2. What is Osmosis?
Osmosis is a special type of diffusion, It is the movement of water molecules across a
semi-permeable membrane. This means only water can pass through from an area
of high water concentration to an area of low water concentration in order to
balance the level of solute and water in the cell.
3. Isotonic, Hypertonic and Hypotonic
Isotonic means that the water and solutes within and outside the cell are the
same. There is no movement in or out the cell. Nothing happens, the cell
does not change.
Hypertonic is where solute is higher outside the cell than inside the cell,
water goes through the semi-permeable cell and balances the water and
solute levels. This makes the cell shrivel.
Hypotonic is exactly the opposite, solutes are higher inside the cell than
outside, water moves inside the cell to balance it out, this makes the cell
burst.
4. Osmosis in Fish
Fresh water fish have high concentration of salt in their body, so the water is
absorbed into the fish. This means, the fish do not drink water, instead, they
get rid off excess water through gills, urine and faeces, they use hypotonic
osmoregulation, meaning they control osmosis in their body. While salt water
fish are the opposite. They have high water concentration in their body, with
being in salt water, the water leaves their body, so they drink in order to keep
it balanced. They get rid of excess water through gills, urine and faeces.
