Question

What is osmosis?

Answer 1

Osmosis is a type of diffusion that, in biology, is usually related to cells. Diffusion is when molecules or atoms move from an area of high concentration to an area of low concentration. Osmosis is when a substance crosses a semipermeable membrane in order to balance the concentrations of another substance. In biology, this is usually when a solvent such as water flows into or out of a cell depending on the concentration of a solute such as salt. Osmosis happens spontaneously and without any energy on the part of the cell.

Osmosis deals with chemical solutions. Solutions have two parts, a solvent and a solute. When solute dissolves in a solvent, the end product is called a solution. Salt water is an example of a solution; salt is the solute, and water is the solvent.

Osmosis affects plant and animal cells differently because plant and animal cells can tolerate different concentrations of water. In a hypotonic solution, an animal cell will fill with too much water and lyse, or burst open. However, plant cells need more water than animal cells, and will not burst in a hypotonic solution due to their thick cell walls; hypotonic solutions are ideal for plant cells. The optimal condition for an animal cell is to be in an isotonic solution, with an equal amount of water and solutes both inside and outside. When a plant cell is in an isotonic solution, its cells are no longer turgid and full of water, and the leaves of the plant will droop. In a hypertonic solution, water will rush out of both animal and plant cells, and the cells will shrivel (in plants, this is called plasmolyzation). This is why slugs and snails shrivel and die when salt is sprinkled onto them; water leaves their cells in order to balance the higher concentration of salt outside the cells.