NCERT Solutions for Class 9 Science Exploration Chapter 3: Tissues in Action
Revise, Reflect, Refine
1. Meristematic tissues divide repeatedly. What property of their cells allows them to do this?
Answer: (iii) They have thin walls, dense cytoplasm and large prominent nucleus.
Explanation: Meristematic cells are specialised for continuous and rapid cell division. Their properties that enable this are: Thin cell walls allow easy expansion and division without rigid constraints. Dense cytoplasm is rich in organelles needed for active metabolism and cell division. Large prominent nucleus contains genetic material and controls cell division actively. Vacuoles are absent so cells are tightly packed, with maximum space for organelles needed for division.
Explanation: Meristematic cells are specialised for continuous and rapid cell division. Their properties that enable this are: Thin cell walls allow easy expansion and division without rigid constraints. Dense cytoplasm is rich in organelles needed for active metabolism and cell division. Large prominent nucleus contains genetic material and controls cell division actively. Vacuoles are absent so cells are tightly packed, with maximum space for organelles needed for division.
2. If a plant is unable to transport food from leaves to roots which tissue is malfunctioning?
Answer: (ii) Phloem.
Explanation: Phloem is the vascular tissue responsible for transporting food (sugars prepared by photosynthesis) from the leaves to other parts of the plant including roots, fruits, and growing regions. This process is called translocation. Xylem transports water and minerals from roots to leaves, epidermis is a protective tissue, and sclerenchyma provides mechanical support; they do not transport food.
Explanation: Phloem is the vascular tissue responsible for transporting food (sugars prepared by photosynthesis) from the leaves to other parts of the plant including roots, fruits, and growing regions. This process is called translocation. Xylem transports water and minerals from roots to leaves, epidermis is a protective tissue, and sclerenchyma provides mechanical support; they do not transport food.
3. Why are the epithelial tissues that line an animal's internal organs usually only one or a few cells thick?
Answer: (iii) To allow quick exchange of materials across them.
Explanation: The distance for diffusion is minimal, meaning substances can cross the membrane rapidly. This is critical in the lungs where oxygen must quickly pass into blood and carbon dioxide must exit. In the intestine, nutrients must be quickly absorbed into blood capillaries. Thick epithelium (like skin) is for protection against friction and microbes, not for exchange. Hence internal exchange surfaces are thin while external protective surfaces are thick.
Explanation: The distance for diffusion is minimal, meaning substances can cross the membrane rapidly. This is critical in the lungs where oxygen must quickly pass into blood and carbon dioxide must exit. In the intestine, nutrients must be quickly absorbed into blood capillaries. Thick epithelium (like skin) is for protection against friction and microbes, not for exchange. Hence internal exchange surfaces are thin while external protective surfaces are thick.
4. You can perform these two jumps: Straight-leg jump – keep knees and ankles stiff; Normal jump – bend knees and ankles naturally. How did your ankle, knee and hip positions differ between the two jumps?
Answer:
| Body Part | Straight-leg Jump | Normal Jump |
|---|---|---|
| Knees | Kept stiff and straight – no bending. | Bend naturally on landing, absorbing impact. |
| Ankles | Stiff – toes point down rigidly. | Flex and extend to provide push-off force and cushion landing. |
| Hips | Remain mostly fixed – little movement. | Flex and extend to aid jumping height and balance. |
| Experience | Painful, jarring impact on landing; difficult to balance. | Smooth, controlled landing with good balance. |
5. Which type of joint is involved when you bend your knees and ankles?
Answer: (ii) Hinge.
Explanation: The knee and ankle are classic examples of hinge joints. Like a door hinge, these joints allow movement in only one plane – bending (flexion) and straightening (extension). They do NOT allow rotation or sideways movement.
Explanation: The knee and ankle are classic examples of hinge joints. Like a door hinge, these joints allow movement in only one plane – bending (flexion) and straightening (extension). They do NOT allow rotation or sideways movement.
