What do you think plants need to make food
What do you think plants need to make food?
Plants need water, carbon dioxide, and sunlight to make food, but in order to stay healthy and survive, they also need minerals and other substances found in the soil. These substances assist the plant in creating special cells and chemicals that aid in photosynthesis. Many students think that plants need soil to make food. They don’t, as long as they are provided the necessary substances to stay healthy. (This is what the science of hydroponics is based on.) Encourage groups to develop an experiment to determine if plants need one of these items: water, gases (carbon dioxide), sunlight, or soil. Listed below are sample experiments. They can also serve as teacher demonstrations if a group of students does not complete one of the experiments.
Water Experiment: Use two plants. Water one plant every day or every other day with the same amount of water. Be careful not to over-water the plant, as this can also adversely affect its ability to survive. The second plant will have all of the same conditions as the first — gases, sunlight, and soil, but it will not receive any water.
Carbon Dioxide Experiment: A simple experiment to determine if plants need carbon dioxide to make food is to use two plants. Place one plant in a reclosable plastic bag and seal the bag. Make a hole the size of a half dollar in a second reclosable plastic bag. This hole will allow carbon dioxide to enter the bag. Place a second plant into the reclosable plastic bag with the hole and seal the bag.
Sunlight Experiment: Use two plants. Place one plant under a grow lamp or in an area that gets sunlight. Place the second plant in a dark area such as a closet. Both plants should receive the same amounts of water and carbon dioxide.
Soil Experiment: In this experiment, one plant will be planted in soil, and the other plant will not. Both plants should receive the same amounts of sunlight, water, and carbon dioxide. To really see that soil is not necessary to make food, you might want to use plants that grow well out of soil, such as water plants available at the local nursery or lima bean plants. Students conducting this experiment should start with two healthy plants, to ensure that the cells and chemicals necessary for photosynthesis are already developed.
MISCONCEPTION: Students think that plants get their food from the environment rather than manufacturing it internally. Students have difficulty in identifying sources of energy for plants and animals. Students believe that plants get their food from soil. Plants do get minerals and nitrogen based substances from the soil that provide some of the building materials and are used in the process of photosynthesis. However, a large percentage of the building material that makes up plants comes from carbon in carbon dioxide from the air, and plants get energy from the food they manufacture internally. Observation and discussion of the experiments developed in this section will help students better understand these concepts.