- - AGRICULTURE CORE CURRICULUM - - (CLF7000) Advanced Core Cluster: PLANT AND SOIL SCIENCE (CLF7200) Unit Title: PHYSIOLOGY AND GROWTH ____________________________________________________________________________ (CLF7201) Topic: FUNCTIONS OF Time Taught in Year(s) PLANT STRUCTURES 18 hours 3 AND 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson the student will be able to: Learning Outcome #: (C-1) - Diagram and label the five primary plant organs indicating the functions of each (i.e., root, stem, leaf, flower, fruit). (C-3) - Compare and contrast monocotyledons and dicotyledons with respect to leaf, stem, and flower structure. (C-4) - Diagram the transpiration and translocation systems of a plant. (C-4) - Describe the functions of the vascular cambium, xylem and phloem. (C-5) - Explain why knowledge of the vascular cambium system of plants is necessary for successful grafting. (C-5) - Describe and explain the effect of girdling on a woody plant. (C-7) - Distinguish between specialized roots, stems, and leaves (e.g., stolons, rhizomes, bulbs, corms, and tubers). (C-8) - Distinguish between roots and underground stems. (C-8) - Sketch and label roots of carrot, potato, corm and grass. (C-8) - Compare tap and fibrous root systems. (C-9) - Explain the function of stomata. (C-9) - Explain how water affects the function of stomata. (C-10) - Define transpiration. (C-10) - Discuss four environmental factors that affect transpiration (e.g. wind, humidity, temperature, solar radiation, and soil conditions). (C-11) - Define the term hormone. (C-11) - Describe how hormones are transported to target structures in plants. (C-12) - Define translocation and its importance to the plant. (C-14) - Trace the stages of development from germination to first seed leaf of bean, pea, onion, and corn. (C-14) - Compare and contrast the growth of bean, pea, onion, and corn. (C-15) - Describe the life cycle of a dicotyledonous plant from seed to seed production. (C-16) - Discuss the effects of photoperiodism on plant growth and give examples of the effects. (C-17) - Sketch and name three types of leaf arrangements on a stem. Special Materials and Equipment: Plant samples with fibrous and tap root systems. Plant samples with specialized roots, stems and leaves. Stolons (e.g., strawberry), Rhizomes (e.g., Johnson grass, Bulbs (e.g., onions), and Tubers (e.g., potatoes). Girdled tree. Crossections of stems and grasses, herbaceous dicots, and woody dicots. Leaves of ivy geranium, sedum and lily. Leaves of grass and broadleaf plants. Flowers from four different plants (select different types). Fruit of citrus, apple, peach, and strawberry. Note: Stolons - Strawberry Rhizomes - Johnson grass (weed) Bulbs - Onions Tubers - Potatoes References: Hartman, H., Flocker, W., and Kofranek, A. PLANT SCIENCE, GROWTH DEVELOPMENT AND UTILIZATION OF CULTIVATED PLANTS. Evaluation: Quiz by instructor TOPIC PRESENTATION: FUNCTIONS OF VARIOUS PLANT STRUCTURES (root, stem, leaf, flower, fruit, seed, meristematic tissue). A. Large masses of organized cells that perform a collective function are called tissues. 1. Various types of tissues combine to form plant organs such as roots, stems, flowers, fruits and seeds. 2. These make up the plant body. B. Roots perform several functions. 1. They absorb water and mineral nutrients from the soil. 2. They conduct these materials both upwards to the stem and downward to the growth and storage regions of the root. 3. They anchor the plant to the soil. 4. Roots also act as storage organs for the plant. a. As an example, sugar beets (used as a commercial source of sugar) store nutrients needed by the plant in the root. b. Carrots, radishes, and beets are used for human consumption, but their roots also store nutrients for the plants. 5. Roots also can be used for: a. reproduction as in the sweet potato, b. photosynthesis in some aerial roots, c. nitrogen assimilation, d. synthesis of essential hormones, and e. nodulation as found on legume roots. 6. There are two basic types of roots systems in plants. a. The fibrous type of root system is found mostly in grasses like corn and barley. 1) These roots grow into the top two or three feet of the soil, so are shallow-rooted. 2) They are many-branched, with no one root markedly longer or larger than the rest. 3) Measuring the total root system of a single rye plant showed that the plant had about 380 miles of roots. b. The tap root system is found on most other plants like alfalfa and deciduous fruit trees. 