Think It Over
Question 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 is very significant because cells are the basic units of life and tissues are groups of cells that perform specific functions. By studying cells and tissues, we understand how living organisms grow, move, breathe, digest food, transport materials, respond to stimuli, heal wounds and reproduce.
For example, in animals, muscle tissue helps in movement, nervous tissue helps in control and coordination, and blood transports oxygen and nutrients. In plants, xylem transports water and minerals, while phloem transports food.
This knowledge is also useful for human welfare. It helps in areas such as medicine, treatment of diseases, tissue culture, crop improvement, bone marrow transplant, and genetic engineering. For example, plant tissue culture helps in growing improved and disease-free plants, and the study of stem cells helps in treating some blood-related diseases.
Question 2. How are tissues in plants and animals different, and why?
Answer:
Plant tissues and animal tissues are different because plants and animals have different structures, functions and ways of living.
Plants are mostly fixed in one place, so they need strong and supportive tissues to remain upright. Plant cells have a cell wall, which gives strength and rigidity. Plants also have special tissues like xylem and phloem for transporting water, minerals and food.
Animals usually move from one place to another, so their tissues are more flexible. Animal cells do not have a cell wall, so they can change shape more easily. Animals have tissues such as muscular tissue for movement, nervous tissue for coordination, epithelial tissue for protection and connective tissue for support.
Thus, plant tissues are mainly adapted for support, growth, protection and transport, while animal tissues are adapted for movement, protection, connection, control and coordination.
Question 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, different cells, tissues, organs and organ systems perform different functions. This is called division of labour. It makes the body more efficient.
The structure of each cell or tissue is suited to its function. For example, muscle cells are long and contractile, so they help in movement. Nerve cells have long axons and branches, so they transmit messages. Xylem cells are tube-like and thick-walled, so they transport water and provide support. Epithelial cells are closely packed, so they protect body surfaces and linings.
This means that at every level of organisation, structure and function are closely related:
Cell → Tissue → Organ → Organ system → Organism
For example, muscle cells form muscular tissue, muscular tissue helps form muscles, muscles work with bones in the musculoskeletal system, and this system helps the organism move.
Pause and Ponder – Page 33
Question 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 sclerenchyma tissue. Sclerenchyma cells have thick walls due to the deposition of lignin. These cells are mostly dead and provide strength, hardness and rigidity.
On the other hand, coriander leaf stalks are soft and flexible because they contain more collenchyma and parenchyma tissues. Collenchyma cells are living cells with unevenly thickened corners due to pectin. They provide support as well as flexibility. Parenchyma cells are thin-walled and living, so they make the stalk soft.
Therefore, coconut husk is hard due to sclerenchyma, while coriander stalk is soft and flexible due to collenchyma and parenchyma.
Pause and Ponder – Page 34
Question 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 is advantageous for a desert plant because deserts have very hot and dry conditions. The thick cuticle reduces water loss through transpiration and protects the plant from drying.
But for an underwater plant, a thick cuticle is disadvantageous because water is already present all around the plant. Such plants need easy exchange of gases and substances through their surface. A thick cuticle would block or reduce this exchange and make absorption and gaseous exchange difficult.
So, a thick cuticle is useful in desert plants for water conservation, but it is not useful in underwater plants because it can interfere with exchange of materials.
Question 3. Once water is absorbed by plant roots, it has to travel against gravity through xylem. How do the ‘dead’ cells of the xylem work together with the living cells of leaves at the top to keep the water moving?
Answer:
Xylem contains mostly dead cells such as tracheids and vessels. These cells are long, hollow and tube-like, so they form continuous channels for water transport from roots to leaves.
The living cells of leaves help in this process through transpiration. Water evaporates from the leaves through stomata. This creates a pulling force called transpiration pull. Because of this pull, water is drawn upward through the xylem from the roots to the leaves.
