Activity 5: For You To Do
Teaching Suggestions and Sample Answers

Part A: Competition among Plants
1. You may wish to substitute the milk containers with plastic flower pots of a similar size. They are relatively inexpensive and can be reused.

Teaching Tips
This is a good opportunity to remind students of the importance of controlling variables in any experiment.

You may wish to substitute the seeds suggested for this activity with rapid-growing plant seeds.

2. a) All variables except the one being studied must be controlled.

4. A sieve is handy to use to spread a thin and even layer of soil over the seeds.

6. a) You can expect that some seeds will not germinate.

Teaching Tip
You may wish to have the students make quantitative observations by measuring the height of the plants. If you do, this is also an excellent chance to introduce
or remind students of the uncertainty in measurements.

8. a) Student observations will vary.
b) The cress plants will be tallest in the container with only five seeds.

c) The cress plants will have the greatest number of leaves in the container with only five seeds. d) As the number of cress plants in a container increased, each individual plant appeared to be smaller. e) Cress seeds planted together with lettuce seeds is an example of interspecies competition.

Part B: Competition under Different Conditions

Teaching Tip
Factors that students might consider include such things as temperature, nutrients, light, soil characteristics (other than nutrients), and moisture.

3. Students may choose to vary the amount of water, in which case they do not need to water with the same amount of water. However, they must still record the amount of water used.

4. a) and b) Data will depend on the type of seeds used and the conditions chosen to investigate.

c) Students should come to realize that plants have adapted to the environments in which they live. Therefore, a plant that naturally grows in the shade will thrive in a low-light situation. Desert plants will be more tolerant of low-moisture situations.