Tissues in Action — Class 9 Science
Exploration · Chapter 3
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Chapter summary
Key ideas & terms
- Meristematic tissue
- Tissue of small, thin-walled, dividing cells with dense cytoplasm and no vacuole, responsible for plant growth.
- Differentiation
- The process by which dividing meristematic cells become specialised permanent cells for support, transport or storage.
- Xylem and phloem
- Complex permanent (vascular) tissues — xylem carries water and minerals upward, phloem carries food made in leaves to the rest of the plant.
- Epithelial tissue
- Animal tissue forming the outer covering of the body and the lining of internal organs; cells are closely packed.
- Connective tissue
- Tissue that connects and supports other tissues (blood, bone, cartilage, tendons, ligaments); cells lie in a matrix.
- Neuron
- The cell of nervous tissue, with a cell body, dendrites and an axon, specialised to receive and transmit messages.
- Musculoskeletal system
- The system of bones, muscles, joints, cartilage, tendons and ligaments that supports the body and produces movement under nervous control.
Extra questions & answers
Why are plant and animal tissues different?
Plants are mostly fixed and make their own food, so they need rigid, cell-walled supporting and conducting tissues; animals move and ingest food, so their flexible cells form tissues suited to locomotion, digestion and rapid response.
Name the three types of meristematic tissue and what each does.
Apical meristem (root and shoot tips) increases length, lateral meristem (a ring in the stem) increases girth and forms annual rings, and intercalary meristem (base of internodes) lets grasses regrow after being cut or grazed.
What is differentiation in plants?
It is the process by which newly formed meristematic cells lose the ability to divide and become specialised permanent cells that perform specific functions such as support, transport or storage.
Compare parenchyma, collenchyma and sclerenchyma.
Parenchyma has thin-walled living cells that store food and can photosynthesise; collenchyma has cells thickened at the corners giving flexible support; sclerenchyma has thick lignified, mostly dead cells giving hard rigid strength like in coconut husk.
How do xylem and phloem differ in function?
Xylem transports water and minerals from roots upward and gives strength (mostly dead cells), while phloem transports food from leaves to other parts and is mainly made of living cells like sieve tubes and companion cells.
List the four types of animal tissue.
Epithelial (covering and lining), connective (joining and supporting), muscular (producing movement) and nervous (control and coordination) tissues.
Why is blood considered a connective tissue?
Its cells (RBCs, WBCs, platelets) are suspended in a fluid matrix called plasma, and it connects body parts by transporting nutrients, gases and wastes, which is the defining role of connective tissue.
Distinguish the three kinds of muscle.
Skeletal muscle is striated, multinucleate and voluntary (moves the skeleton); smooth muscle is spindle-shaped, single-nucleus and involuntary (gut, blood vessels); cardiac muscle is branched, striated and involuntary, beating tirelessly in the heart.
Name the parts of a neuron and their roles.
The cell body holds the nucleus and controls activities, dendrites receive signals from other neurons, and the long axon carries messages away, ending at axon terminals that pass them to other cells.
Match each joint type with a movement: shoulder, elbow, neck, skull.
The shoulder is a ball-and-socket joint (movement in all directions), the elbow is a hinge joint (one direction), the neck has a pivot joint (side-to-side turning), and the skull bones have fixed joints (no movement, protecting the brain).
Think It Over
How is the study of cells and tissues significant for understanding the life processes and human welfare?
Studying cells and tissues helps us understand how living bodies are built, how they grow, repair and carry out functions like protection, support, transport and coordination. This knowledge is useful for human welfare in medicine, such as understanding diseases, healing wounds, growing plants by tissue culture, and developing treatments, and in agriculture for improving crops.
How are tissues in plants and animals different, and why?
Plant and animal tissues differ because their lifestyles differ. Plants are stationary and need rigid support, so they have tissues with cell walls, and growth tissues that allow continuous growth in length and girth. Animals can move, so they have flexible tissues without cell walls, and more tissues for movement, sensitivity and transport of food after digestion. Differences in nutrition, locomotion and growth pattern make their tissues structurally and functionally distinct.
How is the division of labour at various levels of organisation in multicellular organisms correlated with their structure and function?
In multicellular organisms division of labour means different groups of cells do different jobs. At the tissue level, cells with similar structure perform a common function, such as muscle for contraction. Different tissues form organs for larger functions, and organs form organ systems, and systems form the organism. Structure suits function at each level, so the whole body works efficiently and can carry out complex life processes.
