Impressions of the new Topic 9 - Plants

Friday 14 November 2014

The new plants topic is more appropriate for HL biology than the old one but it may take longer to teach. Some easy material has been removed. Knowing the difference between onions and potatoes was always a bit like a middle school project. New material reflects recent advances in molecular biology and genetics which provides a couple of good examples of gene expression to support new concepts in topic 7.

We will still want students to know some of the removed easy material, for example; what stomata are, the abiotic factors affecting transpiration and the basic structure of roots, stems and leaves. These are important in the understanding of transport for the new 9.1 & 9.2.  I see these as knowledge which students are likely to have covered before beginning their IB studies. Many national curricula include work on leaf structure and transpiration so this seems reasonable.

There is quite a lot of new material in the topic, including auxin efflux pumps, micropropagation, control of gene expression as well as the structure and function of primary xylem vessels, and phloem sieve tubes.

The IB teacher support material, 'Changes in the syllabus content' has a clear list of concepts which have been removed from the topic. It includes; plan diagrams of tissues in stem and root, differences between structures of mono & dicotyledons, leaf tissues and function, modification of roots, stems and leaves and comparing growth due to apical and lateral meristems.

To avoid running out of teaching time in the second year I'm going to be clear about this and only include any of these removed concepts in my lessons if the students need basic reminders to understand the details of transpiration in 9.1 and translocation in 9.2

In both growth in plants, 9.3 and reproduction, 9.4 there is mention of gene regulation.  I'm going to keep this simple. This links to other areas of the the new guide, for example proteomes in 2.4 and gene expression in 7.2.  These make good examples which could be used as an introduction to 7.2 or a reminder of it depending on when the plants topic is covered. Personally I usually leave this plants topic until the third term or the autumn of the second year as it complements the SL ecology topic so students will already know  that gene expression is regulated by proteins binding to DNA.


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