Complex sentence: In biology, a hotbed is a pile of decaying organic matter warmer than its surroundings due to the heat given off by the metabolism of the microorganisms in the decomposing pile.
Split into simpler sentences: In biology, a hotbed is a pile of decaying organic matter that is warmer than its surroundings. This is due to the heat given off by the metabolism of the microorganisms in the decomposing pile.