Class 9 Science | Chapter 3 | Worksheet | Extra Questions | NCERT Biology
Tissues in Action Class 9 — Worksheet with Answers
Comprehensive practice worksheet for Class 9 Science Chapter 3: Tissues in Action. Includes Fill in the Blanks, True or False, Match the Following, Assertion-Reason, HOTS, Diagram Labelling, and Short Answer questions — all with a complete answer key. Covers meristematic tissue, permanent tissues, xylem and phloem, epithelial, connective, muscular, and nervous tissue. Aligned with CBSE 2026–27.
Fill in Blanks · True/False · Match
Assertion-Reason · HOTS · Diagrams
Complete Answer Key
Complete Practice Worksheet | All Question Types | CBSE Pattern | Reading Time: 35 minutes
Practice and reinforce your understanding of the Tissues in Action chapter with this comprehensive worksheet. Attempt all sections in your notebook and check your answers at the end. For detailed explanations, visit the Tissues Q&A page and for objective practice, see the Tissues MCQ page.
Instructions
- Attempt all questions in your notebook before checking the answer key
- For diagram labelling, draw the diagram and label all indicated parts
- For Assertion-Reason, use the standard four-option code given in Section F
- Time yourself: aim to complete the full worksheet in 50–60 minutes
- Review the relevant concept pages for any topic you find difficult
Section A: Fill in the Blanks
Complete each sentence with the correct word or phrase. (25 questions)
- A group of cells that are similar in structure, origin, and function is called a __________.
- The tissue responsible for the growth of plants is __________ tissue.
- Meristematic tissue located at the tips of roots and shoots is called __________ meristem.
- The meristem located between the nodes of a stem or at the base of a leaf is called __________ meristem.
- The meristem responsible for the increase in girth (secondary growth) in dicot stems is called __________ meristem.
- The process by which meristematic cells mature and become specialised permanent cells is called __________.
- Parenchyma tissue found in aquatic plants, which has large intercellular air spaces for buoyancy, is called __________.
- Parenchyma containing chloroplasts and performing photosynthesis is called __________.
- The simple permanent tissue that provides flexible mechanical support and has living cells with unevenly thickened walls at the corners is __________.
- The simple permanent tissue with dead cells and uniformly lignified walls is __________. It is used commercially in making ropes from __________ and __________ plants.
- The two complex permanent tissues in plants are __________ and __________.
- In xylem, the main water-conducting dead cells are __________ and __________.
- The living cells in phloem that assist sieve tube elements are called __________ cells.
- The outermost protective layer of a plant body is formed by __________ tissue. In older woody stems, this is replaced by __________ (cork).
- Stomata are surrounded by specialised cells called __________ cells that control their opening and closing.
- The four types of animal tissue are __________, __________, __________, and __________.
- The tissue that lines the inner surface of the intestine and is involved in absorption of digested food is __________ epithelium.
- Stratified squamous epithelium forms the outer layer of the skin and is also known as the __________.
- The connective tissue that connects muscle to bone is called __________, while the tissue that connects bone to bone is called __________.
- The three types of muscular tissue are __________ (skeletal), __________ (smooth), and __________ muscle.
- Striated muscle tissue is under __________ control, while smooth muscle is under __________ control.
- The structural and functional unit of the nervous system is the __________ (nerve cell).
- Short branched extensions of the neuron that receive impulses are called __________, while the single long fibre that carries impulses away from the cell body is called the __________.
- The fatty insulating sheath around a neuron's axon that speeds up nerve impulse conduction is called the __________ sheath.
- The gap between two adjacent neurons across which a nerve impulse is transmitted chemically is called a __________.
Section B: True or False
Write T for true and F for false. If false, write the corrected statement. (20 statements)
- Meristematic cells have large central vacuoles and thin cell walls.
- Intercalary meristem allows grasses to regrow quickly after being grazed or mowed.
- Collenchyma cells are dead at maturity with uniformly thickened lignified walls.
- Sclerenchyma provides rigid mechanical support and is responsible for the hardness of the coconut husk and nut shells.
- Xylem parenchyma is the only living component of xylem tissue.
- Phloem transports water and dissolved minerals from the roots to the leaves.
