Practical Skill: Investigate the Effect of Minerals on Plant Growth (AQA A Level Biology): Revision Note

Investigating the effect of minerals on plant growth

• Many of the biological molecules in plants cannot be produced from the products of photosynthesis alone, but require additional chemical elements, e.g.

  • proteins and nucleic acids require nitrogen

  • phospholipids, nucleic acids and ATP require phosphorus

  • chlorophyll requires magnesium

• Plants obtain these elements in the form of mineral ions, e.g. nitrate ions or phosphate ions, that they actively absorb from the soil

• The effect of these minerals on plant growth can be investigated by growing plants under controlled conditions and selectively removing minerals

Apparatus

• Bryophyllum plantlets

• Nutrient solutions containing a combination of nitrates, phosphates, magnesium and calcium, e.g.:

  • Solution 1 = all minerals present (this is the control solution)

  • Solution 2 = nitrate absent

  • Solution 3 = phosphate absent

  • Solution 4 = magnesium absent

  • Solution 5 = calcium absent

• Measuring cylinder

• Test tubes

• Test tube rack

• Aluminium foil

Method

1. Fill each of five tests tube with a set volume of each of the nutrient solutions

2. Cover the top of each test tube with foil and create a small hole in the foil

3. For each test tube, take a Bryophyllum plantlet and push the roots through the hole in the foil, ensuring that the roots are submerged in the nutrient solution

4. Place the test tubes in the same location

5. After a set period of time, e.g. 2 weeks, observe the plantlets and take qualitative and quantitative measures of their growth

   • Qualitative measures could include the colour of the plantlets and their leaves, or how wilted the plantlet has become

   • Quantitative measures could include the height or mass of the plantlets, or the length and width of their leaves