Final answer:
The correct answer to how auxin is thought to activate expansins is by activating proton pumps to decrease pH in a section of the cell wall. This acidification allows expansins to loosen the cell wall, enabling the cell to elongate.
Step-by-step explanation:
Expansins are proteins involved in the process of loosening cell walls, facilitating the elongation of plant cells. They play a crucial role in allowing cell walls to extend and accommodate plant growth. On the other hand, auxin is a plant hormone essential for various growth processes, including cell elongation, which is central to phototropism and gravitropism.
Auxin is believed to stimulate expansins in part by activating proton pumps that acidify the cell wall, thereby reducing its pH. This process leads to the activation of expansins that subsequently loosen the cell wall and allow for elongation.While this question lists multiple options, the correct answer is B) activating proton pumps to decrease pH in a section of the cell wall. Aligning cellulose microfibrils, depositing lignin, increasing turgor pressure, and increasing pectin hydration are functions related to cell wall structure and water regulation but do not directly correspond to the activation of expansins by auxin.