Auxin and cytokinin concepts
By the end of this lesson
- Describe common auxin/cytokinin associations
- Explain the limits of a simple ratio model
- Retain chemical identity and absolute concentrations
See it
Classic tissue-culture experiments showed that changing auxin and cytokinin balance can strongly influence organ development. That historical model is foundational, but modern regeneration biology is more complex than a simple high/low ratio rule.
Understand it
Describe common auxin/cytokinin associations
Auxins are often associated with rooting and callus responses in many contexts.
These are common associations in many contexts, not unconditional rules for every tissue and species.
Explain the limits of a simple ratio model
Cytokinins are often associated with shoot proliferation in many contexts.
A ratio omits absolute concentrations and chemical identities, which can change the treatment and response.
Retain chemical identity and absolute concentrations
Absolute concentrations, specific molecules, genotype, and tissue competence all matter.
Complete treatment context includes molecule identity and absolute concentration rather than ratio alone.
Worked example
Two treatments share the same auxin:cytokinin ratio but have different absolute concentrations or different molecules. They are not necessarily equivalent. The ratio is a useful organizing concept, not a complete recipe.
Explain your decision before opening the worked reasoning below.
Show the worked reasoning
A historical ratio model does not establish one universal modern regeneration treatment.
Different regulator molecules can behave differently, so equal ratios do not remove a substitution's significance.
Do not reduce modern regeneration decisions to one universal auxin:cytokinin ratio.
Try it
What should be retained for the example treatments?
Use the worked example above to explain your answer in your own words before taking the quiz.
Lesson quiz
Assessment version: 2026-10-15-v2. Previous reading-completion markers are retained. This revised quiz has its own result.
Apply it
Use the worked example to write a short decision record: what did you observe, which rule did you apply, and what would you check before acting?
Completion marks reading progress, not a quiz pass or professional certification.