1) The tap root usually penetrates deep into the soil. 2) It often is used to store plant food. 3) Many branch roots may occur, but the branch roots are more slender than the tap root. 7. The root system usually consists of about 1/3 of the dry weight of the plant. 8. A balance is needed between the root system and the shoot system. a. Roots supply water and minerals to shoots, while shoots supply foods to roots. b. Hormones normally balance the growth of roots and shoots. 1) Roots make the hormone cytokinin, which travels to the shoot system through the xylem, promoting the initiation and outgrowth of buds. If the root system is inadequate, the low cytokinin supply limits shoot growth. 2) Shoots make the hormone auxin, which moves through ground tissue to the roots, promoting the initiation of roots. Thus, a vigorous shoot system calls for an increase in rooting. 9. The need for a root/shoot balance affects agricultural practices. a. Trees should be pruned at the time of transplanting, since the root system is weakened by transplanting. b. Cultivation may be needed to preserve the root system (e.g., tilling the soil to improve aeration; addition of fertilizers). 10. Shoot systems may need pruning to give the best fruit size and quality. a. Many plants set too many fruits, leading to crowding and competition that reduce fruit size and promote fungal disease. Pruning can reduce the fruit set. __________________________________________________________ ACTIVITY: 1. Provide samples of plants with fibrous and tap root systems. 2. Assign students to make written observations of the noticeable variations between a fibrous and a tap root system. __________________________________________________________ __________________________________________________________ ACTIVITY: 1. Grow specialized roots, stems and leaves (e.g, stolons, rhizomes, bulbs, and tubers). 2. Describe and discuss their differences and similarities in class. __________________________________________________________ C. Roots and stems differ in external appearance. 1. Roots lack the nodes and internodes found in stems. 2. On roots, branches arise from an internal meristem, the pericycle, while on stems branches arise from lateral buds. 3. Roots lack stems, leaves, and flowers that are found on stems. 4. The growing point of a root is protected by a root cap, whereas the terminal buds of stems have no such cap. 5. Young roots are usually white, whereas young stems are often red and green. D. Stems have three major functions. 1. Stems transport materials up and down the plant. a. The system that conducts materials within the plant is called the vascular system. 1) The vascular system consists of XYLEM and PHLOEM tissues. 2) In young stems, the vascular system consists of several strands called vascular bundles, each with xylem and phloem. 3) Woody stems have a continuous vascular cylinder, in which the outer portion is phloem and the inner portion is xylem. 4) Xylem moves water and minerals upward from the roots, through stems, to the leaves. 5) Phloem moves nutritive materials (photosynthate, usually sugars) in a water solution through the plant. a) The direction of movement in the phloem can change with time, but is always from organs that make or store foods, to organs that consume foods. b) For example, sugar beets send sugar from leaves to the tap root in the first year of growth. In the second year, sugar moves up the stem from the root, to feed the growing stem and flowers. 2. Stems provide physical support for leaves and flowers. This aids photosynthesis and seed dispersal, and limits animal damage, by holding the organs above ground. 3. Stems store food. E. Stems also have three minor functions. 1. Green stems have chlorophyll and can conduct photosynthesis. 2. Reproduction of plants by stolons, runners, rhizomes, bulbs, and corms (which are all types of stems). 3. Providing climbing ability to plants in the form of tendrils (as found on grapes, vetch, morning glory). F. A knowledge of the structure and function of stems is fundamental in the horticultural practices of pruning, girdling and grafting. 1. To form a graft, two plant parts must be placed with their cambium tissues in contact. 