Two Minute Endurance

City buses move far more people than private cars using the same amount of road space. A single bus lane can carry thousands of passengers each hour, while a normal lane carries only a few hundred. That is why many cities now paint dedicated lanes, add raised platforms, and give buses priority at traffic lights. Every cell in your body runs on tiny structures called mitochondria. They take sugar and oxygen and turn them into usable energy. Muscle cells that work hard, such as those in the heart, contain far more mitochondria than cells that rest most of the day. Training increases their number, which is one reason exercise makes daily effort feel easier. Light from the Sun needs about eight minutes to reach the Earth. When you look at the sky, you are always looking into the past. The nearest star after the Sun is more than four light years away, so its light left long before you woke up this morning. Distance in space is measured in time as much as in kilometers.