Written for this site from the class slides, with textbook page references for each statement. The chapter is on pages 118–124 of the course textbook. Image credits are on slide 13.
The biological species concept depends on interbreeding. Asexual organisms produce clones and never interbreed, so each line could count as a separate species. Bacteria also pass genes sideways by horizontal gene transfer, even between distant groups, so their gene pools are not isolated.
Members of a species share one chromosome number. A hybrid of parents with different numbers, such as a mule (63), has chromosomes that cannot all pair in meiosis, so it is usually infertile.
A key is a series of couplets: pairs of opposite statements about one feature. Use features that are easy to see and do not vary, and check that every route ends at one species. Test your key by swapping it with another group.
Organisms shed DNA into water, soil and air. Barcode regions, short standard sections that differ between species, are copied by PCR, sequenced and matched to a database. This shows quickly which species are present, but not how many individuals there are.
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Print this guide and complete it as you work through the slides and videos. It asks for your own explanations, so close the notes while you try each section.
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A printable worksheet covering all four statements, from quick recall to data questions and a longer answer. It has 20 marks and takes about 20 minutes, or you can do one section at a time.
Your teacher has the mark scheme.
You will need: Six to eight local plants or leaves, photographs, ruler
Safety: Avoid plants that irritate skin, and do not pick protected plants. Wash hands afterwards.
Carry this out with your teacher's supervision and follow your school's lab rules.
DNA barcoding relies on shared international databases, where researchers across the world compare sequences.
Different species concepts can give different answers. Consider what this means for the claim that a new species has been found.
Summarised in our own words. Use each code to find the exact wording in your textbook or the IB subject guide.
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