1. Answer Key (Revise, Reflect, Refine)
Question 1
Question: 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.
Answer: (iii) They have thin walls, dense cytoplasm and large prominent nucleus.
Explanation: These cytological characteristics allow continuous and rapid cell division.
Question 2
Question: If a plant is unable to transport food from leaves to roots which tissue is malfunctioning?
(i) Xylem
(ii) Phloem
(iii) Epidermis
(iv) Sclerenchyma
Answer: (ii) Phloem
Explanation: Phloem transports food from leaves to other parts of the plant.
Question 3
Question: 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.
Answer: (iii) To allow quick exchange of materials across them.
Explanation: A thin, single layer of cells is structurally adapted to help in the rapid diffusion and exchange of liquids and gases.
Question 4
Question: 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?
Answer: * Straight-leg jump: The positions of the ankle, knee, and hip remain locked, stiff, and unbent. This prevents natural cushioning, limits mechanical propulsion, and increases the impact force traveling up the legs.
Normal jump: The ankle, knee, and hip joints bend naturally. This bending allows the musculoskeletal system to store energy during take-off and absorb shock safely upon landing.
Question 5
Question: Which type of joint is involved when you bend your knees and ankles?
(i) Ball and socket
(ii) Hinge
(iii) Pivot
Answer: (ii) Hinge
Explanation: Bending and straightening the knee or ankle occurs primarily in one plane/direction, which functions like a door hinge.
Question 6: Assertion & Reason
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.
Answer: (iii) (A) is true, but (R) is false.
Reasoning: Epithelium in the blood vessels and lungs consists of a single layer of thin, flat cells to facilitate rapid exchange, not multiple layers of tall cells.
B. Assertion: Cardiac muscle can contract continuously without fatigue.
Reason: Cardiac muscle cells have a high number of mitochondria and an abundant blood supply.
Answer: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A).
Reasoning: The text states cardiac muscles work tirelessly throughout life without fatigue. Biologically, this continuous work is fueled by an abundant blood supply and dense mitochondria.
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.
Answer: (iv) (A) is false, but (R) is true.
Reasoning: Ligaments connect bone to bone. Tendons connect muscle to bone and transmit force to produce joint movement.
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: (iii) (A) is true, but (R) is false.
Reasoning: A hinge joint restricts movement to one direction only. The bone ends do not allow sliding in all directions.
Question 7 (Teak Tree Graph Analysis)
Question: 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 Table 3.7.
(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) Analysis: The graph shows that the diameter at breast height (DBH) increases as the tree gets older. Over the span of 40 years, the tree grows from a diameter of 4 cm up to 40 cm, showing a steady expansion in thickness over time.
(ii) Relation: There is a direct, matching relationship. The number of annual growth rings formed corresponds to the age of the tree. As more rings accumulate, the overall diameter of the teak tree increases.
(iii) Specialised Tissue: Lateral Meristem. It is located along the circumference of the stems and roots, arranged in a ring.
Question 8 (Elephant Debarking)
Question: In a forest, it was observed that one of the trees was severely debarked by an elephant to meet its food requirements... Based on your learning, answer the following:
(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? How would the answer change if your assumptions are also changed?
Answer:
(i) Hampered functions: Protection against mechanical injury, invasion by parasites, extreme weather, and excessive water loss is hampered because the protective outer cork layer is lost.
(ii) Affected tissue with deeper damage: The complex conducting tissues, specifically the phloem, as well as the lateral meristem (cambium).
(iii) Consequences of deeper damage: The translocation of food prepared by the leaves down to the roots will be completely blocked. This will cause the roots to starve and eventually kill the tree.
(iv) Assumptions: We assume the debarking strips the tissue completely around the entire circumference of the tree trunk (girdling). If the assumption changes to only partial debarking on one side, the tree will survive because food can still be transported through the undamaged phloem on the other side.
Question 9 (Mango Sapling & Flexibility)
Question: 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:
Tissue responsible: Collenchyma. It consists of living cells with unevenly thickened corners containing pectin, which provides mechanical flexibility.
If replaced by Sclerenchyma: Sclerenchyma cells have thick, rigid walls heavily deposited with lignin and are mostly dead. If sclerenchyma replaces collenchyma, the young mango stem will lose its flexibility and become hard and brittle. Instead of bending safely, it will break or snap when hit by strong monsoon winds.
Question 10 (Sugarcane Cuttings)
Question: Sohan designed an experiment for the regeneration of 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?