6. In each of the following cases (A, B, C and D), choose the correct option: (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.
B. Assertion: Cardiac muscle can contract continuously without fatigue; Reason: Cardiac muscle cells have a high number of mitochondria and an abundant blood supply.
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.
D. Assertion: In a hinge joint, movement occurs primarily in one plane; Reason: The bone ends are shaped to allow sliding in all directions.
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.
B. Assertion: Cardiac muscle can contract continuously without fatigue; Reason: Cardiac muscle cells have a high number of mitochondria and an abundant blood supply.
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.
D. Assertion: In a hinge joint, movement occurs primarily in one plane; Reason: The bone ends are shaped to allow sliding in all directions.
Answer:
A. (iii) — A is true, but R is false.
B. (i) — Both A and R are true and R is the correct explanation of A.
C. (iv) — A is false, but R is true.
D. (iii) — A is true, but R is false.
A. (iii) — A is true, but R is false.
B. (i) — Both A and R are true and R is the correct explanation of A.
C. (iv) — A is false, but R is true.
D. (iii) — A is true, but R is false.
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. (i) Analyse the graph in terms of the diameter of the stem over time and share the interpretation. (ii) What is the relation between the diameter of the teak tree to the annual rings formed? (iii) Which specialised tissue is responsible for the girth of the stem and where is it located?
Answer:
(i) The diameter of the teak tree increases steadily with age, but not at a uniform rate. Between year 10 and year 20, the diameter shows a large jump (from 8 cm to 24 cm), suggesting a period of very rapid growth. After year 20, growth continues but at a slower, more gradual rate. Overall, the older the tree, the wider its trunk – showing continuous lateral growth throughout the tree's life.
(ii) The number of annual rings exactly equals the age of the tree in years. The diameter also increases with age. Therefore, more annual rings equals greater diameter. Each ring represents one year of growth by the lateral meristem. Thus, the diameter is directly related to the number of annual rings formed.
(iii) The tissue responsible for increase in girth (thickness) is the Lateral Meristem. It is located along the circumference of stems (in a ring running around the stem). The lateral meristem divides and produces new cells inside and outside, leading to an increase in the diameter of the stem. Each year, one new ring of wood is added by this tissue, forming the annual growth rings visible in a cross-section of the trunk.
(i) The diameter of the teak tree increases steadily with age, but not at a uniform rate. Between year 10 and year 20, the diameter shows a large jump (from 8 cm to 24 cm), suggesting a period of very rapid growth. After year 20, growth continues but at a slower, more gradual rate. Overall, the older the tree, the wider its trunk – showing continuous lateral growth throughout the tree's life.
(ii) The number of annual rings exactly equals the age of the tree in years. The diameter also increases with age. Therefore, more annual rings equals greater diameter. Each ring represents one year of growth by the lateral meristem. Thus, the diameter is directly related to the number of annual rings formed.
(iii) The tissue responsible for increase in girth (thickness) is the Lateral Meristem. It is located along the circumference of stems (in a ring running around the stem). The lateral meristem divides and produces new cells inside and outside, leading to an increase in the diameter of the stem. Each year, one new ring of wood is added by this tissue, forming the annual growth rings visible in a cross-section of the trunk.
8. In a forest, it was observed that one of the trees was severely debarked by an elephant to meet its food requirements. (i) Which function(s) of the tree is/are hampered by debarking? (ii) Which plant tissue would be affected by further damage to the tree trunk even after debarking? (iii) Which function of the tree would be hampered if the tissues beneath the bark were severely damaged? (iv) What assumptions are you making to answer the questions above?
Answer:
(i) Functions hampered by debarking: Protection is lost because the bark protects the inner tissues from mechanical damage, pathogens, water loss, and temperature extremes; removal exposes inner living tissues to infection and drying out. Food transport is disrupted because the phloem lies just beneath the bark, and debarking damages it, preventing the transport of food from leaves to roots. Water loss increases as the waxy cuticle and cork layer prevent excessive water loss, and without it, the tree desiccates rapidly.
