1. Differentiated by its location and function.
Plant Tissue
Differentiated by its location and function.
1. Dermal (outermost layer)
2. Ground (bulk of the cell – between dermal and vascular)
3. Vascular (venous system)

2. Main Tissue Systems
1. Dermal
2. Vascular
3. Ground

3. Dermal Tissue Epidermis or "skin" of the plant
Often has a cuticle, a waxy coating to prevent water loss
Functions:
Prevent water loss
Protects ground tissue
Place of gas exchange
Usually 1 cell layer thick

4. Dermal Tissue: Stomata (mouth)
Regulated by Guard Cells
Turgid: Swell - open stomata.
Flaccid: Shrink - close stomata.
Controlled by K+ conc.
Turgid - Open
Flaccid - Closed

5. Turgor Pressure of Guard Cells
Controlled by K+ concentrations

6. Vascular Tissue Made of Xylem and Phloem
Functions: Transport and support
Xylem – Water - Phloem - Sugar

7. Ground Tissue: Mesophyll
1. Palisade upright cells
2. Spongy loosely organized cells with air spaces
Function: major sites for Ps

8. Differentiated by structure.
Fundamental Tissues
Differentiated by structure.
1. Parenchyma (soft tissue)
2. Collenchyma (glue tissue)
3. Sclerenchyma (hard tissue)

9. Parenchyma Cells Primary wall only Thin cell wall Alive when mature
“Typical" plant cell
Function:
Ps (photosynthesis)
Storage
"Filler" cells
Cell division (mitosis)

10. Collenchyma Cells Primary wall only
Wall is thickened, especially in the corners
Alive when mature
Function:
Support of non-woody plant parts
Ex: veins, stems

11. Sclerenchyma Cells Secondary wall present
Wall strengthened with lignin
Dead when mature
Function:
Support and transport
Types:
1. Fibers
2. Sclereids
3. Xylem cells
a. tracheids
b. vessel members

12. Observe the different types of tissues in these images!!

13. How do plants acquire and move materials from one location to another?
Transpiration Lab
How do plants acquire and move materials from one location to another?

14. ψ = ψρ + ψs Water Potential
The potential energy of water to move from one location to another.
Abbreviated as ψ
Has two components:
Pressure potential: ψρ
Solute potential: ψs
ψ = ψρ + ψs
(Greek letter = psi)

15. Water always moves from an area of higher water potential (closer to 0) to an area of lower water potential (more negative #).

16. Water Potential Practice Problems
If a plant cell’s ψρ = 2 bars and its ψs = -3.5 bars, what is the resulting ψ (inside the cell)?
If this plant is placed in a beaker of sugar water with ψs = -4.0 bars, in which direction will the net flow of water be? Hint: an open beaker has a ψρ = 0
Lastly, the plant is placed in a beaker of sugar water with ψs = MPa (megapascals). We know that 1 MPa = 10 bars. In which direction will the net flow of water be?

17. Answers to Water Potential Practice Problems
ψ = ψρ + ψs = 2 bars + (-3.5 bars) = -1.5 bars
The ψρ of a solution open to the air is 0. Therefore, the water potential of the sugar water is -4.0 bars [ψ = 0 bars + (-4.0) bars]. Since free water always flows towards the solution with a lower water potential (more negative #), the flow of water would be OUTSIDE of the cell.
-1.5 bars (inside cell) > -4.0 bars (beaker)
-0.15 MPa = -1.5 bars
The water potential of the sugar water is -1.5 bars [ψ = 0 bars + (-1.5) bars]. Since the ψ of the original cell is also -1.5 bars, there would be no net flow of water. The cell and sugar water are in equilibrium.

18. Bulk Flow
The movement of water between two locations due to fluid pressure or tension.
Bulk flow is a mechanism for long distance transport in plants.
Important in both xylem and phloem sap transport.

19. How do plants get water to the tops of trees??
TCTM Theory
How do plants get water to the tops of trees??
Transpiration Cohesion
Tension Mechanism
Water evaporates from leaves because water potential of the air is usually much less than that of the cells.
Water always moves from an area of higher water potential (closer to 0) to an area of lower water potential (more negative #).

21. 2 Main Factors of Xylem Sap Transport
Transpiration (Ts)
Root Pressure

22. Transpiration (Ts)
Evaporation of water from aerial plant parts is the major force that pulls xylem sap up tall trees.
Xylem sap replaces the water lost due to evaporation.
The loss of water from the leaves creates “tension” or negative pressure between the air and the water in the plant.

23. Xylem Sap (= water, nutrients, inorganic ions)
Xylem sap is “pulled” by the resulting tension all the way down the plant to the roots and soil.
air (pulls on water in) - leaf - stem - roots – soil
Other forces help water flow upward, such as
Cohesion: water molecules sticking together by H bonds.
Adhesion: water molecules sticking to other materials (cell walls)

24. Root pressure also assists in the upward movement of xylem sap.
Root cells actively transport minerals (solute) into xylem
Water potential (ψ) is lowered in roots
Higher solute concentration, more -ψ
Water potential (ψ) is higher in soil
Water flows into roots from soil
(roots)
(soil)

25. Guttation is a result of root pressure
At night, little transpiration, but water is still entering into roots
Excess water may leave plant through guttation.

27. Environmental Factors
In our lab, we learned about some of the environmental factors that affect movement of water through a plant. What are these factors?
1. Humidity
2. Temperature
3. Light
4. Soil Water Content
5. Wind

28. Phloem Transport Moves sugars (food) Transported in live cells
Ex: Sieve & Companion Cells

29. Source - Sink Transport
Model for movement of phloem sap
from a Source to a Sink.
Source: Sugar production site
Sink: Sugar usage site - growth, reproduction, storage
Transport around the plant happens in multiple directions

30. Phloem Transport Source - builds pressure Sink - reduces pressure
Pressure caused by:
Sugar content changes
Water potential changes