Tissue & Tissue System Exercise Solutions | KalviGavani

| Feature | Meristematic Tissue | Permanent Tissue | |---|---|---| | Cell division | Actively dividing | Lost ability to divide | | Cell wall | Thin, primary | May be thin or thick (secondary) | | Cytoplasm | Dense | Thin | | Vacuoles | Absent or very small | Large (in parenchyma) | | Nucleus | Large, prominent | May be present or absent | | Intercellular spaces | Absent | Present (in parenchyma) | | Function | Growth | Various (support, storage, conduction) |

1. Parenchyma: Thin-walled, living cells; large vacuoles and intercellular spaces; functions include storage, photosynthesis (chlorenchyma), and buoyancy (aerenchyma) 2. Collenchyma: Thickened corners (cellulose + pectin), living cells; provides mechanical support in young stems, petioles, and midribs 3. Sclerenchyma: Thick, lignified secondary walls, dead cells; provides mechanical strength and protection; two types — fibres (long, narrow) and sclereids (short, irregular)

| Feature | Xylem | Phloem | |---|---|---| | Function | Conducts water and minerals | Conducts food (sugars) | | Direction | Unidirectional (upward) | Bidirectional | | Elements | Tracheids, vessels, fibres, parenchyma | Sieve tubes, companion cells, fibres, parenchyma | | Living/Dead | Mostly dead (only parenchyma living) | Mostly living (only fibres dead) | | Location | Inner side of vascular bundle | Outer side of vascular bundle |

1. Dermal tissue system: Epidermis (with cuticle, stomata, trichomes) and cork (in older stems) — provides protection, reduces transpiration, allows gas exchange 2. Ground tissue system: Parenchyma, collenchyma, sclerenchyma — provides support, storage, photosynthesis, and aeration 3. Vascular tissue system: Xylem and phloem (vascular bundles) — transports water, minerals, and food throughout the plant

Meristematic tissue consists of actively dividing, undifferentiated cells responsible for plant growth. General features of meristematic cells: - Small, isodiametric cells - Thin primary cell wall (cellulose only) - Dense cytoplasm with large, prominent nucleus - Absence of vacuoles (or very small vacuoles) - No intercellular spaces (cells tightly packed) - Abundant plastids in proplastid stage Types of Meristems: 1. Apical Meristem: - Location: At the tips of roots and shoots (apices) - Function: Primary growth — increases the LENGTH of the plant - Root apical meristem: Present just behind the root cap - Shoot apical meristem: Present at the tip of the stem - Forms primary tissues (primary xylem, primary phloem, epidermis, ground tissue) 2. Lateral Meristem: - Location: Along the sides (lateral position) of stems and roots - Two types: Vascular cambium (between xylem and phloem) and Cork cambium (in outer cortex) - Function: Secondary growth — increases the GIRTH (diameter) of the plant - Forms secondary xylem (wood) and secondary phloem, and cork (bark) - Found only in dicots and gymnosperms (not in monocots) 3. Intercalary Meristem: - Location: At the nodes (base of internodes) in grasses and monocots - Function: Regrowth of plant parts after damage by grazing or mowing - Adds growth at internodes - Present in grasses, wheat, bamboo

| Feature | Parenchyma | Collenchyma | Sclerenchyma | |---|---|---|---| | Cell wall | Thin, primary (cellulose) | Thickened at corners (cellulose + pectin) | Thick, lignified secondary wall | | Living/Dead | Living | Living | Dead (at maturity) | | Vacuole | Large central vacuole | Present | Absent (lumen very narrow) | | Intercellular spaces | Present | Absent or very small | Absent | | Nucleus | Present | Present | Absent at maturity | | Function | Storage, photosynthesis, aeration | Mechanical support in young stems | Mechanical strength, protection | | Location | Cortex, pith, mesophyll | Petioles, midribs, young stems | Veins, hard seeds, husks, bark | | Special types | Chlorenchyma (chloroplasts), Aerenchyma (air spaces) | — | Fibres (long), Sclereids (short, irregular) | | Elasticity | Can stretch | Can stretch and provide flexible support | Cannot stretch; rigid | Parenchyma: - Most common and least specialised tissue - Forms the ground tissue, pith, cortex, and mesophyll - Can differentiate into other tissues (meristematic, sclerenchyma) - Chlorenchyma: Parenchyma with chloroplasts (photosynthesis) — e.g., mesophyll of leaves - Aerenchyma: Parenchyma with large air spaces (buoyancy in aquatic plants) — e.g., lotus, water hyacinth Collenchyma: - Found in young stems, petioles, and leaf midribs - Provides flexible mechanical support (allows growth) - Cell walls are thickened at corners with pectin and cellulose (no lignin) - Not found in roots or monocots Sclerenchyma: - Found in mature stems, veins of leaves, hard seeds, fruit husks, and bark - Provides rigid mechanical support and protection - Two types: Fibres (long, narrow — e.g., jute, flax) and Sclereids (short, irregular — e.g., stone cells in pear, coconut shell) - Cells are dead at maturity; lumen is very narrow due to thick walls

XYLEM (Water-conducting tissue): Xylem is a complex permanent tissue that conducts water and minerals from roots to leaves. Elements: 1. Tracheids: Dead, elongated cells with tapered ends; thickened lignified walls; water moves through pits. Found in all vascular plants. 2. Vessels (Tracheae): Dead, tubular structures; formed from vessel elements joined end-to-end; more efficient water conduction than tracheids. Absent in gymnosperms (present only in angiosperms). 3. Xylem fibres: Dead, long, narrow cells with thick walls; provide mechanical support. 4. Xylem parenchyma: The only living element; stores food and aids in lateral conduction of water. PHLOEM (Food-conducting tissue): Phloem is a complex permanent tissue that conducts food (sugars) from leaves to all parts of the plant. Elements: 1. Sieve tube elements: Living cells without nucleus; end walls form sieve plates with pores; main conducting element for food transport. 2. Companion cells: Living, nucleated cells; associated with sieve tubes; regulate sieve tube function and loading/unloading of sugars. 3. Phloem parenchyma: Living cells; store food and aid in lateral conduction. Absent in most monocots. 4. Phloem fibres (Bast fibres): Dead, long, narrow cells; provide mechanical support. The only dead element of phloem. Commercially important (jute, flax, hemp).