This paper illustrates Greek students' aged 13-15 misconceptions about food chains. A close-ended questionnaire was constructed and administrated to 1757 students. The main results were that only 30% of the students manage to classify the producers, the consumers end the herbivorous and carnivorous of two food chains. The rest of the students find difficulties in understanding fundamental concepts of food chains. Some of them face the organisms of two food chains systematically wrong. Also, the classification of producers/consumers and of herbivores/carnivores is based in students' preconceptions of size and ferocity.