
Auxin, Cytokinin, and Plant Growth
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Why does cutting the tip off a plant cause new branches to sprout? Two hormones control this behavior. Auxin (produced in the stem tip) blocks side branches. Cytokinin (produced in the roots) promotes them.
You test auxin by cutting the root off a plant. Then you place it in a medium with or without auxin. You also cut the top bud and replace it with cotton soaked in auxin. This shows whether side buds still grow.
For cytokinin, you place a geranium leaf on soil with and without the hormone. The leaf on plain soil grows a few small buds. The leaf with cytokinin grows many more. The results show how these two hormones push growth in opposite directions.
Hypothesis
The hypothesis is that auxin and cytokinin affect the development of roots and buds in plants.
Method & Materials
You will cut off the inferior part of a plant, including the roots, and observe the development of adventitious roots in a medium with or without auxin. You will also replace the apical bud with cotton impregnated with auxin and observe the development of axillary buds in lateral branches. Finally, you will put a geranium leaf on some soil or on a synthetic medium with or without cytokinin and observe the development of adventitious buds.
You will need a plant, a medium with or without auxin or cytokinin, cotton, and a geranium leaf.
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See what’s includedResults
The results showed that without auxin, roots developed, while with auxin, no axillary bud development was observed. With cytokinins, more buds were observed. This suggests that auxin is produced in the apical part of the plant and prevents the development of axillary buds, while cytokinins are produced in the roots and prevent the development of roots.
Why do this project?
This science project is interesting because it allows students to explore the role of hormones in plant growth.
Also Consider
Variations to consider include testing other hormones, such as gibberellins, and testing the effects of different concentrations of hormones.
Full project details
Additional information and source material for this project are available below.Related videos
These videos explain the science behind this project and demonstrate key concepts used in the experiment.
See the detailed steps in an apical dominance experiment with auxin in this video tutorial!
A quick comprehensive video on the different plant hormones, including auxin and cytokinin.
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