5.1 Plant Hormones
1. Growth of shoots towards sunlight is called positive phototropism.
2. Growth of shoots away from sunlight is called negative phototropism.
3. In plants, hormones play an important role in growth processes such as seed germination, growth of roots and development of fruits.
4. There are many types of plant hormones, such as auxins and ethylene.
Effects of Auxins on Growth Responses
1. Auxins are produced in the apical meristems of the shoot tip and the root tip in the cell division zone.
2. In the shoot tip, high concentrations of auxins stimulate cell elongation.
3. The effect of high concentrations of auxins in the root tip is different from that in the shoot tip. In the root tip, a high concentration of auxins inhibits cell elongation.