unlike most other plants — can tolerate regular cutting without dying. This adaptation is also why grasses are the dominant ground cover in areas grazed by animals.
Answer: Jute fibre is obtained from sclerenchyma (specifically, phloem fibres / bast fibres found in the phloem region of the jute stem).
Jute fibre is extremely strong because sclerenchyma cells are dead at maturity and have uniformly, heavily thickened cell walls that are impregnated with lignin — a hard, rigid polymer. The cells are elongated and narrow (fibre-shaped), and are arranged in bundles. Lignification makes the walls almost insoluble and highly resistant to stretching and breaking forces. This combination of dead, elongated, thickly lignified cells bundled together gives jute fibre its characteristic strength, making it suitable for ropes, sacks, carpet backing, and coarse textiles.
Answer: This scenario indicates that the motor (efferent) nerve fibres were damaged, while the sensory (afferent) nerve fibres were spared.
In the context of nervous tissue:
Sensory neurons carry impulses from sense organs (skin, muscles) towards the brain and spinal cord. Since the patient can still feel pain, the sensory pathways are intact.
Motor neurons carry impulses from the brain/spinal cord to muscles (effectors). Since the patient cannot move their legs, the motor pathways from the spinal cord to the leg muscles have been severed or damaged.
This is possible because in the spinal cord, sensory and motor fibres travel in different regions (sensory fibres enter through the dorsal root; motor fibres exit through the ventral root). A partial spinal cord injury can selectively damage one set while sparing the other.
Answer: Girdling (removing a ring of bark) cuts through the phloem, which is located in the bark (outer part of the stem), while leaving the xylem (wood, located inward) intact.
After girdling:
1. Xylem is undamaged, so water and minerals continue to flow upward from the roots to the leaves. The leaves can still carry out photosynthesis, and the tree looks healthy initially.
2. However, Phloem has been destroyed at the cut. Sugars (sucrose) manufactured by leaves during photosynthesis cannot be transported downward past the girdle to the roots.
3. The roots are starved of food and eventually die. Once the roots die, they can no longer absorb water, and the entire tree dies.
This observation directly demonstrates the separate roles of xylem (upward transport of water) and phloem (downward transport of food) in a plant.
Answer: The alveoli are lined with simple squamous epithelium — a single layer of extremely thin, flat cells. This structure is perfectly adapted for gas exchange because:
1. The cells are very thin, so gases (O2 and CO2) can diffuse across the epithelium rapidly — the shorter the diffusion distance, the faster the exchange.
2. A single cell layer (simple epithelium) minimises the barrier between the air in the alveolus and the blood in the surrounding capillary.
If this tissue were replaced by stratified squamous epithelium (multiple layers, like skin):
1. The wall would become much thicker, greatly increasing the diffusion distance.
2. Gas exchange (oxygen into blood, carbon dioxide out) would become extremely slow and inefficient.
3. The body would suffer from hypoxia (oxygen deficiency) as oxygen could not cross into the blood fast enough to meet the body's needs.
This illustrates how the structure of epithelial tissue is precisely matched to its function — protection requires thick stratified epithelium, while rapid diffusion requires thin simple epithelium.
Read each passage carefully and answer the questions that follow.
Priya is studying plant adaptations. She observes two plants: a lotus growing in a pond and a cactus growing in a hot, dry desert. She notes that the lotus has large, flat leaves with many air spaces inside, and its stem is light and spongy. The cactus, on the other hand, has a thick, succulent stem with very few, modified leaves (spines). Both plants have epidermal tissue as their outermost layer, but with very different modifications. The lotus epidermis is thin with numerous stomata, while the cactus epidermis has a very thick waxy cuticle and very few stomata.
Answer the following questions based on your understanding of plant tissue systems:
Answer: Aerenchyma is the type of parenchyma found in the lotus stem. It is parenchyma with large intercellular air spaces. Its function is to store air, providing buoyancy (ability to float on water) and allowing the plant to remain upright in water. It also facilitates the transport of oxygen from the air to the submerged parts of the plant.
Answer: The thick waxy cuticle on the cactus epidermis is an adaptation to prevent water loss through the surface (cuticular transpiration), since the cactus lives in a dry desert with very little water. Having very few stomata also minimises water loss through stomatal transpiration. These modifications of the epidermal tissue are critical for the cactus to survive in arid conditions.
Answer: Parenchyma is the tissue primarily responsible for water storage in the cactus stem. The parenchyma cells in the succulent stem of a cactus have large vacuoles that store large quantities of water (mucilage), acting as a water reservoir for dry periods.
