Class-9 Science Chapter-3 Tissues in Action
Exercise Questions and Answers
Revise, Reflect, Refine
Q.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.
(iii) They have thin walls, dense cytoplasm and large prominent nucleus.
Q.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
(ii) Phloem
Q.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.
(iii) To allow quick exchange of materials across them.
Q.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?
The positions of your ankle, knee, and hip differ between the two jumps as follows:
- Ankle and Knee Positions: In a straight-leg jump, the knees and ankles are kept stiff and do not bend. In a normal jump, these joints bend naturally. This bending is possible because both the knee and the ankle contain hinge joints, which are specifically structured to allow bending and straightening in one direction.
- Hip Position: While the instructions specifically highlight the stiffness of the lower joints for the straight-leg jump, the hip position also changes significantly between the two. In a normal jump, the hip—which is a ball and socket joint — bends to coordinate with the knees and ankles to produce a natural jumping motion. In a straight-leg jump, the hip remains more extended to maintain the rigid posture required for the exercise.
Q.5) Which type of joint is involved when you bend your knees and ankles?
(i) Ball and socket
(ii) Hinge
(iii) Pivot
(ii) Hinge
Q.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.
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. (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.
Q.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.
(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?
(i) As the age of the teak tree increases, the diameter of the stem also increases. The increase is gradual during the early years and becomes more pronounced as the tree matures. This shows that the stem continuously grows in thickness throughout the life of the tree.
(ii) Each annual ring represents one year of growth. As the number of annual rings increases, the diameter of the stem also increases. Therefore, there is a direct relationship between stem diameter and the number of annual rings.
(iii) The lateral meristem is the specialized tissue responsible for increasing the girth (thickness) of the stem. This tissue is located along the circumference of the stems.
Q.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?
(i) As the bark includes the epidermis in younger plants and cork in older ones, it plays several critical protective functions in the plant. Debarking would hamper the plant in following ways:
The protection against water loss will be lost as the bark is impermeable to water, and its removal exposes the tree to excessive evaporation
The bark prevents the entry of harmful microorganisms and parasites from outside and its removal will expose the plant to pathogens.
The protection from mechanical injury and environmental extremes will be lost as the bark acts as a shield against physical damage and harsh environmental conditions.
(ii) The phloem tissue would be affected first after further damage to the tree trunk even after debarking followed by the lateral meristem and xylem tissue.
(iii) If the tissues beneath the bark were severely damaged, the functioning of the vascular bundle and lateral meristems would be compromised. The transport of food material by phloem and water and minerals by xylem along with the increase of girth by lateral meristem would be affected.
(iv) While answering we assume that "debarking" refers to the removal of the outer protective cork/bark and that "further damage" penetrates the vascular bundles. If the damage were superficial (only the outermost dead cork), the transport of food and water might remain unaffected, though the tree would still be vulnerable to infections and drying out.
We are also assuming that "severely damaged" implies the tissues are no longer functional. If the damage was partial, the tree might still function at a reduced efficiency and attempt to heal using its remaining meristematic cells
Q.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.
The tissue responsible for the flexibility observed in the young mango sapling’s stem is collenchyma.
If the collenchyma in the sapling was replaced by sclerenchyma, the impact would be as follows:
- Flexibility of the stem would be lost as sclerenchyma have lignified thick walls that makes them hard and strong rather than flexible.
- The stem would become stiff and brittle and will break during monsoon winds.
Q.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?
(i) Type ‘B’ cuttings were able to grow because they contain the node. The node consists of intercalary meristem which is responsible for the formation of new branches or sprouts.
Type ‘A’ cuttings does not contain any node, hence no intercalary meristems are present which results in formation of no new branches or sprouts.
(ii) Type ‘B’ cutting contained the node while the Type ‘A’ cutting had no node and was only internode region.
(iii) The determination was made by observing whether the cuttings sprouted and developed into sugarcane plants over the course of a few weeks. The length of new growth (shoot length) can also be measured at regular intervals to determine the growth over time.