(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) & (ii) Difference: Type 'B' cuttings contained a node where intercalary meristems are located. These meristems have actively dividing cells that can regenerate new branches and leaves. Type 'A' cuttings consisted only of internodes, lacking these regenerative growth zones.
(iii) Observation: Looking for visible sprouting, bud elongation, and the development of roots or shoots from the cuttings.
(iv) Controlled Parameters: Amount of water supplied, soil composition, depth of planting, temperature, and exposure to sunlight.
Question 11 (Simple vs. Complex Tissues)
Question: 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:
Rajiv is correct. Rohan's definition holds true only for simple permanent tissues (parenchyma, collenchyma, sclerenchyma), which are composed of only one type of cell working together.
Complex permanent tissues (xylem and phloem) are made up of different types of cells that look structurally distinct but work together as a unit to perform a specific common function. For example, xylem consists of tracheids, vessels, parenchyma, and fibres working together to transport water.
Question 12 (Coconut Husk)
Question: 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:
Tissue: Sclerenchyma. Its structural features include cells with highly thickened, lignified walls that make them exceptionally hard, rigid, and strong.
Why Parenchyma fails: Parenchyma cells have thin cell walls, are loosely packed with large intercellular spaces, and are designed primarily for storage or photosynthesis. They lack the thick, tough lignification required to provide mechanical strength or withstand heavy wear and tear.
Question 13 (Vibha vs. Neha on Meristems)
Question: 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 incorrect. While apical meristems are located at the root and shoot tips, plants also contain lateral meristems along their circumference and intercalary meristems at the nodes or base of internodes.
Neha's question: "If meristematic cells are found only at the tips, how are stems able to increase in diameter over time, and how do grasses grow back after their tips are cut or eaten by animals?"
Question 14 (Vacuoles in Plant vs. Animal Cells)
Question: 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) Larger Vacuole: The plant cell will have a much larger vacuole. Mature, permanent plant cells possess large central vacuoles to maintain structural turgidity, rigidity, and store nutrients or waste products. Animal cells generally have very tiny, temporary vacuoles or lack them altogether.
(ii) Assumptions: We assume the plant cell is a mature, differentiated vegetative cell (like parenchyma). If it were an actively dividing meristematic plant cell, vacuoles would be absent.
Question 15 (Tissue Specificity)
Question: 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:
Critical Questions:
"Can a single type of tissue structurally modify itself to perform entirely different functions in different plant habitats?"
"Does a permanent tissue like parenchyma only perform storage, or can it participate in other metabolic actions?"
Examples to use: Parenchyma tissue. It typically stores food, but in the green parts of a plant, it performs photosynthesis (as chlorenchyma), and in aquatic plants, it forms large air spaces to help the plant float (as aerenchyma). This proves that a single tissue type can perform multiple specialized functions.
2. Inside Questions with Answers
Question 1
Question: What is cellular differentiation in multicellular organisms?
Ans: Differentiation is the biological process by which newly formed meristematic cells undergo permanent modifications in their structure and function, losing their ability to divide, and becoming specialized to perform distinct tasks like support, transport, or storage.
Question 2
Question: Why are vacuoles generally absent in meristematic plant tissues?
Ans: Meristematic cells are specialized for continuous, rapid, and active cell division. Because they are constantly dividing, they do not need to store food or cellular waste, nor do they require large vacuolar spaces to maintain turgidity, making vacuoles unnecessary.
Question 3
Question: What are annual growth rings, and what two key pieces of information can scientists gather from them?
Ans: Annual growth rings are concentric ring-like patterns visible on the cut surface of a tree trunk, created by the cyclic activity of the lateral meristem. By studying them, scientists can:
Estimate the precise age of the tree by counting the rings.
Understand past climatic conditions, as wide rings reflect favorable growth years and narrow rings show unfavorable seasons.
Question 4
Question: Distinguish structurally and functionally between tendons and ligaments.
Ans: * Tendons: Structural bands of tough connective tissue that link skeletal muscles to bones. Functionally, when a muscle contracts, the tendon transmits this force to the bone to cause joint movement.
Ligaments: Connective tissues that link bones directly to other bones at a joint. Functionally, they provide joint stability, limit excessive movement, and help prevent skeletal dislocation.
Question 5
Question: How do the cellular matrices of blood and bone differ, and how does this relate to their functions?
Ans: * Blood: Has a fluid, watery, and soft matrix called plasma. This liquid consistency allows blood to flow freely through vessels to transport nutrients, gases, and hormones to distant parts of the body.
Bone: Has a hard, solid, and rigid matrix containing calcium and phosphorus compounds. This rigid structure provides mechanical strength, framework support, and physical protection to internal organs.
