BACKGROUND:
All plants need light, water, air,
moderate temperatures and most need soil. Some plants, such as mistletoe
and duckweed, do not require soil for growth and life but they do not
constitute the majority of plants. There are wide variations in the
amount of light and water that plants require. A mature Joshua tree, for
example can store enough water to last three years or until another
rainy season.
Most plants, however, need water on a more regular
schedule. Some plants require a full day's hot sun, and others cannot be
taken out of deep shade. Temperature tolerance also varies tremendously.
Tundra and lichens can survive near the Arctic, but many tropical plants
cannot survive being carried from the store to a car when it is near
freezing.
PROCEDURE:
- In this experiment you will
introduce the idea of an experimental control. As part of an experiment
a control determines what the outcome would be if no alterations or
changes occurred. In essence, a control serves to detect a change that
occurred independent of the experiment. In this experiment, for example,
if there were no controls used, it would be difficult to prove that not
watering or placing a plant in darkness had any effect. Any plant that
died could have been sick before you got it, or maybe this kind of plant
did not like classrooms or children!
- Ask the students to bring in 4
similar plants from home. The plants may be grass, weeds, or anything
growing around the house. If your school is near a grassy or weedy area,
you can have the students collect 4 specimens before you complete this
lab.
- In lab, the students will decide
if plants need sun and water to live. The lab content is simple because
the main emphasis of the lab should be on designing a good experiment.
Show them the experimental set-up using their 4 plants as follows:
Plant A: the control
Plant B: sun, no water
Plant C: water, no sun
Plant D: no sun, no water
- Look at all the plants and enter
the first day's (and subsequent) observations into the appropriate place
on the chart as follows: + = alive and growing; - = dying, or looking
unhealthy; and 0 = dead. If there is more information the students
should write it on the back of the lab sheet or on a separate piece of
paper.
Place the plants in their appropriate
locations. The students can cover the plants with a coffee can to
simulate lack of sunshine. It is a good idea to tilt the cans slightly
so that air can circulate through the cans. Continue making observations
on the chart for 2 weeks. You may want to work on Plants 3A - Post
during lab so students can study two experiments at once.
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