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Table of Contents
Plants and Water
Teacher's Notes
This unit is an introduction to Hydrotropism.
Things to Emphasize
Almost all green plants are able to locate a source water;
Water is essential for all plants to survive;
Hydrotropism is a highly evolved survival mechanism;
Science investigation involves a multi-step inquiry process: ask an initial question, plan the investigation, record observations and collect data, analyze data to draw a conclusion, and communicate the findings.
Experiment
The Water Hole
Set up three plastic tumblers as shown. Fill one with plain tap water (to which a drop or two of liquid fertilizer has been added), one with very salty water, and leave the third tumbler dry (It can be filled with dry sand to add stability to the experimental set up).
Cut three holes in the bottom of a large plastic ice cream container so that one tumbler fits easily under each hole.
Cover the bottom of the plastic ice cream container with a course wire screen. This will prevent soil from falling through the holes into the tumblers but will allow the roots of the plants to grow through them.
Set Up
Add stones to the bottom of the ice cream container and cover the stones with a layer of good quality potting soil.
Plant a layer of radish or mustard seeds according to the direction on the package.
Do not over-water once the sprouts have formed. This will encourage the roots to seek out a source of water.
Observations
This response is known as a hydrotropic response. The effect is called hydrotropism.
Some plants, such as the radish, develop roots which grow rapidly and seek out moisture. These plants have evolved to develop roots which spontaneously grow downwards in response to the force of gravity to seek out any suitable source of moisture.
Activities
Vocabulary
Topics for Class Discussion
What are the survival advantages for plants which have evolved to become hydrotropic?
How do plants that grow in deserts survive?
Mars is essentially a desert, with very cold temperatures and low levels of sunlight. This bears a striking resemblance to Canada's arctic regions. What kinds of plants are able to grow in the Canadian arctic and how has evolution allowed them to adapt to these conditions?
for the Canadian Space Agency.