- Sieve tube elements in phloem are alive and possess a nucleus at maturity.
- The epidermis of plant roots secretes a waxy cuticle to prevent water loss.
- Plants need more maintenance energy than animals because all their cells are living.
- Cork (bark) is formed by the lateral meristem called cork cambium, and its cells are dead and filled with a waxy substance called suberin.
- Squamous epithelium lining the alveoli is very thin to facilitate rapid gas exchange.
- Stratified squamous epithelium forms a single layer and lines the mouth and oesophagus.
- Adipose tissue stores fat and acts as an insulator preventing heat loss from the body.
- Tendons are elastic and stretchy because they contain yellow elastic fibres.
- Cartilage has a rich blood supply, which is why it heals quickly after injury.
- Cardiac muscle is striated, involuntary, and found only in the wall of the heart.
- Skeletal (striated) muscle is under voluntary control and can contract very rapidly but fatigues easily.
- Dendrites carry nerve impulses away from the cell body of a neuron, and the axon brings impulses towards it.
- Neurons can regenerate and replace themselves easily after injury, unlike most other cells in the body.
- Blood is considered a connective tissue because its cells are suspended in a fluid matrix called plasma, connecting and serving all organs of the body.
Section C: Match the Following
Match each item in Column A with the correct item in Column B. (4 sets)
Set 1: Plant Tissue Type and Its Key Feature
| Column A (Tissue) |
Column B (Feature) |
| 1. Apical meristem | A. Dead cells; uniformly lignified walls; provides rigidity |
| 2. Parenchyma | B. Found at tips of roots and shoots; increases length |
| 3. Collenchyma | C. Living cells; large vacuoles; stores food and water |
| 4. Sclerenchyma | D. Conducts food; made of sieve tubes and companion cells |
| 5. Xylem | E. Living cells; unevenly thickened at corners; flexible support |
| 6. Phloem | F. Conducts water; contains dead tracheids and vessels |
Set 2: Animal Tissue Type and Its Location
| Column A (Tissue) |
Column B (Location) |
| 1. Ciliated columnar epithelium | A. Beneath the skin; around kidneys and bone marrow |
| 2. Squamous epithelium | B. Wall of the heart (myocardium) |
| 3. Adipose tissue | C. Lining of mouth and oesophagus; walls of alveoli |
| 4. Hyaline cartilage | D. Lining of respiratory tract; moves mucus |
| 5. Cardiac muscle | E. Attached to bones; controls body movements |
| 6. Skeletal muscle | F. Ends of long bones at joints; rings in trachea |
Set 3: Term and Its Definition
| Column A (Term) |
Column B (Definition / Description) |
| 1. Differentiation | A. Fatty insulating layer around the axon |
| 2. Aerenchyma | B. Junction between two neurons for chemical signal transfer |
| 3. Lignin | C. Parenchyma with large air spaces; found in aquatic plants |
| 4. Cutin | D. Hard polymer deposited in sclerenchyma and xylem walls |
| 5. Myelin sheath | E. Waxy substance forming the cuticle on aerial epidermal cells |
| 6. Synapse | F. Process by which meristematic cells become permanent cells |
Set 4: Connective Tissue Type and Its Composition / Function
| Column A (Tissue) |
Column B (Composition / Function) |
| 1. Blood | A. Connects bone to bone; yellow elastic fibres + collagen |
| 2. Bone | B. Rigid matrix of calcium phosphate and collagen (ossein) |
| 3. Ligament | C. Fluid matrix (plasma) with RBCs, WBCs, and platelets |
| 4. Tendon | D. Semi-rigid matrix of chondroitin sulphate; avascular |
| 5. Cartilage | E. Connects muscle to bone; white collagen fibres; inelastic |
| 6. Areolar tissue | F. Loose connective tissue filling spaces between organs; site of repair |
Section D: Match the Column (Advanced)
Each item in Column A may match with one or more items in Column B. Write all correct matches. (2 sets)
Set 1: Tissue Type and Its Characteristics (Multiple Matches)
| Column A (Tissue) |
Column B (Characteristics) |
| 1. Meristematic tissue | A. Cells are dead at maturity |
| 2. Sclerenchyma | B. Cells actively divide |
| 3. Xylem vessels | C. Dense cytoplasm; no vacuole |
| 4. Parenchyma | D. Walls contain lignin |
| E. Living cells with large vacuoles |
| F. Provides mechanical support |
| G. Stores food materials |
Set 2: Muscle Tissue Type and Its Features (Multiple Matches)
| Column A (Muscle Type) |
Column B (Features) |
| 1. Skeletal (striated) muscle | A. Involuntary |
| 2. Smooth (unstriated) muscle | B. Voluntary |
| 3. Cardiac muscle | C. Has striations (alternate light and dark bands) |
| D. Spindle-shaped uninucleate cells |
| E. Branched cells; never fatigues |
| F. Multinucleate (many nuclei per fibre) |
| G. Found in walls of blood vessels and digestive tract |
Section E: Label the Diagram
Use the word bank to label the indicated parts in each diagram. Draw the diagram in your notebook and label it.
