Plants capture light by using colored pigments. The colors of pigments are the colors of light the pigments reflect rather than absorb. For example, the most common pigment in plants is chlorophyll a, which is green. Therefore, chlorophyll a reflects green light. Students should grow seeds of the same species under lights covered in different colors of cellophane. Students should record and graph the growth of the plants and draw conclusions regarding which colors of light are most beneficial to the plants.
Hygroscopic crystals adsorb water by trapping water molecules within the crystal structure or by reacting with the water to form polymers. These crystals can often absorb 50 to 100 times their own weight in water. Have students mix various hygroscopic crystals into soil and grow plants in the different soil mixtures. Students should record and graph the growth of the plants and draw conclusions about why certain crystals were more beneficial to the plants.
Because of factors such as industrial pollution, acid rain is becoming an increasing problem all over the world. One effect of acid rain is it can lower the pH of the soil on which it falls. Because plants have adapted their biochemistry to the pH of the soil in which they evolved, they are not as well suited for soils with different pH values. To investigate the effects of acidic soil on plants, students should grow seeds of the same species in soils with different pH values and compare the growth rates of the seedlings.
Much of the available nitrogen on earth exists as pure nitrogen gas or highly oxidized forms of nitrogen, such as nitrates and nitrites. However, most organisms need reduced forms of nitrogen, such as ammonia. Organisms that can convert oxidized nitrogen to reduced nitrogen are called nitrogen-fixing organisms. Nitrogen-fixing bacteria live in the root nodules of legumes. To investigate the effects of reduced nitrogen availability, students should grow vegetables in a field with legumes and in a field without legumes and compare the growth rates of both sets of crops.