Presenter notes: Ask the class to put a hand on their chest and find the beat, then ask a question nobody expects: why does an amoeba not need one of these? Give it a moment. Then widen it. A sponge does not need a heart either. Nor does a hydra, which is far bigger than an amoeba. So a heart is clearly not something every animal needs, and the interesting question for today is not what a heart does but who has to have one and why. Tell them that by the end of the period they will be able to look at an animal they have never studied and predict its transport system.