2. When a plant is girdled (removing the bark and phloem in a ring around the stem of a plant), sugar and other carbohydrates accumulate above the girdle. (Commercially this technique has been used to increase the size of seedless grapes.) __________________________________________________________ ACTIVITY: Girdle the stem of a woody potted plant: (Results will not be visible for several weeks.) Discuss observations with the class. Note that the cambium tissue above the girdle produces more new tissue than below the girdle. This shows that there is a larger supply of sugars and other carbohydrates above the cut. (Note: This procedure will harm the plant.) __________________________________________________________ __________________________________________________________ ACTIVITY: 1. Provide students with crossections of stems of several different plants for microscope study. 2. Compare, describe, and discuss the differences, especially between monocot and dicot stems. __________________________________________________________ G. Leaves vary in form. 1. In most broadleaf plants leaves are made up of the blade (flat thin part); the stem-like petiole which attaches the blade to the stem; and in some plants, the stipules at the base of the petiole. a. Some leaf blades are attached directly to the stem and lack petioles or stipules. (These are termed sessile leaves.) 2. Most monocot leaves have a leaf sheath that clasps the stem, instead of a petiole. a. Leaves have several types of arrangements. 1) Alternate leaves are found one at each node, sometimes spiralling around the stem. 2) Opposite leaves appear two at each node (one opposite the other). 3) Whorled leaves are found three or more at each node. b. Leaves are either simple or compound. 1) A simple leaf has arc blades. 2) A compound leaf has several blades called leaflets. 3) There are two basic kinds of compound leaves, pinnately compound and palmately compound. 4) A compound leaf with three leaflets is commonly referred to as trifoliate (e.g. ladino clover). H. Leaves serve chiefly for photosynthesis. 1. The structure and form of leaves promotes their photosynthetic function. a. The blade has a large surface area that allows it to intercept a large amount of light, providing energy for photosynthesis. b. The surface area also exposes the leaf to a large volume of air from which it absorbs carbon dioxide. Carbon dioxide is used to make sugars. c. Veins, which are vascular bundles, bring water into the leaf. The hydrogen of water is used in making sugar, and the oxygen of water is released as O2. d. The veins also carry sugars out of the leaf. e. Veins also keep the leaf blade extended, acting like the ribs of an umbrella. 2. Some features of leaves are important in cooling the leaf and limiting water loss. a. The leaf is covered with a waterproof, waxy material (the cuticle) through which water cannot pass. This prevents the leaf from uncontrolled water loss. b. The cuticle also blocks the entry of carbon dioxide. Thus, to let in carbon dioxide, leaves have thousands of tiny, controllable openings called stomata. 1) A stoma is a pore between two guard cells that are part of the leaf surface. 2) To open the stoma, the guard cells actively take up potassium ions (K+). This causes water to enter the cells. As they swell, they bend so a pore opens between them. a) Sugars, formed by photosynthesis, can also accumulate in guard cells. They also attract water and help to keep the guard cells bent. 3) To close the stoma, the guard cells release solutes (chiefly K+); water leaves, and the cells lose their curvature. 4) The guard cells respond to signals so that stomata only open when there is a need for carbon dioxide. This limits the loss of water. a) In most plants, light causes stomata to open; they close in darkness. b) Some plants in very hot areas open the stomata at night, when temperatures are cooler, and store carbon dioxide for use when stomata are closed in the daytime. c) Most plants keep their stomata closed when there is already plenty of carbon dioxide inside the leaf. d) When leaves absorb light, some of the energy is converted to heat that must be removed to prevent damage. e) The large surface area helps to release heat by radiation and convection, much like the metal fins on a motorcycle engine or a car radiator. f) Most of the heat is released by evaporation of water through the stomata (the process of transpiration). The principle is the same as sweating to cool the human body. I. Some leaves perform functions in addition to photosynthesis 1. They may store foods and water, as in onion bulbs and succulent leaves. 