Below the epidermis of dicot leaves are layers of cells known as the mesophyll, or “middle leaf.” The mesophyll of most leaves typically contains two arrangements of parenchyma cells: the palisade parenchyma and spongy parenchyma. In many epiphytic bromeliads, the pseudotrunk also functions as a water reservoir. Answer: The main function of leaf is photosynthesis. The structure of a ... A cross-section through a leaf Features of leaves and their functions. The structure of the umbrella tree leaf is typical of leaves in general (Above left photo). Moreover, the vein structure is striated and each node contains only one leaf. Answers: Leaf Structure and Function: Printable Read-and-Answer Worksheet A printable worksheet on leaves, with a short text, a cross section of a leaf to label, and questions to answer. You need to understand the structure of the tissues in a leaf together with their functions. Chlorophyll, the substance that gives plants their characteristic green colour, absorbs light energy. As the primary sites of photosynthesis, leaves manufacture food for plants, which in turn ultimately nourish and sustain all land animals. However, in plants that grow in very hot or very cold conditions, the epidermis may be several layers thick to protect against excessive water loss from transpiration. Tendrils and hooks are the most common of these modifications. In perennial plants, leaf fall is usually associated with approaching winter dormancy. The central leaf, or mesophyll, consists of soft-walled, unspecialized cells of the type known as parenchyma. LEAF STRUCTURE & FUNCTION 2. Or go to the answers. Leaf Structure and Function For a typical leaf, we use that of the umbrella tree, which is commonly sold as a foliage plant throughout North America and Europe. In the flame lily (Gloriosa superba), the leaf tip of the blade elongates into a tendril and twines around other plants for support. In most plants, leaves are the major site of food production for the plant. Missed the LibreFest? Below the palisade parenchyma are loosely-arranged cells of an irregular shape. Spines are also modified leaves. Quiz. It has a photosynthetic pigment chlorophyll which converts solar energy into chemical energy. When only a single blade is inserted directly on the petiole, the leaf is called simple. There are some indications that day length may control leaf senescence in deciduous trees through its effect on hormone metabolism; both gibberellins and auxins have been shown to retard leaf fall and to preserve the greenness of leaves under the short-day conditions of autumn. Gelatinous interior of the leaves of aloe (, Pitcher-shaped leaves of the carnivorous slender pitcher plant (. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. It is where photosynthesis takes place. All leaves have the same basic structure - a midrib, an edge, veins and a petiole. A single vascular bundle, no matter how large or small, always contains both xylem and phloem tissues. The leaf is also involved in the transpiration process. The margins of simple leaves may be entire and smooth or they may be lobed in various ways. Tannins give oak leaves and certain other plants their dull brown colour. They are attached by a continuous vascular system to the rest of the plant so that free exchange of nutrients, water, and end products of photosynthesis (oxygen and carbohydrates in particular) can be carried to its various parts. Black Friday Sale! Leaves are, however, quite diverse in size, shape, and various other characteristics, including the nature of the blade margin and the type of venation (arrangement of veins). Leaves are initiated in the apical bud (growing tip of a stem) along with the tissues of the stem itself. In many trees leaf senescence is brought about by declining day length and falling temperature toward the end of the growing season. Save 50% off a Britannica Premium subscription and gain access to exclusive content. Chlorophyll production in deciduous plants slows as the days get shorter and cooler, and eventually the pigment is broken down completely. New Phytol 134:35–51 CrossRef Google Scholar. A local concentration of cell divisions marks the very beginning of a leaf; these cells then enlarge so as to form a nipple-shaped structure called the leaf buttress. Leaves do not shade each other To trap as much light as possible 4. A great variety of base and apex shapes also are found. As much as one-fifth of the mesophyll is composed of chlorophyll-containing chloroplasts, which absorb sunlight and, in conjunction with certain enzymes, use the radiant energy in decomposing water into its elements, hydrogen and oxygen. In cacti, spines are wholly transformed leaves that protect the plant from herbivores, radiate heat from the stem during the day, and collect and drip condensed water vapour during the cooler night. The structures of leaves are adapted for efficient photosynthesis as shown in the table below. Leaf structure 1. Printout Many desert plants, such as Lithops and aloe, develop succulent leaves for water storage. Typically, a leaf consists of a broad expanded blade (the lamina), attached to the plant stem by a stalklike petiole. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Have questions or comments? Upper Epidermis: this is the tissue on the upper surface of the leaf. The air space found between the spongy parenchyma cells allows gaseous exchange between the leaf and the outside atmosphere through the stomata. The epidermis consists of the upper and lower epidermis; it aids in the regulation of gas exchange via stomata. Leaf margins of simple leaves may be lobed in one of two patterns, pinnate or palmate. Leaves of dicots possess a network of interconnecting veins…, Leaves originate on the flanks of the shoot apex. Other leaves may have small hairs (trichomes) on the leaf surface. A waxy layer known as the cuticle covers the leaves of all plant species. In hot climates, plants such as cacti have succulent leaves that help to conserve water. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. The basic angiosperm leaf is composed of a leaf base, two stipules, a petiole, and a blade (lamina). Our editors will review what you’ve submitted and determine whether to revise the article.