Class 9 Science
PART 1 — SHORT NOTES
1. What is a Tissue?
A tissue is a group of similar cells that work together to perform a particular function.
Examples: Muscle tissue helps in movement, nervous tissue carries messages, xylem transports water and minerals, and phloem transports food in plants.
2. Why Are Plant and Animal Tissues Different?
- Plants generally remain fixed in one place and need strong supporting tissues.
- Plant cells have a cell wall that provides rigidity and strength.
- Animal cells do not have a cell wall, allowing greater flexibility and helping movement.
- Plants make food by photosynthesis, while animals obtain food from other sources.
- Plant and animal tissues are specialised for different functions, such as growth, transport, protection and movement.
3. Plant Tissues
Plant tissues are broadly divided into two groups:
- Meristematic tissues: Cells divide actively and help plants grow.
- Permanent tissues: Cells become specialised to perform particular functions.
4. Meristematic Tissues
Meristematic cells are usually small, tightly packed and have thin cell walls, dense cytoplasm and a prominent nucleus. Vacuoles are generally absent or very small because these cells are actively dividing.
| Type | Location | Function | Example |
|---|---|---|---|
| Apical meristem | Tips of roots and shoots | Increases length | Root and shoot tips |
| Lateral meristem | Along the sides of stems and roots | Increases girth or thickness | Cambium in woody stems |
| Intercalary meristem | At the base of internodes or near nodes in certain plants | Helps regrowth after cutting or grazing | Grass |
Important terms:
- Node: Point on a stem from which leaves or branches arise.
- Internode: Part of a stem between two nodes.
- Annual growth rings: Rings in the wood of some trees that help estimate their age and record growth conditions.
- Differentiation: The process by which cells become specialised to perform particular functions.
5. Permanent Tissues
Permanent tissues develop from meristematic cells that become specialised. They may be simple or complex.
- Simple permanent tissues: Mainly made of one type of cell.
- Complex permanent tissues: Made of different types of cells working together.
6. Protective Tissue — Epidermis
- The epidermis is the outermost protective covering of a plant.
- It protects against injury, water loss and harmful microorganisms.
- Cuticle: A waxy covering that reduces water loss.
- Root hairs: Increase the surface area for absorbing water and minerals.
- Stomata: Pores that allow gaseous exchange and the loss of water vapour during transpiration.
- Transpiration: Loss of water vapour from the plant, mainly through stomata. It helps create a pull that supports water movement through xylem.
7. Supporting Tissues — Simple Permanent Tissues
| Tissue | Cell features | Functions and examples |
|---|---|---|
| Parenchyma | Living cells with thin walls and spaces between them | Stores food; green parenchyma can perform photosynthesis. Air spaces in some aquatic plants help them float. |
| Collenchyma | Living cells with unevenly thickened corners | Provides support and flexibility. Helps stems and tendrils bend without breaking. |
| Sclerenchyma | Usually dead cells with thick, lignified walls | Provides hardness and strength. Found in coconut husk, seed coverings and other hard plant parts. |
8. Conducting Tissues — Xylem and Phloem
| Feature | Xylem | Phloem |
|---|---|---|
| Main function | Transports water and minerals from roots to other parts | Transports food, especially sugars, from leaves to other parts |
| Main components | Tracheids, vessels, xylem parenchyma and xylem fibres | Sieve tubes, companion cells, phloem parenchyma and phloem fibres |
| Living or dead | Most conducting elements are dead; xylem parenchyma is living | Most components are living; phloem fibres are generally dead |
| Other function | Also provides strength | Also supports food storage and provides strength through fibres |
9. Plant Tissue Systems
- Dermal tissue system: Forms the outer covering and protects the plant.
- Ground tissue system: Forms much of the plant body and includes parenchyma, collenchyma and sclerenchyma.
- Vascular tissue system: Contains xylem and phloem for transport.
10. Animal Tissues
The four main types of animal tissues are epithelial, connective, muscular and nervous tissues.
