Edexcel A (SNAB) A Level Biology:复习笔记4.2.3 Importance of Water & Inorganic Ions to Plants

Importance of Water & Inorganic Ions to Plants

  • Plant cells perform a variety of different functions
  • In order to perform these functions efficiently, the plant requires water and inorganic ions (minerals)
  • They are absorbed through the root hairs on the root and travel up the stem in xylem vessels
  • A plant will show certain symptoms (e.g. yellow leaves, stunted growth) when there is a deficiency in any one of these substances

Water

  • Important component required for photosynthesis
  • Provides a transport medium for minerals
  • Maintains turgidity in plant cells though pressure in cell vacuoles
  • Regulates temperature - to ensure that enzymes can function at their optimum rate

Magnesium ions

  • Important requirement for the production of chlorophyll
  • This provides the green colour of stems and leaves and is essential for photosynthesis

Nitrate ions

  • Without nitrate ions, the plant would be unable to synthesise DNA, proteins and chlorophyll
    • Enzymes are important proteins for which nitrate ions are needed
  • These molecules are essential for plant growth, as well as the production of fruit and seeds

Calcium ions

  • These form important cell wall components
  • Plants require calcium ions for proper growth

Diagram showing the importance of magnesium and nitrate ions for plants

 

Practical: Investigating Plant Mineral Deficiencies

  • The following experiment could be done with any one of the mineral ions mentioned earlier
  • For this example, the focus will be on investigating the effect of a calcium deficiency on plants

Apparatus

  • Nutrient broths
  • Test tubes
  • Seedlings
  • Aluminium foil
  • Mass balance

Method

  • Prepare three nutrient broths containing every mineral that a plant requires, but with different concentrations of calcium ions in each (high, medium and low)
    • Label three test tubes for each of the nutrient broths (three 'high', three 'medium' and three 'low' = nine in total)
  • Take nine seedlings, ensuring that they are from the same plant and are the same age, and record the mass of each
  • Place one seedling on top of each test tube, suspending the roots in the nutrient broth
  • Cover the test tubes with aluminium foil to keep light away from the broth
  • Place the test tubes near a source of light and leave them for a few days
  • Remove each plant from the broth and carefully blot it dry before measuring the mass again
  • Record the end mass and use that to calculate the mean change in mass of the plants for each of the different nutrient broths
  • Make a note of any physical differences between the plants of the different groups

Variation of the practical

  • Another variation of the experiment mentioned above, is to investigate the effect on plant growth when the mineral is completely lacking
  • In this experiment you would have broths that contains all of the minerals, except the one that is being investigated
  • There would also need to be two control broths
    • One would contain all the minerals
    • The other would contain no minerals

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