UNIT 5: PLANT TISSUE

PLANT BODY ORGANS Plants have organs that compose of different tissue, which in turn are composed of cells of different types. A tissue is a group of cells with a common function, structure or both. An organ consist of several types of tissues that together carry out particular functions.

The three basis plant organs are: Roots, stems leaves. The organs are divided into the root system (roots and mycorhiza) shoot system (leaves and stems) SHOOT SYSTEM ROOT SYSTEM

ROOTS Anchor plants Root hairs absorb water and minerals. Stores carbohydrates. Eudicots have a taproot system (one main vertical root that give rise to lateral roots) Monocots have an adventitious root system (roots that originate from the stem of a plant)

Roots can be modified to perform different functions: Fig. 35-4 Roots can be modified to perform different functions: Prop roots Many plants have modified roots “Strangling” aerial roots Storage roots Buttress roots Pneumatophores

STEMS Consist of nodes (where leaves grow) and internodes. The angle between the leave and the stem is called the axillary bud, this can form a lateral shoot. The shoot tip consist of an apical (end) bud. The inhibition of axillary buds by an apical bud is called apical dominance. Stems support the leaves and lateral branches of a plant. Stems keep the plant upright.

Many plants have modified stems Fig. 35-5 Rhizomes Bulbs Storage leaves Many plants have modified stems Stem Stolon Tubers

Rhizome: Horizontal shoot that grows just below the surface Rhizome: Horizontal shoot that grows just below the surface.Vertical shoots emerge from auxillary buds on the rhizome. Stolon: Horizontal shoots that grow along the surface. Reproduce asexually. Tubers: Enlarged ends of rhizome or stolon, specialized to store food. The eyes are clusters of auxillary buds that mark the nodes.

LEAVES Main photosynthetic part of the plant (in most vascular plants). Consist of a flattened blade and a stalk, called a petiole. Monocots have no petiole. Monocots have parallel veins on the leaves and Eudicots have net venation. Leaf shape differs: simple leaves (single leaf) and compound leaves (where the blade consist of smaller leaflets – leaflets have no axillary buds.)

DIFFERENT LEAF STRUCTURES Fig. 35-6 (a) Simple leaf DIFFERENT LEAF STRUCTURES Petiole Axillary bud Leaflet (b) Compound leaf Petiole Axillary bud (c) Doubly compound leaf Leaflet Petiole Axillary bud

Tendrils Spines Storage leaves Reproductive leaves Bracts Fig. 35-7 Tendrils Some plant species have evolved modified leaves that serve various functions Spines Storage leaves Reproductive leaves Bracts

Tissue categories in plants Each plant organ has: dermal, vascular and ground tissues. Each of these three categories forms a tissue system. The dermal tissue system is the plant’s outer protective covering. In non-woody plants it is a single layer called the epidermis protected by a waxy layer called the cuticle found on stems and leaves. In woody plants, the protective tissue is called periderm.

Ground tissue are neither dermal or vascular. Internal ground tissue is called the pith. Ground tissue that is external to the vascular tissue is called cortex. Ground tissue includes various cells with specialized functions such as storage, photosynthesis and supports.

MERISTEMATIC TISSUE A flowering plant has the ability to grow its entire life because it possesses meristematic (embryonic) tissue. The apical meristem are located at or near the tips of stems and roots, where they increase the length of their structures by means of mitosis. This increase in length is called primary growth. Monocots also have an intercalary meristem, this allows them to regrow lost parts. (It is found between mature tissues). EXAMPLE: GRASS CUT - GROW

Organization of a plant body MERISTEMATIC TISSUE AT TIP OF STEM MERISTEMATIC TISSUE AT TIP OF ROOTS

SPECIALIZED PRIMARY TISSUES: APICAL MERISTEM Produces three types of meristems, and these develop into the three types of specialized primary tissues in the body of the plant: SPECIALIZED PRIMARY TISSUES:  Protoderm gives rise to the epidermis Ground meristem produced ground tissue Procambium produces vascular tissue

FUNCTIONS OF SPECIALIZED TISSUES Epidermal tissue: forms the outer protective covering of a plant. Ground tissue fills the interior of a plant. Vascular tissue transports water and nutrients in a plant and provides support.

