Tissues in Action Class 9 Notes Science Chapter 3

Reviewing Class 9 Science Notes and Exploration Chapter 3 Tissues in Action Class 9 Notes regularly helps in retaining important facts.

Class 9 Science Chapter 3 Tissues in Action Notes

Class 9 Science Exploration Chapter 3 Notes

Class 9 Science Chapter 3 Notes – Class 9 Tissues in Action

→ Cell: The smallest unit of life that makes up all living organisms. Cells carry out all basic life functions.

→ Organisms: All living things are called organisms. They may be unicellular (Amoeba) or multicellular (plants and animals).

→ Tissue: A group of cells that are similar in structure and function. Different types of tissues together form organs, different organs group together, forming organ systems; these systems further form a complete organism.

→ a Plants and animals differ in nutrition and tissue functions. Animals have tissues for digesting food, while plants have tissues that help them utilise solar energy for photosynthesis to make their own food. Both have tissues for transport, but their growth patterns differ due to different types of growth tissues.

→ Plant Tissues: Specialised tissues that help plants synthesise food through photosynthesis, transport water and nutrients, provide support,
and control growth.

→ Plants grow in different ways-by increasing length (height of stem and depth of roots), increasing girth (thickness of stem), and regrowing after being cut or grazed.

→ Based on the dividing capacity, plant tissues are of two types: meristematic tissues and permanent tissues.

→ Meristematic Tissues: Consist of actively dividing cells. Meristematic tissues are of three types:

• Apical meristem: Growth zones present at the tips of stems and roots. Its main function is to help the plants grow in length.
• Lateral meristem: Present on the lateral sides of the stems and roots. It increases the girth of stems and roots.

→ Intercalary meristem: Present at the base of internode or near the nodes. It helps in the longitudinal growth of plants, gives bushy appearance (as in grasses) after cutting.

→ Differentiation: A process by which meristematic tissue becomes specialised to perform specific functions. Meristematic tissue becomes permanent by this process.

→ Permanent Tissues: Formed from meristematic tissues, the cells in the tissue that loose the ability to divide. These are specialised to perform functions such as support, transport, and storage.

→ Permanent tissues are of two types:
Protective Tissue-Epidermis: Outermost layer of plant body, made of a single layer of tightly packed, flat, and rectangular cells. It protects plants from mechanical injury, water loss, harmful microorganisms, and extreme environmental conditions.

→ Cuticle: Cells are covered with a waxy layer called cuticle, which reduces water loss and provides protection against injury and parasites.

→ Epidermal Projections-Root Hairs and Stomata: Hair-like projections arise from epidermal cells. Root hairs increase surface area for absorption of water and minerals from the soil. In leaves, the epidermis has small pores called stomata. Stomata in leaves help in gaseous exchange and transpiration.

→ Transpirations: Evaporation of water vapour through stomata creates a transpiration pull in xylem for water transport and helps in elimination of wastes from the plant body.

→ Permanent tissues are divided into two categories: Supporting Tissue-Simple permanent tissue: Consists of only one type of cells.

→ There are three types of simple permanent tissues:

1. Parenchyma: Composed of living cells with relatively thin cell walls that are loosely packed, leaving intercellular spaces between them. Its main function is storage. Aquatic plants have specialised parenchyma with air spaces, helping them float.
2. Collenchyma: Composed of living and elongated cells with cell walls irregularly thickened at the corners. Very little intercellular spaces are present. It provides mechanical support and flexibility to plant. It helps in bending of leaves and stems.
3. Sclerenchyma: Composed of long, narrow, and thick-walled cells. This tissue is made up of dead cells and there are no intercellular spaces. Sclerenchyma cells are present in stems, leaf veins, seeds, nuts, husk of coconut, fibres of jute, etc.

• Conducting Tissues-Complex permanent tissue: Made up of more than one type of cells.

→ There are two types of complex permanent tissues:

• Xylem: Conducts water and minerals from the roots to the different parts of the plant and provides strength to the plant. It is composed of four different types of cells: tracheids, vessels, xylem parenchyma and xylem fibres. Tracheids and vessels have a thick-walled tubular structure. The only living component among these is the xylem parenchyma.
• Phloem: Conducts food material from the leaves to the different parts of the plant. It is composed of four different types of cells: sieve tubes, companion cells, phloem parenchyma and phloem fibres. Sieve tubes transport food; companion cells monitor the loading and unloading of sugars. Materials like food, resin, tannins and latex are stored by phloem parenchyma. Phloem fibres support the sieve tubes.

