Biology/ Ecology Sample Questions Yeast digests sugar and creates a gas. Where are the more complex molecules in this situation? Where are the less complex molecules? What gas is formed? How can we test our inference about what this gas is? How do we know a bird needs energy? Where does a bird get the energy it needs? A seed grows into a tree. Much of the mass of the tree is Carbon. Where did this Carbon come from? Draw a diagram labeling the less complex molecules and the more complex molecules in this situation.