Chapter 22, Problem 35A

Summary Introduction

To write:The cell elongation caused by auxin

Introduction:Hormones are chemical molecules that are produced in one part of an organism, and then moved to another part where the result occurs. This just takes a tiny quantity of a hormone to make an organism move. Plant hormones may impact cell division, development, or cell differentiation. The plant hormones act by chemical binding at certain positions to the plasma membrane called receptor proteins.

Explanation of Solution

Auxin was the first hormone to be identified for the plants. There are different types of auxins but indoleacetic acid (IAA) is the most widely studied. IAA is produced from apical meristems, roots, youthful leaves and other quickly growing tissues. It moves through some form of active transport from one parenchyma cell to the next inside the plant.The rate estimated for this movement was 1 cm an hour. These auxins often shift in the phloem. The auxin flies often in only one direction from where it was made. Auxin usually facilitates lengthening, or elongation, of cells. Auxin facilitates the transfer of hydrogen ions by proton pumps from the cytoplasm to the cell wall.It produces a more acidic environment that weakens the bonds between the cellulose fibers inside the cell wall. This also stimulates the enzymes that help break down the cell wall.

Conclusion

Thus, water reaches the cell because of a lack of hydrogen ions in the cytoplasm. Cell elongation results from the combination of compromised cell walls and elevated internal pressure.