→ Plant tissues are organised into three tissue systems:

• Dermal tissue system: Forms the outer covering of the plant. Protects the inner parts and reduces water loss.
• Ground tissue system: Forms the main body of the plant between the dermal and vascular tissues. Includes parenchyma, collenchyma, and sclerenchyma.
• Vascular tissue system: Consists of conducting tissues: xylem and phloem.

→ Animal Tissues: Specialised tissues help animals digest food, transport nutrients, provide flexibility for movement, and control growth. Animal tissues are classified into four types based on the functions they perform:

1. Epithelial
2. Connective
3. Muscular
4. Nervous.

→ Epithelial Tissues: Form the covering of the external surfaces, internal cavities and organs of the animal body. Various types of epithelial tissues are:

• Simple squamous epithelium: Single layer of thin, flat cells. Helps in rapid diffusion of liquids and gases. Located in the lining of blood vessels and lungs.
• Stratified squamous epithelium: Many layers of cells; outer cells are flat and tightly packed. Protects underlying tissues from mechanical injury, friction, and entry of microbes. Located in the skin, mouth, and oesophagus.
• Glandular epithelium: Cells specialised for producing and releasing substances; may be cuboidal or columnar. Produces and secrets mucus, enzymes, hormones, sweat, and saliva. Located in salivary glands, sweat glands, and stomach lining.
• Sensory epithelium: Specialised receptor cells with hair-like cilia. Performs smell, taste, sound, and balance functions. Located in nostrils, taste buds, and inner ear.
• Columnar epithelium: Single layer of tall, pillar-like cells, often with hair-like structures. Efficient uptake of nutrients and water. Located in the lining of small intestine.

→ Connective Tissues: Specialised to connect various body organs. Various types of connective tissues are:

• Blood: Has a fluid matrix called plasma, in which red blood corpuscles (RBCs), white blood corpuscles (WBCs) and platelets are suspended.
• Bone: Forms the framework of the body. It is a hard, strong and non-flexible tissue. Bone cells are embedded in a hard matrix that is composed of calcium and phosphorus compounds.
• Cartilage: Has a soft, jelly-like matrix; provides flexibility and cushioning.
• Tendons: Connect muscles to bones.
• Ligaments: Connect bones to bones and prevent excessive movement.

→ Voluntary Movements: Movements that occur under conscious control, e.g., running, writing, lifting objects.

→ Involuntary Movements: Movements that occur automatically, e.g., movement of food in the intestine, heartbeat.

→ Muscular Tissues: The main function of muscular tissues is to provide movement to the body.

→ Muscular tissues are of three types:

• Striated muscles or skeletal muscles or voluntary muscles: Skeletal muscles are attached to the skeleton and made of bundles of long, cylindrical muscle fibres that are unbranched, multinucleate, and striated (show light and dark bands).
• Smooth muscles: Smooth muscle cells are spindle-shaped, have a single nucleus, lack striations, and help in slow, continuous movements like digestion.
• Cardiac muscles: Found only in the heart. Fibres are cylindrical, branched, with a single nucleus and faint striations. Work rhythmically and tirelessly, enabling the heart to beat continuously without fatigue.
• Nervous Tissue: Forms the body’s control and coordination network. Controls reflex actions, memory, and responses. The brain acts as the control centre, coordinating activities of muscles and other organs.
• Neurons (Nerve Cells): Specialised to receive, process, and transmit messages.

→ Structure of a Neuron:

• Cell body: Contains the nucleus; controls cell activities.
• Dendrites: Receive signals from other neurons.
• Axon: Long fibre that carries messages away from the cell body to axon terminals, which transmit messages to other cells.

• Musculoskeletal System: Made up of bones, muscles, joints, cartilage, tendons, and ligaments. Helps in standing upright, movement, maintaining posture, and protecting delicate organs. It functions under the control of the nervous system.
• Joints: Junctions between two or more bones that allow movement. Joints themselves do not move bones; muscles cause the movement.

→ Types of Joints:

• Ball and socket joint: Rounded bone fits into a shallow hollow bone. It allows forward, backward, sideways, and circular movements. Found in shoulder and hip.
• Hinge joint: Moves in one direction like a door hinge. Found in elbow and knee.
• Pivot joint: Allows rotational movement. Found between skull and backbone; enables head to turn side to side.
• Fixed joints: Bones are tightly joined and cannot move. Found in skull; protects brain, eyes, and ears.
• Skeletal System: Framework of bones that provides strength and protects delicate internal organs. Includes skull, vertebral column, and rib cage.

→ Backbone or Vertebral Column (Spine): Made of a series of small bones called vertebrae. Supports the body, helps in standing upright, and allows bending and twisting. Cartilage discs between vertebrae act as cushions and provide flexibility.

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