A mung bean is a type of legume that is rich in protein and other nutrients, especially when sprouted. Dry mung beans are easy to sprout at home, making them a practical addition to a healthy diet, and especially beneficial to vegetarians. Since mung beans are easy to sprout, they are also suited well to experiments designed to observe the processes involved in plant growth. This experiment examines the effect of light on how mung bean sprouts grow in length over time.

Tear paper towels into pieces 1 inch square and put the pieces from one paper towel into each of five opaque cups. Place five mung beans into each cup on top of the paper towel squares. Pour 1 tablespoon of water into each cup.

Calculate what fraction of a cup's top a hole made by the pen or dowel would cover. The formula for the area of a circle is pi x radius^2. For example, if you are using a dowel with a radius of 0.5cm and round cups with a radius of 4cm, the area of the cup top is 4^2 x pi, or 16pi, and the area of a hole the dowel would make is 0.5^2 x pi, or 0.25pi. Dividing the hole's area by the top of the cup, 0.25pi/16pi, the hole would cover 1/64 of the top's area.

Cut out four cardboard shapes to make covers that match the size and shape of the cup rims. Poke holes in three of the covers with the dowel. The holes should constitute 25, 50 and 75 per cent of the areas of the covers, respectively. For example, if each hole is 1/64 of the cover's area, make one cover with 16 holes, one with 32, and one with 48.

Tape the covers onto the cups, leaving one cup uncovered. One cup should have a cover with no holes in it.

Open the cups each day to add a teaspoon of water per cup and measure the sprouts' lengths. Measure the length of each sprout to the nearest millimetre and graph the average length of the sprouts in each cup with length on the y-axis and time in days on the x-axis. Use a different colour for each cup.