Plant Hormones and Tropisms
Hormones like auxin control plant growth.
About this topic
Plants respond to stimuli by growth movements called tropisms. Phototropism is growth toward light and gravitropism growth in response to gravity (roots down, shoots up). Auxin, produced in shoot tips, makes cells on the shaded side elongate more, bending the shoot toward light.
Other hormones: gibberellins trigger germination, ethylene ripens fruit, cytokinins promote cell division and abscisic acid closes stomata. Growers use hormones in rooting powders and weedkillers.
If you cover a shoot tip with foil, it does not bend towards light, showing that the tip detects light. Auxin moves to the shaded side and makes cells there elongate, so the shoot bends towards the light. In roots, high auxin on the lower side inhibits growth, so roots bend down.
Other hormones include gibberellins, which promote germination, and ethylene, which ripens fruit; one bad banana can ripen a whole bowl. Farmers use rooting powder, containing auxin, to help cuttings, and selective weedkillers that mimic auxin and make weeds grow too fast. Students often say plants grow toward light because they want to; the response is chemical, not a choice, and the cells on the dark side simply grow more.
Key ideas
- Phototropism: toward light
- Gravitropism: roots down
- Auxin concentrates on shaded side
Quick check
Use cases: where Plant Hormones and Tropisms helps
- Homework: review the key idea behind Plant Hormones and Tropisms before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Plant Hormones and Tropisms without notes.
- Visual learning: play with the interactive lab to see how Plant Hormones and Tropisms changes when you adjust its inputs.
- Teaching a friend: explain Plant Hormones and Tropisms in your own words, then compare your version with the key ideas.
Biology underpins medicine, farming, conservation and biotechnology.
Frequently asked questions
What is Plant Hormones and Tropisms?
Hormones like auxin control plant growth.
What will I learn in Plant Hormones and Tropisms?
Phototropism: toward light. Gravitropism: roots down. Auxin concentrates on shaded side.
Is Plant Hormones and Tropisms part of Biology?
Yes. It is one of 150 Biology topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Plant Hormones and Tropisms lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Plant Hormones and Tropisms?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.