SESSION 4: PLANT TISSUES - Mindset Learn

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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:

Life Sciences Grade 10

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.

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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

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Life Sciences Grade 10

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.

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learnxtra.co.za Transverse and Longitudinal Section of Collenchyma:

Life Sciences Grade 10

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.

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Life Sciences Grade 10

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:

Vascular (Transport)

Tissue:

Xylem Phloem

tracheids

vessel elements sieve-tube elements

companion cells

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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:

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Tracheids

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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

Companion Cells

Sieve - Tube

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