Thus, dead xylem cells act like strong water-conducting tubes, while living leaf cells and stomata create the transpiration pull that keeps water moving upward against gravity.
Question 4. What do you think will happen if there were no stomata in the epidermis of the stem or leaves?
Answer:
If there were no stomata in the epidermis of the stem or leaves, the plant would face many problems.
First, gaseous exchange would not take place properly. Carbon dioxide would not enter the leaves easily, so photosynthesis would be affected. Oxygen produced during photosynthesis would also not come out properly.
Second, transpiration would be greatly reduced. Due to this, transpiration pull would become weak, and the upward movement of water through xylem would be affected.
Third, the plant may not be able to remove some wastes through transpiration.
Therefore, without stomata, photosynthesis, gaseous exchange, transpiration and water transport would be badly affected.
Table 3.5: Different types of movements our body can make
Question: Table 3.5: Different types of movements our body can make
Answer:
| Body Parts | Complete Rotation | Partial Rotation | Bending | Turning, Side-raising, Up-down or Any Other Movement |
|---|---|---|---|---|
| Elbow | No | No | Yes | Up-down movement of forearm |
| Shoulder | Yes | Yes | Yes | Forward, backward, sideways and circular movement |
| Knee | No | No | Yes | Bending and straightening of leg |
| Neck | No | Yes | Yes | Turning head side to side and up-down movement |
| Fingers | No | No | Yes | Bending, gripping and slight spreading |
| Toes | No | No | Yes | Bending and slight up-down movement |
| Wrist | No | Yes | Yes | Up-down, side-to-side and partial circular movement |
Explanation: Different body parts show different movements because they have different types of joints. The shoulder has a ball and socket joint, so it can move in many directions. The elbow and knee have hinge joints, so they mainly bend and straighten. The neck has a pivot joint, so it allows side-to-side movement.
Pause and Ponder – Page 40
Question 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:
In classical and folk dance poses, many joints of the body work together. The main joints involved are shoulder, elbow, wrist, hip, knee, ankle, neck and fingers.
| Joint Involved | Type of Joint | Movement Allowed |
|---|---|---|
| Shoulder | Ball and socket joint | Movement of arms forward, backward, sideways and circularly |
| Elbow | Hinge joint | Bending and straightening of arms |
| Wrist | Gliding/partly movable joint | Bending, turning and hand gestures |
| Fingers | Hinge joints | Bending and forming mudras or hand gestures |
| Hip | Ball and socket joint | Movement of legs in many directions |
| Knee | Hinge joint | Bending and straightening of legs |
| Ankle | Hinge-type joint | Up-down movement of foot |
| Neck | Pivot joint | Turning head side to side and slight up-down movement |
| Skull bones | Fixed joints | No movement; protect the brain |
Dance movements are possible because bones, muscles and joints work together. Muscles pull bones, and joints allow movement in particular directions. For example, bending of knees in dance occurs due to hinge joints, while circular movement of arms occurs due to ball and socket joints in the shoulders.
Think as a Scientist – Page 42
Question (a). What do you conclude about the characteristics of phloem cells of carrot?
Answer:
We conclude that phloem cells of carrot show totipotency. This means that even a single mature plant cell can develop into a complete plant under suitable conditions.
In F. C. Steward’s experiment, carrot phloem cells were grown in a nutrient medium containing sugars and hormones. These cells first divided to form a mass of cells. Then they differentiated into roots, shoots and finally a complete plant.
This shows that carrot phloem cells can dedifferentiate, divide and redifferentiate to form a whole plant.
Question (b). In which of the three combinations would you obtain the highest and lowest biomass? What could be the possible reason(s) for this observation?
Answer:
According to Table 3.6, the highest biomass would be obtained in the condition where light is present, air is present, and the cells are grown in a liquid medium with nutrients. In this condition, the fresh weight of cells increased by 20%.
