- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: PLANT AND SOIL SCIENCE (CLF6200) Unit Title: PLANT PHYSIOLOGY AND GROWTH ____________________________________________________________________________ (CLF6201) Topic: GROWTH STRUCTURES Time Taught in Year(s) AND FUNCTIONS 9 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 four primary plant structures (leaf, stem, root, and flower). Indicate the functions of each and list an example of each. (C-2) - Explain the importance of meristematic tissue in growth and physiology, and in its relationship to plant reproduction. (C-3) - Plant examples of monocotyledons (one seed-leaf) and dicotyledons (two seed leaves) and make written observations of the leaf and flower structures of each as they grow. (C-4) - Diagram the transpirational and translocational system of a plant and describe the functions of each (e.g., cambium, xylem, and phloem). (C-5) - Explain why knowledge of the translocational system of plants is necessary for successful grafting. Girdle a tree and discuss observations. (C-7) - Make a collection of specialized roots, stems, and leaves (e.g., stolons, rhizomes, bulbs, tubers) and discuss their differences and similarities in class. (C-8) - Sketch and label each of the following root types: carrot, potato, corn, and grass. Distinguish between roots and underground stems and compare tap and fibrous root systems. (C-9) - Discuss the function of the stomata and explain how water affects this function. (C-10) - Define transpiration and discuss four environmental factors that affect the transpiration rate (e.g., wind, humidity, temperature, and insolation (exposure to sun). (C-11) - Define the term "hormone," and describe how hormones are transported to target structures in plants (e.g., vascular tissue). (C-12) - Define translocation and its importance to the plant. (C-13) - List The requirements for seed germination and indicate factors that might reduce germination rates (e.g., temperature, water, oxygen, seed dormancy, and disease). (C-14) - Trace the stages of development (using bean, pea, onion, and corn plants) from germination to the stage of first true leaves. Compare and contrast the types of growth. (C-15) - Describe the life cycle of a dicotyledonous plant from seed to seed production. (C-16) - Discuss and give examples of the effects of photoperiodism on plant growth. (C-17) - Sketch and name four types of leaf arrangement on a stem (e.g., alternate, opposite, whorled, trifoliate). 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. Cross sections 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: Hartmann, H. T., Flocker, W. J., & Kofranek, A. M. (1981). PLANT SCIENCE: GROWTH, DEVELOPMENT, AND UTILIZATION OF CULTIVATED PLANTS. Englewood Cliffs, NJ: Prentice-Hall. Evaluation: Quiz by instructor TOPIC PRESENTATION: GROWTH STRUCTURES AND FUNCTIONS 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 leaves 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. 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 in 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) When the total root system of a single rye plant was measured, it was learned that the plant had about 380 miles of roots. b. The taproot system is found on most other plants, for example, deciduous fruit trees, and landscape shrubbery. __________________________________________________________ ACTIVITY: 1. Provide samples of plants with fibrous and taproot systems. 2. Assign students to make written observations of the noticeable variations between a fibrous and a taproot system. __________________________________________________________ 1) The taproot 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 horticultural 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). 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 buds, 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. __________________________________________________________ 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. __________________________________________________________ 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 downward 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 taproot 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. Plants can reproduce by stolons, runners, rhizomes, bulbs, and corms (which are all types of stems) as well as by stem cuttings. 3. Stems provide 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 proper 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 broad 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. __________________________________________________________ ACTIVITY: 1. Provide leaves of dicot (green bean) and (corn) monocot plants. 2. Observe, draw and explain the differences between broadleaf and grass leaves. Note especially the differences in veination. __________________________________________________________ a. Leaves have several types of arrangements. 1) Alternate leaves are found one at each node, sometimes spiraling 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. __________________________________________________________ ACTIVITY: 1. Given a list of botanical terms relating to leaf parts, shapes and arrangements, send the students (in teams of two) on a "botanical scavenger hunt." Note: This activity requires prior permission of the school's groundskeeper. __________________________________________________________ b. Leaves are either simple or compound. 1) A simple leaf has one blade. 2) A compound leaf has several blades called leaflets. 3) There are two basic kinds of compound leaves, pinnately compound (many finely divided leaflets) and palmately compound (fewer leaflets). 4) A compound leaf with three leaflets is commonly referred to as trifoliate (e.g., ladino clover and poison oak). __________________________________________________________ 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 indicate whether leaves are simple or compound. __________________________________________________________ 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. Aditionally, veins 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 or cutin) through which water cannot pass. This prevents uncontrolled water loss from the leaf. 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 evaporates, and the cells lose their curvature. 4) The guard cells respond to signals so that stomata open only 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 of leaves helps to release heat by radiation and convection, functioning 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, as in grapes. 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's flytrap. 6. Some desert plants have evolved to no leaves as a means of survival. Their stem completes the normal leaf and stem functions of a plant. __________________________________________________________ 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 slip, 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. __________________________________________________________ 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, the sticky surface which captures pollen. b) A style, the support structure which leads from stigma to ovary. c) An ovary, the basal enlarged part in which seeds are formed in compartments known as ovules. __________________________________________________________ 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 of only one ripened ovary. 2. In addition to the ovary, some fruits (example: apple) contain receptacle tissue, a thickened tissue serving as a base for the pistil. 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 seed coat (or testa). Most seeds have two seed coats. c. The seed, then, is a miniature plant (embryo), containing storage tissue which is protected by the seed coat. __________________________________________________________ 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. __________________________________________________________ 12/14/90 PJK/sg #%&C