Diagram 1: Structure of a Neuron
Label parts 1–6 of the neuron diagram below.
Word Bank: Axon | Cell body (Cyton) | Dendrites | Myelin sheath | Nucleus | Axon terminals (Synaptic knobs)
1. _____________________ 2. _____________________ 3. _____________________
4. _____________________ 5. _____________________ 6. _____________________
Diagram 2: Transverse Section (T.S.) of a Sunflower Stem
Label parts 1–6 of the sunflower stem T.S. diagram below.
Word Bank: Epidermis | Collenchyma | Cortex (Parenchyma) | Phloem | Xylem | Pith (Medulla)
1. _____________________ 2. _____________________ 3. _____________________
4. _____________________ 5. _____________________ 6. _____________________
Section F: Assertion-Reason Questions
Each question contains an Assertion (A) and a Reason (R). Choose the correct option from the codes 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.
AR1.
Assertion (A): Plants need much less maintenance energy than animals.
Reason (R): A large proportion of the plant body is made up of dead cells, which do not require metabolic energy for their upkeep.
Answer: __________
AR2.
Assertion (A): Grass regrows quickly after being mowed or grazed.
Reason (R): Grasses have apical meristem at the tips of their shoots that remains unharmed when the upper portions are cut.
Answer: __________
AR3.
Assertion (A): Cork (bark) makes an excellent insulating and waterproofing material.
Reason (R): Cork cells are dead and their walls are impregnated with a waxy substance called suberin, which makes them impermeable to water and gases.
Answer: __________
AR4.
Assertion (A): The alveoli (air sacs) in the lungs are lined with squamous epithelium.
Reason (R): Squamous epithelium consists of flat, thin cells that minimise the diffusion distance for gases, allowing rapid exchange of oxygen and carbon dioxide.
Answer: __________
AR5.
Assertion (A): Blood is classified as a connective tissue.
Reason (R): All connective tissues must have a solid, fibrous matrix.
Answer: __________
AR6.
Assertion (A): Cardiac muscle can sustain rhythmic contraction throughout a person's life without fatigue.
Reason (R): Cardiac muscle cells are branched and connected by intercalated discs, allowing impulses to spread across the entire heart rapidly, and their metabolism is adapted for continuous aerobic activity.
Answer: __________
AR7.
Assertion (A): Cartilage heals very slowly after injury.
Reason (R): Cartilage is avascular (has no blood vessels), so nutrients and repair cells can only reach chondrocytes by slow diffusion through the matrix.
Answer: __________
AR8.
Assertion (A): Xylem is called a complex permanent tissue.
Reason (R): Xylem is made up of more than one type of cell (tracheids, vessels, parenchyma, and fibres) that work together as a functional unit.
Answer: __________
Section G: Higher Order Thinking Skills (HOTS)
These questions require careful reasoning and application. Stop and think before answering.
HOTS 1 (Conceptual)
A gardener girdled (removed a complete ring of bark from) a tree trunk. After several weeks, she observed a bulging swelling of tissue just above the girdle, while the part of the tree below the girdle gradually withered. Explain this observation in terms of the tissues involved. Which tissue was cut? Which tissue remained functional? What accumulated above the cut and why?
