New NCERT Solutions for Chapter 3 Tissues in Action Class 9 Science
- Chapter Name: Tissues in Action
- Textbook Name: Class 9 Science
Chapter 3 Tissues in Action NCERT Solutions Class 9 Science
Page No. 28
Think it Over
1. How is the study of cells and tissues significant for understanding the life processes and human welfare?
Answer
The study of cells and tissues helps us understand how living organisms function, grow, repair themselves and reproduce. Since cells are the basic structural and functional units of life, understanding them explains various life processes such as nutrition, respiration, transport and excretion. Knowledge of cells and tissues is also important in medicine, disease diagnosis, tissue engineering, organ transplantation and the development of new treatments for improving human welfare.
2. How are tissues in plants and animals different, and why?
Answer
Plant tissues and animal tissues differ in their structure and function.
Plant tissues are mainly concerned with growth, support, storage and transport of materials. Since plants are fixed at one place, many tissues provide mechanical strength and support.
Animal tissues are specialised for movement, coordination, protection and various body functions. Animals move from one place to another and respond quickly to environmental changes, so they possess specialised tissues such as muscular and nervous tissues.
Thus, the differences arise because plants and animals have different lifestyles and functional requirements.
3. How is the division of labour at various levels of organisation in multicellular organisms correlated with their structure and function?
Answer
In multicellular organisms, division of labour means that different cells perform different functions. Similar cells group together to form tissues. Different tissues combine to form organs, and organs work together as organ systems.
Each level of organisation has a specialised structure suited to its function. For example, muscle cells are specialised for movement, nerve cells for transmission of messages, and blood cells for transport of substances. This specialisation increases efficiency and enables the organism to perform complex life processes effectively.
Page No. 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 hard and brittle because they contain a large amount of sclerenchyma tissue. The cells of sclerenchyma have thick, lignified cell walls that provide great strength and rigidity.
On the other hand, the leaf stalks of coriander are soft and flexible because they contain mainly parenchyma and collenchyma tissues. Collenchyma cells have unevenly thickened walls that provide flexibility and support, allowing the leaf stalk to bend without breaking.
Therefore, the difference in hardness and flexibility is due to the different types of tissues present in these plant parts.
Page No. 34
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 the loss of water through evaporation. This is advantageous for desert plants because water is scarce in deserts and the thick cuticle helps conserve water.
However, in underwater plants, water is available in abundance and there is no danger of water loss. A thick cuticle would hinder the exchange of gases and absorption of dissolved substances from the surrounding water. Therefore, it is disadvantageous for aquatic plants.
3. Once water is absorbed by plant roots, it has to travel against gravity through xylem. How do the ‘dead’ cells of xylem work together with the living cells of leaves at the top to keep the water moving?
Answer
Xylem vessels are made up of dead cells that form continuous hollow tubes for water transport. The living cells of leaves lose water through transpiration. This creates a pulling force called transpiration pull.
The transpiration pull generated by the living leaf cells draws water upward through the xylem vessels from the roots to the leaves. Thus, the dead xylem cells and the living leaf cells work together to maintain the continuous upward movement of water against gravity.
4. What do you think will happen if there were no stomata in the epidermis of the stem or leaves?
Answer
If stomata were absent from the epidermis of stems and leaves, the exchange of gases between the plant and the atmosphere would be severely affected. Carbon dioxide would not enter the plant efficiently for photosynthesis, and oxygen produced during photosynthesis would not be released properly.
Transpiration would also stop, reducing the upward movement of water and minerals from the roots. As a result, the plant would not be able to carry out its normal life processes effectively and may eventually die.
Page No. 40
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
The dancers are using different joints of the body to perform various movements and poses.
1. Shoulder Joint (Ball and Socket Joint)
This joint allows movement of the arms in all directions, including rotation, lifting, lowering and circular movement.
2. Hip Joint (Ball and Socket Joint)
This joint allows the legs to move in all directions and helps the dancers maintain balance while performing complex steps.
3. Elbow Joint (Hinge Joint)
This joint allows bending and straightening of the arms in one plane.
