Hydrangea plants can produce flowers that are either pink or blue. Two students propose different hypotheses to explain the primary factor that determines this flower color.
Student 1
The color change of hydrangea flowers is determined directly by the pH of the surrounding soil. When the soil is acidic (pH less than ), the hydrogen ion concentration directly alters the chemical structure of the pigment anthocyanin within the flower petals, causing it to reflect blue light. In alkaline soil (pH greater than ), the pigment's structure remains unchanged, and the flowers appear pink.
Student 2
The color change of hydrangea flowers is determined directly by the absorption of aluminum ions () from the soil, which form a chemical complex with the pigment anthocyanin to produce the blue color. Soil pH is only an indirect factor: acidic soil makes aluminum ions soluble and available for the plant to absorb, while alkaline soil binds aluminum ions in insoluble compounds, preventing absorption and resulting in pink flowers.
Based on Student 2's hypothesis, which of the following is the direct cause of the blue color in hydrangea flowers?
- AA direct change in the pigment's chemical structure caused solely by the concentration of hydrogen ions in the soil
- The formation of a chemical complex between aluminum ions and the pigment anthocyaninCevap
- CThe accumulation of insoluble compounds of aluminum in the plant's roots under alkaline conditions
- DThe direct modification of anthocyanin by water molecules in highly acidic environments