EPIDERMAL TISSUE

EPIDERMAL TISSUE Single layer of closely packed, flat, brick shaped cells, with a large vacuole. The aerial parts of the plant are covered with a cuticle. Functions: - Cuticle minimizes water loss (because it has cutin) - Protects the plant against bacteria. Longitudinal section Cross section

Leaf contain upper and lower epidermal cells

SPECIALIZE EPIDERMAL CELLS TRICHOMES ROOT HAIR TRICHOMES STOMA OF LEAF CORK OF OLDER STEMS ROOT HAIRS STOMATA CORK CELLS

ROOT HAIRS They are specialized epidermal cells of roots. Unicellular outgrowth of the epidermal cell. Functions: Increase the surface area of the root for absorption of water and minerals. Anchor the plant.

TRICHOMES Specialized epidermal cell of stems and leaves. Multicellular outgrowths of the epidermis of stems and leaves. Functions: Protect the plant from sun Conserve moisture. Protect plant from herbivores, produce toxic substance. CUTICLE MULTICELLULAR

STOMATA Specialized epidermal cells called guard cells, which are bean shaped, enclose an opening called the stoma or pore. The guard cells contain a nucleus and chloroplasts. It has a thick inner membrane and a thin outer membrane. Woody plants have lenticels. FUNCTIONS: Transpiration Gaseous exchange take place through the stomata.

CLOSED- NIGHT OPEN - DAY

PARENCHYMA COLLENCHYMA SCLERENCHYMA GROUND TISSUE PARENCHYMA COLLENCHYMA SCLERENCHYMA

GROUND TISSUES

PARENCHYMA TISSUE FUNCTIONS: Occur in roots, stems and leaves. If they have chloroplasts – photosynthesis. If they have leucoplasts – they store products of photosynthesis. They can divide to form more specialized cells Occur in roots, stems and leaves. Spherical, loosely packed, big, thin-walled cells with large vacuoles. Intercellular airspaces between cells.

INTERCELLULAR AIR SPACES PARENCHYMA CELLS

COLLENCHYMA TISSUE FUNCTIONS: Mechanical strengthening and support to plant organs It is composed of unevenly thickened primary walls with additional cellulose and pectin deposits especially in the corners. Found just beneath the epidermis of young stems. The cells are slightly elongated, tightly packed and overlap each other.

SCLERENCHYMA TISSUE Cell walls have been thickened by impregnation with lignin. The cell wall is evenly thickened and forms a waterproof barrier impermeable to water. In the cell walls are pit canals that serve as channels between cells and to the outside world. The lumen is small. Two types of Sclerenchyma: Stone cells and fibers FUNCTIONS: Strengthening, support and protection. Found in shell of nuts and hard parts of fruits Fibers give rigidity and flexibility to the plant.

Vascular tissue XYLEM PHLOEM

XYLEM Contains 2 types of conducting cells: tracheids and vessel elements (VE). Both cells are hollow and non-living but the VE is larger and has perforated plates in their end walls and are arranged to form a continuous vessel. Tracheids have tapered ends with pits. It also has other tissue: Xylem fibers, and Xylem parenchyma.

FUNCTIONS OF XYLEM Transports water and minerals from the roots to the leaves. Support and strengthening. Xylem vessels Xylem tracheids Xylem fibers

PHLOEM Consist of sieve-tubes and companion cells. The sieve-tubes form a continuous tube, they have cytoplasm but no nuclei. They have sieve plates between cells. The companion cell has a nucleus that controls both cells because they are connected by plasmodesmata. It also has other tissue: Phloem fibers and phloem parenchyma

FUNCTIONS OF PHLOEM Transports sucrose and other organic substances, including hormones, from the leaves to the roots. Support and strengthening.

Tissue organization of Leaves KNOW CROSS SECTION THROUGH LEAF