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Structure - Whole Plant

 

In their photosynthesis CAM and C4 plants:

  1. do not use Rubisco
  2. form PGA first
  3. form OAA first

  1. There is no way of making sugar without Rubisco. All plants combine CO2 with RuBP to make PGA

     

  2. PGA is the first product in C3 plants; CAM and C4 plants still make it, but later in the pathway

     

  3. Yes, the key to these alternate photosynthetic pathways is CO2 fixation into a 4 carbon compound (OAA) which is converted to malate.

By comparison with conifers, dicot trees are better at water movement:

  1. under dry conditions
  2. at high rates
  3. past blockages in the xylem

  1. No, conifers generally are at an advantage in dry conditions because they depend on tracheids which provide a safer path for water transport.

     

  2. Dicots have vessels (and tracheids) in their xylem, whereas conifers only have tracheids. As long as there is plenty of water, it can be moved faster through vessel elements than through tracheids

     

  3. No, conifers have tracheids and it is easier to re-establish or re-route water flow in tracheids than in vessel elements when they are blocked by air or vapor bubbles.

Guttation occurs:

  1. on sunny days
  2. during winter
  3. on humid nights

  1. Exudation of water droplets is unlikely when transpiration is causing tension in the xylem.

     

  2. Sap tends not to be flowing in the winter, although the first rise of sap in the spring may have a similar mechanism to guttation.

     

  3. When transpiration stops and there is no tension in the xylem, its water potential can be lower than the soil solution's so water is taken in and forced up the plant.

The xylem is different from the phloem because the flow in the xylem:

  1. involves water
  2. is up the plant
  3. is unidirectional

  1. Water movement is an essential part of phloem transport.

     

  2. Materials can move up the plant in the phloem.

     

  3. Yes water flows in one direction only in the xylem, whereas material can flow in either direction in the phloem, depending on source-sink relations.

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