Life Cycle - Plants (3A)
Lab

   
OBJECTIVES:
  • Designing an experiment testing two variables.
  • Using controls in an experiment.

VOCABULARY:

  • control
  • requirement
MATERIALS:
  • 4 test plants per group that will readily show problems when deprived of sun and water (i.e. lettuce seedlings or grass)
  • 2 coffee cans per station
  • Worksheet

Students determine the growth requirements of plants through experimentation.


plant lab at The University of California at Davis
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:

  1. 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!
      
  2. 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.
      
  3. 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
      
  4. 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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