Biology 1060 Unit 3 3-18-16 Notes
Biology 1060 Unit 3 3-18-16 Notes Bio 1060
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This 3 page Class Notes was uploaded by Margaret Notetaker on Wednesday March 30, 2016. The Class Notes belongs to Bio 1060 at Saint Louis University taught by Dr. Thole in Spring 2016. Since its upload, it has received 9 views. For similar materials see General Biology II in Biology at Saint Louis University.
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Date Created: 03/30/16
Margaret S Biology 1060 (General Biology II) 3-18-16 Lecture Notes Unit 3: Plants 3-18-16 Shoot from the Top Down: The Tip: just meristem tissue Just Under the Tip: meristem and procambium Just Under That: pith and primary xylem Just Under That: secondary xylem in addition to pith and primary xylem Some plants have wood under this, and some are herbaceous (don’t have wood) Extra Shoot Review: Flowers are grown from and also consume shoot meristems o The original meristem converts to a floral meristem Xylem o Transports water and minerals up only o Is made of sclerenchyma cells that are dead at maturity o Has thick secondary walls made of lignin Phloem o Transports food (sucrose) up and down o Is made of parenchyma cells that are alive at maturity Vascular System: Transport Vascular system ensures that plants have water and nutrients needed o Water and minerals enter through the roots, water travels up the xylem, and then exits through the stomata (this is called transpiration) Transpiration means that water or sugars move towards the parts of the plant with more negative potentials (another way to say this is the parts of the plant with lower water potentials) All water transport is passive: it happens either through diffusion or osmosis ΨW + ΨS +Ψ P Ψ G = Ψ o Ψ W is water potential o Ψ Sis solute potential, which is always negative o Ψ P is pressure potential, which is always positive o Ψ G is the pressure from gravity, but is mostly neglected because it only has an effect in very tall trees o The units for Ψ are MPa Turgor pressure (Ψ) helps plants withstand gravity; when the cell is full of water and the cell wall is pressing on the outer membrane, this is turgor pressure, and it allows plants to hold their leaves up: turgor pressure is always positive Osmosis: the diffusion of water from an area of high water potential to an area of lower water potential A flaccid cell is lacking water and therefore has no turgor pressure (causes leaves to limp, and this is why plants wilt when they are not watered) Hypertonic solution: has a greater concentration of solutes than the inside of the cell, so water will flow out of the cell Hypotonic solution: has a lesser concentration of solutes than the inside of the cell, so water will flow into the cell and the cell may eventually lyse (burst) Isotonic solution: there are equal concentrations of solute on the inside and outside of the cell, so there is no net movement of water Pure Water Flaccid Cell Pure Water Turgid Cell Ψ = 0.0 MPa ΨP = 0.0 MPa Ψ = 0.0 MPa Ψ P = 1.0 MPa Ψ S= -1.0 MPa ΨS = -1.0 MPa Ψ = -1.0 MPa Ψ = 0.0 MPa Water goes into the cell (hypotonic)No net movement of water In these solutions, animal cells burst, but (isotonic) plant cells don’t because of their rigid cell walls; eventually the imbalanced turgor pressure will cause osmosis to even it out Solution Cell ΨS = -0.7 MPa Ψ S = -0.2 MPa ΨP = 0.0 MPa Ψ P= 0.5 MPa Ψ = -0.7 MPa Ψ = 0.3 MPa Water flows out of the cell in this case, because the water will always flow to the area with the lower potential, in this case, the solution. The cell membrane might eventually undergo plasmolysis (the membrane on the inside shrinks away from the outer cell wall). This is an example of a hypertonic solution, because water flows out of the cell (ignore the negatives and just pay attention to where the water flows for these problems). After equilibrium is achieved (isotonicity), W of the cell = W of the solution, so in the example above, at equilibrium, both the Ψ of the cell and the solution will be -0.7 MPa. Pressure potentials ( ΨP ) are always positive, as noted above Water potential is measured for individual cells, tissues, root and shoot systems, and entire plants
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