Diffusion,Osmosis & Active Transport
Diffusion
Is is the movement of molecules from a region of higher concentration to a region of lower concentration. It occurs in all the three states of matter.
Applications of diffusion
_absorption of nutrients from the soil by plants
_exchange of gases in the lungs of mammals
_detecting the smell of perfume
_ the spread of crystals of potassium permanganate in water ( KMnO4)
_birds and insects detecting the scents of flowers leading to pollination
_the spreading of sugar and salt particles in water
Experiment to show diffusion in liquids
Put potassium permanganate in a beaker filled with water. Allow the set-up to stand still for about 30 minutes. It would be observed that the molecules of the potassium permanganate are evenly distributed in the water.
Examples of diffusion in plants
_ absorption of mineral salts from the soil by plants
_gaseous exchange in the stomata of a leaf
Examples of diffusion in animals
_Gaseous exchange in the lungs of mammals
_diffusion of hormones out of the endocrine glands
_absorption of end products of digestion
_ absorption of food nutrients through the placenta to an embryo
_absorption of oxygen by an embryo in the uterus
Factors that affect diffusion
1. Concentration gradient
2. Particles size
3. Surface area
4. Temperature
Osmosis
It is the movement of water molecules from a region of lower concentration to a region of higher concentration through semi-permeable membrane.
Semi-permeable membrane
It is a membrane that allows certain substances to pass though based on their sizes.
Osmosis in a living cell
Two scoped yams were used for the experiment. One was filled with salt solution and the other filled with water and both of them placed in separate water trough with the same volume of water. After that, the set-up was allowed to stand still for 24hours.
Observation
The water level in setup A increased meaning osmosis occured. But in setup B, the water levels in the initial and final experiments remain same.
Osmosis in non- living tissue( cellophane)
The mechanism is the same as in the yam cup. The only known non-living semi-permeable membrane is cellophane
The figure below represents the beginning of an experiment to demonstrate osmosis in a living cell using yam.
a. Draw and label a diagram to illustrate the final experiment.
b. What does the yam represents?
c. Explain the principle involved in the experiment
d. How would you set a control experiment above?
Give one example of the osmotic process in;
I. Flowering plants
Ii. Humans
Solution
a. Final stage 
b. A semi-permeable membrane
c. Water moves across the yam by osmosis into the strong Suger solution that is of higher concentration until the the concentration of the sugar solution and the water are equal.
d. A trough is filled with distilled water and a living yam cup is placed in it. Distilled water is poured into the scoped yam. Since the same distilled water is poured into the water trough and in the scoped yam, no movement of molecules will occur since they are of the same concentration.
e. I. Absorption of water into the root hairs
Ii. Absorption of water in the kidneys
Examples of osmosis in plants
1. Absorption of water by the roots and stems of plants.
2. Absorption of water between cells within a plant
3. Transpiration in plants
Examples of osmosis in animals
1. Absorption of water in the kidneys
2. The movement of water into the cytoplasm of amoeba
3. Absorption of water in the large intestines of mammals
Importance of osmosis
1. It helps cells to undergo plasmolysis
2. It also helps cells to undergo turgidity
3. It helps plants to absorb water from the soil
4. It helps mammals to absorb water in the large intestines
5. It helps in urine formation by helping the kidneys to absorb water
6. It helps a developing embryo to absorb water from the mother through the placenta.
Difference between osmosis and diffusion
1. In osmosis, the movement of molecules is from a region of lower concentration to a region of higher concentration but in diffusion, the movement is from a region of higher concentration to a region of lower concentration
2. Osmosis requires a semi-permeable but in diffusion, there is no semi-permeable membrane.
3. Osmosis occurs in only liquids while diffusion occurs in all the three states of matter.
Solution
It is a uniform mixture of solute and solvent.
Types of solution
_dilute solution
_concentrated solution
Dilute solution: it is a solution that contains more solvent dissolving less amount of solute
Concentrated solution: it is a solution with large amount of solute dissolving in a small amount of solvent.
Note : the difference between solute and solvent is that, a solute is a substance that dissolves in a solvent but a solvent is a substance that dissolves a solute. The solvent does the dissolving.
Types of concentrated solution
_hypertonic solution
_hypotonic solution
_isotonic solution
Hypertonic solution: it is a solution that is of higher concentration than the content of a cell it is placed in.
Hypotonic solution: it is a solution with lesser concentration than the content of the cell place in.
Isotonic solution: it is a solution that is of equal concentration as the content of the cell placed in it.
Plasmolysis
It is the striking away of a cell when placed in hypertonic solution
Cell absorbs water and becomes turgid but will burst at the end.
Plant cell in hypotonic solution. It absorbs water but can not burst as in animal cell.
Plant cell in hypertonic solution
Animal cell in hypertonic solution.
Turgidity
It is a situation where by a cell absorbs more water than the one it loses. It occurs when the cell is placed in hypotonic solution. For plant cell, it absorbs the water become turgid without bursting because of the rigid cell wall. In the case of animal cell, it will burst after absorbing water to some level because animals do not have cell wall to protect them.
Flaccidity
It occurs when plant cell looses water to the atmosphere faster than it can it can obtain when placed in hypertonic solution. This means that, during plasmolysis in plants, flaccidity occurs.
Turgor pressure
It is the pressure exerted against the rigid cell wall when plant cell is placed in hypotonic solution. This pressure helps the cell wall to protect the cell against bursting even after too much absorption of water.
Active Transport
It is the movement of substances from a lower concentrated area to a higher concentrated area across the cell membrane using energy from the cell.
Factors that affect active Transport
1. Temperature
2. Change in pH (hydrogen ions concentration)
3. Light
4. Enzymes actions
Nb. Transport system is possible in plants because of the xylem and phloem tissues
Xylem tissues
It transport water and mineral salts from the soil to all parts of ♦the plants.
Phloem tissues
This transport manufactured food by the leaves to all parts of the plant.
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