Answer: Sclerenchyma. Cactus spines are hard and rigid, which is characteristic of sclerenchyma — dead cells with heavily lignified, thickened walls. Sclerenchyma provides maximum mechanical strength and rigidity, making the spines suitable for protecting the plant from herbivores and reducing surface area to minimise water loss. Visit the simple permanent tissue page for more on sclerenchyma.
Ravi is a 14-year-old football player who injured his knee during a match. An MRI scan revealed that he had torn his anterior cruciate ligament (ACL) and damaged the cartilage at the end of his femur (thigh bone). The doctor told him that the ligament would need surgical repair and that the cartilage damage would heal very slowly on its own since cartilage has a very poor blood supply and limited ability to regenerate.
Answer: A ligament is a type of dense fibrous connective tissue. It connects bone to bone at a joint. In the knee, the ACL connects the femur (thigh bone) to the tibia (shin bone), preventing the tibia from sliding forward and stabilising the knee joint during movement.
Answer: Cartilage heals slowly because it is avascular (lacks blood vessels). Nutrients and oxygen reach chondrocytes (cartilage cells) only by diffusion through the matrix — a slow process that limits the rate of repair and regeneration. The matrix of cartilage is made of chondroitin sulphate (a glycosaminoglycan), a firm, gel-like substance that gives cartilage its characteristic resilience and smooth, slippery surface for reducing friction at joints.
Answer:
1. Ear pinna (auricle): Elastic cartilage gives the ear its flexible shape and allows it to be bent without breaking.
2. Trachea (windpipe): C-shaped rings of hyaline cartilage in the trachea wall prevent the airway from collapsing during breathing, keeping the passage open for airflow.
Answer: Both ligament and tendon are types of dense fibrous connective tissue composed mainly of closely packed collagen fibres. They are both very strong and can withstand large tensile (pulling) forces. Since the primary requirement for an ACL replacement is high tensile strength to stabilise the joint, a tendon graft can functionally substitute for the ligament, even though tendons (collagen fibres only) are slightly less elastic than ligaments (which also contain some elastic fibres).
A 55-year-old man is admitted to hospital after suffering a heart attack (myocardial infarction). The doctor explains that a blood clot blocked one of the coronary arteries, cutting off the blood supply to a region of the heart muscle (myocardium). Unlike skeletal muscle or the liver, which can regenerate to some extent, the heart muscle that is damaged is permanently lost and replaced by scar tissue (fibrous connective tissue). The doctor says that the patient's left arm was also feeling numb and weak — a common symptom during a heart attack, known as referred pain.
Answer: Cardiac muscle tissue forms the myocardium. Two structural features that distinguish it from skeletal muscle:
1. Cardiac muscle cells are branched (Y-shaped), while skeletal muscle fibres are straight and cylindrical.
2. Cardiac muscle cells have intercalated discs (specialised junctions between cells) that allow electrical impulses to spread rapidly from cell to cell; skeletal muscle cells are independent and lack these. See muscular tissue for details.
Answer: Cardiac muscle cells (cardiomyocytes) are highly differentiated and have almost no capacity to divide and regenerate after injury in adult humans. When cardiac muscle cells die due to oxygen deprivation (ischaemia), they are replaced by non-contractile fibrous scar tissue, permanently reducing the heart's pumping efficiency.
Skeletal muscle has satellite cells (muscle stem cells) that can divide and fuse to form new muscle fibres to repair damaged muscle to some extent. The heart lacks a comparable pool of stem cells, making cardiac damage largely irreversible.
Answer: The nerves carrying these signals are made of nervous tissue. The specific cells that transmit electrical impulses are neurons (nerve cells). In this case, sensory neurons carry impulses from the heart and left arm region to the brain, which interprets the signals as arm pain — a phenomenon known as referred pain (pain felt in a different location from its source).
Answer: Scar tissue is fibrous connective tissue (dense collagenous connective tissue). It is unable to perform the functions of cardiac muscle because:
1. Connective tissue cells (fibroblasts) do not contain the contractile proteins actin and myosin, so they cannot contract and generate the force needed to pump blood.
2. Scar tissue is not electrically excitable — it cannot generate or conduct electrical impulses that coordinate the heartbeat.
3. It lacks the intercalated discs that allow cardiac muscle cells to work as a coordinated unit.
Thus, scar tissue restores structural integrity to the damaged region but permanently reduces the heart's contractile power.
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