The lowest biomass would be obtained in the conditions where growth is reduced. These include:
- light present, air absent, solid medium with nutrients, and
- light absent, air present, liquid medium with nutrients.
The best growth occurs when cells get proper light, air and nutrients in a liquid medium. Light helps in photosynthesis, air provides gases needed for respiration and growth, and nutrients provide materials for cell division. Liquid medium also allows better availability of nutrients to the cells.
Growth is reduced when either air or light is absent because cells do not get all the necessary conditions for proper division and development.
Question (c). Will you get the same results if you culture animal cells instead of carrot cells?
Answer:
No, we will generally not get the same results if animal cells are cultured instead of carrot cells.
Plant cells, such as carrot phloem cells, can show totipotency. Under suitable conditions, a single plant cell can develop into a complete plant.
Animal cells are usually more specialised and do not easily develop into a complete animal from a single body cell in the same way. Animal cell culture is also more complex and requires very specific conditions. Some animal cells, like stem cells or early embryonic cells, may have the ability to form many types of cells, but ordinary specialised animal cells cannot normally form a complete animal.
Therefore, the same results are not expected with animal cells.
Question (d). Think and mention any two commercial applications of the study above.
Answer:
Two commercial applications of this study are:
- Plant tissue culture:
This technique can be used to produce many plants from a small piece of plant tissue or even from single cells under controlled conditions. - Crop improvement and production of disease-free plants:
Tissue culture can help produce improved, healthy and disease-free plants in large numbers. It is useful in agriculture, horticulture and production of valuable crops.
Other applications include production of valuable plant chemicals, genetic engineering of plants and conservation of rare plant species.
Revise, Reflect, Refine
Question 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:
Correct option: (iii) They have thin walls, dense cytoplasm and large prominent nucleus.
Meristematic cells divide repeatedly because they are actively dividing cells. They have thin cell walls, dense cytoplasm, many organelles, and a large prominent nucleus. These features help them divide quickly and continuously.
Question 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:
Correct option: (ii) Phloem
Phloem transports food prepared in the leaves to other parts of the plant, including roots. If food cannot move from leaves to roots, the phloem is not functioning properly.
Question 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:
Correct option: (iii) To allow quick exchange of materials across them.
Epithelial tissues lining internal organs are thin so that substances like gases, nutrients and waste materials can pass through them quickly. For example, thin epithelial lining in the lungs helps in rapid exchange of oxygen and carbon dioxide.
Question 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 stiff and almost straight. The hip also has limited bending. Because the joints are not used properly, the jump feels difficult and less balanced.
In a normal jump, the knees, ankles and hips bend naturally before jumping. During the jump, these joints straighten to push the body upward. This makes the jump smoother, stronger and more balanced.
So, in a normal jump, the ankle, knee and hip joints bend and straighten actively, while in a straight-leg jump, these joints remain mostly stiff.
Question 5. Which type of joint is involved when you bend your knees and ankles?
(i) Ball and socket
(ii) Hinge
(iii) Pivot
Answer:
Correct option: (ii) Hinge
The knee and ankle mainly show bending and straightening movements. Such movement occurs at a hinge joint, which works like the hinge of a door.
Question 6. 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: Correct option: (iii) (A) is true, but (R) is false.
The assertion is true because epithelium in the lungs helps in gas exchange. But the reason is false because the lung epithelium is not made of multiple layers of tall cells. It is thin and usually one cell thick, which allows rapid diffusion of gases.
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: Correct option: (i) Both (A) and (R) are true, and (R) is the correct explanation of (A).
Cardiac muscles work continuously throughout life. They need a constant supply of energy. A high number of mitochondria and good blood supply help cardiac muscle cells produce enough energy, so they can contract continuously without getting tired easily.
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: Correct option: (iv) (A) is false, but (R) is true.
The assertion is false because tendons do not connect bone to bone. Ligaments connect bone to bone. Tendons connect muscle to bone.
