Question

When a cell is placed in isotonic solution water moves across the cell membrane in both directions but the amount going in and out are same then why its said that there is no overall movement of water

Answer 1

If the medium has exactly the same water concentration as the cell,there will be no net movement of water across the cell membrane.such a solution is known as isotonic solution.
Water crosses the cell membrane in both the directions,but the amount going in is as the same as the amount going out ,so there is no overall movement of water.the cell will stay in the same size.