Question

About Osmosis:

Potato section A: the mass before soaking in distilled water was 3.12g and after soaking 3.21g.

Potato section B: The mass begore siaking in 10% NaCl.

Explain, write and answer separately question 1 and 2 clearly:

1- Causes of any changes in the masses of the potato.

2- if the texture of potato A and B changes, explain the cause of the difference at the molecular level.

Answer 1

Osmosis is the process whereby water moves across a cell membrane by diffusion. Diffusion takes place when the molecules of a substance tend to move from areas of higher concentration to areas of lower concentration. OR Osmosis is the movement of solvent particles e.g. water along its concentration gradient - from high to low concentration - via a semi-permeable membrane.

1. The increase in mass of the potato strip in water is due to the movement of water molecules into the plant cells via osmosis. Water molecules in the petri dish are at a higher concentration than water molelcules in the cytoplasm of cells and so move along their concentration gradient into the cells.
As more water molecules are present in cells - and water has mass - the final mass of the potato strip will be greater than the first. Shown in below figure.

2. More water molecules occupy more space - volume - and push against the cell membrane and the proximate cellulose cell wall. The push of the water molecules result in expansion in all dimensions, including length. The expansion is limited - and regulated by the cellulose cell is inelastic. The push/force acting upon the surface area of the rigid cell produces turgor pressure (recall pressure is force acting per unit area), and hence strips are turgid.