Write your answer: _______________________________________________
HOTS 2 (Application)
Ramesh notices that the stems of young herbaceous plants (like grass and spinach) are flexible and bend without breaking, whereas the stems of woody plants (like oak and teak) are stiff and rigid. Explain this difference in terms of the types of permanent tissue present in each stem.
Write your answer: _______________________________________________
HOTS 3 (Analysis)
A scientist found that the root cells of a plant can be induced to grow into a complete new plant when placed on a suitable growth medium. This suggests that even differentiated cells can regain the ability to divide. What does this tell you about plant cells compared to most animal cells? What is the term for this ability of plant cells?
Write your answer: _______________________________________________
HOTS 4 (Reasoning)
A patient suffers damage to only the motor neurons in her spinal cord but her sensory neurons are intact. Predict: (a) Can she feel pain if you pinch her hand? (b) Can she voluntarily move her fingers? (c) Will her heart still beat? Give a reason for each answer.
Write your answer: _______________________________________________
HOTS 5 (Evaluation)
Sieve tube cells in phloem are living cells that conduct food, yet they have no nucleus at maturity. How can a cell without a nucleus remain alive and functional? What structure compensates for the lack of a nucleus in sieve tube cells?
Write your answer: _______________________________________________
HOTS 6 (Cross-Concept)
Both collenchyma and sclerenchyma provide mechanical support to plants, yet plants have both. Why are two separate tissue types needed for mechanical support? Under what specific conditions would collenchyma be more suitable than sclerenchyma?
Write your answer: _______________________________________________
Section H: Short Answer Practice
Answer each question in 3–5 sentences. (5 questions)
SA1. Name the tissue that forms the outer covering (bark) of old trees. How is this tissue different from the epidermis of young herbaceous plants? (2 marks)
Your answer: _____________________________________________________
_________________________________________________________________
SA2. You observe two muscle samples under a microscope. Sample X has long cylindrical cells with many nuclei and clear alternating bands. Sample Y has spindle-shaped cells with a single central nucleus and no visible bands. Name the muscle types and state one location where each is found. (2 marks)
Your answer: _____________________________________________________
_________________________________________________________________
SA3. Jute fibres used to make sacks and ropes come from the stem of the jute plant. Name the plant tissue from which jute fibre is obtained and explain what makes it so strong and durable. (2 marks)
Your answer: _____________________________________________________
_________________________________________________________________
SA4. A doctor tells a patient: "Your ACL (anterior cruciate ligament) is torn; it will need surgery. The cartilage damage in your knee will take much longer to heal on its own." Why would cartilage take longer to heal than other tissues? Name two properties of cartilage that explain this. (2 marks)
Your answer: _____________________________________________________
_________________________________________________________________
SA5. Why is a multicellular organism more efficient at performing life processes than a unicellular organism? How do tissues contribute to this efficiency? (2 marks)
Your answer: _____________________________________________________
_________________________________________________________________
Answer Key — All Sections
Attempt the worksheet fully before checking answers.
Section A — Fill in the Blanks: Answers
- Tissue
- Meristematic
- Apical meristem
- Intercalary meristem
- Lateral meristem (vascular cambium / cork cambium)
- Differentiation
- Aerenchyma
- Chlorenchyma
- Collenchyma
- Sclerenchyma; commercially important from jute and flax (linen) plants
- Xylem and Phloem
- Tracheids and vessel elements (tracheae)
- Companion cells
- Epidermis; replaced by cork (periderm)
- Guard cells
- Epithelial tissue, Connective tissue, Muscular tissue, Nervous tissue
- Columnar epithelium (with microvilli / brush border)
- Epidermis (stratified squamous epithelium)
- Tendon (muscle to bone); Ligament (bone to bone)
- Striated (skeletal); Smooth (unstriated); Cardiac muscle
- Voluntary control; involuntary control
- Neuron (nerve cell)
- Dendrites (receive); Axon (carries away)
- Myelin sheath
- Synapse
Section B — True or False: Answers
- False. Meristematic cells have dense cytoplasm, a prominent nucleus, thin cellulose walls, and no (or very small) vacuoles. Large central vacuoles are a feature of permanent parenchyma cells.
- True. Intercalary meristem is located at the base of internodes and leaf blades in grasses; mowing removes the top but leaves this meristem intact to regenerate the leaf.