(iv) The following parameters should be kept same for both types of cuttings to ensure a fair comparison:
- Growth condition like availability of sunlight, water, air and temperature.
- The length of both the cuttings should remain the same.
- Both the cuttings should be sourced from a single parent plant.
- They should be planted in the same soil or nutrient medium.
- Both the cuttings should be planted at the same time.
Q.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.
Both Rohan and Rajiv are partially correct. Rohan’s statement is true for simple permanent tissue where only one type of cells makes up the tissue and perform a single function like the collenchyma tissue that provides flexibility to plant parts.
On the other hand Rajiv’s argument is true in case of complex tissues where more than one type of cells makes up the complex permanent tissue. Here each of the cells of the tissue has individual function but all together they perform a common function. For example, the xylem tissue consists of four types of cells (tracheids, vessels, xylem parenchyma, and xylem fibres) that have their individual different role but as a unit they are responsible for the transport of water in plants.
Q.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 tissue is responsible for the toughness and strength of coconut husk fibres.
Structural Features of Sclerenchyma Providing Strength
- The cells of sclerenchyma is very thick due to the deposition of lignin, that makes the tissue hard and strong.
- Most of the cells of sclerenchyma tissue are dead at maturity, which allows them to act as a purely structural woody framework without needing any metabolic resources.
- Long and fibrous shaped cells along with bundle arrangement provides tissue with tensile strength and resistance to tearing.
Why Living Parenchyma Cannot Serve the Same Purpose
- Cells of parenchyma tissue are thin hence cannot provide strength to the tissue.
- Parenchyma cells are loosely packed with significant intercellular spaces that makes the tissue soft and cannot provide rigidity to the tissue.
- It lacks the hardness and "fibrous" structural integrity provided by lignin, meaning it would be too soft and fragile to withstand the pulling forces and wear and tear that a coconut fiber mat must endure.
Q.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 made by Vibha is not correct. This is because meristems are also found in other location like the periphery of stems and roots, base of internodes in addition to the root and shoot apices.
Questions that could be asked by Neha to Vibha is as follows:
- If growth only happens at the tips, how do you explain a tree trunk getting thicker and wider as it gets older?
- How does grass regrow after the top part has been mowed or eaten by animals?
- When the tip of the plant is cut off, new branches appear from the sides (nodes). As the shoot apical meristem is removed how is it possible for the new branches to appear from the sides?
Q.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?
(i) Plant cell will have a larger vacuole. It is because mature plant cells have a single large central vacuole that occupies almost 80-90% cell volume. It is involved in the storage of water, minerals, sugars and waste materials and also maintains the turgor pressure.
Animal cells either have no vacuoles or small vacuoles and are not prominent and permanent as in case of plant cell. Therefore, between a plant and animal of same size, the plant cell will have a larger vacuole.
(ii) We are making the following assumptions:
- The plant cell is a mature plant cell and not a young meristematic cell.
- The plant cells have undergone differentiation process and have a specialized functions like storage.
- The animal cell is a typical body cell and not a specialised cell like fat cell.
Q.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?
The statement “Each plant tissue performs only one specific function” is not entirely correct and needs to be examined critically for its correctness by asking questions like the following:
Question: Can a single tissue be responsible for both physiological processes (like transport) and mechanical roles (like support)?
Example: Xylem is a complex permanent tissue that performs two major functions: it transports water and minerals from the roots to the rest of the plant and also provides structural strength to the plant body.
Question: In tissues made of more than one type of cell, does every cell perform the exact same task, or do they have diverse roles that contribute to a larger goal?
Example: Phloem: Phloem is composed of four different cell types, each with a specific role: sieve tubes transport food, companion cells regulate the loading and unloading of sugars, phloem parenchyma stores materials like resins and tannins, and phloem fibres provide mechanical strength.
Question: Does a tissue maintain a single function throughout its life, or can it transition into a different role?
Example: Cells in meristematic tissues have the sole initial function of rapid cell division. However, through the process of differentiation, these cells lose their ability to divide and become permanent tissues specialized for support, transport, or storage.
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