1 Stem Anatomy Lesson Plan: NRES B5-4

2 Anticipated Problems 1. What are the functions of a stem? 2. What are some of the external structures of stems? 3. What are some kinds of specialized stems? 4. What are the functions of the internal structures of stems? 5. What factors are involved in translocation?

3 Terms apical meristem bud scale scar bud scales bulb cambium cladophyll climbing stems corm cortex heartwood herbaceous stems internode lateral bud leaf scar lenticels node

4 Terms phloem pith rays rhizome sapwood scape spine stolon terminal bud translocation tuber water potential woody stems xylem

5 Monocot Stems vs Herbaceous Dicot Stems Monocot stems and herbaceous dicot stems have similarities and differences

Monocot Stems Epidermis (provides protection) Vascular tissues, xylem and phloem, are grouped into vascular bundles __________________________________________ __________________________________________ __________________________________________ Vascular bundles lack cambium, which would give rise to woody, secondary growth 6 Monocot Stems vs Herbaceous Dicot Stems

Herbaceous Dicot Stems Epidermis (provides protection) Inside the epidermis is the_____________-composed of parenchyma, collenchyma, and sclerenchyma cells Inside the cortex are the vascular bundles- ________________________ Xylem is on the inner portion of the vascular bundle; the phloem makes up the outside portion ___________________________________________ ___________________________________________ 7 Monocot Stems vs Herbaceous Dicot Stems

Herbaceous Dicot Stems ___________________________________________ ___________________________________________ The vascular bundles are separated by masses of pith cells that extend into areas between the bundles - known as the _______________. 8 Monocot Stems vs Herbaceous Dicot Stems

9 Cross Section of a Tree Trunk When an individual views the cross section of a tree trunk, the age and two different colors of wood are evident: heartwood and sapwood.

10 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.

11 Sapwood The lighter wood circling the heartwood is called the sapwood. _____________________ ______________________

12 Age of a Tree The age of a tree can be determined by counting annual growth rings. ________________________________________

13 Translocation The movement of materials through vascular tissues is known as ________________ A dilute solution of water and dissolved minerals moves through the xylem: move in only one direction ____________________________________________ ____________________________________________

14 Water Potential Water potential is involved in the movement of materials through the vascular tissues. Water potential is described as the free energy of water. __________________________________________ __________________________________________

15 Water Potential Water moves from: An area of higher water potential (less negative) to an area of lower water potential (more negative). Water potential is a measure of a cell’s ability to absorb water. __________________________________________ __________________________________________

16 The Movement of Water The movement of water and dissolved minerals begins with absorption into the plant. Under moist soil conditions, the water potential in the root is more negative than that of the soil. _________________________________________

17 The Movement of Water __________________________________________ __________________________________________ Once in the xylem, the water and dissolved minerals are carried upward. The plant uses no energy to move the solution because it is “pushed” from the bottom and “pulled” from the top.

18 Root Pressure Root pressure moves water up the xylem. __________________________________________ __________________________________________ The root tissues, full of water, exert pressure that forces water up the xylem. __________________________________________ __________________________________________ The height at which solutions can be forced up the stem is limited.

19 Cohesion-Adhesion Mechanism Translocation of water also is made possible by a cohesion-adhesion mechanism. __________________________________________ __________________________________________ This tension creates a pull on water molecules the entire length of the stem. The water is pulled up the stem from tension caused by the evaporative pull. __________________________________________ __________________________________________

20 Sugars ________________________________________ May be moved from the leaves to actively growing regions of the plant where they are used up. __________________________________________ __________________________________________

21 Sugars The movement of materials through the phloem is a complex operation that is not fully understood. __________________________________________ Sugars move from the cells where they are produced to companion cells in the phloem. ATP energy is used to make the movement of sugar to the companion cells possible. __________________________________________ __________________________________________

22 Sugars The water potential in the sieve tube cell is lowered with the increased concentration of dissolved sugars. 1. _______________________________________ 2. __________________________________________ __________________________________________ 3. When it reaches its destination, the sugar is transferred out of the phloem with energy provided by ATP.

23 Sugars The water potential in the sieve tube cell (cont’d) 4. _________________________________________ _________________________________________ 5. _________________________________________ _________________________________________ 6. Water moves to surrounding cells with more negative water potentials.

24 Sugars The movement of sugar through the sieve tube cells does not require energy. __________________________________________ __________________________________________

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