BRAINCAKEHow Auxins Work
Auxin causes cell elongation by a mechanism described by the acid growth hypothesis.
1. IAA binds to receptors in the target cell.
2. This stimulates proton pumps in the cell surface membrane to actively transport hydrogen ions (H+) out of the cytoplasm into the cell wall.
3. The pH of the cell wall falls to around 5.
4. The acidic conditions activate proteins called expansins, which break the hydrogen bonds between cellulose microfibrils and other wall polysaccharides.
5. The cell wall becomes looser and more flexible.
6. The cell takes up water by osmosis, and the pressure of the expanding vacuole stretches the loosened wall, so the cell elongates.
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Key terms in this lesson
- phototropism
- A growth response of a plant shoot or root towards or away from the direction of light.
- geotropism
- A growth response of a plant shoot or root towards or away from the direction of gravity.
More in Chemical Control
- Plant Stimuli
- Plant Responses
- Plant Growth
- Auxins
- Gibberellins
- Cytokinins
- Synergy and Antagonism
- Apical Dominance
All 30 lessons in Chemical Control · All Edexcel A-level Biology topics