Acid Rain and Plants: How does acid rain affect plant growth?
In this experiment, you will use cuttings of plants that are easy to grow, such as ivy, philodendron, begonia, or coleus. You will place two cuttings in water with a pH level of 7.0, which is neutral, and two cuttings in water with a pH of 4.0, which is in the range of acid rain. Your goal is to determine how the acidity affects the growth of roots.
Before you begin, make an educated guess or hypothesis about the outcome of this experiment based on your understanding of acid rain. This educated guess, or prediction, is your hypothesis. A hypothesis should explain these things:
- the topic of the experiment
- the variable you will change
- the variable you will measure
- what you expect to happen
A hypothesis should be brief, specific, and measurable. It must be something you can test through observation. Your experiment will prove or disprove whether your hypothesis is correct. Here is one possible hypothesis for this experiment: "Cuttings placed in water with a pH level of 4.0 will not grow any roots, while cuttings in water with a pH of 7.0 will begin to grow roots during the experiment."
In this case, the variable you will change is the pH level of the water, and the variable you will measure is the amount of roots that grow. You expect no roots to grow in the water with a pH level of 4.0.
The cuttings in the water with a pH of 7.0 serve as a control experiment, allowing you to observe root growth when the pH of the water remains neutral. After the two-week period of the experiment, if the cuttings in the neutral water have grown roots, but those in the acid water have not, you will know your hypothesis is correct.
Level of Difficulty
Moderate, because of the time involved.
- 4 small, clear jars
- 4 labels and a marker
- 2 large water containers
- litmus paper and a color scale
- white vinegar
- baking soda
- measuring cups and spoons
- a stirrer
- 2 cuttings each of two easily grown plants, such as ivy, philodendron, begonia, or coleus (Make sure each cutting has the same number of leaves and same amount of stem.)
$5 for the plants and litmus paper. (Ask friends, neighbors, or family members for cuttings so you will not need to buy plants, and the other materials should be available in most households.)
Two weeks to observe plant growth.
How to Experiment Safely
Be careful in handling glass jars.
- Label the four small jars in this way:
(name of plant 1), neutral
(name of plant 1), acid
(name of plant 2), neutral
(name of plant 2), acid
- Pour 2 cups of water into each of the large containers.
- Use the litmus paper and a litmus color scale to measure the pH level of the neutral or control container. It should be 7.0. If it is higher, add a drop or two of vinegar, stir, and check it again. If it is lower than 7.0, sprinkle in a little baking soda, stir, and check again. Repeat until the color scale shows that the pH level is 7.0.
- Pour 1 tablespoon (15 ml) of vinegar into the acid or experimental container, stir, and check the pH level. It should be 4.0. If it is higher or lower, add vinegar or baking soda, as in Step 3.
- Nearly fill the two small jars labeled Neutral with the neutral water. Then pour the same amount of acid water into the two small jars labeled Acid. Label and save any leftover water so you can keep the small jars full of water with the correct pH level.
- Place the four plant cuttings in their labeled jars. Make sure the stem and part of the lowest leaf is under water.
- Place all four jars in a warm, sunny place.
- Create a chart or print out this one. Draw each cutting to show how it looked at the beginning.
- For the next two weeks:
- Every day, make sure all cuttings are still in the water. Add more acid or neutral water to replace any that evaporates. (Be careful to add the right kind to each cup.)
- Every other day, check the pH of the water in each cup, and use vinegar or baking soda to adjust it so it is 7.0 or 4.0.
- Every day, record any changes or growth on the chart. Clearly show any roots that grow longer or branch out, leaves that grow larger, and the emergence of new leaves.
Summary of Results
Study the drawings on your chart and decide whether your hypothesis was correct. Did both cuttings in acid water not grow at all? Or did they grow some, but less than those in neutral water? Was the cutting of one plant more tolerant of acid water than the cutting of the other plant? Did both cuttings in neutral water grow as you expected? Write a paragraph summarizing your findings and explaining whether they supported your hypothesis.
Source: Experiment Central. U·X·L, 2000.