UNIT 5: PLANT TISSUECampbell and Reece, 2010. Chapter 35 p. 738 – 745 and 750 - 751, Edulink and learning guide notes
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. SHOOT SYSTEM ROOT SYSTEM The organs are divided into the root system (roots and mycorhiza) shoot system (leaves and stems)
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)
Fig. 35-4 Roots can be modified to Prop roots Many plants have modified perform different functions: 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.
Fig. 35-5 Rhizomes Bulbs Storage leaves Many plants Stem have modified stems Stolon Tubers
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.)
Fig. 35-7 TendrilsSome plant species have evolved modified leaves Spines that serve various functions 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.
Some epidermal cells are modified to form hairs – roothairs on roots and trichomes on leaves and stems. The vascular tissue system carries out transport of materials between the root and the shoot system. The two types are xylem and phloem. 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
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 Single layer of closely Functions: packed, flat, brick - Cuticle minimizes shaped cells, with a water loss (because it large vacuole. has cutin) The aerial parts of the - Protects the plant plant are covered with against bacteria. a cuticle. Longitudinal section Cross section
SPECIALIZE EPIDERMAL CELLS TRICHOMES ROOT HAIR TRICHOMES ROOT HAIRS STOMA OF LEAF CORK CELLS STOMATA CORK OF OLDER STEMS
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. CUTICLE Multicellular outgrowths MULTICELLULAR of the epidermis of stems and leaves. Functions: Protect the plant from sun Conserve moisture. Protect plant from herbivores, produce toxic substance.
STOMATA Specialized epidermal FUNCTIONS: cells called guard Transpiration cells, which are bean shaped, enclose an Gaseous exchange opening called the take place through the stoma or pore. stomata. The guard cells contain a nucleus and chloroplasts. It has a thick inner membrane and a thin outer membrane. Woody plants have lenticels.
PARENCHYMA TISSUE Occur in roots, stems and FUNCTIONS: leaves. If they have Spherical, loosely chloroplasts – packed, big, thin-walled photosynthesis. cells with large vacuoles. If they have leucoplasts Intercellular airspaces – they store products between cells. of photosynthesis. They can divide to form more specialized cells
COLLENCHYMA TISSUE It is composed of FUNCTIONS: unevenly thickened Mechanical primary walls with strengthening and additional cellulose and support to plant organs 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 FUNCTIONS: thickened by impregnation with lignin. Strengthening, support The cell wall is evenly and protection. thickened and forms a Found in shell of nuts waterproof barrier and hard parts of fruits impermeable to water. Fibers give rigidity and In the cell walls are pit flexibility to the plant. canals that serve as channels between cells and to the outside world. The lumen is small. Two types of Sclerenchyma: Stone cells and fibers
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 P. 750 – 751 (SELF STUDY) KNOW CROSS SECTION THROUGH LEAF