- False. Collenchyma cells are living and have walls thickened unevenly at the corners with cellulose. It is sclerenchyma that has dead cells with uniformly thick, lignified walls.
- True. Sclerenchyma fibres (dead, heavily lignified cells) form the tough outer husk of coconut and the hard inner shell; also found in seed coats.
- True. Xylem parenchyma cells are the only living cells in xylem. They store starch and fats and assist in lateral water transport.
- False. Phloem transports prepared food (sucrose) from leaves to all parts of the plant. Xylem conducts water and dissolved minerals from roots upward to leaves.
- False. Sieve tube elements are living but they lose their nucleus at maturity. Their metabolic functions are maintained by the companion cells that remain nucleated.
- False. Root epidermis does not secrete a cuticle — it needs to remain permeable for water absorption. The cuticle (made of cutin) is secreted by the aerial parts (stem and leaf) epidermis to prevent water loss.
- False. Plants need less maintenance energy than animals because a large proportion of their body is dead tissue (sclerenchyma, xylem vessels) that requires no metabolic energy.
- True. Cork cambium (phellogen) is a lateral meristem that produces cork. Cork cells are dead, and their walls are impregnated with suberin, a waxy lipid that makes them impermeable to water and gases.
- True. Simple squamous epithelium is a single layer of very thin, flat cells — ideal for rapid diffusion of oxygen into and carbon dioxide out of the blood in alveoli.
- False. Stratified squamous epithelium has multiple layers of cells (not a single layer). Simple squamous epithelium is a single layer. Stratified squamous epithelium lines the skin, mouth, and oesophagus where protection from abrasion is needed.
- True. Adipose cells (adipocytes) store fat in large droplets. The fat layer under the skin acts as a thermal insulator, and fat around organs cushions them from mechanical shock.
- False. Ligaments contain yellow elastic fibres and are stretchy, allowing some movement at joints. Tendons are made of white collagen fibres only and are inelastic, transmitting muscle force efficiently to bones.
- False. Cartilage is avascular (has no blood vessels). This is precisely why it heals slowly — nutrients can only reach cells (chondrocytes) by diffusion through the matrix, which is a slow process.
- True. Cardiac muscle is striated (faint bands) and involuntary (under autonomic nervous system control), and it is found exclusively in the myocardium (heart wall).
- True. Skeletal (striated) muscle is under somatic/voluntary nervous control; it can contract very rapidly (fast-twitch fibres) but accumulates lactic acid and fatigues with prolonged use.
- False. It is the opposite: dendrites bring impulses towards the cell body; the axon carries impulses away from the cell body.
- False. Neurons have very limited capacity for regeneration. In the peripheral nervous system some regeneration is possible, but neurons in the central nervous system (brain and spinal cord) can rarely regenerate after injury. This is why spinal cord injuries are often permanent.
- True. Blood has a fluid matrix (plasma) in which cells are suspended — this is the defining feature of connective tissue (cells + non-living matrix). Blood "connects" all organs by transporting oxygen, nutrients, hormones, and waste products.
Section C — Match the Following: Answers
Set 1: 1–B, 2–C, 3–E, 4–A, 5–F, 6–D
Set 2: 1–D, 2–C, 3–A, 4–F, 5–B, 6–E
Set 3: 1–F, 2–C, 3–D, 4–E, 5–A, 6–B
Set 4: 1–C, 2–B, 3–A, 4–E, 5–D, 6–F
Section D — Match the Column (Advanced): Answers
Set 1 — Tissue Characteristics:
- 1. Meristematic tissue → B, C (cells actively divide; dense cytoplasm with no vacuole)
- 2. Sclerenchyma → A, D, F (dead at maturity; walls contain lignin; provides mechanical support)
- 3. Xylem vessels → A, D, F (dead at maturity; lignified walls; provide mechanical support and water conduction)
- 4. Parenchyma → E, G (living cells with large vacuoles; stores food materials)
Set 2 — Muscle Tissue Features:
- 1. Skeletal (striated) muscle → B, C, F (voluntary; has striations; multinucleate fibres)
- 2. Smooth (unstriated) muscle → A, D, G (involuntary; spindle-shaped uninucleate cells; found in blood vessels and digestive tract)
- 3. Cardiac muscle → A, C, E (involuntary; has faint striations; branched cells that never fatigue)
Section E — Label the Diagram: Answers
Diagram 1: Neuron (in order from receiving to transmitting end)
1. Dendrites 2. Cell body (Cyton) 3. Nucleus 4. Axon 5. Myelin sheath 6. Axon terminals (Synaptic knobs)
Diagram 2: Sunflower Stem T.S. (outside to inside)
1. Epidermis 2. Collenchyma 3. Cortex (Parenchyma) 4. Phloem 5. Xylem 6. Pith (Medulla)
Refer to plant tissue systems and nervous tissue for fully labelled diagrams.
