Just like other organism, plants come in many different sizes. There are very small plants and very large ones. For example, you can only see tiny ferns with a microscope; in contrast, you cannot see the top of some of the giant redwood trees in northern California that grow to more than 100 meters. Plants also have some structural features in common with other organism. Like other living things, plants are made up of cells that have a cell membrane, cytoplasm, and a nucleus. One difference is that plant cells also have a thick, rigid cell wall that surrounds the membrane. These cell walls give the plant structure and support, and allow it to grow straight and tall. Cell walls also help protect the cells.