BIO 104 4/17/96

Chapter 32 and Photosynthesis
Water Transport
Cohesion-Tension Hypothesis
Four factors effecting water movement through the plant:
 -water moves through a plant through evaporation
1) Capillarity: adhesion of water to the walls of thin tubes (xylem)
     If you place two tubes, one wide and the other narrow, into a pool
     of water; the water will rise very little in the wide tube, but in the 
     thin narrow tube the water will rise much more.

2) Cohesion of water by hydrogen bonds
     -water molecules tend to stick to one another.
     -In a water molecule the oxygen atom has a slightnegative charge, and
      the hydrogen atoms have a slight positive charge.  So, if there are two
      water molecules near each other the hydrogen atoms of molecule 1 will
      be attracted to the oxygen atom of molecule 2;  thus creating a hydrogen
      bond.

3) Root pressure (osmosis)
     -this brings the water into the plant since the root has a higher solute
      concentration and water moves into the solution with a higher solute
        concentration
4) Evaporation from the leaves
     -transpiration
          1) water enters through the roots
          2) water moves up the plant through xylem
          3) water leaves through stomata
Structure of Stomates
-control the movement of water and the taking in of
     gases
Guard Cells
   Open
     -When the stomates are open the guard cells are turgid.  The solute
     level is high and water moves into the guard cells.

   Closed
     -When the stomates are closed the guard cells are flaccid.  The solute
 level is lowered and water moves out of the guard cells.

-guard cells transport potassium ions by active transport; which is the main
  control of the guard cells
     -as potassium ion enter the guard cells, the potassium concentration
      increases, and because of this, water enters the guard cells.



-photosynthesis is used to produce ATP, which is key to the active transport
 of potassium ions into the guard cells

The main controller of this process is the balance plants need to have between
open stoma(and water loss) vrs. the need for open stoma for carbon dioxide to
enter the plant for photosynthesis. 
 Factors that effect guard cells
     1) humidity
     2) sun light
     3) water loss

Movement of solutes
Carbohydrate Transport
-Translocation
     -mechanism is pressure-flow hypothesis
     -combination of active transport and osmosis
Source and Sink Pressure Model
1) active transport of sucrose into the phloem-thus creating a high
   concentration of sucrose
2) water moves through osmosis into the "source" and increases the pressure
     -the pressure pushes the sucrose through the "pipe" into the sink.
3) active transport "unloads" the sucrose out of the sink

In plants the leaves are the source and the roots are the sink.  The phloem
acts as the pipe.
1) Active transport of sucrose from leaf cells into the
     sieve tube cells (source)
2) Transport of water into sieve tube cells by osmosis
3) Active transport of sucrose out of sieve tube cells into 
     root and other growth areas (sink)


Photoperiod: amount of sunlight for a particular day at a particular location

Dr. Barstow got ahead of himself. Back up

Plants perceive:
     1) gravity: gavitropism
     -positive geotropism: goes with gravity
     -negative geotropism: goes against gravity
     2) light: phototropism
     -positive phototropism: goes toward light
     -negative phototropism: goes away from light
          a. direction
          b. intensity
          c. photoperiod
     3) Wind/touch: thigmotropism
     -Ex. venus fly trap

Plant Growth:
     Meristem
          1) primary growth
          2) secondary growth
     -meristem is involved in cell division (mitosis)
          -these cells grow by cell expansion
          -the vacuole takes up water; thus putting 
          pressure on the cell wall causing it to expand