In Plants vs. Zombies, the player takes on the role of a homeowner whose house is constantly under attack by zombies from a cemetery located across the street. To protect the house from zombies, the player must plant plants that damage or otherwise harm the advancing enemies. As the level progresses, the player collects "sun" units, which, when possessed by a certain number, allow the player to plant a particular plant. Zombies approach the house in several parallel lines running across the lawn near the house, requiring the player to plant plants on all of these lines. If at least one zombie reaches the end of its line, the level is lost .