Biology

The Earth’s atmosphere is made up of a deep, multilayered blanket of gases. One layer is rich in carbon dioxide and other gases that are capable of trapping heat. This is the "greenhouse" layer of gases, named so because it works like the glass in a greenhouse, permitting sunlight to shine through but preventing the loss of heat. Thanks to the greenhouses gases, Earth can maintain temperatures that are warm enough to support life.

Over recent years, the concentration of greenhouse gases has increased, causing scientists to worry that Earth’s temperatures may one day increase to abnormally high levels. Many feel that higher temperatures on the Earth’s surface could create environmental problems. For example, scientists express concerns about temperatures that would be warm enough to melt the polar ice caps or change the normal patterns of plant growth.

The roles of plants, like everything else in an ecosystem, are delicately balanced. Temperature is one of the primary determiners of plant distribution and abundance. Species of plants are specifically adapted for their thermal habitats; that is why you never see a cactus growing under a snow drift or a blue spruce tree in the tropics. If temperatures became warmer, plants well adapted to temperature fluctuations would flourish, and those species that are poorly adapted would die, upsetting the natural balance.

• soil
• bean seedlings
• large half soda bottles
• 3 thermometers
• clear plastic wrap
• pitcher of water
• ruler
• 100-milliliter (ml) graduated cylinder
• data table

1. Fill each container about one-half full of soil. Place each soil-filled container in an aluminum pie plate.
2. In each container, plant three bean seedlings. The seedlings will need to be watered during this experiment, but it is important that they each receive the same amount of water. Measure 50 ml of water in a graduated cylinder and pour it around the plants.
3. Place a thermometer inside each bottle.
4. Bottle A is complete as it is. Cover the top of bottle B with two layers of clear plastic wrap. Cover the top of bottle C with four layers of clear plastic wrap. Seal it against the bottle so that it fits tightly.
5. Turn on the lamp above each bottle.
6. Copy the data table in your notebook. Write down the temperature in each bottle in the column labeled “Day 1, temperature.” Hold your ruler up to the outside of bottle A and measure the heights of the three plants inside it. Record their heights on the data table under “Day 1, Plant height.” Do the same for plants in containers B and C.
7. Water the plants once a day.
8. Enter the temperature and height of the plants in the data table on day 3 and every other day after that for two weeks. Also observe the color of the leaves. If any leaves change color, make a note about that on the data table in the same block where you wrote down the measurement. Leaves may change from green to yellow, pale green, or brown.

1. Which container stayed the warmest?
2. At the end of 2 weeks, did the seedlings in all three containers look the same? Describe any differences.
3. Offer an explanation for the results of this experiment.
4. How could changes in the rates at which the plants grow affect an ecosystem?

1. C
2. Answers will vary. Student may suggest that the plants grew the fastest in option C.
3. Answers will vary. Students may suggest that plants grew faster in warmer temperatures.
4. Answers will vary. Students could mention changes in oxygen levels, changes in food available for carnivores, and changes in shelter for animals.