General Biology lab Lab 11 Plant Tissues

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

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

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

The epidermis contains: 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 Parenchyma Collenchyma Sclerenchyma النسيج الأساسي وهو مجموعة الأنسجة التي تتواجد فيما بين البشرة والحزم الوعائية وهى أنسجة بسيطة بمعنى أن كل نسيج يتكون من نوع واحد من الخلايا

Parenchyma Characteristics: 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. كثرة المسافات البيئية رقة جدار خلاياها خلايا حية تستعيد قدرتها على الانقسام

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

Collenchyma Locations: Characteristics: Functions 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

Sclerenchyma Functions: Types: 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: Sclereids or stone cells Fibers Both collenchyma and sclerenchyma are mechanical tissues of support

Fibers Sclereids 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 Types: Specialized for long-distance transport of water and dissolved substances. Types: 1. Xylem 2. phloem الأنسجة الوعائية (الناقلة)

Xylem is a complex tissue formed from of : 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 العناصر التوصيلية والقصبيات البدائية Tracheids .

both are elongated, dead at maturity, lignified secondary cell walls. 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. عناصر وعائية

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 اللحاء Phloem

Sieve elements: Companion cells 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. عناصر غر بالية Sieve elements :الخلايا المرافقة Companion

تتركب الأنابيب الغربالية من خلايا تتصل مع بعضها البعض مكونة أنبوب طويل ويوجد عند أخر كل خلية حواجز مثقبة تسمى بالصفائح الغربالية