Tissues in ActionClass 9 Science NCERT Solutions
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Q1Revise, Reflect, Refine
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.
Solution
The correct option is (iii) They have thin walls, dense cytoplasm and large prominent nucleus.
Explanation:
According to the chapter, cells of meristematic tissues are characterized by being small, having thin cell walls, a large and prominent nucleus, and dense cytoplasm. They generally lack vacuoles. These features are adapted for continuous and rapid cell division, as they allow for quick synthesis of new cellular material and easy division without the hindrance of a large vacuole or thick wall.
Q2Revise, Reflect, Refine
If a plant is unable to transport food from leaves to roots which tissue is malfunctioning?
(i)
Xylem
(ii)
Phloem
(iii)
Epidermis
(iv)
Sclerenchyma
Solution
The correct option is (ii) Phloem.
Explanation:
Phloem is the complex permanent tissue responsible for transporting food, synthesized in the leaves during photosynthesis, to all other parts of the plant, including the roots for storage or energy. Xylem transports water and minerals from the roots upwards. Therefore, a failure in food transport indicates a malfunction in the phloem tissue.
Q3Revise, Reflect, Refine
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.
Solution
The correct option is (iii) To allow quick exchange of materials across them.
Explanation:
Epithelial tissues lining internal organs like the lungs (for gas exchange) and the small intestine (for nutrient absorption) are very thin, often a single layer of cells. This minimal thickness reduces the diffusion distance, allowing for rapid and efficient transport of substances such as gases, nutrients, and waste products across the tissue layer.
Q4Revise, Reflect, Refine
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?
Solution
The positions of the ankle, knee, and hip joints differ significantly between the two types of jumps:
-
Straight-leg jump: In this jump, the knees and ankles are kept stiff and extended with very little bending. The power for the jump is generated primarily from the hip joints, which flex and then extend rapidly, and the calf muscles pushing off from the ankles. The range of motion at the knee and ankle is minimal.
-
Normal jump: In a normal jump, the ankle, knee, and hip joints all bend (flex) during the preparatory crouch. This stores elastic energy in the muscles and tendons. Then, they all extend forcefully and in coordination to propel the body upwards. This allows for a much greater range of motion and generates a more powerful jump. The bending also helps in absorbing shock upon landing.
Q5Revise, Reflect, Refine
Which type of joint is involved when you bend your knees and ankles?
(i)
Ball and socket
(ii)
Hinge
(iii)
Pivot
Solution
The correct option is (ii) Hinge.
Explanation:
The knee and ankle joints are primarily hinge joints. A hinge joint allows movement predominantly in one plane, like the hinge of a door. In the case of the knee and ankle, this movement is flexion (bending) and extension (straightening). A ball and socket joint (like the shoulder) allows for rotation and movement in multiple planes, while a pivot joint (like in the neck) allows for rotational movement around an axis.
Q6Revise, Reflect, Refine
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.
Solution
A. Correct option: (iii) (A) is true, but (R) is false.
- Explanation: The assertion is true; the thin epithelial lining of the lungs is ideal for rapid gas exchange. The reason is false; this epithelium is a single layer of thin, flat cells (squamous epithelium), not multiple layers of tall cells, which would indeed slow down diffusion.
B. Correct option: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A).
- Explanation: The assertion is true; cardiac muscle works tirelessly throughout life. The reason is also true; a high number of mitochondria provides the constant energy (ATP) needed for contraction, and an abundant blood supply ensures continuous delivery of oxygen and nutrients. The reason correctly explains why cardiac muscle is fatigue-resistant.
C. Correct option: (iv) (A) is false, but (R) is true.
- Explanation: The assertion is false; tendons connect muscle to bone. Ligaments are the tissues that connect bone to bone. The reason is true; it correctly describes the composition and function of tendons.
D. Correct option: (iii) (A) is true, but (R) is false.
- Explanation: The assertion is true; hinge joints like the knee or elbow allow movement primarily in one plane (bending and straightening). The reason is false; the ends of the bones in a hinge joint are shaped to restrict movement to one plane, not to allow sliding in all directions.
Q7Revise, Reflect, Refine
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
S. No. Age of the teak tree (Years) DBH (Diameter at Breast Height) of tree (cm) Number of annual rings formed 1. 5 4 5 2. 10 8 10 3. 20 24 20 4. 25 28 25 5. 30 32 30 6. 40 40 40
(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?
Solution
Graph:
A graph would be plotted with 'Age of the teak tree (Years)' on the x-axis. The y-axis would represent both 'DBH (cm)' and 'Number of annual rings'. Two lines would be plotted:
- A line connecting the points for DBH against age: (5, 4), (10, 8), (20, 24), (25, 28), (30, 32), (40, 40).
