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 a large prominent nucleus.
These features of meristematic cells support continuous and rapid cell division. They generally have little or no intercellular space and lack prominent vacuoles.
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
Phloem transports food prepared in the leaves to other parts of the plant, including the roots.
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.
Epithelial tissues involved in exchange, such as those lining blood vessels and lungs, consist of a single layer of thin, flat cells. Their thin structure allows rapid diffusion of gases and other materials.
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?
In a straight-leg jump, the knees and ankles remain relatively stiff, so there is less bending at these joints. In a normal jump, the knees and ankles bend naturally, while the hip also changes position to help the body lower and then push upward. Thus, the normal jump involves greater bending and coordinated movement of the ankle, knee and hip joints.
5. Which type of joint is involved when you bend your knees and ankles?
(i) Ball and socket
(ii) Hinge
(iii) Pivot
(ii) Hinge joint
The knee and ankle are involved in bending and straightening movements. A hinge joint primarily permits movement in one direction, 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.
6. 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.
(iii) (A) is true, but (R) is false.
The epithelium involved in gas exchange consists of a single layer of thin, flat cells, which allows rapid 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.
(i) Both (A) and (R) are true, and (R) is the correct explanation of (A).
Cardiac muscles work continuously and rhythmically. Their high energy requirements are supported by mitochondria and 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.
(iv) (A) is false, but (R) is true.
Tendons connect muscles to bones, whereas ligaments connect bones to bones. Tendons transmit the force produced by muscle contraction 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.
(iii) (A) is true, but (R) is false.
A hinge joint permits movement mainly in one direction. The reason is incorrect because sliding in all directions is not the characteristic of a hinge joint.
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?
Given Data:
Age of tree (years) | Diameter (cm) | Annual rings |
5 | 4 | 5 |
10 | 8 | 10 |
20 | 24 | 20 |
25 | 28 | 25 |
30 | 32 | 30 |
40 | 40 | 40 |
(i) Analysis:
The graph shows that the diameter of the teak tree generally increases as its age increases. The increase is not perfectly uniform; for example, the diameter rises from 8 cm at 10 years to 24 cm at 20 years and then continues increasing with age.
(ii) Relation between diameter and annual rings:
The number of annual rings corresponds directly to the age of the tree. As the tree grows older, more annual rings are formed. The diameter also generally increases with the formation of new growth layers.
(iii) Specialised tissue:
The lateral meristem is responsible for increasing the girth of the stem. It is present as actively dividing cells arranged in a ring along the circumference of 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?
Debarking damages/removes the protective outer tissues of the tree and can interfere with the protection of inner tissues and the normal transport functions associated with tissues beneath the bark.
(ii) Which plant tissue would be affected by further damage to the tree trunk even after debarking?
The conducting tissues, particularly the phloem and xylem, could be affected if damage extends into the trunk.
(iii) Which function of the tree would be hampered if the tissues beneath the bark were severely damaged?
If phloem is severely damaged, the transport of food from leaves to other parts of the plant would be affected. If xylem is also damaged, the transport of water and minerals from roots to other parts would be affected.
(iv) What assumptions are you making to answer the questions above? How would the answer change if your assumptions are also changed?
The answer assumes that:
- the debarking mainly removes the outer bark;
- the underlying conducting tissues are initially intact;
- further damage may reach phloem and/or xylem.
If the damage is deeper, both food transport and water/mineral transport may be affected. If only the outer protective layer is damaged, the conducting functions may initially continue.
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 is collenchyma.
Collenchyma consists of living cells with unevenly thickened corners due to pectin deposition. It provides support and flexibility, allowing stems and tendrils to bend without breaking.
If the collenchyma were replaced by sclerenchyma, the stem would become harder and less flexible. Sclerenchyma has thick, lignified walls and provides strength and rigidity. Therefore, the young stem would be less capable of bending freely in 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?
Type B cuttings were able to grow because they contained the necessary part of the stem containing a node, where intercalary meristem is located. Type A apparently lacked this required region.
(ii) What difference was present in type ‘B’ compared to type ‘A’?
Type B had a node, whereas type A did not have the required node.
(iii) What observation or measurement was made to determine whether this change had an effect?
The researcher observed whether the cuttings sprouted and developed into sugarcane plants after a few weeks. The appearance of sprouts and subsequent plant growth indicated successful regeneration.
(iv) What parameters should be kept the same for both types of cuttings to ensure a fair comparison?
Parameters that should remain the same:
For a fair comparison, factors such as:
- size/length of cuttings,
- variety and age of sugarcane,
- soil or growth medium,
- amount of water,
- light,
- temperature,
- planting depth, and
- duration of observation
should be kept the same. The presence or absence of the node should be the main variable being tested.
The chapter explains that intercalary meristem is located at the base of an internode or just above a node and helps plants regenerate after cutting.
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.
Rohan’s statement is generally applicable to simple tissues, but it is not completely suitable for complex tissues.
A simple permanent tissue consists of only one type of cell. Examples are parenchyma, collenchyma and sclerenchyma.
A complex permanent tissue consists of more than one type of cell. Different cell types work together to perform a common function. For example, xylem contains tracheids, vessels, xylem parenchyma and xylem fibres, while phloem contains sieve tubes, companion cells, phloem parenchyma and phloem fibres.
Therefore, in complex tissues, cells may differ in structure but coordinate to perform a common function.
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.
The tissue responsible for the toughness and strength of coconut husk is sclerenchyma.
Sclerenchyma cells have thick walls due to lignin deposition, making them hard and strong. Most of these cells are dead. Sclerenchyma occurs in hard structures such as coconut husk and provides mechanical strength.
Parenchyma cannot serve the same purpose because its cells are living, have thin walls and are loosely packed with intercellular spaces. Its major functions include food storage and, in green parts, photosynthesis.
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?
Vibha’s statement is incorrect.
Meristematic tissues are not located only at the root and shoot apices. There are three types:
1. Apical meristem – present at root and shoot tips; increases length.
2. Lateral meristem – located along the circumference of stems; increases girth.
3. Intercalary meristem – located at the base of certain internodes or near nodes; helps regeneration after cutting, particularly in plants such as grasses.
A suitable question Neha could ask:
“Are there meristematic tissues in parts of the plant other than the root and shoot apices? If yes, where are they located and what functions do they perform?”
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) The plant cell will generally have a larger vacuole.
Plant cells commonly have a prominent vacuole, which can occupy a considerable part of the cell and is involved in storage and maintaining cell structure.
(ii) This answer assumes that:
- both cells are typical, mature plant and animal cells;
- they are being compared under normal conditions;
- the cells have similar overall dimensions;
- the question refers to a typical plant cell rather than a specialised plant cell.
The conclusion can vary because different types of cells can have different structures and functions.
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” should be critically examined rather than accepted without questioning.
Useful questions include:
1. Does every tissue perform only one function?
2. Can the same tissue contribute to more than one function?
3. Does the function of a tissue depend upon its location?
4. Are some tissues specialised for a main function while also contributing to other functions?
Examples:
- Parenchyma mainly stores food but can also perform photosynthesis in green parts of plants. In aquatic plants, specialised parenchyma forms air spaces that help the plant float.
- Epidermis protects the plant, but its specialised structures also perform other functions. Root hairs increase surface area for absorption of water and minerals, while stomata help in gaseous exchange and transpiration.
- Xylem transports water and minerals and also provides strength to the plant.
Therefore, plant tissues may have a main specialised function while also contributing to other functions. The statement that every plant tissue performs only one function is therefore an oversimplification.