Diffusion and Osmosis – The Cell And Its Environment
DIFFUSION: is the process by which molecules of substances, such as liquid gases move randomly from a region of higher concentration to a region of lower concentration until the particles are evenly distributed. Diffusion can occur in air, liquid and solid.

Biological significance: It is a process by which fine particles or molecules flow in and ;out of cells living things and it can occur in non-living material. By diffusion molecules of substance evenly spread in any available space.

Factors Affecting rate of diffusion

(i)State of matter of diffusing molecules

(ii)Molecular size of the diffusing molecules

(iii)Differences in concentration of diffusing molecules and the medium

(iv)Temperature: High temperature increases the speed at which molecules move thus, the higher the temperature, the faster the rate of diffusion.

Demonstration Diffusion in Liquid

Fill a beaker with distilled water use pipette to deliver small quantity of potassium permanganate solution gently at the bottom of the beaker and leave it to stand for few minutes. The purple colour of the potassium permanganate solution starts to spread outside.

Gradually, the colour spreads evenly throughout the water medium so that the water have the same shade of purple colour.

Demonstration of Diffusion in Gases

Take a bottle of ammonia solution, open the bottle and move some distance away from the bottle and wait for some time. The smell of the ammonia gas shows that diffusion of ammonia gas has taken place.

Importance of Diffusion in Plant

(i)Diffusion acids movement of oxygen produced during photosynthesis into the atmosphere

(ii)Diffusion assists easy movement of carbon (iv) oxide from the atmosphere into the leaves through the stomata cell

(iii)Diffusion promotes free movement of oxygen needed for respiration from the atmosphere into the plant through stomata cell

(iv)Movement of water vapour from the leaves of plant to outside in a process called transpiration is possible because of diffusion

Importance of diffusion in Animal

(i)Absorption of glucose and other food material through the villi in the small intestine in through diffusion

(ii)Diffusion aids the exchange of body nutrients in the placenta from the mother to a developing foetus

(iii)Diffusion aids gaseous exchange in many cells and organisms for instance amoeba takes in oxygen and get rid of carbon (iv) oxide by diffusion

(iv)Diffusion aids the movement of carbon (iv) oxide form the lungs capillaries into the air sac and vice- versa.


Osmosis is defined as the movement of water molecules from a region of low concentration fo solute to a region of high concentration of solute through a semi-permeable membrane separating the two solution until equilibrium is attained.

A solution with higher solute concentration has a smaller amount of water left for dissolution of more solute, while a solution with lower concentration of solute has more water available.

Condition necessary for osmosis to take place

(i)Presence of a stronger solution e.g. sugar or salt solution

(ii)Presence of weaker solution e.g. distilled water

(iii)Presence of a selective or differentially permeable membrane/pig bladder

Types of solution

(i)Hypertonic Solution is a solution which gains water in osmosis or that is higher in concentration

(ii)Hypotonic Solution is a solution that lose water in osmosis or a solution that is weak-distilled water

(iii)Isotonic solution: when a state of equilibrium is established between two solution, that is neither solutions gains or loses water.

Osmosis is a special form of diffusion

Differences between Diffusion and Osmosis:

1. Diffusion occurs in gases and liquidDifferently permeable membrane is not
2. Differently permeable membrane is notDifferentially permeable membrane is required
3.  It occurs in living and non-living organismsIt occurs naturally in living organisms
4.   Molecules diffuse into any space accessible to themWater molecules move between two solutions of different osmotic pressure leading to the Establishment of an osmotic equilibrium

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