(ii) If the trunk is further damaged beneath the bark, the Xylem would be affected. Xylem is the inner woody tissue of the trunk that transports water and minerals from the roots to the leaves. Damage to xylem would cut off water supply to the entire tree, causing wilting and death.
(iii) If the phloem and xylem are severely damaged, water transport (by xylem) would fail so roots cannot receive water signals and leaves wilt and dry. Food transport (by phloem) would fail so roots starve as they cannot receive food from leaves, stopping root growth and mineral absorption. The tree would eventually die due to failure of both conducting systems.
(iv) Assumptions made: We assume the phloem is located just beneath the bark and that the elephant's debarking exposed this layer. We assume the xylem is largely intact after initial debarking. We assume the tree has no alternative pathways to compensate for the loss. If our assumption that phloem is intact changes (i.e., phloem is also removed), then even water transport would be affected sooner, as roots would lose the signal to absorb water.
(i) Functions hampered by debarking: Protection is lost because the bark protects the inner tissues from mechanical damage, pathogens, water loss, and temperature extremes; removal exposes inner living tissues to infection and drying out. Food transport is disrupted because the phloem lies just beneath the bark, and debarking damages it, preventing the transport of food from leaves to roots. Water loss increases as the waxy cuticle and cork layer prevent excessive water loss, and without it, the tree desiccates rapidly.
(ii) If the trunk is further damaged beneath the bark, the Xylem would be affected. Xylem is the inner woody tissue of the trunk that transports water and minerals from the roots to the leaves. Damage to xylem would cut off water supply to the entire tree, causing wilting and death.
(iii) If the phloem and xylem are severely damaged, water transport (by xylem) would fail so roots cannot receive water signals and leaves wilt and dry. Food transport (by phloem) would fail so roots starve as they cannot receive food from leaves, stopping root growth and mineral absorption. The tree would eventually die due to failure of both conducting systems.
(iv) Assumptions made: We assume the phloem is located just beneath the bark and that the elephant's debarking exposed this layer. We assume the xylem is largely intact after initial debarking. We assume the tree has no alternative pathways to compensate for the loss. If our assumption that phloem is intact changes (i.e., phloem is also removed), then even water transport would be affected sooner, as roots would lose the signal to absorb water.
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.
Answer: Collenchyma is responsible for this flexibility. Collenchyma consists of living cells with unevenly thickened corners due to pectin, providing both support and flexibility to young plant stems, leaf stalks, and tendrils so they can bend without breaking under mechanical stress like monsoon winds.
Impact if replaced by sclerenchyma: Sclerenchyma cells have thick, lignified cell walls; they are dead cells that provide rigidity and strength but no flexibility. If the mango sapling's stem had sclerenchyma instead of collenchyma, the stem would become stiff and brittle. During monsoon winds, instead of bending, the stem would snap and break, causing serious damage. This would also prevent growth movements (like growing toward light), as rigid sclerenchyma cannot bend, severely compromising the plant's survival in windy conditions.
Impact if replaced by sclerenchyma: Sclerenchyma cells have thick, lignified cell walls; they are dead cells that provide rigidity and strength but no flexibility. If the mango sapling's stem had sclerenchyma instead of collenchyma, the stem would become stiff and brittle. During monsoon winds, instead of bending, the stem would snap and break, causing serious damage. This would also prevent growth movements (like growing toward light), as rigid sclerenchyma cannot bend, severely compromising the plant's survival in windy conditions.
10. Sohan designed an experiment for the regeneration of sugarcane, using two types of cuttings, type 'A' and type 'B'. 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? (ii) What difference was present in type 'B' compared to type 'A'? (iii) What observation or measurement was made to determine whether this change had an effect? (iv) What parameters should be kept the same for both types of cuttings to ensure a fair comparison?
