Living yeast cells placed in a particular type of red dye (called Congo red) remain colourless. However, dead yeast cells placed in the same dye turn red. Explain this observation.

The observation that living yeast cells remain colorless when placed in Congo red dye, while dead yeast cells turn red, can be explained by the different interactions between the dye and the cells.

1. Congo red is known to bind to certain components in cell walls, such as polysaccharides or beta-glucans, which are present in fungal cell walls, including yeast cells.

2. Living yeast cells have a functional and intact cell membrane. As a result, the cell membrane acts as a barrier, preventing the Congo red dye from penetrating the cell wall and binding to the components present within it. Therefore, the living yeast cells do not take up the dye, and they remain colorless.

3. In contrast, dead yeast cells have a compromised cell membrane, which allows the Congo red dye to freely enter the cell and interact with the cell wall components. The dye binds to the beta-glucans or other relevant cell wall components, resulting in a characteristic red color.

4. This observation helps distinguish between living and dead yeast cells based on their ability to retain or take up the Congo red dye. Living cells with intact cell membranes remain colorless, while dead cells with compromised membranes turn red in the presence of the dye.

Overall, the difference in coloration between living and dead yeast cells when treated with Congo red dye is due to the intact cell membranes of living cells preventing dye uptake, while dead cells with damaged membranes allow the dye to interact with and stain the cell walls.

The observation that living yeast cells placed in Congo red dye remain colorless while dead yeast cells turn red can be explained by the selective binding between the dye and the components of the cells.

Congo red is a dye that has an affinity for certain types of organic molecules, particularly those that have a specific spatial arrangement or structure. It has an affinity for beta-sheet structures, which can be found in certain proteins.

Living yeast cells possess intact cell membranes, which regulate the transport of molecules in and out of the cell. The cell membrane acts as a barrier, preventing Congo red from entering the cell. As a result, the dye does not bind to any intracellular components and remains unable to impart color to the cell.

On the other hand, dead yeast cells have compromised cell membranes. When the cells die, their cell membranes break down, allowing Congo red to freely diffuse into the cytoplasm. Inside the dead cells, Congo red can bind specifically to proteins or other cellular components that may contain beta-sheet structures, resulting in red coloration.

In summary, the living yeast cells do not take up Congo red dye due to the intact cell membranes that prevent the dye's entry, while the dead yeast cells allow the dye to enter and bind to specific molecules, causing them to turn red.