NCERT Solutions for Class 9 Science Chapter 3, Tissues in Action, help students understand how groups of specialised cells work together to perform specific functions in living organisms. This chapter from the new NCERT textbook, Exploration: A Textbook of Science for Grade 9, explores the organisation, structure, and functions of different types of tissues.
In this chapter, students learn how tissues are organised in plants and animals and how their structure is related to the functions they perform. The solutions provide clear explanations for textbook questions and activities, helping students understand the concepts, revise important topics, and prepare effectively for examinations.
NCERT Exercise answers
(For the exact question, refer to the NCERT textbook.)
- Meristematic tissues divide repeatedly. What property allows them to do this?
Answer: (iii) They have thin walls, dense cytoplasm and large prominent nucleus.
- If a plant is unable to transport food from leaves to roots, which tissue is malfunctioning?
Answer: (ii) Phloem
Reason: Phloem transports food from leaves to other parts of the plant.
- Why are epithelial tissues usually only one or a few cells thick?
Answer: (iii) To allow quick exchange of materials across them.
- Difference between straight-leg jump and normal jump
Answer: Straight-leg jump:
- Ankles, knees and hips remain stiff and less bent.
Normal jump:
- Ankles, knees and hips bend naturally.
- Movement is smoother and more flexible.
- Which type of joint is involved when you bend your knees and ankles?
Answer: (ii) Hinge joint
- Assertion and Reason
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.
Reason: Gas exchange occurs through thin squamous epithelium, not multiple thick layers.
B. Assertion: Cardiac muscle can contract continuously without fatigue.
Reason: Cardiac muscle cells have a high number of mitochondria and 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: Assertion is false, Reason is true.
Explanation: Tendons connect muscle to bone, while ligaments connect bone 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.
Answer: Assertion is true, Reason is false.
Explanation: Hinge joints (knee, elbow) allow movement mainly in one plane, while sliding in all directions occurs in gliding joints.
- (i) Analyse the graph in terms of the diameter of the stem over time and share the interpretation.
Answer: The graph shows that as the age of the teak tree increases, the diameter of the stem also increases. The increase is gradual and indicates continuous secondary growth in the tree.
(ii) What is the relation between the diameter of the teak tree and annual rings formed?
Answer: The diameter of the teak tree increases with an increase in annual rings. More annual rings indicate older age and greater stem girth.
(iii) Which specialised tissue is responsible for the girth of the stem and where is it located?
Answer: The specialised tissue responsible for increase in girth is lateral meristem (cambium).
Location: It is present between xylem and phloem along the sides of the stem and roots.
- (i) Which function(s) of the tree is/are hampered by debarking?
Answer: Debarking hampers:
- Transport of food from leaves to other parts of the plant
- Protection of inner tissues
- Normal growth of the plant
(ii) Which plant tissue would be affected by damage to the tree trunk even after debarking?
Answer: Phloem tissue would be affected because it lies beneath the bark and transports food.
(iii) Which function of the tree would be hampered if the tissues beneath the bark were severely damaged?
Answer: The transportation of prepared food from leaves to other parts of the plant would be hampered.
(iv) What assumptions are you making? How would the answer change if assumptions changed?
Answer: Assumption: Damage caused by debarking has also affected the tissues below the bark, especially phloem and cambium.
If assumptions change:
If only the outer bark is removed and inner tissues remain undamaged, the effect on food transport and growth would be less severe, and the tree may recover.
- Answer: The tissue responsible for flexibility is Collenchyma because its cells provide support along with flexibility.
If collenchyma were replaced by sclerenchyma, the stem would become hard and rigid due to thick lignified walls. The young mango stem would lose flexibility and may break easily during strong winds.
- (i) Why were type ‘B’ cuttings able to grow as sugarcane but type ‘A’ could not?
Answer: Type B cuttings contained nodes with buds (meristematic tissue) that developed into new shoots. Type A lacked these buds, so it could not grow.
(ii) What difference was present in type ‘B’ compared to type ‘A’?
Answer: Type B had nodes/axillary buds, whereas type A did not.
(iii) What observation or measurement was made to determine whether this change had an effect?
Answer: The observation made was the appearance of sprouts and growth of new shoots after a few weeks.
(iv) What parameters should be kept the same for both types of cuttings?
Answer:
- Length of cuttings
- Amount of water
- Soil type
- Temperature
- Sunlight exposure
- Planting depth
- Answer: Rohan’s statement is true for simple tissues because they consist of similar cells performing similar functions.
Rajiv is also correct because complex tissues consist of different types of cells working together for a common function.
Example: Xylem contains tracheids, vessels, fibres and parenchyma.
- Answer: Sclerenchyma tissue provides the strength required for coconut husk fibres because its cells have thick lignified walls.
Living parenchyma cannot perform the same function because it has thin cell walls and mainly functions in storage and photosynthesis, not strength.
- Answer: Vibha’s statement is incorrect because meristematic tissues are not only present at root and shoot apices. They are also present as:
- Lateral meristem → for increase in girth
- Intercalary meristem → at nodes or base of leaves
Question Neha can ask: “If meristematic tissue is present only at root and shoot tips, then how does a stem increase in thickness?”
- (i) Which cell will have a larger vacuole? Give reasons.
Answer: The plant cell will have a larger vacuole because it stores cell sap and helps maintain turgidity and rigidity.
(ii) What assumptions are you making?
Answer: Assumptions:
- Both cells are mature cells
- Both are healthy and functioning normally
- Same environmental conditions are considered
- Answer: Questions to examine the statement:
- Does a tissue perform only one function?
- Can one tissue perform more than one role?
- Are there tissues with multiple functions?
Examples:
- Parenchyma → storage, photosynthesis, healing
- Collenchyma → support and flexibility
- Xylem → transport of water and support
- Phloem → transport of food
Intext question answer
(For the exact question, refer to the NCERT textbook.)
Question 1.
Answer: The fibres of coconut husk are hard and brittle because they contain more sclerenchyma tissue, which has thick and lignified cell walls that provide strength and hardness.
The leaf stalks of coriander are soft and flexible because they contain more collenchyma tissue, which has living cells with unevenly thickened walls that provide flexibility and support.
Question 2.
Answer: A thick cuticle on the epidermis is helpful for desert plants because it reduces water loss through transpiration.
But for underwater plants, a thick cuticle is disadvantageous because they need to absorb water and gases directly from their surroundings, and a thick cuticle would prevent this.
Question:3
Answer: The dead cells of xylem form hollow tubes that carry water upward. The living cells in the leaves lose water through transpiration, creating a suction pull that helps move water continuously upward through the xylem.
Question 4
Answer: If there were no stomata in the epidermis of stems or leaves, exchange of gases would not take place properly and transpiration would stop. As a result, photosynthesis and respiration would be affected, and the plant may eventually die.
Question 5.
Answer: The joints involved in these dance movements are mainly:
- Ball and socket joints – present in the shoulders and hips; they allow movement in all directions.
- Hinge joints – present in knees and elbows; they allow back-and-forth movement.
- Pivot joints – present in the neck; they help in turning the head.
- Gliding joints – present in wrists and ankles; they allow slight sliding movements.
These joints together help dancers perform flexible and graceful movements.