P1 Basic Genetics
In this experiment, hydrochloric acid (HCl) serves three critical purposes to ensure you get a clear look at the cells under the microscope:
1. It breaks down the "glue" holding the cells together
Plant cells are tightly packed and glued together by a substance called pectin (in the middle lamella) and a tough cellulose cell wall. The HCl breaks down these connections. This softens the root tissue so that when you press down on the coverslip later (the "squash" step), the cells will easily spread out into a single, flat layer instead of staying clumped in a thick pile.
2. It stops cell division (mitosis) instantly
HCl acts as a fixative that kills the cells and freezes them in their current state. Because cell division is a continuous process, the acid provides a "snapshot" of the tissue, trapping different cells in various stages of mitosis (prophase, metaphase, anaphase, etc.) so you can actually observe them.
3. It makes the cells more permeable to stain
By partially breaking down the cell walls, HCl increases the permeability of the cells. This allows the DNA stain (like acetocarmine or toluidine blue) to easily penetrate the tissue and bind to the chromosomes, making them highly visible under the microscope.
