Supported by. Pat Tillman walked away from a lucrative career in the National Football League to join the military and fight in Afghanistan, where he was ultimately killed by friendly fire in an incident that was initially covered up.
A membrane-enclosed sac that is part of the endomembrane system of a eukaryotic cell, having diverse functions. central vacuole. A membrane-enclosed sac occupying most of the interior of a mature plant cell, having diverse roles in reproduction, growth, and development. peroxisome. sac made of membrane in the cytoplasm of a eukaryotic cell. endoplasmic reticulum (ER). An extensive membranous network in a eukaryotic cell, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.
Eukaryotic cells contain a nucleus and membrane-bound organelles. All multicellular organisms consist of eukaryotic cells. Eukaryotic cells are thought to have evolved from primitive single-celled prokaryotic cells. All cells are surrounded by a cell membrane (plasma membrane). The cell membrane is semipermeable, allowing some substances to pass into the cell and blocking others. It is composed of a double layer of phospholipids and embedded proteins. Plant cells have an additional layer surrounding them called the cell wall. The cell wall is made of nonliving material called cellulose. The centrosome (also called the microtubule organizing center) is a small body located near the nucleus. The centrosome is where microtubules are made.