Living things need transport systems to supply all their cells with food, oxy-gen, and other materials in order to carry out life processes such as growth, respiration, and reproduction. Lungs take in oxygen for the combustion of food and they eliminate the carbon dioxide produced. The urinary system disposes of dissolved waste molecules (urea), the intestinal tract removes solid wastes, and the skin and lungs rid the body of heat energy. The circulatory system moves all these substances to and from cells where they are needed or produced, responding to changing demands. The methods of transport are Diffusion, osmosis and mass ow.
These activities can be prepared by the teacher and performed easily by students to show the importance of Diffusion, osmosis, and mass ow in living organisms.
Demonstration of Diffusion
Diffusion is the movement of particles from an area of high concentration to an area of low concentration. Diffusion continues until the particles are evenly distributed.
To carry out experiment to demonstration the process of Diffusion.
Beakers*, water, soda or water bottle caps, GV stain*, droppers*.
1. Put a very small amount of GV in the bottle cap.
2. Fill the beaker about half way with water.
3. Draw a drop of GV from their cap using the dropper.
4. Put one drop of GV into the beaker.
5. Observe what is happening in the container for the rst 5 minutes.
6. After 20 minutes, observe their beaker again and record their observa-tions.
Collect all used materials, storing items that will be used later. The chemicals used in this experiment require no special disposal.
GV stains skin and clothes.
Apart from this experiment, where else have you seen Diffusion taking place?
Immediately after putting the drop of GV in water, GV molecules start mov-ing towards areas with lower concentration of GV molecules. The movement continues until the whole solution will have the same concentration of GV molecules.
Diffusion can take place through any substance. Other examples of Diffusion include colour of tea spreading in hot water, the smell of perfume molecules spreading through the air, and the sight of heavy smoke thinning into the air. Molecules are always moving. Solid particle remain in the same loca-tion, however liquid, gas, and solute particles move randomly through space. Because there are more molecules in an area of high concentration than in an area of low concentration, more molecules are available to move from the area of high concentration to the area of low concentration than are available to move from the area of low concentration to the area of high concentra-tion. While particles are always moving in all directions, over time there is a net ow of particles from the area of high concentration to low concentra-tion. Eventually, the concentration in all parts is the same. In this state the molecules continue to move from one place to another, but no net change is observed. This is called equilibrium.