Pause and Ponder
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.
Coconut husk fibres are made mostly of sclerenchyma tissue. Its cells have thick walls with lignin, are usually dead at maturity, and provide hardness and strength. Coriander leaf stalks contain mainly parenchyma and collenchyma, which are living cells with thin or only corner-thickened pectin walls, giving softness and flexibility without brittleness.
Pause and Ponder
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?
In desert plants a thick waxy cuticle reduces water loss by transpiration, protects against heat, mechanical injury and microbes, which is advantageous. Underwater the plant needs to exchange gases and absorb water directly through the surface; a thick waterproof cuticle would block this exchange and is therefore disadvantageous.
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?
Xylem vessels and tracheids are dead, hollow, thick-walled tubes that form a continuous pipeline with low resistance. Living leaf cells lose water by transpiration through stomata, creating a suction or transpiration pull. Cohesion between water molecules and adhesion to walls helps the column stay continuous, so the pull from above draws water up through the dead xylem elements.
4. What do you think will happen if there were no stomata in the epidermis of the stem or leaves?
Without stomata, gaseous exchange for photosynthesis and respiration would be severely reduced, transpiration and the resulting transpiration pull for water transport would stop, and cooling and removal of excess water would fail. The plant would overheat, wilt, and growth would be hampered.
Pause and Ponder
5. Look at the picture given below (Fig. 3.17). Carefully observe the various poses of classical and folk dances of India. Can you identify which joints are involved? Also, what type of movement each joint allows?
Dance poses involve multiple joints: shoulder and hip show ball and socket joints allowing rotation in all directions and circular movement; elbow, knee, finger and toe joints show hinge joints allowing bending and straightening in one plane; neck shows a pivot joint allowing rotation of the head side to side; wrist and ankle show partial rotation and gliding. Different classical poses combine these movements to give graceful, flexible expressions.
Think as a Scientist
(a) What do you conclude about the characteristics of phloem cells of carrot?
Phloem cells of carrot are living and retain totipotency. They can dedifferentiate, regain the ability to divide, form an undifferentiated callus, and then redifferentiate into roots, shoots and a complete plant when given suitable nutrients and hormones, showing that differentiated plant cells are not irreversibly committed.
(b) In which of the three combinations would you obtain the highest and lowest biomass? What could be the possible reason(s) for this observation?
Highest biomass is obtained with liquid medium plus nutrients in the presence of light and air, with about
(c) Will you get the same results if you culture animal cells instead of carrot cells?
No, the same result is generally not obtained with typical differentiated animal cells. Most animal cells lack totipotency and do not readily dedifferentiate and regenerate a whole organism under simple nutrient conditions. They need very specific growth factors and even then only stem cells show limited potency, unlike plant phloem cells.
(d) Think and mention any two commercial applications of the study above.
Two applications are micropropagation for rapid production of disease-free, uniform planting material of crops, fruits and ornamentals, and genetic engineering using tissue culture to produce improved or disease-resistant varieties and to produce valuable phytochemicals, vaccines or secondary metabolites in culture.
Revise, Reflect, Refine
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.
Correct option is (iii). Meristematic cells are small, isodiametric, with thin cellulose walls, dense cytoplasm, many organelles, a large prominent nucleus and almost no vacuoles, with little intercellular space, which allows continuous and rapid mitotic division. Thick walls, large vacuoles and differentiation are features of permanent tissues, not meristems.
2. If a plant is unable to transport food from leaves to roots which tissue is malfunctioning? (i) Xylem (ii) Phloem (iii) Epidermis (iv) Sclerenchyma
Correct option is (ii) Phloem. Phloem, composed of sieve tubes with companion cells, transports photosynthates from source leaves to sink organs like roots. Xylem transports water and minerals, epidermis protects, and sclerenchyma provides mechanical support.
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.
Correct option is (iii) To allow quick exchange of materials across them. A single layer of thin, flat cells creates a short diffusion distance for rapid exchange of gases, nutrients and wastes in places like alveoli, capillaries and intestine, while still providing a selective barrier.
4. You can perform these two jumps (Fig. 3.21): 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?
In the straight-leg jump the knees and ankles remain extended and stiff, so the hinge joints bend very little and most push comes from the hips with limited shock absorption, making the jump stiff and lower. In the normal jump the knees and ankles flex and then extend, and the hips also bend, using hinge joints at knee and ankle and ball and socket at hip to store and release energy, giving a higher, smoother jump with cushioning.
