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.
Both eukaryotic cells, including plant cells and animal cells, and prokaryotic cells, e.g. bacteria, are enclosed by a cell membrane. A cell membrane (see the simple diagram on the right) is a thin structure that is also known as the plasma membrane.The main functions of the cell membrane are: The cell membrane forms a barrier between the inside of the cell and the environment outside the cell-enclosing cytoplasm and any organelles within the cell, and enabling different chemical environments to exist on each side of the cell membrane.