Plants and the Environment:

Experiments With Light, Soil, and Water

INTRODUCTION

How do light, water and soil affect a plant? We can find out if we watch how seeds grow in different conditions.

MATERIALS

9 small glass jars or paper cups
Labels
Fast-growing seeds such as grass, radish, or mustard seeds
Water
Sand
Topsoil

WHAT TO DO

Divide the jars into groups of three (3 for light, 3 for water, and 3 for soil).
Label the jars (Light: no light, partial light, light; Water: 1 spoonful, 3 spoonfuls, 5 spoonfuls; Soil: sand, soil and sand, soil)
Fill the light and water jars approximately half full with soil, fill the sand jar with sand, fill the soil jar with soil, and fill the soil, sand jar with an equal mixture of sand and soil.
Place several seeds in each jar and cover up with the appropriate ground material.
Water the group of light and soil jars with approximately 3 spoonfuls of water. Water the group of water jars with the appropriate amounts of water.
For the light jars place the "light" jar in the window, the "no light" jar in the dark in a drawer. For the partial light jar, alternate days in the window and in the drawer.
For the Soil jars place the jars in the window.
For Water jars place the jars in the window. Water daily as labeled.
Keep the light and soil jars moist with water.
Each day record observations for each jar.

QUESTIONS

In which jar did the seeds grow best for the light group? Water group? And the soil group?
If you were to plant a garden, what conditions would you want to use from each condition (light group, water group, soil group)?

SUMMARY

Plants need light, water and nutrient rich soil to grow and stay healthy. When seeds are planted they do not need light to germinate because they are planted beneath the soil, where it is already dark. Seeds contain a plant embryo and stored food to give the baby plant all the energy it needs to sprout. After the seeds sprout the plants do need light to grow. Light is needed for the plants to produce their own food through photosynthesis. Shortly after sprouting the plant grown in the dark will grow just as the ones in the light and partial light because they all have stored energy from their seeds, but the plant grown in the dark will not have any color, the partial light plant will have a faint yellow-green color, and the plant grown in the light will have the healthy green color of a plant capable of photosynthesis. Over time the plant growing in the light will continue to use the light to produce its own food and it will grow, but the plants grown without full light will die since they cannot produce food without light.
In addition to the food a plant produces for itself it needs nutrients from the soil in which it grows. As organic material decomposes it enriches soil with the minerals Nitrogen, Phosphorus, and Potassium. Nitrogen helps plants take their form and it also helps them turn the food they produce into energy for growth. The mineral phosphorus is important for plant respiration. Plants use potassium to help them metabolize food and it also helps them control the amounts of water and chemicals used in normal plant functions. Soil that is enriched with these nutrients will help plants grown and stay healthy. Sand does not contain these nutrients and minerals, so plants grow better in soil than in sand.
All plants need water for germination and growth, but some plants need more water than others. For example, a cactus plant can live with very little water, but other plants such as the rubber plant need large amounts of water all the time. Plants are affected by the amount of water they receive, too much or too little water can kill them.

SOURCES

"The Science of Plants." Jonathan Bocknek. Gareth Stevens Publishing: Milwaukee, 1999. ISBN 0-8368-2467-9
"Experiences with Plants for Young Children." Frank C. Gale and Clarice W. Gale, Pacific Books: Palo Alto, California, 1975. ISBN 0-87015-211-4.
http://ltpwww.gsfc.nasa.gov/globe/index.html , Soil Science Education Home Page.

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