5. Which type of joint is involved when you bend your knees and ankles? (i) Ball and socket (ii) Hinge (iii) Pivot
Correct option is (ii) Hinge. Knees and ankles act as hinge joints, allowing movement mainly in one plane like bending and straightening, similar to a door hinge, with the kneecap protecting the knee joint.
6. In each of the following cases (A, B, C and D), choose the correct option as given below: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A). (ii) Both (A) and (R) are true, but (R) is not the correct explanation of (A). (iii) (A) is true, but (R) is false. (iv) (A) is false, but (R) is true. A. Assertion: Epithelium is well-suited for gas exchange in the lungs. Reason: It consists of multiple layers of tall cells that slow down diffusion.
Option (iii) (A) is true, but (R) is false. Lung alveolar epithelium is a single layer of thin flat cells that allows fast diffusion. Multiple layers of tall cells would slow diffusion and is not the structure present there.
6. In each of the following cases (A, B, C and D), choose the correct option as given below: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A). (ii) Both (A) and (R) are true, but (R) is not the correct explanation of (A). (iii) (A) is true, but (R) is false. (iv) (A) is false, but (R) is true. B. Assertion: Cardiac muscle can contract continuously without fatigue. Reason: Cardiac muscle cells have a high number of mitochondria and an abundant blood supply.
Option (i) Both (A) and (R) are true, and (R) is the correct explanation of (A). Cardiac muscle is branched, striated, involuntary and rich in mitochondria with constant blood supply, providing continuous aerobic energy so the heart beats lifelong without fatigue.
6. In each of the following cases (A, B, C and D), choose the correct option as given below: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A). (ii) Both (A) and (R) are true, but (R) is not the correct explanation of (A). (iii) (A) is true, but (R) is false. (iv) (A) is false, but (R) is true. C. Assertion: Tendons connect bone to bone and allow joint movement. Reason: Tendons are made of tough connective tissue that transmits force from muscle to bone.
Option (iv) (A) is false, but (R) is true. Tendons connect muscle to bone, not bone to bone; ligaments connect bone to bone. The reason about tendons transmitting force from muscle to bone is correct, so assertion is false.
6. In each of the following cases (A, B, C and D), choose the correct option as given below: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A). (ii) Both (A) and (R) are true, but (R) is not the correct explanation of (A). (iii) (A) is true, but (R) is false. (iv) (A) is false, but (R) is true. D. Assertion: In a hinge joint, movement occurs primarily in one plane. Reason: The bone ends are shaped to allow sliding in all directions.
Option (iii) (A) is true, but (R) is false. A hinge joint indeed allows movement mainly in one plane like elbow and knee. The reason is false because the articular surfaces are shaped to restrict motion to that plane, not to allow sliding in all directions, which is a feature of ball and socket joints.
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 the Table 3.7. Table 3.7: Data related to the age of a teak tree, and corresponding increase in the diameter of stem and number of annual rings (i) Analyse the graph in terms of the diameter of the stem over time and share the interpretation.
When age in years
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 the Table 3.7. Table 3.7: Data related to the age of a teak tree, and corresponding increase in the diameter of stem and number of annual rings (ii) What is the relation between the diameter of the teak tree to the annual rings formed?
The number of annual rings equals the age in years, and diameter increases in proportion. Each year one new ring is added by the lateral meristem, so a tree with
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 the Table 3.7. Table 3.7: Data related to the age of a teak tree, and corresponding increase in the diameter of stem and number of annual rings (iii) Which specialised tissue is responsible for the girth of the stem and where is it located?
The lateral meristem, mainly the vascular cambium and cork cambium, arranged as a ring along the circumference of the stem between xylem and phloem and in the outer cortex, divides to add cells inside and outside concentrically, increasing girth.
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?
Debarking removes the outer protective layers including epidermis, cork and phloem. Protection against microbes, water loss and mechanical injury is lost, and transport of food from leaves to other parts through phloem is interrupted.
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: (ii) Which plant tissue would be affected by further damage to the tree trunk even after debarking?
Further damage would affect the vascular tissues deeper inside, especially the lateral meristem or cambium and the xylem, and the ground tissues. If cambium is destroyed, growth in girth stops.
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: (iii) Which function of the tree would be hampered if the tissues beneath the bark were severely damaged?
If tissues beneath the bark like cambium and xylem are damaged, water and mineral transport to leaves and food distribution are blocked, growth in diameter stops, and structural support weakens, which can lead to wilting and death of the tree.
