A cell is the smallest unit of living matter that can exist by itself. Some organisms, such as bacteria, are made up of only one single cell. As for other organisms, such as humans and redwood trees, billions of cells are required. That means that those multitudinous cells have to work together to enable people to do things such as walk, talk, and eat, and for trees to send down roots, sprout branches, and grow leaves. Readers of this authoritative book will discover how such cells function, get energy, grow, reproduce, specialize, and communicate.