Section F — Assertion-Reason: Answers
- AR1 → (a) Both A and R are true and R correctly explains A. Dead cells (sclerenchyma, xylem) require no metabolic energy, reducing the plant's maintenance energy needs.
- AR2 → (c) A is true but R is false. It is the intercalary meristem (at the base of internodes/leaves) — not the apical meristem — that remains uncut and allows rapid grass regrowth.
- AR3 → (a) Both A and R are true and R correctly explains A. Suberin-impregnated dead cork cells are waterproof and gas-impermeable, making cork an excellent insulator and sealant.
- AR4 → (a) Both A and R are true and R correctly explains A. Simple squamous epithelium's single layer of thin flat cells creates the minimum barrier between alveolar air and blood, facilitating rapid gas diffusion.
- AR5 → (c) A is true but R is false. Blood is correctly classified as connective tissue (A is true) because cells are suspended in a non-living matrix (plasma). However, R is false — connective tissue does NOT need a solid fibrous matrix; the matrix can be fluid (plasma in blood), semi-solid (chondroitin in cartilage), or solid (calcium salts in bone).
- AR6 → (a) Both A and R are true and R correctly explains A. Intercalated discs enable rapid electrical coupling across the entire heart, and cardiac muscle is rich in mitochondria adapted for sustained aerobic metabolism.
- AR7 → (a) Both A and R are true and R correctly explains A. Cartilage is avascular; without a blood supply, healing depends entirely on slow diffusion through the matrix, greatly limiting repair speed.
- AR8 → (a) Both A and R are true and R correctly explains A. Xylem contains four different cell types (tracheids, vessels, parenchyma, fibres) working as one unit — the definition of a complex tissue.
Section G — HOTS: Answers
HOTS 1 (Girdling): The bark contains phloem, which was destroyed by the girdle. Xylem (wood) inside the bark remained intact. Leaves continued to photosynthesise and produced food (sucrose), but since phloem was cut, the food could not be transported downward past the girdle. The excess sucrose accumulated just above the girdle, causing a swelling of living tissue (callus). The roots were starved of food, died, and could no longer absorb water — eventually killing the tree. This elegantly proves that phloem is the food-conducting tissue and xylem is the water-conducting tissue. See xylem and phloem notes.
HOTS 2 (Stem flexibility): Young herbaceous stems are flexible because they contain mainly collenchyma — living cells with unevenly thickened cellulose walls at the corners that allow bending and stretching without breaking. They also lack secondary growth. Woody stems of older dicots undergo secondary growth, accumulating large amounts of sclerenchyma (and secondary xylem/wood) with dead, uniformly and heavily lignified walls. Lignin is rigid and insoluble, making the stem hard and inflexible. Additionally, in woody stems, a thick bark (cork) replaces the epidermis, adding further rigidity. See simple permanent tissue.
HOTS 3 (Plant totipotency): This ability shows that plant cells are totipotent — a differentiated plant cell retains the full genetic information to develop into a complete organism when given the right conditions. Unlike most animal cells, which permanently lose this ability after differentiation, plant cells can de-differentiate (regain the ability to divide) and then re-differentiate to form an entire new plant. The term for this is totipotency. This property is used in tissue culture technology to propagate plants commercially on a large scale.