2. When modified into tendrils, leaves may assist the climbing of a vine by attaching to supports. 3. Leaves with clasping bases (leaf sheaths) may hold the shoot system erect, as in young corn plants. 4. A minority of plants have leaves that form buds and roots, leading to new plants when the leaf is detached. This is a form of vegetative reproduction. 5. Some marsh plants have leaves that serve as insect traps, as in the Venus fly trap. __________________________________________________________ ACTIVITY: 1. Provide leaves of ivy, geranium, sedum and lily. 2. Peel a piece of the lower epidermis of each leaf, mount in water on a glass slide, cover with cover slip, and observe stomata in a compound microscope. 3. To see stomated opening and closing draw a salt solution under the cover step, observe, then replace the salt solution with distilled water and observe again. 4. Draw the guard cells and explain the differences in stomatal openings (size, arrangements and shapes). 5. Discuss factors that would cause stoma to open and close. __________________________________________________________ __________________________________________________________ ACTIVITY: 1. Provide stems of plants with the three types of leaf arrangments and simple and compound leaves. 2. Sketch and name the arrangements and whether leaves are simple or compound. __________________________________________________________ __________________________________________________________ ACTIVITY: 1. Provide leaves of dicot and monocot plants. 2. Observe, draw and explain the differences between broadleaf and grass leaves. Note expecially the differences in veination. __________________________________________________________ J. Flowers perform sexual reproduction 1. A complete flower is made up of five parts. a. The receptacle is the enlarged stem tip, to which other flower parts are attached. b. The sepals form an outer circle of leaf-like structures collectively called the calyx. They protect the flower bud, and they may attract pollinating animals. 1) Pollinators are animals that carry male reproductive cells (in pollen grains) from flower to flower. c. The petals, collectively called the corolla, make up the colorful parts of most flowers. 1) The may secrete nectar (a sugar solution) that rewards animal pollinators. 2) They may secrete aromatic compounds that attract animals. 3) Each species has characteristic numbers and shapes of flower parts. This uniformity helps to assure that pollinating animals will visit flowers of the same kind one after another. d. Stamens are the male parts of the flower. 1) They are situated inside the petals. 2) They consist of a filament (stalk) and a pollen bearing anther at its apex. e. Pistils are the female parts of the flower. 1) They are located in the center of the flower. 2) They have three parts: a) A stigma, (which captures pollen) b) A style, which leads from stigma to ovary. c) An ovary. the basal enlarged part in which seeds are formed. __________________________________________________________ ACTIVITY: 1. Provide flowers from at least four different plants. 2. By using tweezers and razor blades, dissect the flowers into their parts (receptacle sepals, petals, stamens and pistils). 3. Draw each of the four parts. 4. Discuss and compare the differences between each of the four parts. 5. Draw one complete flower and label all of its parts. __________________________________________________________ K. A fruit is the ripened ovary of a plant. 1. Simple fruits (example: peach) consist only of one ripened ovary. 2. In addition to the ovary, some fruits contain receptacle tissue (example: apple). 3. Some fruits have more than one ovary (examples: strawberry and blackberry). 4. A seed is a matured ovule. a. Seeds vary greatly in size, shape, and structure. b. Three basic parts of the seed include: 1) The embryo. 2) The food storage tissue. 3) The seedcoat. c. The seed then is a miniature plant (embryo), containing storage tissue which is protected by the seedcoat. __________________________________________________________ ACTIVITY: 1. Provide the fruit of several different plants. Good examples would be citrus, apples, peaches and strawberries. 2. Dissect each fruit from stem end through the blossom end. 3. Study the various parts, drawing and labeling them. __________________________________________________________ 7/20/90 sg #%&C