Write the effects of gibberellins, cytokinins, ethylene and abscisic acid on plants.

1. 1 · Define. Plant hormones are chemicals made in small amounts that control growth and development.
2. 2 · Gibberellins.
   • Discovered from Gibberella fujikuroi (foolish seedling of rice).
   • Stem lengthening, bolting in cabbage, breaking dormancy, bigger grapes.
3. 3 · Cytokinins.
   • Kinetin and zeatin.
   • Cell division, delay of leaf ageing, side bud growth, tissue culture.
4. 4 · Ethylene.
   • The only gaseous hormone.
   • Fruit ripening, fall of leaves and fruits, ageing.
5. 5 · Abscisic acid.
   • The stress hormone.
   • Closes stomata, causes dormancy, slows growth.
6. 6 · Link to daily life. Bananas and mangoes are ripened with ethylene; tissue-culture banana plantlets are grown with cytokinins.
7. 7 · Close. So growth promoters and growth inhibitors together control the life of a plant.

Scoring tip: Give one discovery fact and two effects for each hormone. A four-row table saves time.