11. Epithelial Tissue
Epithelial tissue covers the body and lines internal organs. Its cells are closely packed.
| Type or arrangement | Main function | Example or location |
|---|---|---|
| Thin, flat cells | Rapid exchange of gases and liquids | Lining of lungs and blood vessels |
| Many layers | Protection from friction and injury | Skin, mouth and oesophagus |
| Secretory cells | Produce and release substances | Sweat glands, salivary glands and stomach lining |
| Sensory epithelial cells | Receive sensory information | Nostrils, taste buds and inner ear |
| Tall cells | Absorption | Lining of small intestine |
12. Connective Tissue
Connective tissue joins, supports, protects or connects different parts of the body. Its cells are present in a surrounding material called the matrix.
| Tissue | Function |
|---|---|
| Blood | Transports oxygen, nutrients, hormones and waste materials. |
| Bone | Provides strength, support and protection. |
| Cartilage | Provides flexibility and cushions the ends of bones. |
| Tendon | Connects muscle to bone. |
| Ligament | Connects bone to bone and stabilises joints. |
Blood components: Red blood cells carry oxygen with the help of haemoglobin; white blood cells help defend the body against infection; platelets help blood clot; plasma is the liquid part of blood.
13. Muscular Tissue
| Type | Structure | Control and location |
|---|---|---|
| Skeletal muscle | Long, cylindrical, unbranched, striated fibres with many nuclei | Usually voluntary; attached to bones and helps body movement |
| Smooth muscle | Spindle-shaped cells with one nucleus and no striations | Involuntary; found in organs such as the stomach and intestines |
| Cardiac muscle | Branched, striated cells, usually with one nucleus | Involuntary; found only in the heart and contracts rhythmically |
14. Nervous Tissue
Nervous tissue receives and transmits messages and helps control and coordinate body activities.
A nerve cell is called a neuron.
- Cell body: Contains the nucleus and controls cell activities.
- Dendrites: Receive signals.
- Axon: Carries messages away from the cell body.
- Axon terminals: Pass messages to other cells.
15. Musculoskeletal System
The musculoskeletal system includes bones, muscles, joints, cartilage, tendons and ligaments.
- Muscles contract and pull on bones to produce movement.
- Tendons transmit the pulling force from muscles to bones.
- Joints are places where two or more bones meet.
- Cartilage cushions the ends of bones and reduces friction at many joints.
- Ligaments connect bones and help stabilise joints.
16. Types of Joints
| Joint | Movement | Example |
|---|---|---|
| Ball and socket | Movement in many directions, including rotation | Shoulder and hip |
| Hinge | Mainly bending and straightening in one plane | Elbow and knee |
| Pivot | Rotation around an axis | Joint between the first two vertebrae of the neck |
| Fixed | No movement between the bones | Joints between many skull bones |
17. Skeletal System
- The skeleton supports the body and protects delicate organs.
- The skull protects the brain.
- The vertebral column or backbone supports the body and protects the spinal cord.
- Cartilage discs between vertebrae provide cushioning and flexibility.
- The rib cage has 12 pairs of ribs and protects the heart and lungs.
- Flexible cartilage connections allow the rib cage to expand and contract during breathing.
- Good posture, balanced nutrition, regular exercise and suitable physical activity help maintain bone and muscle health.
18. Totipotency and Plant Tissue Culture
Totipotency is the ability of a single plant cell to develop into a complete plant under suitable conditions.
- F. C. Steward demonstrated the regeneration of a complete carrot plant from cultured cells.
- In tissue culture, cells are grown in a suitable nutrient medium under controlled conditions.
- Cells may divide, form an unspecialised mass and later differentiate into roots and shoots.
- Plant tissue culture is useful in plant propagation, crop improvement and research.
- Dedifferentiation: Specialised cells regain the ability to divide.
- Redifferentiation: Cells become specialised again.
