Function and Structure of Leaf, Stem and roots

1. TRANSPORT IN FLOWERING PLANTS STRUCTURE AND FUNCTION OF LEAF, STEM AND ROOTS

2. PRESENTED BY MUHAMMAD TALAL AKBAR CAMBRIDGE 2 FOR RESPECTIVE TEACHER UNIVERSITY PRESS

3. IMPORTANCE OF PLANTS  Plants are living organisms that cover large amounts of the surface of our planet. They come in many shapes, sizes and colours and include trees, shrubs, grasses, herbs, vines, ferns, mosses and green algae. Most plants have roots, stems and leaves and they either produce flowers or cones for reproduction. Plants can live in water and on land, usually with their roots firmly secured in soil. However, some live off other host plants and don’t need soil – these are ‘air plants’ and ‘epiphytes’ (e-pee-fites). Botanists (scientists who study plants) have identified about 391,000 living species of plants across the world. Plants are special because they all have green parts within their cells called ‘chlorophyll’ (klor-o-fill) that helps them turn sunlight (energy) and carbon- dioxide (what animals breathe out) into oxygen (what animals breathe in) and sugar (the food that helps plants grow). This process is known as photosynthesis. Without plants, we could not survive because the oxygen in the atmosphere would not be replenished.

4. LEAF Leaves are parts of plants. In most plants, leaves are the major sites of photosynthesis, the conversion of energy from sunlight into chemical energy (food). Leaves take in carbon dioxide from the air and produce oxygen through stomata (tiny pores in the leaf). Leaves come in many sizes and shapes; they are often used to help identify plants. Some leaves are flat and wide; others are spiky and thin. Plant spines (like cactus spines) are actually modified leaves. Leaves are also responsiblE for respiration and transpiratION..

5. STRUCTURE OF LEAF Each leaf typically has a leaf blade called the lamina, which is also the widest part of the leaf. Some leaves are attached to the plant stem by a petiole. Leaves that do not have a petiole and are directly attached to the plant stem are called sessile leaves. Leaves also have stipules, small green appendages usually found at the base of the petiole. Most leaves have a midrib, which travels the length of the leaf and branches to each side to produce veins of vascular tissue. The edge of the leaf is called the MARGIN. Within each leaf, the vascular tissue forms veins. The arrangement of veins in a leaf is called the venation pattern. Monocots and dicots differ in their patterns of venation. Monocots have parallel venation in which the veins run in straight lines across the length of the leaf without converging. In dicots, however, the veins of the leaf have a net-like appearance, forming a pattern known as reticulate venation. Ginkgo biloba is an example of a plant with dichotomous venation.

6. FUNCTION OF LEAF Photosynthesis: Photosynthesis is the process of conversion of carbon dioxide and water to food (glucose) and oxygen in the presence of sunlight. The green pigment called chlorophyll present in the leaves can entrap the solar energy which is used during photosynthesis. The food (glucose) produced in photosynthesis is transported to the other parts of the plants from the leaExchange of Gasses: Exchange of gasses takes place through the minute pores called stomata. Carbon dioxide required for photosynthesis moves in through the stomata while the oxygen moves out. Transpiration: Removal of excess water in the form of water vapor through the stomata is called transpiration. Excess water needs to be removed to cool down the leaf surface or allow the conduction of water from the roots.f.

7. STEM  stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaves, flowers and fruits, transports water and dissolved substances between the roots and the shoots in the xylem and phloem, stores nutrients, and produces new living tissue.[1] The stem can also be called halm or haulm or culmsThe stem is normally divided into nodes and internodes: The nodes hold one or more leaves, as well as buds which can grow into branches (with leaves, conifer cones, or flowers). Adventitious roots may also be produced from the nodes. Vines may produce tendrils from nodes. The internodes distance one node from another. The term "shoots" is often confused with "stems"; "shoots" generally refers to new fresh plant growth including both stems and other structures like leaves or flowers. In most plants stems are located above the soil surface but some plants have underground stems..

8. STRUCTURE OF STEM The stem and other plant organs are primarily made from three simple cell types: parenchyma, collenchyma, and sclerenchyma cells. Parenchyma cells are the most common plant cells. They are found in the stem, the root, the inside of the leaf, and the pulp of the fruit. Parenchyma cells are responsible for metabolic functions, such as photosynthesis. They also help repair and heal wounds. In addition, some parenchyma cells store sCollenchyma cells are elongated cells with unevenly-thickened walls. They provide structural support, mainly to the stem and leaves. These cells are alive at maturity and are usually found below the epidermis. The “strings” of a celery stalk are an example of collenchyma As with the rest of the plant, the stem has three tissue systems: dermal, vascular, and ground tissue. Each is distinguished by characteristic cell types that perform specific tasks necessary for the plant’s growth and survival..