The reason is true because tendons are tough connective tissues that transmit force from muscles to bones and help in movement.
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: Correct option: (iii) (A) is true, but (R) is false.
The assertion is true because hinge joints allow movement mainly in one plane, such as bending and straightening. The reason is false because hinge joints do not allow sliding in all directions. Ball and socket joints allow movement in many directions.
Question 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.
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 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 |
Answer:
To plot the graph:
- Take Age of the teak tree on the x-axis.
- Take Diameter of the tree and number of annual rings on the y-axis.
- Plot two lines:
- one line for diameter,
- one line for number of annual rings.
Points for diameter: (5, 4), (10, 8), (20, 24), (25, 28), (30, 32), (40, 40)
Points for annual rings: (5, 5), (10, 10), (20, 20), (25, 25), (30, 30), (40, 40)
Question 7(i). Analyse the graph in terms of the diameter of the stem over time and share the interpretation.
Answer:
The graph shows that the diameter of the teak tree increases as the age of the tree increases.
From 5 to 10 years, the diameter increases slowly from 4 cm to 8 cm. From 10 to 20 years, the diameter increases more rapidly from 8 cm to 24 cm. After 20 years, the diameter continues to increase, but the rate of increase becomes slower.
This shows that the tree keeps growing in girth with age, but the rate of growth may vary depending on environmental conditions such as availability of water, nutrients, sunlight and climate.
Question 7(ii). What is the relation between the diameter of the teak tree to the annual rings formed?
Answer:
As the number of annual rings increases, the diameter of the teak tree also increases. This means that annual rings are related to the growth in girth of the tree.
Each annual ring generally represents one year of growth. Therefore, the number of annual rings can help estimate the age of the tree. More annual rings usually mean an older tree and a thicker trunk.
Question 7(iii). Which specialised tissue is responsible for the girth of the stem and where is it located?
Answer:
The specialised tissue responsible for the girth of the stem is lateral meristem.
It is located along the circumference or sides of the stem. Its cells divide and add new cells inside and outside in a ring-like manner, which increases the diameter or girth of the stem.
Question 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:
Question 8(i). Which function(s) of the tree is/are hampered by debarking?
Answer:
Debarking damages the outer protective layer of the tree. So, the following functions are hampered:
- Protection: The bark protects the inner tissues from injury, microorganisms, insects and drying.
- Food transport: The bark region contains phloem. Damage to phloem affects the transport of food from leaves to roots and other parts.
- Prevention of water loss: Bark helps reduce water loss from the stem.
- Healing and defence: The tree becomes more exposed to infections and further injury.
Thus, debarking mainly affects protection and food transport.
Question 8(ii). Which plant tissue would be affected by further damage to the tree trunk even after debarking?
Answer:
After debarking, further damage to the tree trunk may affect the vascular tissues, especially phloem first and then xylem if the injury goes deeper.
Phloem lies closer to the outer region and transports food. Xylem lies deeper and transports water and minerals.
Question 8(iii). Which function of the tree would be hampered if the tissues beneath the bark were severely damaged?
Answer:
If the tissues beneath the bark were severely damaged, the transport functions of the tree would be affected.
- If phloem is damaged, food prepared in leaves will not reach roots and other parts.
- If xylem is damaged, water and minerals absorbed by roots will not reach leaves and other parts.
As a result, the tree may become weak, leaves may dry, roots may not receive food, and the tree may eventually die.
Question 8(iv). What assumptions are you making to answer the questions above? How would the answer change if your assumptions are also changed?
Answer:
The assumptions are:
- The debarking is severe and has removed a large part of the bark.
- The phloem tissue has been damaged because it is present near the bark.
- The xylem is not completely damaged yet.
- The tree is still alive and trying to repair the wound.
If the assumptions change, the answer will also change. For example:
- If only a small patch of bark is removed, the tree may survive and repair the wound.
- If bark is removed all around the trunk in a ring, food transport to roots may stop, and the tree may die.
