Things change: the weather, plants and animals. Living things change as they develop. For example, a seed grows into a plant, a baby human grows into an adult, and a caterpillar turns into a very different form as an adult butterfl y or moth. Non-living things change too. For instance, in certain circumstances, water can change to a solid, ice, or a gas. Items can also join together to change into a new substance. If different substances are mixed together, such as sand and water, they can be separated by various methods such as fi ltering. Some things change when something happens to them and cannot be changed back. A cooked egg for instance is white round the yolk, compared to its yellowish see-through colour uncooked. However, some materials can change back into the substance they were before. For example, ice can change back into water when heated. Sounds change as does the light around us.