9. The dermal tissue of the stem consists primarily of epidermis: a single layer of cells covering and protecting the underlying tissue. Woody plants have a tough, waterproof outer layer of cork cells commonly known as bark, which further protects the plant from damage. Epidermal cells are the most-numerous and least-differentiated of the cells in the epidermis. The epidermis of a leaf also contains openings, known as stomata, through which the exchange of gases takes place. Two cells, known as guard cells, surround each leaf stoma, controlling its opening and closing and, thus, regulating the uptake of carbon dioxide and the release of oxygen and water vapor. Trichomes are hair-like structures on the epidermal surface. They help to reduce transpiration (the loss of water by aboveground plant parts), increase solar reflectance, and store compounds that defend the leaves against predation by herbivores. The xylem and phloem that make up the vascular tissue of the stem are arranged in distinct strands called vascular bundles, which run up and down the length of the stem. Both are considered complex plant tissue because they are composed of more than one simple cell type that work in concert with each other. When the stem is viewed in cross section, the vascular bundles of dicot stems are arranged in a ring. In plants with stems that live for more than one year, the individual bundles grow together and produce the characteristic growth rings. In monocot stems, the vascular bundles are randomly scattered throughout the ground tissue.Xylem tissue has three types of cells: xylem parenchyma, tracheids, and vessel elements. The latter two types conduct water and are dead at maturity. Tracheids are xylem cells with thick secondary cell walls that are lignified. Water moves from one tracheid to another through regions on the side walls known as pits where secondary walls are absent. Vessel elements are xylem cells with thinner walls; they are shorter than tracheids. Each vessel element is connected to the next by means of a perforation plate at the end walls of the element. Water moves through the perforation plates to travel up the plant. Phloem tissue is composed of sieve-tube cells, companion cells, phloem parenchyma, and phloem fibers. A series of sieve-tube cells (also called sieve- tube elements) are arranged end-to-end to create a long sieve tube, which transports organic substances such as sugars and amino acids. The sugars flow from one sieve-tube cell to the next through perforated sieve plates, which are found at the end junctions between two cells. Although still alive at maturity, the nucleus and other cell components of the sieve-tube cells have disintegrated. Companion cells are found alongside the sieve-tube cells, providing them with metabolic support. The companion cells contain more ribosomes and mitochondria than do the sieve-tube cells, which lack some cellular organelles. Ground Tissue Ground tissue is mostly made up of parenchyma cells, but may also contain collenchyma and sclerenchyma cells that help support the stem. The ground tissue towards the interior of the vascular tissue in a stem or root is known as pith, while the layer of tissue between the vascular tissue and the epidermis is known as the cortex. :

10. FUNCTION  OF STEM Stems have four main functions which are:[2] Support for and the elevation of leaves, flowers, and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits. Transport of fluids between the roots and the shoots in the xylem and phloem (see below). Storage of nutrients. Production of new living tissue. The normal lifespan of plant cells is one to three years. Stems have cells called meristems that annually generate new living tissue. Stems have two pipe-like tissues called xylem and phloem. The xylem tissue transports water by the action of transpiration pull, capillary action, and root pressure. The phloem tissue consists of sieve tubes and their companion cells. The two tissues are separated by cambium, a tissue that divides to form xylem or phloem cells.

11. ROOTS Root is the most essential part of a plant that grows down to the soil and water. Root avoid the sunlight, as it grows down to soil and water, and absorbs mineral salt and water from the soil. Roots However, some typical roots are also aerial or aerating, that grow up above the ground or especially above the water. Roots do not have leaves, buds, and nodePlants have specialized organs that help them survive and reproduce in a great diversity of habitats. Major organs of most plants include roots, stems, and leaves. Roots are important organs in all vascular plants. Most vascular plants have two types of roots: primary roots that grow downward and secondary roots that branch out to the side. Together, all the roots of a plant make up a root system.s.

12. STRUCTURE OF ROOTS There are three different types of root structure. A taproot, characteristic of dicots, is a single dominant root from which smaller, secondary roots extend. In a fibrous root system, composed of many small roots, no single root dominates. Taproots stretch deep into the soil, while fibrous roots spread out close to the surface. Adventitious roots develop on vines after embryonic development and help plants cling to substrates other than the soil, such as a tree trunkTypical roots contain three different sections, or zones: the meristematic zone, the zone of elongation, and the zone of differentiation. In the meristematic zone, named after the apical meristem, the plant cells undergo rapid mitotic division, creating new cells for root growth. These new cells, once they enter the zone of elongation, begin,unsurprisingly, to elongate, furnishing the root with added length. The zone of differentiation containsmature, specialized cells, such as phloem, xylem, and root hairs.s.

13. FUNCTION OF ROOTS Absorbing water and minerals: Thin-walled epidermal cells and root hairs are well suited to absorb water and dissolved minerals from the soil. The roots of many plants also have a mycorrhizal relationship with fungi for greater absorption. Anchoring and supporting the plant: Root systems help anchor plants to the ground, allowing plants to grow tall without toppling over. A tough covering may replace the epidermis in older roots, making them ropelike and even stronger. As shown in Figure below, some roots have unusual specializations for anchoring plants. Storing food: In many plants, ground tissues in roots store food produced by the leaves during photosynthesis. The bloodroot shown in Figure below stores food in its roots over the winteThe major functions of roots are absorption of water, plant nutrition and anchoring of the plant body to the ground. [2]r.

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