Answer:
(i) Type B cuttings were able to grow because they contained nodes with intercalary meristem – actively dividing meristematic tissue located at the nodes of the stem. This tissue enabled the cutting to regenerate and sprout new shoots and roots. Type A cuttings lacked this meristematic tissue and therefore could not regenerate or sprout.
(ii) Type B cuttings included the nodes of the sugarcane stem, which is the region where intercalary meristematic cells are located. These meristematic cells retain the ability to divide and differentiate into new plant tissues. Type A cuttings were likely taken from internodal regions, which contain only permanent tissues and no meristematic cells, so they cannot regenerate.
(iii) The key observation was whether the cuttings sprouted new shoots and roots or not, which was measured by visible growth after a few weeks. The measurement of the length of new growth over time would quantify the difference. The fact that Type B showed sprouting while Type A showed none was the determining observation.
(iv) Parameters to keep the same for fair comparison include the length of cuttings, age and health of the parent plant, growing conditions like soil type, amount of water, sunlight, and temperature, time of planting, orientation of the cutting, and number of cuttings for statistical comparison.
(i) Type B cuttings were able to grow because they contained nodes with intercalary meristem – actively dividing meristematic tissue located at the nodes of the stem. This tissue enabled the cutting to regenerate and sprout new shoots and roots. Type A cuttings lacked this meristematic tissue and therefore could not regenerate or sprout.
(ii) Type B cuttings included the nodes of the sugarcane stem, which is the region where intercalary meristematic cells are located. These meristematic cells retain the ability to divide and differentiate into new plant tissues. Type A cuttings were likely taken from internodal regions, which contain only permanent tissues and no meristematic cells, so they cannot regenerate.
(iii) The key observation was whether the cuttings sprouted new shoots and roots or not, which was measured by visible growth after a few weeks. The measurement of the length of new growth over time would quantify the difference. The fact that Type B showed sprouting while Type A showed none was the determining observation.
(iv) Parameters to keep the same for fair comparison include the length of cuttings, age and health of the parent plant, growing conditions like soil type, amount of water, sunlight, and temperature, time of planting, orientation of the cutting, and number of cuttings for statistical comparison.
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.
Answer: Both Rohan and Rajiv are partially correct. Rohan's statement is the basic definition of a tissue and holds well for simple permanent tissues like parenchyma, collenchyma, and sclerenchyma, where all cells are of the same type and perform the same function. Rajiv's argument is correct for complex permanent tissues like xylem and phloem. In xylem, tracheids and vessels transport water, parenchyma stores food, and fibres give strength. In phloem, sieve tubes transport food, companion cells regulate sieve tubes, and fibres give support. In complex tissues, the different types of cells work together as a team to perform a common overall function, even though each cell type does a different specific job. So the tissue as a whole has a common function, but the individual cells within it are not all similar in structure or specific 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.
Answer: Sclerenchyma tissue has structural features suitable for providing this strength, as coconut husk fibres are made of sclerenchyma. The structural features that make sclerenchyma suitable are that its cells have thick, lignified cell walls that make them rigid and durable. Most sclerenchyma cells are dead at maturity, acting as hollow tubes of strong lignified material. The cells are long and fibrous in shape, arranged in bundles, providing tensile strength and resistance to tearing. Parenchyma cannot serve the same purpose because its cells have thin cell walls that are soft and flexible, providing no structural rigidity or strength. Parenchyma cells are living and metabolically active, so they would decompose over time if used as a structural material. They contain large vacuoles and intercellular spaces, making them soft, compressible, and unsuitable for fibrous, tough applications.
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?
Answer: Vibha's statement is incomplete and partially incorrect. Plants actually have three types of meristematic tissues located in different positions. Questions Neha can ask Vibha include: "If meristems are only at root and shoot tips, then how does a tree trunk increase in thickness (girth) over years?". "When we mow a lawn or a cow eats grass, how does the grass grow back if the tip is removed? Which meristem is responsible for that?". "When the tip of a plant is cut off and new branches appear from the nodes below, which meristem makes this possible?". These questions would guide Vibha to discover lateral and intercalary meristems on her own.
