General Biology lab Lab 11 Plant Tissues Tissues

General Biology lab Lab 11 Plant Tissues

• Tissues – A group of closely associated cells that perform related functions and are similar in structure. • Plant Tissues can classified into: – Meristematic tissues. – Permanent tissues.

I. Meristematic tissues (meristems) – which are responsible for its growth and development – their cells have the ability to divide. – The cells are small, thin-walled, with usually no central vacuole and no specialized features. • Meristematic tissue is located in: • Primary meristems : (apical meristems). – near tips of roots and stems. • Secondary meristems: (lateral meristems) – found along the sides of roots & stems – increase width or diameter of stems & roots

II. Permanent tissues (mature tissues) – These tissues arise from the meristematic tissue. – They stop dividing. Type of permanent tissue: 1. Dermal tissue: – consists of epidermis which may later be replaced by periderm 2. Ground tissue: – contains three type of tissue parenchyma, collenchyma and sclerenchyma 3. Vascular tissue: – consists of xylem and phloem

Dermal tissue Ground tissue Vascular tissue

Dermal Tissues • Dermal / surface tissue – consist only of one kind of cells(Simple permanent tissues) – external tissues – forms protective covering of the plant body

Epidermis • Locations: – in the outermost layer of the primary plant body. – covering leaves, floral parts, fruits, seeds, stems and roots. • Characteristics: – It composed mostly of unspecialized cells, either parenchyma and or sclerenchyma. – Cells are closed filled together. – The cell has a central vacuole and thin peripheral cytoplasm – the epidermis in generally is only one cell layer thick.

• Functions: – are diverse including desiccation resistance, gas exchange, and protection against herbivores and pathogens. • The epidermis contains: • Guard cells form stomata, (pores for gas exchange). – they are generally kidney shaped cells, rich in cytoplasm and with prominent nucleus and contain chloroplast. • Trichomes – various types of hairs.

• Trichomes

Ground tissues • The ground tissue of plants includes all tissues that are neither dermal nor vascular • fills the interior of the plant • It can be divided into three classes based on the nature of the cell walls A. Parenchyma B. Collenchyma C. Sclerenchyma

A. Parenchyma – is the main ground substance of the plant body in which other important tissues are present • Characteristics: – cells are rounded in shape & have uniformly thin walls. – Cell wall: primary or primary and secondary – have large vacuoles – living at maturity – many contain various secretions.

• Locations: – in the cortex of roots, stems – piths of stems and roots – leaf mesophyll. • Functions: – performs several functions such as storage, respiration, photosynthesis.

B. Collenchyma • Locations: – at the periphery of the stem, and in the outer part of the cortex. • Characteristics: – They are similar to parenchymal cells except that they have thicker cell walls. – living at maturity. – Cell wall: primary only • Functions – provide support

C. Sclerenchyma – non-living and lack protoplasts at maturity. – Have thick, lignified secondary walls – The cells of sclerenchyma are closely packed without intercellular spaces. • Functions: – rigid cells providing support and strength to tissues. • Types: 1. Sclereids or stone cells 2. Fibers

• Fibers – are long slender cells – They provide support and some storage. • Sclereids – they make up the seed coats of seeds. – Their function is primarily for protection.

Vascular tissues • Vascular Tissues – Specialized for long-distance transport of water and dissolved substances. • Types: – 1. Xylem – 2. phloem

1. Xylem (means “wood” ) – transports water and dissolved nutrients from the roots to all parts of a plant – Conducting cells are dead and hollow at maturity. – It may also act a mechanical support to different plant organs. • Xylem is a complex tissue formed from of : – Vascular elements – Xylem fibers – Xylem Parenchyma

• Vascular elements – Tracheids • The only water conducting cells in most woody, non flowering plants • They do not have end openings such as the vessels. – Vessel elements • Vessel elements are the water “pipeline” system in flowering plants. • Vessel elements are generally larger in diameter than tracheids • both are elongated, dead at maturity, lignified secondary cell walls.

2. Phloem (meaning, “bark”) – transports dissolved organic / food materials from the Ieaves to the different parts of the plant • It complex tissues formed of: – Sieve elements – Companion cells – Phloem Parenchyma – Phloem fibers

• Sieve elements: – are commonly long and slender with tapering end. – have large pores on sieve plates, usually on end walls. – not contain a nucleus and possess thin cellulose cell walls. • Companion cells – are highly specialized parenchyma cells – retains its nucleus. – They live only as long as the associated sieve tube member is living.