PART 2 — TEXTBOOK QUESTIONS AND SOLUTIONS
The questions below follow the textbook wording supplied. Short, easy answers are provided after each question.
Question 1
(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.
Meristematic cells have thin walls, dense cytoplasm and a prominent nucleus, which support repeated cell division.
Question 2
(ii) Phloem
(iii) Epidermis
(iv) Sclerenchyma
Phloem transports food made in the leaves to other parts of the plant, including roots.
Question 3
(ii) To provide maximum strength.
(iii) To allow quick exchange of materials across them.
(iv) To reduce friction.
A thin epithelial lining allows substances such as gases to pass across it quickly.
Question 4
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 the hips and other parts have to manage more of the movement. In a normal jump, the knees and ankles bend and straighten, helping absorb the landing impact and making the jump easier.
Question 5
(ii) Hinge
(iii) Pivot
The knee and the main ankle movement joints allow movement mainly by bending and straightening.
Question 6
(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.
- A — (iv): The assertion is true, but the reason is false. Lung epithelium is thin, allowing rapid gas exchange.
- B — (i): Both are true, and the reason helps explain the continuous working of cardiac muscle.
- C — (iv): The assertion is false because tendons connect muscle to bone. The reason is true.
- D — (iii): The assertion is true, but the reason is false. Hinge joints mainly permit bending and straightening in one plane.
Question 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?
How to draw the graph:
- Write age (years) on the x-axis.
- Write diameter (cm) and number of annual rings on the y-axis. Use different symbols for the two sets of data and include a key.
- Plot the diameter points: (5,4), (10,8), (20,24), (25,28), (30,32), (40,40).
- Plot the annual-ring points: (5,5), (10,10), (20,20), (25,25), (30,30), (40,40).
(i) The diameter generally increases as the tree becomes older. The increase is not uniform at every interval.
(ii) The number of annual rings increases with age, with approximately one annual ring formed each year. The diameter also generally increases with age, but it is not equal to the number of rings at every age.
(iii) The lateral meristem, especially the vascular cambium in woody stems, is responsible for increasing girth. It is located along the sides of the stem, in a ring-like arrangement.
Question 8
(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?
(i) Debarking damages protective tissues and may damage phloem. It can increase water loss and make the tree more vulnerable to infection. If phloem is damaged around the trunk, the transport of food to roots may be reduced or stopped.
(ii) The phloem may be affected if the damage extends into the tissues beneath the bark. If damage goes deeper, the cambium and xylem may also be affected.
(iii) Severe damage to phloem affects food transport. Damage to xylem affects water and mineral transport and may also weaken the trunk.
(iv) We assume the bark has been removed deeply enough to damage the phloem, but not necessarily the xylem. If only the outer protective layer is removed, the main effect may be loss of protection. If phloem or xylem is also damaged, food or water transport may be affected as well.
Question 9
Collenchyma provides flexibility to young stems. If it were replaced by sclerenchyma, the stem would become harder and more rigid. It might not bend as easily and could be more likely to break under bending forces.
Question 10
(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?
(i) Type B likely contained a viable node or bud with meristematic tissue that could grow into a new shoot.
(ii) Type B likely had a node or bud, while type A lacked a viable one. The exact difference depends on the illustration in the textbook.
(iii) The sprouting of the cuttings and the growth of new shoots after a few weeks were observed and compared.
(iv) Keep the variety, length and health of cuttings, soil, water, light, temperature, planting depth and observation period the same. Change only the feature being tested.
Question 11
Rohan’s statement describes simple tissues well because they are mainly made of one type of cell. Rajiv is also correct: complex tissues contain different types of cells that work together for one overall function. For example, xylem has vessels, tracheids, fibres and parenchyma that help in water transport and support.
Question 12
Sclerenchyma provides this strength. Its cells have thick, lignified walls. Parenchyma has thin walls and mainly performs functions such as storage and photosynthesis, so it cannot provide the same hardness and toughness.
