Photoreceptors

2. Photoreceptors light (stimulus) phototropin (receptor) cascade of reactions redistribution of auxin phototropism Photoreceptors are structures or pigments that are sensitive to light, often light of specific wavelengths. Phototropins are a group of photoreceptors primarily responsible for triggering phototropisms. When light of the right wavelength is present, changes in the phototropin molecules trigger a cascade of reactions in the cell. This ultimately results in the redistribution of auxin so that there is more on the shaded side of the plant.

3. IAA – an auxin Auxins are made continually in the shoot apex and young leaves (apical meristems). They can move by diffusion from cell to cell, or can be transported long distances via the phloem, e.g. from the shoots to the roots. The primary natural auxin is indoleacetic acid(IAA). It is involved in many important processes, including cell elongation and phototropism.

4. How does IAA work?

5. The discovery of auxin

6. Phototropism in the classroom There are many ways phototropic responses can be shown in a school laboratory. How would you use this apparatus to investigate the effects of light on a growing plant? • What variable could you change? • What control experiment would you use? • How would you present your results if they were qualitative, rather than quantitative? • How might you extend this investigation to gain further information about how plants respond to light?

7. True or false?