Positive phototropism is shoot growth towards lateral light. In IB Biology HL C3.1.18, practise how auxin redistribution makes the shaded side elongate more and bends shoots towards light.
Hormones are produced in plants and animals and cause changes in the organism.
Describe the role of the plant hormone auxin in phototropism.
a. phototropism is a growth response to direction of light/differences in light intensity
OR
(positive) phototropism is growth towards the light (source);
b. auxin is produced in the shoot (apical) meristem
OR
auxin promotes cell/stem growth/elongation;
c. auxin (efflux) pumps set up a concentration gradient;
d. auxin is transported to the shaded side (of the stem)/side with lower light intensity;
e. (auxin) changes transcription/gene expression (in stem cells);
f. (auxin) causes more growth/elongation on the shaded part of the stem/shoot tip/meristem;
g. stem/shoot (tip)/coleoptile/plant bends towards the light;
Marking guidance:
Allow points made using annotated diagrams.
4 max