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: (iv) What assumptions are you making to answer the questions above? How would the answer change if your assumptions are also changed?
We assume bark includes phloem and protective dermal tissues, that debarking is extensive around the stem, and that deeper xylem is initially still intact. If debarking is only partial or only outer cork is lost, food transport may continue through remaining phloem. If assumptions about depth or completeness change, the degree of functional loss changes from partial to total, and the tree may recover or die accordingly.
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.
Flexibility is due to collenchyma, with living cells and uneven pectin thickenings at corners, which provide support while allowing bending. If replaced by sclerenchyma with thick lignified dead walls, the stem would become hard, rigid and brittle, able to bear strength but would break rather than bend in strong wind, and would lose flexibility needed for young growing parts.
10. Sohan designed an experiment for the regeneration of sugarcane, where he used cuttings to grow sugarcane. He used two types of cuttings, type ‘A’ and type ‘B’ (Fig. 3.23). After a few weeks, type ‘B’ cuttings sprouted and developed into sugarcane plants, whereas the type ‘A’ cuttings did not sprout. (i) Why were the type ‘B’ cuttings able to grow as sugarcane but type ‘A’ could not?
Type B cuttings contained a node with intercalary meristem, which can divide and produce new shoots and roots. Type A was an internode piece without a node or meristem, so it lacked dividing cells needed for regeneration.
10. Sohan designed an experiment for the regeneration of sugarcane, where he used cuttings to grow sugarcane. He used two types of cuttings, type ‘A’ and type ‘B’ (Fig. 3.23). After a few weeks, type ‘B’ cuttings sprouted and developed into sugarcane plants, whereas the type ‘A’ cuttings did not sprout. (ii) What difference was present in type ‘B’ compared to type ‘A’?
Type B includes the node region where intercalary meristem is located, while Type A is only internode tissue composed of permanent cells without active meristem.
10. Sohan designed an experiment for the regeneration of sugarcane, where he used cuttings to grow sugarcane. He used two types of cuttings, type ‘A’ and type ‘B’ (Fig. 3.23). After a few weeks, type ‘B’ cuttings sprouted and developed into sugarcane plants, whereas the type ‘A’ cuttings did not sprout. (iii) What observation or measurement was made to determine whether this change had an effect?
Sprouting and development of new shoots and roots after a few weeks was observed. Length of sprouts, number of buds growing, and survival count were the visible measurements showing growth in Type B and no growth in Type A.
10. Sohan designed an experiment for the regeneration of sugarcane, where he used cuttings to grow sugarcane. He used two types of cuttings, type ‘A’ and type ‘B’ (Fig. 3.23). After a few weeks, type ‘B’ cuttings sprouted and developed into sugarcane plants, whereas the type ‘A’ cuttings did not sprout. (iv) What parameters should be kept the same for both types of cuttings to ensure a fair comparison?
Soil type, water, light, temperature, humidity, size and age of cuttings, planting depth and time of observation should be kept identical, varying only the presence or absence of the node, to ensure a fair test.
11. During the discussion in class, Rohan gives a statement that, “A tissue is a group of similar cells performing similar functions”. But Rajiv counter argues that, “this is true in case of simple tissues but little different in case of complex tissues”. Provide your explanation in view of the discussion in class.
Rohan is correct for simple tissues like parenchyma, collenchyma and sclerenchyma, which have only one cell type. Rajiv is also correct that complex tissues like xylem and phloem contain more than one type of cell, including living and dead, that work together for a common function such as conduction. Thus the definition is broadened for complex tissues: a group of different cell types cooperating for a function.
12. Coconut husk fibres are used for mats 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.
Sclerenchyma provides this strength. It has thick, lignified walls, is mostly dead at maturity and forms strong fibres like coconut husk and jute. Living parenchyma has thin walls, large vacuoles and is soft, mainly for storage and photosynthesis, and lacks the rigidity and tensile strength needed for tough mats.
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?
The statement is incorrect and incomplete. Meristems are also lateral along the stem circumference for girth and intercalary at nodes of grasses and near leaf bases for regrowth after cutting. Neha could ask: If meristems are only at apices, how does a tree increase in thickness or grass regrow after mowing, and where are those dividing cells located?
14. A plant cell and an animal cell are of the same size. (i) Which cell will have a larger vacuole? Give reasons.
The plant cell will have a larger vacuole, often a single central vacuole occupying
14. A plant cell and an animal cell are of the same size. (ii) What assumptions are you making to answer the question above?