4. Knee Joint (Hinge Joint)
This joint allows bending and straightening of the legs during dancing.
5. Wrist Joint (Gliding Joint)
This joint allows limited movement of the hand in different directions and helps create graceful hand gestures.
6. Ankle Joint (Hinge Joint)
This joint allows movement of the foot and helps in walking, jumping and maintaining body posture during dance.
7. Neck Joint (Pivot Joint)
This joint allows the head to turn from side to side and contributes to expressive dance movements.
Page No. 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.
Meristematic cells actively divide because they have thin cell walls, dense cytoplasm, a prominent nucleus and lack large vacuoles. These features help them carry out continuous cell 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
Phloem is the conducting tissue responsible for transporting food prepared in the leaves to all parts of the plant, including the roots. If food transport is affected, the phloem is malfunctioning.
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.
Epithelial tissues are generally thin so that substances such as oxygen, carbon dioxide, nutrients and wastes can pass through them easily and rapidly.
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 a straight-leg jump, the knees and ankles remain almost straight and stiff, while the hips show very little bending.
In a normal jump, the knees and ankles bend before the jump and straighten during take-off. The hip joints also bend and straighten, helping the body generate greater force and maintain balance.
Thus, the normal jump involves greater movement and flexibility of the ankle, knee and hip joints than the straight-leg jump.
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
The knee and ankle joints mainly function as hinge joints. They allow movement in one plane, mainly bending and straightening, similar to the movement of a door hinge.
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
(iii) (A) is true, but (R) is false.
The alveoli of lungs are lined by simple squamous epithelium, which is only one cell thick and allows rapid diffusion of gases. Multiple layers of tall cells would 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.
Answer
(i) Both (A) and (R) are true, and (R) is the correct explanation of (A).
Cardiac muscles contain numerous mitochondria and receive a rich blood supply, ensuring a continuous supply of oxygen and energy. Therefore, they can work continuously without fatigue.
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.
Tendons connect muscles to bones, not bone to bone. Ligaments connect bone to bone. The reason statement is correct because tendons transmit the force generated by muscles to bones.
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.
Hinge joints allow movement mainly in one plane, such as bending and straightening. Sliding in different directions is a characteristic of gliding joints, not hinge joints.
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 teak tree increases with age. As the tree grows older, secondary growth causes the stem to become thicker. The graph shows a steady increase in stem diameter over time, indicating continuous growth of the tree.
(ii) As the number of annual rings increases, the diameter of the tree also increases. Each annual ring represents one year of growth. Therefore, older trees with more annual rings generally have a larger stem diameter.
(iii) The specialised tissue responsible for the increase in girth of the stem is lateral meristem (cambium).
It is located along the sides of stems and roots, between the xylem and phloem tissues. The cambium continuously divides and produces new cells, causing secondary growth and an increase in stem thickness.
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) Debarking removes the protective outer covering of the tree. As a result:
- The protection of inner tissues from mechanical injury, pathogens and water loss is affected.
- The transport of food through the bark region may be disturbed.
- The overall growth and survival of the tree may be adversely affected.
Therefore, protection and food transport are the main functions hampered by debarking.
(ii) Further damage to the trunk may affect the vascular tissues (phloem and xylem) and the cambium present beneath the bark.
Among these, phloem is most likely to be affected first because it lies just below the bark.
(iii) If the tissues beneath the bark, especially the phloem and cambium, are severely damaged:
- Transport of food from leaves to other parts of the plant will be disrupted.
- Secondary growth and increase in girth may stop due to damage to the cambium.
- The roots may not receive food and can eventually die.
Thus, food conduction and growth of the tree would be severely hampered.
(iv) The answers above are based on the following assumptions:
- The bark has been removed from a large portion of the trunk.
- The phloem and cambium beneath the bark are damaged.
- The xylem remains largely intact initially.
If these assumptions change, the answers may also change.
- If only the outer bark is removed and the inner tissues remain unharmed, the effect on food transport may be minimal.
- If the damage extends deeper and reaches the xylem, water and mineral transport will also be affected.