14. A plant cell and an animal cell are of the same size. (i) Which cell will have a larger vacuole? Give reasons. (ii) What assumptions are you making to answer the question above?
Answer:
(i) The plant cell will have a larger vacuole. Mature plant cells typically have a single large central vacuole that can occupy up to 80–90% of the cell volume, surrounded by a selectively permeable membrane called the tonoplast. The plant cell vacuole stores water, minerals, sugars, and waste materials, and it also maintains turgor pressure. Animal cells may have small, temporary vacuoles used for transport or storage of materials, but these are much smaller and not as prominent or permanent. Since both cells are the same size, the plant cell's large vacuole would leave less space for cytoplasm and other organelles, while the animal cell would have more cytoplasm and organelles relative to its volume.
(ii) Assumptions made: We assume the plant cell is a mature plant cell, not a young meristematic cell which has no vacuole. We assume the animal cell is a typical body cell, not a specialised cell like a fat cell which stores large fat droplets. If the plant cell is a young meristematic cell, then neither cell would have a large vacuole.
(i) The plant cell will have a larger vacuole. Mature plant cells typically have a single large central vacuole that can occupy up to 80–90% of the cell volume, surrounded by a selectively permeable membrane called the tonoplast. The plant cell vacuole stores water, minerals, sugars, and waste materials, and it also maintains turgor pressure. Animal cells may have small, temporary vacuoles used for transport or storage of materials, but these are much smaller and not as prominent or permanent. Since both cells are the same size, the plant cell's large vacuole would leave less space for cytoplasm and other organelles, while the animal cell would have more cytoplasm and organelles relative to its volume.
(ii) Assumptions made: We assume the plant cell is a mature plant cell, not a young meristematic cell which has no vacuole. We assume the animal cell is a typical body cell, not a specialised cell like a fat cell which stores large fat droplets. If the plant cell is a young meristematic cell, then neither cell would have a large vacuole.
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?
Answer: To test this statement, we should ask questions like: Does parenchyma only store food or does it perform other functions too? Does epidermis only provide protection or does it also help in other processes? Do complex tissues like xylem perform only one function?.
Examples to test the answers: Parenchyma mainly stores food, but it also performs photosynthesis in the green parts of the plant, and in aquatic plants, specialised parenchyma forms air spaces which help them float. Epidermis forms the outermost protective layer of the plant body, but it also contains stomata in leaves which help in gaseous exchange and transpiration, and in roots, epidermal cells form root hair which absorb water and minerals. Xylem not only transports water and minerals from roots to other parts of the plant but also provides mechanical strength and support to the plant. Therefore, the statement is incorrect, as multiple plant tissues perform more than one specific function.
Examples to test the answers: Parenchyma mainly stores food, but it also performs photosynthesis in the green parts of the plant, and in aquatic plants, specialised parenchyma forms air spaces which help them float. Epidermis forms the outermost protective layer of the plant body, but it also contains stomata in leaves which help in gaseous exchange and transpiration, and in roots, epidermal cells form root hair which absorb water and minerals. Xylem not only transports water and minerals from roots to other parts of the plant but also provides mechanical strength and support to the plant. Therefore, the statement is incorrect, as multiple plant tissues perform more than one specific function.
Very Short Answer Type Questions
1. What is a tissue?
Answer: A tissue is a group of cells that are similar in structure and work together to perform a specific function.
2. Name the three types of meristematic tissues found in plants.
Answer: Apical meristem, Lateral meristem and Intercalary meristem.
3. Where is the apical meristem located?
Answer: At the tips of roots and shoots of a plant.
4. Which meristematic tissue is responsible for the increase in girth (thickness) of a stem?
Answer: Lateral meristem.
5. What is differentiation?
Answer: Differentiation is the process by which meristematic cells lose the ability to divide and become specialised to form permanent tissues.
