Problem Statement: Using new media in the teaching - learning process, especially when complex subjects are treated, has recently become very important. Among the various new media environments, computer simulations have a special value, as they offer high potential for interactive learning. Combining a high degree of clearness and autonomy, computer simulations are expected to support learners both cognitively and emotionally, and thus lead to increased learning gains. In order to convey complex biological subject matter, this study used a computer simulation and evaluated its effects with regard to cognitive and motivational learning characteristics. The focus was on knowledge gain as a cognitive learning characteristic and interest as a motivational learning characteristic.