HOTS 4 (Motor neuron damage): (a) Yes, she can feel pain — sensory neurons are intact; they carry pain signals from the skin to the brain. (b) No, she cannot voluntarily move her fingers — motor neurons carry signals from the brain to skeletal muscles; these are damaged, so the muscle cannot receive the command to contract. (c) Yes, her heart will still beat — cardiac muscle is controlled by the autonomic nervous system (involuntary) via the sinoatrial node, not via somatic motor neurons in the spinal cord. Damage to somatic motor neurons does not affect the heart's automatic rhythm. See nervous tissue and muscular tissue.
HOTS 5 (Sieve tube without nucleus): Sieve tube cells lose their nucleus at maturity to maximise space for food flow through the sieve pores. They can remain alive because their metabolic functions (protein synthesis, energy production) are carried out by the adjacent companion cells, which are nucleated and connected to sieve tubes by numerous plasmodesmata (cytoplasmic channels). The companion cells essentially act as the "control centre" for the sieve tubes, supplying ATP and proteins needed for their function. This is a remarkable example of division of labour at the cellular level within a single tissue.
HOTS 6 (Two support tissues): The two tissues serve different mechanical needs: Sclerenchyma provides maximum, permanent, rigid support — ideal for parts that will not grow further and need to withstand large compressive or tensile forces (stems, seed coats, nut shells). However, since it is dead, it cannot expand or change shape. Collenchyma provides flexible, living support — ideal for young, growing regions that need to bend (petioles, young stems, the periphery of growing parts). Because collenchyma cells are alive, they can expand as the plant grows, whereas sclerenchyma cannot. If sclerenchyma were the only support tissue, a growing stem's rigid dead cells would crack and break as it tried to elongate. Collenchyma is therefore specifically suited to regions undergoing active growth and movement. See simple permanent tissue.
Section H — Short Answer Practice: Answers
SA1. The outer covering of old tree trunks is formed by cork (periderm), produced by the cork cambium (phellogen — a lateral meristem). Cork cells are dead, impermeable to water and gases (walls impregnated with suberin), and form a thick protective bark. The epidermis of young herbaceous plants is a single layer of living cells that secretes a thin waxy cuticle. As the tree grows in girth, the epidermis tears and is replaced by the thicker, tougher, multi-layered cork. See meristematic tissue.
SA2. Sample X is striated (skeletal) muscle — its long cylindrical multinucleate fibres with alternating dark and light bands (striations) are characteristic of this tissue. It is found attached to bones (e.g., biceps, quadriceps). Sample Y is smooth (unstriated) muscle — spindle-shaped, uninucleate cells with no visible bands; found in walls of internal organs such as the intestine, stomach, and blood vessels. See muscular tissue.
SA3. Jute fibre is obtained from sclerenchyma (specifically phloem fibres / bast fibres in the phloem region of the jute stem). Sclerenchyma cells are dead at maturity with uniformly thick, heavily lignified walls. Lignin is an extremely tough, rigid, water-insoluble polymer that makes the cell wall almost unbreakable. The fibres are long, narrow, and arranged in bundles, giving jute its exceptional tensile strength. This makes it ideal for ropes, sacks, and coarse textiles. See simple permanent tissue.
SA4. Cartilage heals slowly for two main reasons: (i) Avascularity — cartilage has no blood vessels; nutrients and repair cells can only reach chondrocytes (cartilage cells) by slow diffusion through the semi-solid matrix. Without a blood supply, the rate of nutrient and oxygen delivery is extremely limited, slowing all repair processes. (ii) Low cell density and mitotic activity — chondrocytes are sparse and divide very slowly under normal conditions; the capacity for regenerative cell division is much lower than in well-vascularised tissues like bone or muscle. See connective tissue.
SA5. A multicellular organism is more efficient because it practises division of labour — different cells specialise in different functions, performing each function much more efficiently than a single cell that must do everything. Tissues contribute to this by grouping similar specialised cells together so that they can perform their specific function collectively and continuously (e.g., all muscle cells in a tissue contract together to produce force; all neurons in a nerve carry signals rapidly in one direction). This allows complex functions like digestion, circulation, immunity, and locomotion to occur simultaneously. A unicellular organism like Amoeba must perform all functions — feeding, excretion, movement, reproduction — with a single cell, limiting its complexity and efficiency. See Tissues in Action notes.
Explore More: Tissues in Action — Chapter 3
