Chapter 3

Scientists who look for life outside Earth have a favorite candidate for an element that could take on the role that carbon does here on Earth. The element is silicon, which has 14 electrons, compared to carbon's 6. Based on the rules of chemical bonding you learned about last chapter, why should silicon's electron number make it a candidate for a central biological element?

One piece of advice that nutritionists give today is to favor complex carbohydrates, such as those found in wholegrain bread, over simple carbohydrates, such as those found in soft drinks. One reason for this is that simple sugars result in "spikes" in blood sugar levels, while complex carbohydrates usually do not. Why should the two kinds of carbohydrates differ in this regard?