- If the damage reaches xylem, water transport will also be affected.
- If microorganisms enter through the wound, infection may spread and cause further damage.
Question 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 flexibility in the young mango sapling’s stem is collenchyma.
Collenchyma is a living simple permanent tissue. Its cells have unevenly thickened corners due to pectin deposition. This structure provides both support and flexibility to young stems, leaf stalks and tendrils. Due to collenchyma, the young mango stem can bend during strong monsoon winds without breaking.
If collenchyma were replaced by sclerenchyma, the stem would become harder, stronger and more rigid because sclerenchyma cells have thick lignified walls and are mostly dead. However, the stem would lose flexibility. During strong winds, instead of bending easily, the young stem might become brittle and may break.
Question 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) 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 had nodes with buds/meristematic tissue. These buds contain actively dividing cells that can form new shoots and roots. Therefore, type ‘B’ cuttings sprouted and developed into sugarcane plants.
Type ‘A’ cuttings could not grow because they likely did not have a node or bud. Without meristematic cells, new growth could not begin.
(ii) What difference was present in type ‘B’ compared to type ‘A’?
The main difference was that type ‘B’ had a node or bud, while type ‘A’ did not.
In sugarcane, new plants grow from the nodes of stem cuttings. Nodes contain buds and meristematic cells that help in regeneration.
(iii) What observation or measurement was made to determine whether this change had an effect?
The observation made was whether the cuttings sprouted or did not sprout after a few weeks.
Other possible measurements could be:
- number of sprouts formed,
- length of new shoots,
- number of roots formed,
- height of the new plant,
- survival of the cutting.
Since type ‘B’ sprouted and type ‘A’ did not, it shows that the presence of nodes or buds affected regeneration.
(iv) What parameters should be kept the same for both types of cuttings to ensure a fair comparison?
To ensure a fair comparison, the following parameters should be kept the same:
- length and thickness of cuttings,
- variety of sugarcane,
- amount of water,
- type of soil,
- depth of planting,
- amount of sunlight,
- temperature,
- humidity,
- number of cuttings used,
- time allowed for growth,
- method of planting.
Only the presence or absence of the node/bud should be different, so that its effect on sprouting can be studied properly.
Question 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 many tissues, especially simple tissues. A simple tissue is made up of only one type of cell. These similar cells perform similar functions. For example, parenchyma is made up of similar living cells and mainly helps in storage, photosynthesis and support.
Rajiv’s point is also correct because complex tissues are made up of more than one type of cell. These cells may differ in structure, but they work together to perform a common function.
For example, xylem is a complex tissue made up of tracheids, vessels, xylem parenchyma and xylem fibres. These cells are not all similar, but together they transport water and minerals and also provide support.
Similarly, phloem is made up of sieve tubes, companion cells, phloem parenchyma and phloem fibres. These different cells work together to transport food.
Therefore, a better definition would be:
A tissue is a group of cells that work together to perform a specific function. In simple tissues, the cells are mostly similar, while in complex tissues, different types of cells work together for a common function.
Question 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:
The tissue responsible for the toughness and strength of coconut husk fibres is sclerenchyma.
Sclerenchyma cells have thick walls due to the deposition of lignin. These cells are mostly dead, hard, strong and fibrous. This makes coconut husk tough and suitable for making mats, ropes and brushes.
Living parenchyma cannot serve the same purpose because parenchyma cells have thin cell walls and are soft. They are mainly used for storage, photosynthesis and filling spaces. They do not have thick lignified walls, so they cannot provide the same strength, hardness and toughness as sclerenchyma.
Question 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:
Vibha’s statement is incorrect.
Meristematic cells are present at root and shoot tips, but they are not found only there. The meristematic tissue present at root and shoot tips is called apical meristem, and it helps in growth in length.
Plants also have:
- Lateral meristem — located along the sides or circumference of stems. It helps increase the girth or thickness of the stem.
