Chapter 3 — Tissues in Action

Chapter 3 of the Class 9 Science NCERT textbook, "Tissues in Action", covers tissues in plants and animals: how groups of similar cells work together to perform specific functions, enabling division of labour and complex life processes.

• Tissues and Division of Labour — Similar cells group into tissues so different tasks can be shared. This division of labour lets plants and animals carry out protection, support, transport, movement, and coordination efficiently.
• Plant Tissues — Meristematic tissues (apical, lateral, intercalary) drive growth in length, girth, and regrowth. Permanent tissues are simple (parenchyma, collenchyma, sclerenchyma) or complex (xylem, phloem) for support and conduction.
• Animal Tissue Types — Animals have four tissue types: epithelial for covering and lining, connective such as blood and bone, muscular in skeletal, smooth, and cardiac forms, and nervous tissue of neurons that transmit impulses.
• The Musculoskeletal System — Bones, muscles, joints, cartilage, tendons, and ligaments form the musculoskeletal system, producing movement under nervous system control and protecting organs; the adult skeleton is about 12 to 15% of body weight.

1. 01Plant meristematic tissues (apical, lateral, intercalary) drive growth in length, girth, and regeneration after cutting respectively; their cells have thin walls, dense cytoplasm, large nucleus, and no vacuoles.
2. 02Permanent plant tissues are either simple (parenchyma — food storage/photosynthesis; collenchyma — flexibility; sclerenchyma — strength via lignin) or complex (xylem — water/mineral transport; phloem — food transport via sieve tubes).
3. 03The epidermis, covered by a waxy cuticle, forms the outermost protective layer of plants; stomata in leaves enable gaseous exchange and transpiration.
4. 04Animal tissues are of four main types: epithelial (body covering and lining), connective (blood, bone, cartilage, tendons, ligaments), muscular (skeletal, smooth, cardiac), and nervous (neurons that receive and transmit impulses).
5. 05Skeletal muscles are voluntary (striated, multinucleate, cylindrical fibres); smooth muscles are involuntary (spindle-shaped, single nucleus, non-striated); cardiac muscles are involuntary, branched, and work without fatigue.
6. 06The musculoskeletal system — bones, muscles, joints (ball-and-socket, hinge, pivot, fixed), cartilage, tendons, and ligaments — produces movement under nervous system control; the adult skeleton accounts for about 12–15% of body weight.