Transport in the Xylem and the Phloem (9.1 & 9.2)
An overview of Vascular Plants
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A vascular plant is any organism from the Plant Kingdom that contains xylem and phloem. From the phylum classification we have studied three of four (Filincinophyta, Coniferaphyta, and Angiospermaphyta) are considered vascular!
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Microscope Identification of Xylem and Phloem
When identifying the different parts of vascular tissue under a microscope, keep the following in mind:
- Xylem usually has larger holes than the phloem.
- Xylem is always closer to the center of the plant/ pith
- Careful not to identify the phloem fibers as phloem.
- Some plants have a Cambium layer that runs between the phloem and xylem. (Found in Coniferphyta and Angiospermaphyta)
Transport in the Xylem (Transpiration)
Transpiration is the movement of water from the roots of the plant through the xylem to the leaves of the plant.
Main Force= evapotranspiration (ie. evaporation from the leaves of the plant). Functions: movement of minerals and cooling of the plant. Properties used: adhesion, cohesion, and osmosis (See 2.2 and 1.4 for more information)
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Transport in the Phloem (Translocation)
Translocation is the movement of nutrients out of the source (the leaves generally) through the phloem to the sink (anything that needs nutrients). Sinks could be fruit, leaves, growing stems, etc.
Main Force = hydrostatic pressure. Properties used: Active transport, osmosis, (See 1.4 for more information) and hydrostatic pressure Stages:
Water Potential and Translocation |
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Measuring Translocation and Transpiration
Using a Potometer to measure transpiration (Practical #7)
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Using glass chambers & aphids to measure phloem transport
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Nutrient/ Mineral Uptake into Roots
- Minerals are can be passively transported into roots. but are more commonly transported by indirect active transport with hydrogen ions. Root hairs contain specific mineral protein pumps and mitochondria from which they use active transport to bring nutrients into their cells.
- The high concentration of solute in the plant root causes osmosis of water into the plant.
- Consider that certain nutrients can only be absorbed in specific forms, examples include Nitrogen and Phosphorus. (See Nitrogen and Phosphorous cycles for more information.) Plants need magnesium (chlorophyll), nitrates (amino acids), sodium, potassium, phosphate, which sometimes requires the plant to change the form of a nutrient into its usable form.
- Any polar mineral, dissolved in water, can then be carried up the xylem via adhesion.
Plant Adaptations to Conserve Water
Dessert Plants called Xerphytes
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Saline soil plants called Halophytes
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