1. Transport in Plants
Ch. 36

4. Transport of Xylem Fluid rises in the xylem without requiring energy
Fluid rises AGAINST gravity
Two ways this happens:
Pushed up by root pressure
Results from water flowing into stele from the ground because of high mineral content in root cells
Can only push xylem sap up a little bit
Guttation: escape of water droplets on leaves that can be seen as morning dew

5. Pulled up by transpirational pull
Much stronger force
Transpiration: evaporation of water from leaves
Causes tension (negative pressure) in the xylem
Due to the cohesion of water you can pull a large amount of water up through the xylem
Cohesion: binding together of similar molecules, usually by hydrogen bonds
For each molecule of water that is lost by transpiration, another is gained at the roots
Factors that can change rate of transpiration:
Humidity
Closing stomates
Light Intensity

7. Controlling Transpiration
Guard cells control opening and closing of stomates
Cell walls of guard cells are not uniform in thickness
When guard cells become turgid they curve, causing the stomates to open
Due to radially oriented cellulose microfibrils
When guard cells become flaccid the stomata close

8. Things that cause stomates to open:
Low CO2 levels in the leaf: happens when photosynthesis begins
Increase in potassium ions in guard cells: causes water to diffuse into them, making them turgid
Stimulating the Blue light receptor: causes proton pumps in the guard cell’s membrane to turn on, which causes uptake of potassium ions (see above)
Things that cause the stomates to close:
Lack of water: causes guard cells to lose their turgor
Hot Temperatures: starts cellular respiration, which increases CO2 levels in the leaves (see above)
Abscisic Acid: made in mesophyll cells due to dehydration, signals guard cells to close stomates

12. Translocation of Phloem Sap
Translocation: transport of food (sugar) in a plant
Phloem sap travels from sugar source to sugar sink
Sugar source: plant organ in which sugar is being produced
Ex: Mature leaves
Sugar sink: plant organ that is a net consumer or storer of sugar
Ex: Growing roots and fruit

13. Water and Mineral Absorption
Lateral movement: movement of water and nutrients across a plant
Symplast: system of cytoplasm in cells connected by plasmodesmata
When water reaches the endodermis it can continue to the xylem through the symplast
Apoplast: system of cell walls and intercellular spaces that allows extracellular movement of water in a plant
When water reaches the endodermis it must pass through the endodermis by diffusion

16. Helping Out the Roots
Mycorrhizae: Symbiotic structures constructed from plants roots and filaments (hyphae) of a fungus
These structures increase the amount of nutrients a plant can absorb
This helps older regions of roots that no longer have root hairs, thus poor absorption
Rhizobium: Symbiotic bacteria nodules that live on roots and fix nitrogen gas from air into a nitrogenous form that the plant requires.

17. Mycorrhizae

18. Rhizobium