- A line connecting the points for annual rings against age: (5, 5), (10, 10), (20, 20), (25, 25), (30, 30), (40, 40). This will be a straight line.
(i) Analysis and Interpretation:
The graph shows that the diameter of the stem (DBH) increases as the tree gets older. The growth is not perfectly linear; it appears to be faster in the earlier years (e.g., from 10 to 20 years, the diameter increases by 16 cm) and might slow down slightly in later years. The overall interpretation is that the tree continuously grows thicker over its lifetime.
(ii) Relation between Diameter and Annual Rings:
From the table and graph, it is clear that as the number of annual rings increases, the diameter of the tree also increases. The number of annual rings is directly proportional to the age of the tree (one ring per year). Therefore, the diameter increases as the number of annual rings increases, reflecting the cumulative growth over the years.
(iii) Specialised Tissue for Girth:
The specialised tissue responsible for the increase in the girth (diameter) of the stem is the lateral meristem. As stated in the chapter, this tissue is located as a ring in the stem and its cells divide to produce new cells towards the inside and outside, leading to an increase in the stem's diameter.
Q8Revise, Reflect, Refine
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?
Solution
(i)
Functions hampered by debarking:
Debarking removes the outer protective layers and the phloem tissue. This hampers two critical functions:
- Protection: The tree loses its protective covering, making it vulnerable to mechanical injury, water loss, and invasion by pests and microorganisms.
- Transport of Food: Phloem, which is part of the bark, transports food from the leaves to other parts of the plant, including the roots. If the bark is removed all the way around the trunk (a process called girdling), this transport is completely cut off, and the roots will eventually starve and die, leading to the death of the entire tree.
(ii)
Tissues affected by further damage:
Beneath the bark (phloem) lie the lateral meristem (cambium) and the xylem. Further damage to the trunk would affect these tissues.
(iii)
Function hampered by deeper damage:
If the tissues beneath the bark, specifically the xylem, were severely damaged, the following function would be hampered:
- Transport of Water and Minerals: Xylem is responsible for transporting water and minerals from the roots to the leaves. Severe damage to the xylem would disrupt this upward flow, causing the leaves to wilt and die, ultimately killing the tree.
- Structural Support: Xylem also provides mechanical strength to the stem. Severe damage would weaken the trunk.
(iv)
Assumptions and changes:
- Assumption: The primary assumption is that 'debarking' refers to the complete removal of the bark in a ring around the entire circumference of the trunk.
- How the answer would change: If this assumption is changed, and the debarking was only partial (i.e., not all the way around the trunk), the tree might survive. Some phloem and xylem pathways would remain intact, allowing for partial transport of food and water. The tree could be weakened and more susceptible to disease, but it would have a chance of recovery by callusing over the wound.
Q9Revise, Reflect, Refine
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.
Solution
Tissue responsible for flexibility:
The tissue responsible for the flexibility of the young stem is collenchyma. The chapter explains that collenchyma consists of living cells with unevenly thickened corners that provide both support and flexibility. This allows plant parts like stems to bend without breaking.
Impact of replacement by sclerenchyma:
If the collenchyma tissue were replaced by sclerenchyma, the stem would lose its flexibility and become hard and rigid. Sclerenchyma cells have thick, uniformly lignified walls that make them strong but brittle. When faced with strong monsoon winds, the rigid stem would be unable to bend. Instead of flexing, it would be highly likely to snap and break under the force of the wind.
Q10Revise, Reflect, Refine
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?
Solution
(i)
& (ii) Reason for growth difference:
Cutting 'B' was able to grow because it included a node, whereas cutting 'A' was an internode section without a node. The key difference is the presence of intercalary meristem at the node. This meristematic tissue consists of actively dividing cells that can differentiate to form new shoots and roots, allowing the cutting to regenerate into a new plant. Cutting 'A' lacked this essential meristematic tissue and thus could not sprout.
(iii)
Observation or measurement:
The observation made to determine the effect was whether the cuttings sprouted or not. The growth of new shoots and roots from the nodes of cutting 'B' was the positive result, while the lack of any growth and eventual decay of cutting 'A' was the negative result.
(iv)
Parameters for a fair comparison:
To ensure a fair comparison, all other conditions (controlled variables) should have been kept the same for both types of cuttings. These include:
- The source plant for the cuttings.
- The length and diameter of the cuttings.
- The growth medium (e.g., soil type, water).
- Environmental conditions like temperature, humidity, and amount of sunlight.
- The orientation of the cutting when planted.
Q11Revise, Reflect, Refine
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.
Solution
Rajiv's counter-argument is correct. The definition of a tissue needs to be nuanced.