- If only a small area is debarked, the tree may recover with little long-term damage.
- If the entire circumference of the trunk is debarked (girdling), food transport to the roots may stop completely, eventually causing the death of the tree.
Therefore, the severity of the effects depends on the extent and depth of damage to the tissues beneath the bark.
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
The tissue responsible for the flexibility of a young mango sapling's stem is collenchyma.
Collenchyma cells provide mechanical support along with flexibility because their cell walls are unevenly thickened. This allows the stem to bend during strong winds without breaking.
If the collenchyma tissue were replaced by sclerenchyma, the stem would become hard, rigid and less flexible because sclerenchyma cells have thick, lignified walls and are dead at maturity.
As a result, the sapling would lose its ability to bend easily and might break under strong monsoon 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 contained at least one node with a bud (meristematic tissue). The bud divided continuously and produced new shoots and roots, allowing the cutting to grow into a new sugarcane plant.
Type ‘A’ cuttings lacked a viable bud or growing point and therefore could not produce a new plant.
(ii) Type ‘B’ contained a node with an active intercalary meristem, whereas type ‘A’ did not contain a node or sufficient meristematic tissue required for regeneration.
(iii) The appearance of new shoots, leaves and roots was observed. The growth and development of the cuttings into healthy sugarcane plants indicated that regeneration had occurred successfully.
(iv) The following conditions should be kept the same:
- Length and age of the cuttings
- Type of soil
- Amount of water supplied
- Sunlight exposure
- Temperature and environmental conditions
- Time of observation
This ensures that the only difference is the presence or absence of the node.
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
Rohan's statement is correct for simple tissues because they consist of only one type of similar cells performing similar functions. Examples include parenchyma, collenchyma and sclerenchyma.
Rajiv is also correct because complex tissues are made up of different types of cells that work together to perform a common function. For example, xylem consists of tracheids, vessels, xylem fibres and xylem parenchyma, while phloem consists of sieve tubes, companion cells, phloem fibres and phloem parenchyma.
Therefore, the definition of tissue as a group of similar cells applies mainly to simple tissues, whereas complex tissues contain different kinds of cells working together.
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 provides the strength and toughness found in coconut husk fibres. Its cells have thick, lignified walls that make them hard, strong and resistant to wear and tear.
Living parenchyma cells have thin cell walls and large intercellular spaces. They are mainly involved in storage and photosynthesis and do not possess the mechanical strength required for making strong and durable mats. Therefore, parenchyma cannot perform the same function as sclerenchyma.
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. Meristematic tissues are not found only at the root and shoot apices. Besides apical meristems, plants also possess lateral meristems in the stem for increase in girth and intercalary meristems at the nodes and base of internodes for regeneration and growth.
Neha may ask:
“If meristematic tissues are present only at root and shoot tips, then how do stems increase in thickness and how does grass regrow after being cut?”
14. A plant cell and an animal cell are of the same size.
(i) Which cell will have a larger vacuole? Give reasons.
Answer
The plant cell will have a larger vacuole. Plant cells usually contain a large central vacuole that stores water, cell sap and other substances. It also helps maintain turgidity and provides support to the plant.
Animal cells generally have small and temporary vacuoles or may even lack them.
(ii) What assumptions are you making to answer the question above?
Answer
The answer assumes that both cells are mature, healthy and performing their normal functions. It is also assumed that the plant cell is not meristematic and the animal cell is a typical body cell.
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 examine the correctness of the statement, the following questions may be asked:
- Does a tissue perform only one function or multiple functions?
- Can the same tissue provide support as well as storage?
- Can a conducting tissue also provide strength?
- Do protective tissues have functions other than protection?
Examples that can be studied:
- Parenchyma – storage, photosynthesis and buoyancy in aquatic plants.
- Epidermis – protection, gaseous exchange and transpiration through stomata.
- Xylem – transport of water and minerals as well as mechanical support.
- Phloem – transport and storage of food materials.
These examples show that many plant tissues perform more than one function. Therefore, the statement is not completely correct.
