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What are hormones? What do they do? What function do hormones have in plants? What are hormones? What do they do? Auxin controls plant growth. Auxin promotes growth in the shoot and inhibits growth in the root Coordination and Response in Flowering Plants In order to be successful in this lesson you must be able to: Learning Objective: explain that auxin distribution causes unequal growth in roots and shoots. Coordination and Response in Flowering Plants State that plants respond to light , gravity and moisture Describe negative and positive tropisms in plants PROGRESS Explain that auxin stimulates cell elongation in shoots and inhibits cell elongation in roots Plants respond to their environment by altering their growth. This is called tropism. Show clips 3 main tropisms: Phototropism (Light) Geotropism (Gravity) Hydrotropism (all of which are controlled by auxin) Tropisms can be described as positive and negative: positive tropism – the plant grows towards the stimulus negative tropism – the plant grows away from the stimulus. Does the shoot grow towards or away from the light? Plant sensitivity: Glossary Key Word Sensitivity Meaning Stimulus hydrotropism phototropism geotropism Negative tropism Positive tropism Use p 155 and 156 in iGCSE Biology to help Phototropism Shoots grow towards light = positive phototropism How? The hormone auxin moves away from the light and stimulates the cells to elongate on the ‘dark side’ Geotropism Roots grow in the direction of the force of gravity = positive geotropism auxin reduces cell elongation in the root, so the root curves downwards Geotropism Roots grow in the direction of the force of gravity = positive geotropism Shoots grow against the force of gravity = negative geotropism auxin reduces cell elongation in the root, so the root curves downwards auxin stimulates cell elongation in the shoot, so the shoot curves upwards Summary of the different types of tropism Part of plant shoot root Light stimulus Gravity stimulus positive phototropism negative gravitropism (grows towards the (grows against the light) force of gravity) positive gravitropism negative (grows in the phototropism (grows direction of the force away from the light) of gravity) Uses of plant hormones Rooting powder contains growth hormones that make stem cuttings develop roots quickly. Selective weedkillers kill some plants but not others. This can be useful for getting rid of dandelions in a lawn without killing the grass Plant hormones are useful for delaying ripening during transport or when fruit is displayed in shops Coordination and Response in Flowering Plants State that plants respond to light , gravity and water. Describe negative and positive tropisms in plants PROGRESS Explain that auxin stimulates cell elongation in shoots and inhibits cell elongation in roots