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Main Curriculum Tie:
Background For Teachers:
It is very important that you do not give students the impression that plants are "fed" from nutrients in the soil the same way a person is fed when they eat food. The "food" for plants comes from the air. The bulk of a plant's body is made from carbon dioxide from the air. Soil nutrients can be compared to a human taking a vitamin pill. You need the vitamin nutrients to stay healthy but the source of your energy and bodybuilding substances comes from somewhere else. In the case of plants, the bulk of nutrients come from air. A famous experiment showed that if you measure the weight of soil, plant an acorn seed, let it grown into a large tree, that the soil will only lose a very small amount of weight - nowhere near the weight of the tree. The weight of the tree came from the air and, to a much smaller degree, water.
The reason hydroponics (growing plants in a water solution) is successful is that plants really don't need soil to grow. Soil helps plants to stay upright, provides mineral nutrients and stores water but it does not feed the plant. Plants will grow on paper towels or in a dish of water.
Intended Learning Outcomes:
Explain to the students that plants need water and nutrients from the soil to survive. Plants take in water and mineral nutrients from their roots through their stems. It is similar to drinking liquid from a straw. When plants take in water from the ground, they are also getting some of the nutrients they need from the soil. Tell students that only a small part of the plants' nutrients come from the soil. The largest part of plant nutrients comes from air. The nutrients in the soil are like "vitamin pills" for plants. There is a way to watch how water travels up the stems of plants using pieces of celery. The nutrients, which come from the soil, are dissolved in water and absorbed through a plant's roots. There are not always enough of these nutrients in the soil for a plant to grow healthy. This is why fertilizers are added to the soil to ensure the growth of plants.
(You could show the students a bottle of vitamins. The nutrients in the pills contribute to their health. But their body cannot grow and survive on just pills. People need to eat plant and animal material in order to grow. Plants do not "eat" the soil they grow in. They get their body-building food from the air.)
Emphasize that plants do not need soil to grow. They use it for structural support. In other words, soil helps plants to stay upright. Soil is a medium for providing mineral nutrients and water but plants could obtain that without soil.
Have students brainstorm different kinds of materials that plants could use for structural support. Some materials include floral foam, wet crumpled newspaper, wet gravel, paper towels, and cotton balls.
Have students design an experiment to show that plants grow without soil and to see what materials can be used for structural support.
Homework & Family Connections
Raise sprouts for salad. Sprouting seeds can be found in many grocery stores and health-food stores. (Combinations of alfalfa and radish are tasty.) Soak one tablespoon of sprouts in water overnight. Drain and put in a one-quart jar. Cover the top with a piece of mesh or cheesecloth fastened with a rubber band. Turn upside down. Rinse sprouts twice a day. Sprouts will be ready to eat in 4-5 days. Keep them out of the sun.
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