7.2 Tropic responses

 Plants grow towards or away from stimuli  The growth response is called a tropism gravity light Shoots will grow towards light – a positive tropism Shoots will grow against gravity – a negative tropism

 Phototropism is the growth response towards or away from light  Geotropism is the growth response with or against gravity geotropism phototropism

 Complete this table: ResponseTropism Shoots growing towards sunlight Positive phototropism Shoots growing against gravity Negative geotropism Roots growing away from sunlight Negative phototropism Roots growing with gravity Positive geotropism

 A hormone called auxin is made in the tip of the shoot  Auxin causes shoot cells to enlarge  When light is directly overhead, auxin diffuses equally down the shoot  The shoot grows straight up light

 When light is directional, the auxin moves to the shaded side of the shoot  The cells on the shaded side elongate more than the cells on the lighted side  The shoot grows towards the light light Auxin at work

gravity shoots grow up roots grow down negative geotropism positive geotropism

 Auxin is made in the shoot and root tips  Auxin causes slowed growth in root cells  When a plant is laid on its side, auxin collects in the lower cells  The lower cells in the shoot elongate and the shoot grows upwards  The lower cells in the root slow in growth and the roots grow down Phototropism and geotropism

 Complete the following summary questions:  P153 exercise 1  P155 exercises 1, 2 and 3  Complete the following exam-style questions:  P156 question 4