What this chapter is about
In Class 8, you studied the cell as the basic unit of life. Now, in Class 9, you learn that cells do not work alone in complex organisms. Cells with similar structure and function group together to form tissues. A tissue is a collection of cells that perform a specific task more efficiently than a single cell could.
This chapter explores the different types of tissues found in plants and animals. You will see how the structure of each tissue is suited to its function — whether it is protection, support, transport or movement. Understanding tissues bridges the gap between knowing about individual cells and understanding how organs and organ systems work.
After studying this chapter, you should be able to identify the main plant and animal tissues, describe their structure, explain their functions, and appreciate why multicellular organisms need specialised tissues instead of having all cells perform the same job.
Key ideas
- A tissue is a group of cells that have a common origin, similar structure and work together to perform a particular function.
- Plants have two broad categories of tissues: meristematic tissues (cells that divide actively) and permanent tissues (cells that have stopped dividing and have taken up specific roles).
- Meristematic tissue is found at root tips, shoot tips and in the cambium; it helps the plant grow in length and girth.
- Permanent tissues in plants include simple permanent tissues (parenchyma, collenchyma, sclerenchyma) and complex permanent tissues (xylem, phloem).
- Animal tissues are classified into four main types: epithelial, connective, muscular and nervous.
- Epithelial tissue covers body surfaces and lines cavities; its cells fit closely together, offering protection and controlling exchange of materials.
- Connective tissue (blood, bone, cartilage, adipose, areolar) binds, supports and protects other tissues and organs.
- Muscular tissue (striated, smooth, cardiac) contracts to produce movement, while nervous tissue transmits electrical signals for coordination.
Formulas and facts to remember
1. Tissue — A group of cells with similar structure and function that work together. 2. Meristematic tissue — Plant tissue whose cells divide continuously, found at growing points (apical, lateral, intercalary). 3. Parenchyma — Thin-walled, loosely packed cells that store food and allow gas exchange; chlorenchyma contains chloroplasts. 4. Collenchyma — Cells with thickened corners providing flexibility and mechanical support in young stems. 5. Sclerenchyma — Cells with thick, lignified walls that are often dead at maturity; provide rigidity (fibres, sclereids). 6. Xylem — Complex tissue that transports water and minerals upward; consists of vessels, tracheids, xylem parenchyma, xylem fibres. 7. Phloem — Complex tissue that transports food (prepared by leaves) to all parts; consists of sieve tubes, companion cells, phloem parenchyma, phloem fibres. 8. Epithelial tissue — Forms protective coverings; types include squamous, cuboidal, columnar and ciliated, depending on cell shape. 9. Connective tissue — Has cells scattered in an extracellular matrix; examples are blood, bone, cartilage, adipose tissue. 10. Striated (skeletal) muscle — Voluntary, shows dark and light bands, attached to bones. 11. Smooth muscle — Involuntary, spindle-shaped cells, found in the walls of stomach, intestines and blood vessels. 12. Cardiac muscle — Involuntary, branched, found only in the heart, contracts rhythmically throughout life. 13. Nervous tissue — Made of neurons; transmits impulses for rapid communication between body parts.
Worked examples
### Example 1: Identifying tissue type from description
Problem: A tissue is found lining the inner surface of the cheek. The cells are flat, thin and fit together like tiles on a floor. Identify the tissue type.
Solution: Step 1: The tissue lines a body surface — this indicates epithelial tissue. Step 2: The cells are flat and tile-like — this shape is called squamous. Step 3: Therefore, the tissue is squamous epithelial tissue.
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### Example 2: Choosing the correct plant tissue
Problem: The husk of a coconut is very hard and rough. Which plant tissue is mainly responsible for this hardness?
Solution: Step 1: Hardness in plant parts comes from cells with thick, lignified walls. Step 2: Sclerenchyma tissue has such cells, which are usually dead at maturity. Step 3: The coconut husk gets its toughness from sclerenchyma (specifically, sclerenchyma fibres).
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### Example 3: Function-based reasoning
Problem: Why does the stem of a young herbaceous plant (like a paddy seedling) bend easily but does not break?
Solution: Step 1: Flexibility without breaking requires a tissue that provides support yet allows bending. Step 2: Collenchyma tissue has cells with unevenly thickened corners; they give mechanical strength while remaining flexible. Step 3: Young stems contain collenchyma beneath the epidermis, which allows bending without snapping.
Common mistakes
- Confusing xylem and phloem → Remember: xylem carries water upward, phloem carries food in both directions; xylem cells are mostly dead, phloem sieve tubes are living.
- Thinking all permanent tissues are dead → Parenchyma and phloem have living cells; only sclerenchyma and mature xylem vessels are dead.
- Mixing up striated and smooth muscle → Striated muscle shows bands and is voluntary (skeletal); smooth muscle has no bands and is involuntary (internal organs).
- Believing epithelial tissue only protects skin → Epithelium also lines the mouth, intestines, blood vessels and respiratory tract.
- Calling blood a liquid rather than a tissue → Blood is connective tissue; its matrix (plasma) is liquid, and it contains cells (RBCs, WBCs, platelets).
Quick revision
1. Tissue = cells with similar structure and function working together. 2. Meristematic tissue divides; permanent tissue is specialised and usually does not divide. 3. Xylem moves water up; phloem moves food to where it is needed. 4. Epithelial tissue covers surfaces; connective tissue binds and supports. 5. Skeletal muscle is voluntary; smooth and cardiac muscles are involuntary. 6. Neurons in nervous tissue transmit electrical impulses for coordination.