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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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