<P> Lysosomes carry out intracellular digestion, in a process called phagocytosis (from the Greek phagein, to eat and kytos, vessel, referring here to the cell), by fusing with a vacuole and releasing their enzymes into the vacuole . Through this process, sugars, amino acids, and other monomers pass into the cytosol and become nutrients for the cell . Lysosomes also use their hydrolytic enzymes to recycle the cell's obsolete organelles in a process called autophagy . The lysosome engulfs another organelle and uses its enzymes to take apart the ingested material . The resulting organic monomers are then returned to the cytosol for reuse . The last function of a lysosome is to digest the cell itself through autolysis . </P> <P> The spitzenkörper is a component of the endomembrane system found only in fungi, and is associated with hyphal tip growth . It is a phase - dark body that is composed of an aggregation of membrane - bound vesicles containing cell wall components, serving as a point of assemblage and release of such components intermediate between the Golgi and the cell membrane . The spitzenkörper is motile and generates new hyphal tip growth as it moves forward . </P> <P> The plasma membrane is a phospholipid bilayer membrane that separates the cell from its environment and regulates the transport of molecules and signals into and out of the cell . Embedded in the membrane are proteins that perform the functions of the plasma membrane . The plasma membrane is not a fixed or rigid structure, the molecules that compose the membrane are capable of lateral movement . This movement and the multiple components of the membrane are why it is referred to as a fluid mosaic . Smaller molecules such as carbon dioxide, water, and oxygen can pass through the plasma membrane freely by diffusion or osmosis . Larger molecules needed by the cell are assisted by proteins through active transport . </P> <P> The plasma membrane of a cell has multiple functions . These include transporting nutrients into the cell, allowing waste to leave, preventing materials from entering the cell, averting needed materials from leaving the cell, maintaining the pH of the cytosol, and preserving the osmotic pressure of the cytosol . Transport proteins which allow some materials to pass through but not others are used for these functions . These proteins use ATP hydrolysis to pump materials against their concentration gradients . </P>

Where are calcium ions stored in the endomembrane system