We assume both are typical mature cells with normal functions, that the plant cell is not meristematic which lacks a large vacuole, and that size comparison is of whole cell volume. If the plant cell were meristematic or the animal cell specialized for storage, the assumption would change.
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?
We would ask: Does one tissue perform multiple roles? Do different tissues share a function? Examples: parenchyma stores food and also does photosynthesis as chlorenchyma and floats as aerenchyma; xylem transports water and also provides mechanical strength; epidermis protects and also exchanges gases via stomata and absorbs water via root hairs. These show tissues can have more than one function.
The Journey Beyond
Visit a doctor and find out what happens in ligament rupture, cartilage rupture and fracture of bones. How can we reduce the risk by changing our lifestyle and nutritional balance?
Ligament rupture causes joint instability and swelling, cartilage rupture causes pain and loss of cushioning, fracture is breaking of bone with pain and deformity. Risk can be reduced by regular exercise and yoga to strengthen muscles and flexibility, maintaining correct posture, adequate calcium, phosphorus, vitamin D and protein intake, drinking water, avoiding obesity and smoking, and using protective gear during sports.
Perform the following activity. (i) Sit with your feet flat on the floor. (ii) Place your fingers on the back of your ankle just above the heel (Fig. 3.24). (iii) Point your toes down and up, and you will feel the tendon moving. Tendons are designed to withstand huge pulling forces. Try exploring other tendons in your body around the different joints.
When toes are pointed down and up, the Achilles tendon at the back of the ankle tightens and moves as calf muscles contract and relax, transmitting pull to the heel bone. Similar tendons can be felt at the wrist when fingers are moved, at the elbow, and at the knee, all connecting muscle to bone and allowing movement.
Reflect on any of the physical practices you are familiar with, such as yoga, kabaddi, etc. How would it support bone and muscle health?
Practices like yoga improve posture, flexibility, balance and joint range, strengthen skeletal and cardiac muscles, improve blood circulation and reduce stress. Games like kabaddi build muscle strength and bone density through weight-bearing activity. Together with good nutrition they keep the musculoskeletal system strong and prevent stiffness.
Reflect on any gardening methods you know, such as pruning, grafting, irrigation or crop rotation. How does each practice support the healthy functioning of plant tissues like meristems, conducting tissues or supporting tissues?
Pruning removes shoot tips to activate intercalary and lateral buds for bushier growth via meristems. Grafting joins vascular tissues for better conduction. Irrigation ensures xylem water supply and turgor for supporting tissues. Crop rotation maintains soil nutrients so parenchyma storage and phloem transport remain healthy.
Turn a nature walk into a research project. (i) Observe different leaves and study their adaptations for various environments, such as desert, very moist or aquatic habitats. (ii) Consult an elder community resource persons about their knowledge on different plant leaves, such as leaves that remain fresh for a long time, repel water or deter insects. Find out their traditional uses, such as making plates, preparing cooling wraps or functioning as insect repellents.
Desert leaves are small, thick with thick cuticle and sunken stomata to reduce transpiration; aquatic leaves are broad with air spaces for floating. Traditional knowledge shows leaves like banana for plates, betel for freshness, neem for insect repellent and lotus for water repellence, reflecting epidermal and cuticle adaptations used by communities.
Study various dance forms of different tribal communities across the country. Each student learn and experience at least five steps. Observe the joint movements involved in performing these steps and then develop a dance or drama on the concept of joint movements. Perform this at the school’s annual function so that students from different grades can learn from it.
Tribal dances like Bihu, Garba and Santhal steps use ball and socket at shoulders and hips for circular movements, hinge at knees and elbows for bending, and pivot at neck for turning. By creating a drama that narrates each joint and movement, students can demonstrate how the musculoskeletal system enables coordinated dance.
The Quest Continues…
Will it be possible to obtain a complete animal from an animal cell like plants? If yes, what would be the advantages and challenges of this development?
In animals complete regeneration from a single somatic cell is not as easy as plant totipotency because animal cells are more differentiated and lack totipotency except for stem cells like zygote and embryonic stem cells. With advanced cloning and stem cell culture it is possible to some extent, as shown by cloned animals. Advantages include producing disease models, conservation of endangered species, and regenerative medicine. Challenges include ethical concerns, low success rate, abnormalities, immune rejection, and complex requirements for growth factors and environment.