-
Rohan's statement is a perfect definition for simple tissues. As the chapter explains, simple tissues like parenchyma, collenchyma, and sclerenchyma are composed of only one type of cell. All these cells are structurally and functionally similar.
-
Rajiv's point correctly applies to complex tissues. A complex tissue, as defined in the chapter, is made up of more than one type of cell, all of which work together to perform a common function. For example:
- Xylem is a complex tissue that transports water. It is composed of four different types of cells: tracheids, vessels, xylem parenchyma, and xylem fibres. Each cell type has a different structure, but they all contribute to the functions of water conduction and support.
- Phloem is another complex tissue that transports food. It consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibres.
Therefore, a more comprehensive definition of a tissue is "a group of cells that are similar in structure and/or work together to achieve a particular function." This covers both simple and complex tissues.
Q12Revise, Reflect, Refine
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.
Solution
Tissue providing strength:
The tissue that provides the toughness and fibrous strength to coconut husk is sclerenchyma. The chapter states that sclerenchyma cells have thick, hard walls due to the deposition of lignin. These cells are typically dead at maturity and their primary function is to provide mechanical support and rigidity. Coconut husk is a classic example of this tissue.
Why parenchyma is unsuitable:
Parenchyma could not serve the same purpose for two main reasons:
- Thin Cell Walls: Parenchyma cells are living cells with thin cellulose walls. They lack the thick, lignified secondary walls that give sclerenchyma its strength and hardness. They are soft and would easily tear.
- Function: The primary functions of parenchyma are storage, photosynthesis, and secretion. It is not structurally adapted for providing mechanical strength and durability required for a product like a mat.
Q13Revise, Reflect, Refine
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?
Solution
Evaluation of the statement:
Vibha's statement is incorrect. It is an incomplete description of the location of meristematic tissues. While meristematic tissue is indeed found at root and shoot apices (called apical meristem), it exists in other parts of the plant as well.
Question Neha can ask:
To help Vibha correct her understanding, Neha could ask one of the following questions based on the chapter content:
- "If meristems are only at the tips, how does a tree trunk get wider every year?" This question would prompt Vibha to think about growth in girth, which is caused by the lateral meristem located along the circumference of the stem.
- "How does grass grow back so quickly after it is mowed or eaten by a cow, even though its tips are cut off?" This question would lead to the concept of the intercalary meristem, which is located at the base of nodes or internodes in plants like grasses and is responsible for regeneration and growth in length from those points.
Q14Revise, Reflect, Refine
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?
Solution
(i)
Cell with a larger vacuole:
The plant cell will have a larger vacuole. In a mature plant cell, the central vacuole is a large, permanent organelle that can occupy 50-90% of the cell volume. Its primary functions are to maintain turgor pressure against the cell wall (providing support), store water, nutrients, and waste products. In contrast, animal cells may have small, temporary vacuoles, but they lack a large central vacuole.
(ii)
Assumptions made:
The key assumption is that we are comparing a mature, differentiated plant cell with a typical animal cell. A young, actively dividing plant cell (like a meristematic cell) has a dense cytoplasm and either very small vacuoles or no vacuoles at all, which would make it more similar to an animal cell in this regard. The premise that the cells are of the 'same size' is also an idealization, as the large vacuole is a major contributor to the overall size of a mature plant cell.
Q15Revise, Reflect, Refine
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?
Solution
The statement "Each plant tissue performs only one specific function" is an oversimplification and largely incorrect. Many tissues are multifunctional.
Questions to critically examine the statement:
- Can a single tissue have both a primary and a secondary function? For example, can a tissue for transport also provide support?
- Does the function of a tissue vary depending on its location within the plant?
- Are there tissues that can perform fundamentally different processes, such as storage and photosynthesis, at the same time?
Examples of tissues to find answers:
- Parenchyma: This tissue is an excellent example to challenge the statement. The chapter states that parenchyma's main function is food storage, but it also performs photosynthesis when it contains chloroplasts (then called chlorenchyma). In aquatic plants, it forms air spaces (aerenchyma) to provide buoyancy. This demonstrates that parenchyma can have multiple functions: storage, photosynthesis, and providing buoyancy.
- Xylem: The primary function of xylem is the conduction of water and minerals. However, its cells (tracheids, vessels, and fibres) have thick, lignified walls. As the chapter mentions, xylem also "provides strength to the plant." This shows a dual function of transport and mechanical support.
- Epidermis: The primary function is protection. However, the epidermis of leaves contains stomata for gas exchange and transpiration, and the epidermis of roots develops root hairs for water and mineral absorption. This shows that the function of the epidermis is specialized depending on its location.