This research aims to analyse the progression of 13-14 year-old students' ideas regarding the concept of energy transfer by means of heat in three biological mechanisms of thermal regulation. The outputs of 270 students, grouped in 77 cooperative groups, are analysed by comparing their explanations before and after conducting an experimental laboratory workshop in which they investigate the topic of energy transfer by means of heat. Students' explanations are analysed by identifying them in a "conceptual landscape" This landscape shows the conceptual frontiers that students must overcome to move from initial ideas to more sophisticated ones. Thus, while at the beginning of the workshop many students explain the thermal regulation mechanisms using the concept of the flow of coldness and give the morphological and behavioural mechanism the ability to generate heat, most students end up conceptualising the studied mechanisms in terms of the heat transfer regulating function from the warm living beings to the cold environment. Although the latter conceptualisation corresponds to an idea that is not the most sophisticated way of describing the transfer of energy through heat, it constitutes a first step in students' concept development towards ideas closer to those that are scientifically accepted.