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Stem Anatomy
Lesson Plan: NRES B5-4
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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?
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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
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Terms
phloem pith rays rhizome sapwood scape spine stolon terminal bud
translocation tuber water potential woody stems xylem
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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
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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
______________________________________________________________________________________
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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 _______________.
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Monocot Stems vs Herbaceous Dicot Stems
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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.
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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.
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Sapwood
The lighter wood circling the heartwood is called the sapwood. ___________________________________________
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Age of a Tree
The age of a tree can be determined by counting annual growth rings. ________________________________________
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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
________________________________________________________________________________________
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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. ______________________________________________
______________________________________ ______________________________________________
______________________________________
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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. ______________________________________________
______________________________________
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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.
_________________________________________
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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.
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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.
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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. ______________________________________________
______________________________________
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Sugars
________________________________________ May be moved from the leaves to actively
growing regions of the plant where they are used up.
____________________________________________________________________________________
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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. ______________________________________________
______________________________________
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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.
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Sugars
The water potential in the sieve tube cell (cont’d)
4. __________________________________________________________________________________
5. __________________________________________________________________________________
6. Water moves to surrounding cells with more negative water potentials.
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Sugars
The movement of sugar through the sieve tube cells does not require energy. ______________________________________________
______________________________________
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