6. Name the only living component of xylem.
Answer: Xylem parenchyma.
7. Which tissue transports food from leaves to other parts of the plant?
Answer: Phloem.
8. What is the waxy layer present on the outer surface of the epidermis called?
Answer: Cuticle.
9. Name the pores present in the epidermis of leaves that help in gaseous exchange.
Answer: Stomata.
10. What are the cells of nervous tissue called?
Answer: Neurons (nerve cells).
11. Which type of muscle tissue is found only in the heart?
Answer: Cardiac muscle.
12. What connects muscle to bone?
Answer: Tendon.
13. What type of joint is present at the shoulder?
Answer: Ball and socket joint.
14. Name the flexible column of small bones that forms the backbone.
Answer: Vertebral column (spine), made up of vertebrae.
15. What is the full form of RBC and how long does an RBC live?
Answer: RBC stands for Red Blood Cell; it lives for about 4 months and is replaced regularly.
Short Answer Type Questions
1. Why do plant cells have a cell wall but animal cells do not?
Answer: Plants are fixed in one place and need rigidity and strength to stay upright, so their cells have a cell wall. Animals need to move, so their cells lack a rigid wall, giving them flexibility for locomotion.
2. What are annual growth rings and what information do they provide?
Answer: Annual growth rings are ring-like patterns visible on the cross-section of a tree trunk, formed by the lateral meristem. By counting these rings, scientists can estimate the age of the tree and understand the climatic conditions during which it grew.
3. Why do meristematic cells lack vacuoles?
Answer: Meristematic cells divide continuously and rapidly. Vacuoles store water and cell sap, and their presence would occupy space needed for active metabolic processes. Without vacuoles, cells remain small and tightly packed, allowing efficient and rapid division.
4. What are sieve tubes and companion cells? What is the function of companion cells?
Answer: Sieve tubes are long, tubular cells in phloem joined end-to-end by perforated walls; they transport food. Companion cells are specialised parenchyma cells that regulate sieve tubes and monitor the loading and unloading of sugars within them.
5. Distinguish between voluntary and involuntary movements with one example each.
Answer: Voluntary movements are under conscious control (e.g., writing, running) and are carried out by skeletal muscles. Involuntary movements occur automatically without conscious control (e.g., heartbeat, movement of food in intestines) and are carried out by smooth and cardiac muscles.
6. What is the role of cartilage in the human body?
Answer: Cartilage has a soft, jelly-like matrix that provides flexibility and cushions the ends of bones for shock absorption. It is found at joints, the nose, ears and between vertebrae, preventing bones from grinding against each other.
7. What is the intercalary meristem, and how does it help a lawn regrow after mowing?
Answer: Intercalary meristem is located at the base of internodes (nodes of the stem). When grass is mowed, the shoot tips are cut but the intercalary meristem at the nodes remains intact, allowing the grass to regenerate and grow back.
8. What is totipotency? Who first demonstrated it, and in which plant?
Answer: Totipotency is the ability of a single mature plant cell to divide, dedifferentiate, and redifferentiate to develop into a complete new plant. It was first demonstrated by F. C. Steward in 1958 using phloem cells of carrot.
Long Answer Type Questions
1. What is the difference between meristematic tissue and permanent tissue in plants?
Answer: Meristematic tissue consists of actively dividing cells that are small, have thin walls, dense cytoplasm, a large prominent nucleus and no vacuoles. These cells continuously divide to add new cells to the plant body. Permanent tissue on the other hand, is formed when meristematic cells lose the ability to divide and undergo differentiation – a process where they become specialised to perform specific functions like support, protection, storage or conduction. Simply put, meristematic tissue is responsible for plant growth, while permanent tissue carries out all the functional roles once growth in that region has stopped.
