Biology
Overview
This resource will help you to understand osmosis
Osmosis
Osmosis is the movement of water molecules from the area with high water potential (low concentrated solution) to area with low water potential (high concentrated solution) through semi permeable membrane.
Hypertonic solution is the solution with low water potential. It contains a lot of solutes.
Hypotonic solution is the solution with high water potential. It contain small amount of solutes.
Isotonic solution is the solution with equal amount of water molecules and solutes.
IMPROTANCE OF OSMOSIS
i. It helps plant roots to absorb water from the soil.
ii. It aid in opening and closing of stomata. When guard cell absorbs water the stomata open and when guard cell loose water the stomata closes.
iii. During germination of seed, the seed absorbs water through osmosis and hence soften the seed coat making it more permeable to dissolved minerals and oxygen.
iv. It helps in re-absorption of water in the colon and kidney.
v. It is used in food preservation by salting and when salt is added to the food, water will move to areas with salt hence the food become dry.
vi. In organisms like amoeba, osmosis helps to remove waste and excess water from their bodies.
EFFECTS OF OSMOSIS IN LIVING ORGANISMS
IN ANIMAL CELLS
• When animal cell is placed in hypertonic solution, it loses water therefore shrinks and shrivels. For example when a red blood cell is placed in hypertonic solution it will lose water and shrink. The shrinking of animal cell due loss of water is called crenation
• When the animal cell is placed in hypotonic solution it absorbs water. if it is left in the hypotonic solution for a long time its will burst because it has no cell wall prevent it from bursting. Haemolysis is the bursting of red blood cells when a placed in hypotonic solution
• When the animal cell is placed in the isotonic solution there will be no effect because water will be moving in both directions until the steady state is reached.
IN PLANT CELLS
• When placed in hypertonic solution the plant cell will lose water causing the vacuole to shrink and the cell surface membrane is pulled away from the cell wall. The pulling of the surface membrane away from the cell wall is called flaccidity.
A flaccid cell is said to be plasmolysed.
Plasmolysis is the process whereby the plant cell water loses water due to osmosis and shrink.
• When place in hypotonic solution the plant cell will absorb water causing the cell membrane to push against the cell wall.
Turgidity is the condition whereby the plant cell absorbs water and become turgid.
Turgidity is a result of presence of cell wall which prevents bursting of the plant cell when it absorbs water.
Turgidity helps the plant cells to maintain their shape.
• When placed in isotonic solution the plant cell neither loses water nor gain because there is steady state condition. I.e. the concentration gradient is zero.
IN UNICELLULAR ORGANISMS
• In hypotonic solution organisms like Amoeba and Euglena have contractile vacuole which collects and remove the excess water which enters into their bodies.