Question 13
The statement is incorrect. Apical meristems are found at root and shoot tips, but lateral meristems occur along the sides of stems and roots, and intercalary meristems occur near nodes or at the base of internodes in certain plants.
Neha could ask: “Which meristem helps stems increase in girth, and which meristem helps grass regrow after cutting?”
Question 14
(i) Which cell will have a larger vacuole? Give reasons.
(ii) What assumptions are you making to answer the question above?
(i) Usually, the plant cell has a larger central vacuole. It stores water and dissolved substances and helps maintain the cell’s firmness.
(ii) We assume the cells are typical mature plant and animal cells of the same overall size. Vacuole size can vary with the type and condition of a cell.
Question 15
The statement is too simple because some tissues perform more than one function. I would ask:
- Does xylem only transport water, or does it also provide support?
- Does parenchyma only store food, or can it also perform photosynthesis?
- Does the epidermis only protect the plant, or do root hairs and stomata also help in absorption and gaseous exchange?
Examples: xylem provides support as well as transport; green parenchyma performs photosynthesis and may store food; epidermal structures help with absorption and gaseous exchange.
THE JOURNEY BEYOND — QUESTIONS AND SOLUTIONS
- Ligament rupture: A ligament is torn, making a joint painful or unstable.
- Cartilage damage: The cushioning tissue in a joint is damaged, which may cause pain and difficulty in movement.
- Bone fracture: A bone cracks or breaks.
Risk can be reduced by regular suitable exercise, safe sports practices, maintaining good posture, using protective equipment, eating a balanced diet with adequate protein, calcium and vitamin D, and avoiding smoking. Injuries need proper medical assessment.
(ii) Place your fingers on the back of your ankle just above the heel (Fig. 3.24).
(iii) Point your toes down and up, and you will feel the tendon moving.
Tendons are designed to withstand huge pulling forces. Try exploring other tendons in your body around the different joints.
The tendon felt above the heel is the Achilles tendon. It connects the calf muscles to the heel bone and helps point the foot downwards during walking, running and jumping. Other tendons can be felt near the wrist, fingers, elbow and knee.
Yoga improves flexibility, balance and posture. Kabaddi and other suitable sports strengthen muscles and can help maintain bone strength. Proper warm-up, safe technique, rest and balanced nutrition help prevent injuries.
- Pruning: Removes selected branches and may encourage new shoot growth from active buds and meristems.
- Grafting: Joins plant parts so that their vascular tissues can connect and transport water and food.
- Irrigation: Supplies water needed for cell activities, growth and transport through xylem.
- Crop rotation: Helps maintain soil fertility and can reduce some pests and diseases, supporting healthy plant growth.
(ii) Consult an elder community resource persons about their knowledge on different plant leaves, such as leaves that remain fresh for a long time, repel water or deter insects. Find out their traditional uses, such as making plates, preparing cooling wraps or functioning as insect repellents.
- Desert plants: Leaves may be small, thick or modified into spines to reduce water loss.
- Moist-habitat plants: Leaves may be broad and thin where water is readily available.
- Aquatic plants: Floating leaves may have a waxy surface and air spaces.
- Traditional leaf uses vary by region. Examples include banana leaves used for serving food and certain leaves traditionally used for wrapping or repelling insects. Record local examples after speaking with community members.
Dance movements may involve the shoulder’s ball-and-socket joint, the elbow and knee hinge joints, and pivot movements of the neck. Fingers, wrists, hips and ankles also help produce different movements. The exact joints involved depend on the dance step.
In general, an ordinary specialised animal cell cannot develop into a complete animal under normal conditions, unlike certain plant cells in tissue culture. Some animal cells, such as early embryonic cells, have the potential to develop into many or all body cell types under particular conditions. Cloning has produced some animals from specialised cells, but it requires complex techniques and is not possible with every cell.
Possible advantages: Scientific research, studying diseases and potentially supporting conservation of some species.
Challenges: Low success rates, developmental abnormalities, animal welfare concerns, high costs and ethical questions.