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Horticulture Science Lesson 8 Understanding Stem Anatomy.

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1 Horticulture Science Lesson 8 Understanding Stem Anatomy

2 Interest Approach Begin the lesson by dividing the class into groups. Give each group a small branch from a tree. Ask the class to closely observe the branch. From the branch, what can they tell about the tree that it was growing on? Ask how many structures on the stem they can identify. Most students will be familiar with buds. If it is spring or fall and leaves are on the stem, lead the students to observe how evenly the leaves are spread and how efficiently they collect the sunlight.

3 Student Learning Objectives Describe the functions of a stem. Recognize the external structures of a stem.

4 Student Learning Objectives Analyze the internal structures of a stem. Distinguish between the different types of specialized stems.

5 Terms apical meristem bud bud scale scar bud scales bulb cambium corm cortex

6 Terms heartwood internode lateral bud leaf scar lenticels node phloem

7 Terms rhizome sapwood stolon terminal bud translocation tuber vascular cambium xylem

8 What are the functions of a stem? Stems have many important jobs in a plant. Stems are responsible for the size and shape of a plant. Some stems are made of wood, and some are herbaceous or soft.

9 What are the functions of a stem? The following are four functions of stems. –Stems support the leaves. They hold the leaves in the most efficient position to collect sunlight. –Stems move water, minerals, and manufactured food throughout the whole plant. The movement of materials through vascular tissues is known as translocation.

10 What are the functions of a stem? –Stems that are green in color help produce food through photosynthesis. While this is not usually the primary food production, it can be quite important in plants with no leaves or very small leaves. –Stems store food that has been manufactured by the plant.

11 What are some of the structures on the outside of a stem? Many structures on the stem are useful to us in identifying plants. The following are some external structures on a stem. –The growing point at the tip of the stem, called the apical meristem, is contained inside of the bud at the end of the stem, which is called the terminal bud. –The apical meristem is the same type of structure that the tip of the root has and is responsible for growth in the length of the plant.

12 What are some of the structures on the outside of a stem? –The leaf is attached to the stem at the node. –The area between leaves is called an internode. –At the node, just above where the leaf is attached, there is always a side bud called the lateral bud. –On the outside of both terminal and lateral buds are small protective structures called bud scales.

13 What are some of the structures on the outside of a stem? –When the leaf falls off of the stem, it leaves behind a small scar just below the lateral bud. This scar is called the leaf scar. –When the buds sprout each spring, the bud scales fall off, leaving behind a ring of scars called the bud scale scar. –The distance between bud scale scars represents one year’s growth of the stem. –Lenticels are small spots on the stem that allow it to exchange gases with its environment.

14 What are some of the structures on the outside of a stem?

15 What are some of the structures inside a stem? Inside of the stem, there are tissues used to transport materials throughout the plant. Stem tissues are organized in one of the following ways. The important vascular tissues are either found in small bundles scattered throughout the stem or arranged in rings or a ring of vascular bundles, which are located in the cortex.

16 What are some of the structures inside a stem? The first way, scattered bundles, is found in monocots. The second way, in rings, is found in dicots. There are three important types of tissue found inside of the stem.

17 What are some of the structures inside a stem? The xylem is tissue that conducts the water and minerals throughout the plant. The xylem is made of tube-like cells that grow together to conduct liquids. Xylem tends to be found closer to the center of the stem. It is responsible for growth in girth of the stem and is generally found between the xylem and the phloem.

18 What are some of the structures inside a stem? The phloem is tissue that conducts food that is produced in the leaf to the rest of the plant. Phloem cells also form tubes. Phloem is generally found toward the outside of the stem.

19 What are some of the structures inside a stem? Vascular cambium is tissue that is responsible for the production of new xylem and phloem. It is responsible for growth in girth of the stem and is generally found between the xylem and the phloem.

20 What are some of the structures inside a stem? The darker wood to the center of the tree is called the heartwood. –The xylem cells of the heartwood have filled with gums, resins, pigments, and tannins. –They provide strength and no longer function in conducting materials. The lighter wood circling the heartwood is called the sapwood. ―The younger sapwood actively conducts water and dissolved minerals.

21 What are some of the structures inside a stem? The age of a tree can be determined by counting annual growth rings. During rapid growth, the cells of the wood are thin walled and large in diameter. As growth slows during mid- to-late summer, the wood cells produced by the cambium become smaller and have thicker walls. Each ring is the growth during one growing season.

22 What are some different kinds of specialized stems? We generally expect stems to be upright and above ground. Some stems are modified to store food or to help the plant reproduce. Some stems grow beneath the soil instead of above it. The following are some types of specialized stems.

23 What are some different kinds of specialized stems? A bulb is a very short flattened stem that has several fleshy leaves attached to it. Bulbs tend to be found beneath the soil. An onion is a bulb. A corm is a spherical structure, much like a bulb. The entire structure, however, is stem as opposed to stem and leaves. A gladiolus is a corm.

24 What are some different kinds of specialized stems? A rhizome is a thick underground stem that lies horizontally. Hostas and Mother-in-law’s Tongue are rhizomes. A stolon is a horizontal stem that lies above the ground. Stolons are sometimes called runners and tend to be involved with the spreading of the plant. Strawberries spread by stolon.

25 What are some different kinds of specialized stems? A tuber is a rhizome with a tip that is swollen with stored food. Irish potatoes are tubers.

26 What are some different kinds of specialized stems?

27 Review/Summary What are the functions of a stem? What are some of the structures on the outside of a stem?

28 Review/Summary What are some of the structures inside a stem? What are some different kinds of specialized stems?


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