2. Why do roots of a plant stop growing if the root tip is cut off?
Answer: Roots grow only from their tips. The root tip contains the apical meristem — a zone of actively dividing cells. When the root tip is cut, these dividing cells are removed and since no other region of the root has the ability to actively divide in the same way, growth stops. This was demonstrated using onion bulbs placed in jars, where roots with cut tips stopped growing, while uncut roots continued to grow normally.
3. What is the role of xylem and phloem in plants? Are they living or dead tissues?
Answer: Xylem transports water and minerals from the roots to other parts of the plant and also provides mechanical strength. It consists of tracheids, vessels, xylem parenchyma and xylem fibres. Xylem parenchyma is the only living component of xylem; the rest are primarily dead cells. Phloem transports food (sugars) prepared in leaves to other parts of the plant. It consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibres. Unlike xylem, phloem is mostly made up of living cells. Together, xylem and phloem are called complex permanent tissues or vascular tissues.
4. What are the four types of animal tissues?
Answer: The four types of animal tissues are: 1. Epithelial tissue — forms the outer covering of the body (skin) and lines internal organs, providing protection, absorption, secretion and sensory functions. 2. Connective tissue — connects and supports other tissues and organs, including blood, bone, cartilage, tendons and ligaments. 3. Muscular tissue — responsible for movement, including skeletal, smooth and cardiac muscle. 4. Nervous tissue — forms the brain, spinal cord and nerves, consisting of neurons that receive and transmit electrical impulses.
5. What is the difference between voluntary and involuntary muscles? Which tissue is the heart made of?
Answer: Voluntary muscles (skeletal muscles) are under conscious control — you can decide to move them. They have long cylindrical cells that are multinucleate and striated. Involuntary muscles (smooth muscles) work automatically without conscious control, such as the muscles in the stomach and intestines. Their cells are spindle-shaped with a single nucleus. The heart is made of cardiac muscle, which works involuntarily and tirelessly throughout life without fatigue. Its cells are cylindrical, branched and have faint striations with a single nucleus.
6. What is the musculoskeletal system and why is it important?
Answer: The musculoskeletal system is made up of bones, muscles, joints, cartilage, tendons, and ligaments. It helps us stand upright, move, maintain posture, and protect delicate organs. Muscles pull on bones via tendons to produce movement at joints. The adult human skeleton makes up about 12–15% of body weight. This system functions under the control of the nervous system — for example, when the brain signals muscles to contract, the force is transmitted through tendons to bones, resulting in movement.
7. What are the different types of joints in the human body?
Answer: The four types of joints are: 1. Ball and socket joint (e.g., shoulder, hip) — allows movement in all directions including forward, backward, sideways and circular. 2. Hinge joint (e.g., elbow, knee) — allows movement in only one direction, like a door hinge. 3. Pivot joint (e.g., neck/skull-backbone junction) — allows rotational movement, like shaking your head “no”. 4. Fixed joints (e.g., skull bones) — bones are joined together and cannot move, protecting the brain.
8. What is differentiation in plants? How does meristematic tissue become permanent tissue?
Answer: Differentiation is the process by which meristematic cells lose the ability to divide and undergo changes in structure to become specialised (permanent) tissues. When meristematic tissue continuously divides, some newly formed cells remain meristematic, while others start to take on specific roles — like providing support, storing food or conducting water. These cells develop thick walls, become elongated or even die, all in service of their particular function. This transformation from meristematic to permanent tissue through differentiation builds the mature plant body.
9. Why can plants regrow after mowing or pruning, but wounds in animals often don't regenerate?
Answer: Plants can regrow after being cut because they possess intercalary meristem located at the nodes of stems — regions of actively dividing cells that survive even after the shoot tip is removed. Grass regrows after mowing because its intercalary meristem at the nodes is untouched. Animals, in contrast, have far fewer regenerative stem cell populations. Most mature animal cells are permanently differentiated and cannot divide freely to rebuild complex tissues. However, stem cells in bone marrow can divide and regenerate blood cells, forming the basis of treatments like bone marrow transplants.