The most basic pigments are flavonoids, carotenoids and chlorophyll. Flavonoids produce red and blue colors, carotenoids produce oranges and yellows, and chlorophyll produces green pigments. Mixing these three compounds can give an array of colors. For this project, you can discuss how these pigments were discovered, what their molecular structures look like, and what other factors contribute to color. For example: acids interact with flavonoids in flowers to change their colors. A simple experiment can be conducted on the effect of hydrangea cell acidity on flavonoids. First, plant three small hydrangea plants in separate pots. Pot #1 will contain the control plant soil (pH 7). Pot #2 will contain soil with a pH of 6.0 and pot #3 will contain soil with a pH of 5.5. You can measure soil acidity with a pH meter. Observe the results. The plant in the soil at pH 6.0 will have pink flowers and the plant in the soil at pH 5.5 will have blue flowers.
Colored flowers serve to draw pollinators like bees to the plant. According to a paper published in the Proceeding of the National Academy of Sciences in 2000, pollinators are more attracted to colored flowers than they are to white flowers. (See References.) For this project, you can discuss the different kinds of flower pollinators and what flower colors are the most effective at attracting pollinators and why.
This science fair staple is an appropriate project for younger children. The object of this project is to learn about water transportation from the bottom stem to the top of the flower. Water is transported up through the plant via water cohesion. Water molecules are very attracted to each other because of strong hydrogen bonding forces between them. These forces make the water molecules stick together. Microscopic openings in leaves, petals and buds allow water to evaporate. As this vapor leaves the plant, it pulls up more water from below. This is how water is "sucked' up from the ground to the top of the plant. You can observe this process by putting a white carnation in a glass of water dyed with a few drops of food coloring. After about a day, you should see that the color from the water has seeped into the leaves and flowers.
There have been many genetic experiments involving plant pigmentation. For this research project, you can discuss discoveries such as the manipulation of RNA to silence color genes or Gregor Mendel's pea plant experiment. Scientists discovered that injecting plant cells with antisense RNA to the color gene mRNA resulted in a lack of pigment. Gregor Mendel is considered the "father of genetics." This scientist studied traits in garden peas by breeding them and observing their offspring. One of the traits he took into account was flower color. He noticed that some colors appeared to be "dominant" over others. His observations led to the formulation of mathematical predictions about heredity.