Class 9 BiologyChapter 3NCERT Exploration, Grade 9
Tissues in Action
One cell becomes skin, muscle, bone and nerve. This is how the jobs get shared out.
- 6 topic pages
- 32 interactives
- 31 quick checks
- 30 flashcards
- 19 practice questions
Think it over
- Labs can raise thousands of banana plants from a few cells. What would you need to understand about tissues before you could do that?
- A plant and an animal both need support, food and transport. Why do they end up with such different tissues for the same needs?
- An ant, a whale and a mango tree all share out work among their cells. Why would sharing the work make a body better at staying alive?
One cell, many jobs
Every plant and animal you know began as one cell. That cell divided, and divided again, and somewhere along the way its descendants took different paths: some became a waterproof skin, some a muscle that can pull, some a bone that can bear weight, some a nerve that carries messages at speed.
Groups of similar cells doing one shared job are tissues. Researchers study how tissues form, grow and repair themselves because the same knowledge lets them grow new plants from a few cells, treat blood disorders with stem cells and breed better crops. Some tissues keep dividing all through life, while others stop; this chapter shows which, where and why.
From cell to organism
An amoeba does every job of life inside one cell. A sunflower or a person hands the jobs out: similar cells team up as tissues, tissues build organs, organs work together as systems. That sharing of work is division of labour.
- CellThe basic unit, such as a single muscle fibre or a phloem cell.
- TissueSimilar cells doing one job: muscle tissue, xylem.
- OrganSeveral tissues built into one part: the heart, a leaf.
- Organ systemOrgans working as a team, such as the musculoskeletal system.
- OrganismAll the systems together: a person, a sunflower.
The chapter, section by section
- NCERT 3.1
Tissues, and why plants and animals build them differently
- Life is organised in levels: cell, then tissue, then organ, then organ system, then the whole organism.
- A tissue is a group of cells, similar in structure, that work together to do one particular job.
- NCERT 3.2 to 3.2.3
Meristems: where a plant grows
- Plants grow in three ways: in length, in girth (thickness), and by regrowing after cutting or grazing.
- Each kind of growth comes from meristematic tissue: groups of cells that keep dividing.
- NCERT 3.2.4
Permanent tissues: protect, support, carry
- Cells that stop dividing specialise into permanent tissues: simple ones of one cell type, complex ones of several.
- Epidermis protects. Its cells carry a waxy cuticle; roots have root hairs; leaves have stomata for gas exchange and transpiration.
- NCERT 3.3 to 3.3.4
Animal tissues: cover, connect, move, control
- Animals have four main kinds of tissue: epithelial, connective, muscular and nervous.
- Epithelium covers the body and lines organs. Its closely packed cells keep germs out, cut water loss, and help absorb, secrete and move substances.
- NCERT 3.4 and 3.4.1
The musculoskeletal system: muscles pull, bones move
- The musculoskeletal system is the team of bones, muscles and joints, held together by cartilage, tendons and ligaments.
- It holds you upright, moves you, keeps your posture and protects delicate organs, all under the control of the nervous system.
- NCERT 3.5 and 3.6
Joints, the skeleton, and tissues that regrow
- Ball and socket (shoulder): movement forwards, backwards, sideways and in circles. Hinge (elbow, knee): bends one way only. Pivot (skull on backbone): turns side to side. Fixed (skull bones): no movement.
- The skeletal system (skull, vertebral column, rib cage) gives strength and protects delicate organs.
The chapter at a glance
- Cells that look alike and share one job form a tissue; different tissues then cooperate to keep a plant or animal alive.
- Plant tissues are meristematic (still dividing) or permanent (no longer dividing). By function they protect, support or conduct.
- Meristems: apical at the tips (length), lateral in a ring in the stem (girth), intercalary at the base of internodes (regrowth).
- Permanent tissues are simple (one cell type: parenchyma, collenchyma, sclerenchyma) or complex (several cell types: xylem and phloem).
- Xylem carries water and minerals; phloem carries food. Plant tissues form dermal, ground and vascular tissue systems.
- Four main kinds of tissue build an animal: epithelial, connective, muscular and nervous.
- Epithelium covers the body and lines organs; connective tissue (blood, bone, cartilage, tendon, ligament) connects and supports.
- Skeletal muscle is voluntary; smooth and cardiac muscle are involuntary. Neurons receive and transmit messages.
- Muscles, bones and joints move you as one team, steered by the nervous system; the skeleton also holds you up and guards your organs.