4. Identify two type of endocytosis and explain how they work to transport molecules across the cell membrane
Two types of endocytosis are phagocytosis and pinocytosis.
1. Phagocytosis: Phagocytosis is a process in which solid particles are engulfed by the cell. It is mainly performed by specialized cells called phagocytes, such as macrophages and neutrophils. The process involves the formation of pseudopods, which are extensions of the cell membrane that surround and engulf the particle. Once the particle is fully enclosed in a membrane-bound vesicle called a phagosome, it fuses with lysosomes containing digestive enzymes. The lysosomes then break down the particle, allowing the cell to extract the necessary molecules.
2. Pinocytosis: Pinocytosis, also known as cell drinking, is a process in which the cell engulfs liquid droplets or small dissolved substances. It occurs in almost all cells and is a non-selective process, meaning it takes in bulk fluids and various molecules present in the extracellular fluid. During pinocytosis, the cell forms small intions in its membrane known as caveolae. These caveolae then pinch off into the cytoplasm, forming small vesicles called pinosomes. The pinosomes then fuse with endosomes, where the molecules can be sorted and transported to different parts of the cell.
Both phagocytosis and pinocytosis play vital roles in bringing essential molecules into the cell and maintaining cellular homeostasis.