GCSE Biology: Plant hormones
For GCSE Biology, students need to be able to explain how plant hormones are important in the control and coordination of plant growth and development, with reference to the role of auxins in phototropism and gravitropisms. Students should be able to describe some of the effects of plant hormones, relating to auxins, gibberellins and ethane, as well as describing some of the different ways in which people use plant hormones to control plant growth.
Students often find it difficult to understand how auxins can have different effects in roots and shoots, so it is worth spending some time on this when teaching this topic. Students need to use accurate terms in this topic area,so throughout the delivery of this topic it is important to stress this, for example use light not "the sun", for geotropism use gravity and not just "ground" or "earth", ensure that when talking about the shoot students say this and not just plant.
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Tropisms and Hormones *suitable for home teaching*
This short film (3 minutes), from Twig World, looks at plant hormones and tropisms. The key points made by the film are:
- Tropisms allow plants to seek out the best conditions for survival.
- Tropisms are controlled by hormones called auxins.
- Tropisms react to varying conditions of light, gravity and water.
- There are both positive and negative tropisms.
Students could watch this video in pairs and then be asked to identify these four key points, either from scratch or provided with a gapped handout. Alternatively this video could be used as an introduction to a practical demonstration to investigate the effect of auxin in plants – (see the protocol included in this list.)
ABPI interactive website
This Association of British Pharmaceutical industry (ABPI) website contains a range of animations which could be used within lessons to consolidate learning. This is page 9 of a resource all about hormones and their effects. This page deals specifically with plant hormones, it provides a summary about Auxins and the commercial use of plant hormones.
Towards the bottom of the page there is an interactive drag and drop activity. This would make a good short self-study/homework activity to consolidate learning for this topic.
Tackling Tropisms: Gravitropism and Phototropism
This set of demonstrations into the effects of tropisms on seedlings is both simple and extendable, making it useful across key stages, including for GCSE Biology students.
In this investigation seeds are sown on damp cotton wool in (plastic) Petri dishes which are either flat or stuck vertically to a wall. Students enjoy the dramatic effect of sticking Petri dishes to the wall, and they will have well-grown seedlings within a week, showing the different effects of gravitropism and phototropism