Introduce the concept of photosynthesis to your children, which you can discuss as you set up the plant pots that will be used during your experiment. Explain to your young scientists about how plants use natural or ultraviolet lights to produce food, keeping plant leaves green, healthy and growing. Tell your youngsters about the experiment you are going to carry out before getting them to secretly write down a hypothesis for the three plant conditions you will set up. Ask youngsters to write whether they think plants will grow bigger or suffer and die.
Educate your young scientists about controlling variables in an experiment, which you will achieve during this project by first filling three identical plant pots 3/4 with the same weight and type of soil. Plant a pair of cress seeds 1/2 an inch beneath the surface in each of the plant pots before labeling the side of the pots "light," "dark" and "UV." Situate plants in the relevant environments, placing the light pot in sunliight, the dark pot in a dark room inside an upside down bucket and the UV plant in a dark environment with a UV light trained on the soil. Provide each plant with 50ml of water once each day to ensure the cress seedlings receive enough water.
Measure the growth of your plants once each day using a tape measure. Note down the plants' height, width and rate the overall health of the growing (or not growing) cress plant out of 10. Make sure you do not accidentally expose the dark or UV condition plants to any natural light by closing any curtains and switching off dark room lights. Compare the growth rates of each of your plants when measuring them --- the role of light in plant growth will very quickly become clear to your young scientists. Continue your experiment for at least two weeks to ensure plants each have an opportunity to grow somewhat.
Educate your experimenting children about the relevance of making results clear and presentable when conducting a plant life experiment. Photographs, for example, are a quick and clear way for young scientists to show the difference in growth rates for the three plant pots in this experiment. Furthermore, youngsters can plot a pair of line graphs with one graph showing plant height on the vertical and time in days on the horizontal axis. The second graph shows plant width on the vertical axis and time in days on the horizontal.