Demonstration of Mass Flow
To carry out experiments to demonstrate the process of mass flow.
Mass flow is the movement of uids within a cell or along a vessel that does not pass through a membrane. This mode of transport is important in large complex organisms where substances are required in large amounts and also have to be transported over large distances to reach the required area at the right time. Diffusion and osmosis cannot perform such large functions. In many animals mass flow is demonstrated in their lymphatic and circulatory systems. In plants, mass flow is responsible for the transport of water and mineral salts. These travel from roots, through the stem and branches to the leaves in xylem vessels. Sugars are also transported from different parts of a plant through phloem vessels by the same process.
Beaker*, water, GV stain*, water drop microscope*, razor blade, dropper*, plastic slide, plastic cover slip, and an uprooted plant (e.g. commelina plant.)
GV stains clothes and skin.
1. Put some water into a beaker and add two drops of GV to colour the water.
2. Place the uprooted plant upright in a plastic beaker containing coloured water.
3. Leave the plant in the sun for one hour.
4. After an hour remove the plant from the sun and put it in a special area to be used by students for observation.
1. Cut a leaf, stem, and root from the plant in half. Make 3 transverse cross sections by cutting a thin slice from the centre of the root, stem, and leaf.
2. Mount the circular cross sections on a slide with a drop of water and cover it with a plastic cover slip.
3. Observe the colour of the specimens carefully using the water drop microscope.
4. Draw the cross section of the root, stem, and leaf you have just ob-served, showing the distribution of colour.
The presence of colour in the leaf, stem, and root cross section indicates the presence of coloured water that was present in the container. This suggests that there was a movement of coloured water molecules from the container to the rest of the plant parts via the xylem tissue. This proves that there is a mass flow of water from the low plant parts like roots to the high plant parts like the stems and leaves.
Collect all the used materials, cleaning and storing items that will be used later. No special waste disposal is required.
The commelina plant species is best to use in this experiment because it is clearly seen by the water drop microscope and brings better results as compared to other plants.