Investigation: How Do Hormones Affect Plant Growth

Introduction: Both plants and animals produce hormones that can regulate growth. Gibberellins are a group of plant hormones that affect growth. The effects of these hormones were first observed in the 1920s in rice plants that were attacked by a fungus, these rice plants grew unusually tall. Scientists isolated the substance responsible for the growth ( Gibberala fujikuroi ). Gibberellic acid is derived from this chemical and is used to make plants grow taller.

Little Marvel and Alaska Peas, and Gibberellic acid can be purchased from biological supply companies or Amazon.

Question: What is the effect of gibberellic acid on the growth of normal and dwarf pea plants?


First, take 8 pea seeds and set them in a petri dish with a paper towel on both the base and the lid. Wet the paper towels and leave undisturbed until germination occurs. You may need to re-wet the paper towels if they become dry. (Make another petri dish as a spare, in case something happens with your first batch)

After germination - record root and shoot length for each seedling. . After approximately 1 week, transplant seeds to containers:


Apply Gibberellic acid to seedlings by using a cotton swab - apply to the leaves and the shoot tips of the seedlings after they have been transplanted. You will need 4 pots each containing 2 -4 seedlings each (if one of them dies, you can still use the data from the alternate.)

Record your data over a period of 8-10 days. You may also check with other groups to get an average for each treatment. You will need to turn in your data tables and your graphs of the data when you turn in your lab report. You can use toothpicks and paper to create tiny "flags" so that you can tell each seedling apart and record the data accurately. Work with your group to develop a comprehensive data table.


1. Why was water applied to the 1st and 3rd pots?
2. Based on the graphs, which group had the fastest rate of growth?
3. Compare the growth of the Little Marvel Pea plants and the Alaska Pea plants with and without the treatment of gibberellic acid.
4. Suggest real world applications for gibberellic acid.

Use the Lab Report Template to write your lab report.

Further Experiments

As a group, choose ONE of the following experiments, conduct it over a two week period and submit a lab report. You will have Little Marvel Peas and Alaskan peas to work with.

A. Gardeners often pinch off the stems of plants to enhance the plants' growth. The pinching off is related to the production of certain hormones. Design an experiment that would show the effect of pinching back the stem tips.

B. In the first experiment you applied the hormone to the shoots and leaves of the plant. Design an experiment to determine whether this hormone can also be absorbed by the roots and have the same effect.

C. Do fully grown plants respond to the presence of gibberellic acid? (Use your control groups from you last experiment to design this experiment)

Other Plant Resources

Rate of Photosynthesis – using baking soda, elodea and light, measure the bubbles to observe how fast a plant photosynthesizes and releases oxygen

What Factors Affect Seed Germination – grow seedlings with different conditions (light, water, temperature)

Algae Beads and Photosynthesis – use algae cultures and sodium alginate, measure photosynthesis by changes in color of indicator

Separation of Plant Pigments – identify plant pigments by separation and isolation of the pigments using thin layer paper chromatography.