- Intercalary meristem — located at the base of internodes or just above nodes. It helps in regrowth after cutting or grazing, especially in grasses.
Neha can ask Vibha:
“If meristematic cells are present only at root and shoot tips, then how does a tree trunk become thicker with age, and how does grass grow again after being cut?”
This question will help Vibha understand that meristematic tissues are also found in other regions of plants.
Question 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?
Answer:
(i) Which cell will have a larger vacuole? Give reasons.
The plant cell will usually have a larger vacuole.
Plant cells generally have a large central vacuole filled with cell sap. This vacuole helps in:
- storing water and dissolved substances,
- maintaining turgidity,
- giving support to the cell,
- helping the plant remain firm.
Animal cells may have small vacuoles, but these are usually smaller and temporary. Since animal cells do not need a large central vacuole for maintaining rigidity like plant cells, their vacuoles are much smaller.
(ii) What assumptions are you making to answer the question above?
The assumptions are:
- The plant cell is a mature plant cell.
- The animal cell is a typical animal cell.
- Both cells are healthy and functioning normally.
- The plant cell is not a meristematic cell, because meristematic cells usually have very small or absent vacuoles.
- The animal cell is not a special cell type with unusually large storage structures.
If the plant cell were a meristematic cell, it might not have a large vacuole. So, the answer depends on the type and stage of the cell.
Question 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:
The statement “Each plant tissue performs only one specific function” is not completely correct. Many plant tissues perform more than one function.
To critically examine this statement, I would ask the following questions:
1. Does one tissue perform more than one function?
Example: Xylem
Xylem transports water and minerals, but it also provides mechanical strength to the plant. So, xylem performs more than one function.
2. Can the same tissue perform different functions in different parts of the plant?
Example: Parenchyma
Parenchyma stores food in some parts of the plant. In green parts, it performs photosynthesis. In aquatic plants, it forms air spaces and helps in floating.
3. Can a tissue help both in support and flexibility?
Example: Collenchyma
Collenchyma supports young stems and also allows them to bend without breaking. Thus, it performs both support and flexibility functions.
4. Can protective tissue also help in exchange or absorption?
Example: Epidermis
Epidermis protects the plant, but root epidermis has root hairs for absorption of water and minerals. Leaf epidermis has stomata for gaseous exchange and transpiration.
5. Can conducting tissues also provide support?
Example: Xylem and phloem fibres
Xylem transports water and minerals, but xylem fibres also provide strength. Phloem transports food, but phloem fibres provide support.
Therefore, plant tissues are usually specialised for a main function, but many of them also perform additional functions depending on their structure and location.
The Quest Continues
Question. Will it be possible to obtain a complete animal from an animal cell like plants? If yes, what would be the advantages and challenges of this development?
Answer:
In plants, a single cell can sometimes develop into a complete plant because many plant cells show totipotency. This means they can divide, differentiate and form a whole plant under suitable conditions.
In animals, it is much more difficult. Most specialised animal cells do not naturally develop into a complete animal like plant cells do. However, some early embryonic cells and stem cells have the ability to form many different types of cells. With advanced biotechnology, it may be possible in special cases to develop an organism using animal cells, but it is complex and not as simple as plant tissue culture.
Advantages:
- It may help in studying animal development.
- It may help in producing healthy tissues or organs for treatment.
- It may help in conserving endangered animals.
- It may help in medical research and testing medicines.
- It may help in understanding genetic diseases.
Challenges:
- Animal cells are more specialised and less totipotent than plant cells.
- Animal development is very complex and requires precise conditions.
- There may be ethical issues related to cloning and animal welfare.
- There may be risks of abnormalities during development.
- It may require advanced technology and strict regulation.
Therefore, obtaining a complete animal from an animal cell may be possible only under special scientific conditions, but it is much more difficult and ethically sensitive than obtaining a complete plant from a plant cell.
