Life as We KnoW it Carbon is one of the most important chemical elements Chemical elements are the building blocks for all matter They are basic substances that cannot be broken down into simpler substances Scientists use symbols to stand for the chemical elements The symbol for carbon is C On its own carbon makes up only a small part of Earth’s crust But it combines with other elements very easily to form substances called compounds Carbon compounds make up 18 percent of all the matter in living things Graphite is one of the forms of pure carbon that can be found in nature It is used to make the leads of pencils 4
Living things are all around us You are a living thing So are animals and plants Living things move grow and take in chemicals and nutrients Vocabulary A cycle is a series of events or actions that repeat regularly Carbon is constantly being used and replaced in nature through what is known as the carbon cycle Carbon passes through living things as well as through Earth’s rocks water and air Sometimes it moves very quickly while other times it can stay in one place for many years All living things including people and other animals are part of the carbon cycle 5
Carbon reservoirs Earth has many carbon reservoirs or places where carbon exists in large amounts Carbon is found in Earth’s hydrosphere waters atmosphere the layer of gases surrounding the planet lithosphere rocky outer layer and biosphere where life happens Without carbon life as we know it would not exist All plants and animals are made of tissues These tissues are built of elements grouped around chains This northern flicker’s tissues contain carbon So do the tissues of the saguaro cactus in which the bird lives 6
Humans and plants exchange carbon dioxide People breathe it out while plants absorb it or rings made of carbon atoms Living Compare and Contrast How are animals and plants similar How are they different things produce carbon dioxide People and other animals breathe out the carbon dioxide they make Plants take in more carbon dioxide than they produce They use it in photosynthesis the process in which they make their own food Photosynthesis requires sunlight chlorophyll a substance in plants and certain algae water and carbon dioxide It produces oxygen and carbon compounds called sugars which plants use and store as food People and other animals breathe in oxygen and depend on the sugars plants make for food 7
