HL 1 Biology

9.2b Plant Transport

<<Translocation in phloem>>

  • phloem tissue: in stems, roots, leaves
  • links parts of plants that need sugars & amino acids to other parts that have a surplus
  • Areas where sugars & amino acids are loaded into phloem
    • photosynthetic tissues: mature green leaves, green stems
    • storage organs unloading stores: storage tissues in germinating seeds, tap roots/tubers at the start of growth season
  • Area where sugars & amino acids are unloaded/used
    • roots growing/absorbing mineral ions using energy from cell respiration
    • parts of plants growing/developing food stores: developing fruits, seeds, growing leaves
  • tubes in phloem must be able to transport biochemicals in either direction = so sinks can turn into sources
  • Similarity in phloem & blood vessels: fluid flows inside tubes because of pressure gradients, energy is needed to generate pressures (so the flow of blood/movement of phloem sap are both active processes)
  • Active translocation: the movement of substances in phloem


  • are plants adapted to growing in deserts/dray habitats
  • strategies to survive: increasing rate of water uptake from soil, reducing rate of water loss by transpiration
  • some are ephemeral (very short life cycle that completes in short time when water is available after rainfall)
  • e.g. cacti: stems contain water storage tissue and become swollen after rainfall
    • pleats enable stems to expand + contract in volume rapidly
    • epidermis of cactus stems: consist thick waxy cuticle + there are stomata
    • stomata open at night than day when its cooler and transpiration occurs more slowly
  • CAM (Crassulacean acid metabolism): plants that release carbon dioxide from the malic acid during the da, allowing photosynthesis even if the stomata is closed
  • e.g. Living Stones


Water Permeance of Waxy Cuticle (p.128)

1) As temperature increases, water permeance also shows an increase. We can also see the relationship of the rate at which the water permeance increase as the temperature increases, especially in the Liriodendron.


2) The consequences for plants of the effect of temperature on cuticular water permeance is the amount of water loss increases. In order to avoid this issue of water loss, the plants will need to undergo a different way in which they could maintain the most water inside of them.


3) (a) The highest water permeance: 1.3 µm

(b) 1.8µm


4) The hypothesis that the water permeance of the cuticle is positively correlated with its thickness is not supported from the data as the higher the value of water permeance was, the lower the thickness of the cuticular wax. Also, the data points are varied and do not show consistency in the trend reducing the amount of reliability . Thus, the hypothesis is not supported.


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