Page 28 – Think It Over
Q. How is the study of cells and tissues significant for understanding the life processes and human welfare?
Answer: Understanding cells and tissues helps explain how the body grows, repairs itself, and functions, which allows researchers to replicate or modify biological processes for human welfare, such as in medicine and tissue culture.
Q. How are tissues in plants and animals different, and why?
Answer: Plant tissues focus on support, photosynthesis, and conduction since plants are fixed in place. Animal tissues focus on movement, digestion, and rapid coordination since animals move and lack a rigid cell wall.
Q. How is the division of labour at various levels of organisation in multicellular organisms correlated with their structure and function?
Answer: Cells of similar structure group into tissues, tissues form organs, and organs form organ systems, each level specialised for a specific function. This division of labour increases the body’s overall efficiency.
Page 30 – Apical Meristem
Q. What trend do you observe in the data you recorded in Table 3.1? Are your observations similar to those presented in the graphical representation (Fig. 3.2)? What do you infer?
Answer: Roots in Jar A continue to grow in length, while roots in Jar B stop growing after their tips are cut. This shows that roots grow only from their tips, since the tips contain actively dividing meristematic cells.
Page 31 – Meristematic Tissue
Q. Why do you think that the cell of meristematic tissues lack vacuoles?
Answer: Meristematic cells are constantly dividing, so they need dense cytoplasm and space for organelles to support rapid division, rather than space for storage in vacuoles.
Page 31 – Permanent Tissues (Sunflower Stem T.S.)
Q. What do you observe? Are all the cells similar in shape and size? How many different types of tissues can you identify? What differences do you notice among them? What might be the reason for the presence of different types of cells and tissues?
Answer: No, the cells are not all similar — several different tissue types are present (epidermis, collenchyma, parenchyma, sclerenchyma, xylem, phloem), each with a different shape and structure, because each tissue is specialised to perform a specific function.
Page 33 – 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.
Answer: Coconut husk fibres are made of sclerenchyma, which has thick, lignified walls, making them hard and brittle. Coriander leaf stalks are made of parenchyma/collenchyma, which have thin or unevenly thickened walls, making them soft and flexible.
Page 34 – 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?
Answer: A thick cuticle reduces water loss, which helps desert plants conserve water, but underwater plants don’t need to prevent water loss, so a thick cuticle would only block the gas exchange they need from the surrounding water.
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?
Answer: Dead xylem cells form hollow tubes that offer minimal resistance for water to rise, while living leaf cells lose water through transpiration, creating a “pull” (suction force) that draws more water upward through the xylem.
4. What do you think will happen if there were no stomata in the epidermis of the stem or leaves?
Answer: Gaseous exchange and transpiration would stop, hampering photosynthesis and respiration, disrupting the transpiration pull that helps move water up through the xylem, and preventing elimination of waste from the plant body.
Page 40 – 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?
Answer: Various joints are involved — the shoulder and hip (ball and socket joints, allowing forward, backward, sideways and circular movement), the knee and elbow (hinge joints, allowing bending in one direction only), and the neck (pivot joint, allowing side-to-side turning movement).
Page 42 – Think as a Scientist
(a) What do you conclude about the characteristics of phloem cells of carrot?
Answer: Phloem cells of carrot are totipotent — even a single mature cell can dedifferentiate, divide, and redifferentiate to regenerate an entire new plant when given suitable nutrients and conditions.
(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?
Answer: The highest biomass (20% increase) was obtained in liquid medium with nutrients, light, and air, since liquid medium gives better nutrient access and both light and air support healthy growth. The lowest biomass occurred when either light or air was missing, since both are essential for proper cell growth.
(c) Will you get the same results if you culture animal cells instead of carrot cells?
Answer: No, animal cells generally do not show the same totipotency as plant cells. Most differentiated animal cells cannot dedifferentiate and regenerate into a whole new organism the way plant cells can.
(d) Think and mention any two commercial applications of the study above.
Answer: Plant tissue culture for mass-producing identical, disease-free plants, and genetic engineering/crop improvement using totipotent cells to introduce desirable traits.
Page 44 – 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.
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 – Rich in organelles needed for active metabolism and cell division.
- Large prominent nucleus – Contains genetic material and controls cell division actively.
- No vacuoles – 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?
