SESSION 4: PLANT TISSUES - Mindset...

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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:

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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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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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.

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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

tracheids

vessel elements

Phloem

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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Vessels 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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PLANT ORGANS: • Organs:

Consist of a number of tissues that work together to perform a common overall function.

Label the main plant organs:

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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

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Internal Structure:

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Guard Cells & Stoma:

Open: Closed:

FUNCTIONS OF LEAVES

PHOTOSYNTHESIS

GASEOUS EXCHANGE

TRANSPIRATION

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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.

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Question 2: Identify each of the following tissues, provide ONE location, ONE function and ONE structural suitability of each. a)

b)

c)

C