CAIE A Level Biology 9700 · Selection and evolution
A population of freshwater cichlid fish lives in a large lake. A river from the lake was diverted by a landslide, creating a new isolated lake. Meanwhile, within the original lake, some cichlids began breeding in the rocky shoreline while others bred in the open water, leading to reproductive isolation.
Describe how allopatric and sympatric speciation can lead to the formation of new species, using examples based on this scenario.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.