(i) Xylem
(ii) Phloem
(iii) Epidermis
(iv) Sclerenchyma
Answer:
(ii) Phloem.
Explanation: Phloem is the tissue responsible for transporting food (made in leaves through photosynthesis) to other parts of the plant, including the roots. Xylem only transports water and minerals, not food.
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.
Answer:
(iii) To allow quick exchange of materials across them.
Explanation: A thinner layer of cells means a shorter distance for substances to travel, allowing faster diffusion of gases, liquids, and nutrients across the tissue — essential in places like the lungs and intestine lining.
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?
Answer: In the straight-leg jump, the ankle, knee, and hip remain stiff and locked, resulting in a harder landing. In the normal jump, these joints bend naturally, absorbing the shock and making the landing smoother.
5. 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: Knees and ankles bend in one direction only, similar to a door hinge, which is the defining feature of a hinge 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.
Answer: (iv) (A) is false, but (R) is true.
Explanation: Epithelium for gas exchange is actually a single layer of thin, flat cells, so the Assertion is false. The Reason statement itself is a true general fact, so option (iv) fits.
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).
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.
Explanation: Tendons actually connect muscle to bone (not bone to bone — that’s ligaments), making the Assertion false. The Reason 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.
Answer: (iii) (A) is true, but (R) is false.
Explanation: Hinge joints do move primarily in one plane (true), but this happens because the bone ends are shaped to restrict movement to one direction, not because they allow sliding in all directions — making the Reason 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, 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) The diameter of the stem increases steadily as the age of the tree increases.
(ii) The diameter of the tree increases proportionally with the number of annual rings formed.
(iii) The lateral meristem is responsible for the girth of the stem, located as a ring of actively dividing cells around the stem.
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?
(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) Protection against water loss, mechanical injury, and entry of microorganisms is hampered.
(ii) The lateral meristem (cork cambium) and vascular tissues (xylem and phloem) would be affected.
(iii) Transport of food (by phloem) and growth in girth (by lateral meristem) would be hampered.
(iv) The assumption is that the damage reaches the phloem/cambium layer, not just the outer bark. If the damage is only superficial, the tree may survive with reduced protection, without major impact on food transport or growth.
Page 46 – Exercise Questions
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, as its unevenly thickened, pectin-rich walls allow bending without breaking. If replaced by sclerenchyma (thick, lignified, rigid walls), the stem would become hard and stiff, losing flexibility, and would likely break instead of bending during strong winds.
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?
(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 likely had nodes with intact meristematic buds; type ‘A’ likely lacked these.
(ii) Type ‘B’ had nodes/buds present, while type ‘A’ did not.
(iii) The observation was whether the cuttings sprouted and developed into new plants.
(iv) Size/length of cuttings, growing conditions (soil, water, temperature, sunlight), and the observation time period should be kept the same.
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: Rajiv is correct. Simple tissues (parenchyma, collenchyma, sclerenchyma) are made of one type of cell performing a similar function, matching Rohan’s definition. Complex tissues (xylem, phloem) are made of more than one type of cell working together for a combined function, so they don’t fit the “similar cells” definition alone.
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 is responsible for this strength, since its thick, lignified cell walls make it hard and strong. Living parenchyma has thin walls and loosely packed cells designed for storage and photosynthesis, so it lacks the rigidity needed for tough, fibrous strength.
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: The statement is incorrect, since meristematic cells are also found in the lateral meristem (around the stem, increasing girth) and the intercalary meristem (at the base of internodes, helping regrowth after cutting). Neha could ask Vibha, “Then how do plants like grass regrow after being cut or grazed, if meristematic cells are only present at the tips?”
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, since mature plant cells usually have one large central vacuole for storing water, minerals, sugars, and waste, while animal cell vacuoles (if present) are much smaller.
(ii) The assumption is that the plant cell is a typical mature plant cell, and the animal cell is a common/typical animal cell type.
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: Questions could include: “Does parenchyma only store food, or does it perform other functions too?” and “Does the epidermis only protect, or does it also help with gaseous exchange and transpiration?” Examples: parenchyma performs storage, photosynthesis, and helps aquatic plants float; the epidermis protects the plant but also helps in transpiration and gaseous exchange through stomata — showing plant tissues can perform more than one function.