Plants and Water

Teacher's Notes

This unit is an introduction to Hydrotropism .

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, analyse data to draw a conclusion, and communicate the findings.

Transparency Master	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 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.

Transparency Master	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.

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.

This response is known as a hydrotropic response. The effect is called hydrotropism.

Transparency Master	Explanation 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.

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?

Prepared by YES I Can! Science
Faculty of Pure and Applied Science, York University