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Plant Hormones B3f OBJECTIVES Key Objective • Describe the role of hormones in plant growth C/D • Use the words phototropic and geotropic to describe the growth of roots and shoots • Identify the chemicals responsible for growth in plants A/B • Interpret data from phototropism experiments in terms of hormone action • Explain how hormones brings about shoot curvature in terms of cell elongation How Does This Plant Know to Send Its Shoots ‘Up’ and Its Roots ‘Down’? Response in plants • • Tropism – plant growth in response to a stimulus Stimulus Light Tropism Phototropism Gravity Geotropism Growth towards the stimulus is a positive tropism and growth away is a negative tropism – e.g. shoots are positively phototropic but negatively geotropic Some Definitions Shoots grow towards light (positive phototropism) and against gravity (negative geotropism). Roots grow away from light (negative phototropism) and in the direction of gravity (positive geotropism). Plant Hormones The growth of roots and shoots is controlled by hormones: In the shoots the hormone auxin is “destroyed” by light, so the shoot will bend towards the light as the cells on the shaded side grow quickest. In the roots hormones slow down growth of the cells in the lower region, which makes the root bend down. Typical Exam Question Typical Exam Question Auxin is made in the tip or top of plant The tip is covered so it doesn’t receive light Auxin levels are equal on both sides Both sides grow at the same rate PLENARY Create a brainstorm/mind/concept map on plant hormones summarising the information discussed in the lesson