Question 6
Question: Define the term 'totipotency' and state who first demonstrated it.
Ans: Totipotency is the inherent ability of a mature, living plant cell to dedifferentiate (regain the ability to divide), form an unspecialized mass of cells, and then redifferentiate into roots, shoots, and eventually an entire complete plant under appropriate laboratory conditions. This biological marvel was first demonstrated by F. C. Steward in 1958 using vascular phloem cells from a carrot root.
Question 7
Question: What biological agent causes crown gall disease in plants, and how did scientists turn this disease into a beneficial agricultural tool?
Ans: Crown gall disease is caused by the bacterium Agrobacterium tumefaciens, which forces rapid, uncontrolled cell division resulting in tumor-like swellings on plant stems. By studying how this bacterium naturally transfers its own genetic material into host plant cells, scientists repurposed it. Today, it is used in genetic engineering as a tool to introduce beneficial genes into plants to produce improved crops and disease-resistant plant varieties.
3. Additional Advanced Inside-Text Questions & Answers
Question 8
Question: Describe how the division of labour at the tissue level increases cellular efficiency in multicellular organisms compared to unicellular organisms.
Ans: * Unicellular Organisms: A single cell must carry out every single function of life (such as movement, digestion, and coordination) on its own, which limits its structural complexity.
Multicellular Organisms: Specialized groups of similar cells form distinct tissues dedicated to a single, specific task. For example, muscle tissues contract only for movement, while nervous tissues focus entirely on carrying messages. This clear division of labour prevents individual cells from being overworked, optimizes performance, and allows the body to successfully carry out highly complex life processes.
Question 9
Question: Based on Section 3.1, why do plant cells require a rigid cell wall, while animal cells thrive with cellular flexibility?
Ans: * Plants: Most plants are fixed in one place and cannot move to escape harsh weather or environmental stress. They require a rigid cell wall composed of tough components to provide static strength, support, and structural firmness to stay upright.
Animals: Animals must move around actively to find food, escape danger, and seek shelter. The absence of a rigid cell wall grants animal cells flexibility, allowing them to shift shape easily, which makes their tissues and limbs suited for rapid locomotion.
Question 10
Question: Explain the structural adaptations of the plant epidermis that facilitate gas exchange and water regulation.
Ans: The plant epidermis uses two specialized structural adaptations:
Cuticle: A waxy outer layer composed of cutin covers the epidermis. In dry habitats, this layer is exceptionally thick to prevent excess water loss via evaporation.
Stomata: These are specialized microscopic pores embedded within the epidermal layer. They can open and close to permit gaseous exchange for photosynthesis while regulating transpiration (the evaporation of water vapour), which helps generate a transpiration pull to draw water up from the roots.
Question 11
Question: Contrast the structural and living characteristics of the elements making up xylem tissue versus those making up phloem tissue.
Ans: * Xylem Tissue: Xylem is primarily composed of dead, hollow, and thick-walled structural units. Tracheids, vessels, and xylem fibres are all dead, highly lignified sclerenchymatous cells designed to handle the high pressure of water transport and provide mechanical strength. Xylem parenchyma is the only living component in xylem.
Phloem Tissue: Phloem is mostly made up of living, active cells. Sieve tubes, companion cells, and phloem parenchyma are all living components that actively manage the transport and storage of food. Phloem fibres (sclerenchymatous supporting structures) are the only dead components in phloem.
Question 12
Question: How does the structure of a cardiac muscle cell explain its ability to work continuously throughout human life without experiencing fatigue?
Ans: Cardiac muscle cells feature a specialized cylindrical and branched structure that allows them to interconnect deeply with one another. This branching architecture ensures that electrical signals for contraction spread quickly and evenly across the entire heart. Furthermore, as noted in the text, these cells are packed with a high number of energy-producing mitochondria and are backed by a continuous, abundant blood supply. This gives them a steady supply of oxygen and ATP, enabling rhythmic, lifelong contractions without fatigue.
Question 13
Question: Explain how the structural flexibility of the human rib cage works to facilitate the process of breathing.
Ans: The rib cage consists of 12 pairs of rigid bones that protect vital organs like the heart and lungs. However, where these ribs attach to the breastbone (sternum) in front, they are joined by flexible cartilage instead of rigid bone joints. This structural flexibility allows the entire rib cage to expand outward and contract inward smoothly. When muscles pull the ribs, this expansion increases the physical volume inside the chest cavity, lowering internal pressure so air moves into the lungs; when it contracts, air is pushed out.
Comments
Post a Comment