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Life Sciences Grade 10 www.learnxtra.co.za SESSION 4: PLANT TISSUES KEY CONCEPTS: Levels of Organisation Definition of a tissue Types of Plant Tissues Plant Organs - The Leaf TERMINOLOGY: Tissue a group of similar cells adapted for a particular function. XPLANATION TYPES OF PLANT TISSUES: Meristematic Tissue: • Cells of meristems divide continuously cells are similar in structure & have thin cellulose cell walls may be spherical, oval, polygonal or rectangular in shape contain few vacuoles • Found in regions of the plant that grow, mainly at tip of root & stem. According to their position in the plant, meristems are apical, lateral & intercalary. Brought to you by Page 1 Life Sciences Grade 10 www.learnxtra.co.za Simple Permanent Tissue: Epidermis: • Structure: Transparent, one cell thick and is usually covered with cuticle usually has guard cells with stomata • Found on the outermost layer of the plant body such as leaves, flowers, stem & roots • Function is to protect the plant from dessication and infection. Guard cells & cuticle helps to reduce water loss Parenchyma: • • • Oval, round or elongated in shape. Thin cell wall& encloses a dense cytoplasm which contains a small nucleus & surrounds a large central vacuole. Intercellular spaces are abundant. WHERE? • Soft parts of the plant - cortex of roots, ground tissues in stems & mesophyll of leaves. • Also - pith, medullary rays & packing tissue in xylem & phloem. WHY? • packing tissue • support to the stem of herbaceous plants water & food storage transport of water & gases Brought to you by Page 2 Life Sciences Grade 10 www.learnxtra.co.za Collenchyma: • • Characterised by the deposition of extra cellulose at the corners of the cells. Intercellular spaces are generally absent. WHERE? • Mainly below the epidermis of dicotyledon stem & petiole.also occur in midribs of dicot leaves. WHY? • Provides mechanical support & elasticity. • Allows plant to bend without breaking. Brought to you by Page 3 Life Sciences Grade 10 www.learnxtra.co.za Transverse and Longitudinal Section of Collenchyma: Scelerenchyma: • • • • • Dead cells with no protoplasm. The walls of cells greatly thickened & lignified. Due to excessive thickening of the wall of sclerenchyma cells, its cell cavity or lumen becomes nearly absent. The cells of are closely packed. No intercellular spaces. WHERE? • Stems, roots, veins of leaves, hard covering of seeds & nuts. • Sclereids form the gritty part of the most of the ripe fruits & contribute hardness to the seed coat & nutshells. WHY? • Mainly mechanical & protective in function. • It gives strength, rigidity, flexibility & elasticity to the plant body • Thus, enables it to withstand various strains. Brought to you by Page 4 Life Sciences Grade 10 www.learnxtra.co.za Sclereids / Stone Cells: • Found flesh of fruit like pears. • Also in pips of fruit and shells of nuts Fibres: • Make stems & roots tough & rigid Complex Permanent Tissue: tracheids Xylem vessel elements Vascular (Transport) Tissue: sieve-tube elements Phloem companion cells Brought to you by Page 5 Life Sciences Grade 10 www.learnxtra.co.za Xylem: Composed of cells of four different types: • Tracheids, vessels, xylem parenchyma, xylem sclerenchyma. • Except xylem parenchyma, all other xylem elements are dead & bounded by thick lignified walls. WHERE? • Vascular bundles of roots, stems and leaves WHY? • Transport water & minerals salts upward from the root to different parts of shoots. • Since walls of tracheids, vessels & sclerenchyma of xylem are lignified, they give mechanical strength to the plant body. Components of Xylem: Brought to you by Page 6 Life Sciences Grade 10 www.learnxtra.co.za Vessels Brought to you by Tracheids Page 7 Life Sciences Grade 10 www.learnxtra.co.za Phloem: • • Composed of following: 1. Sieve Tubes 2. Companion Cells 3. Phloem Parenchyma 4. Phloem Fibres. All phloem cells are living cells, besides fibres. WHERE? • Vascular bundles of roots, stems and leaves WHY? • Transport food materials from the leaves to the storage organs & later from storage organs to the growing regions of the plant body Sieve - Tube Companion Cells Brought to you by Page 8 Life Sciences Grade 10 www.learnxtra.co.za PLANT ORGANS: • Organs: Consist of a number of tissues that work together to perform a common overall function. Label the main plant organs: Brought to you by Page 9 Life Sciences Grade 10 www.learnxtra.co.za Leaves: • Leaves - blade or lamina, an edge called the margin of the leaf, the veins (vascular bundles), a petiole, and two appendages at the base of the petiole called the stipules Type of Leaves: • • Simple - blade not divided into smaller leaflets Compound - blade divided into smaller leaflets Brought to you by Page 10 Life Sciences Grade 10 www.learnxtra.co.za Internal Structure: Brought to you by Page 11 Life Sciences Grade 10 www.learnxtra.co.za Guard Cells & Stoma: Open: Closed: PHOTOSYNTHESIS FUNCTIONS OF LEAVES GASEOUS EXCHANGE TRANSPIRATION Brought to you by Page 12 Life Sciences Grade 10 www.learnxtra.co.za X-AMPLE QUESTIONS: Question 1: Study the following diagram and answer the questions: 1.1 Provide labels for parts labelled A, D, E and G. 1.2 Part labelled C consists of parenchyma tissue. Explain how this tissue is suited for its functions. 1.3 How do cells labelled B and C differ from ordinary parenchyma tissue? 1.4 Draw a fully labelled diagram to illustrate the structure of part labelled F. 1.5 List TWO functions of the leaf. 1.6 Explain how the leaf is suited to its functions. Brought to you by Page 13 Life Sciences Grade 10 www.learnxtra.co.za Question 2: Identify each of the following tissues, provide ONE location, ONE function and ONE structural suitability of each. a) b) c) Brought to you by C Page 14