1.16 Active Transport and Bulk Transport

Energy, Cells, and ATP ATP – adenosine triphosphate; a compound used as a source of energy in cells When ATP releases a phosphate, energy is produced

Active Transport Active Transport – the movement of substances through a membrane against a concentration gradient using carrier proteins and ATP Against the concentration gradient means that it moves from an area of [low] to [high]

Sodium-potassium pump – an active transport mechanism that pumps Na+ and K+ ions into and out of a cell Without this pump, your nerve and muscle cells won’t function properly Pumps require ATP to operate

Bulk Transport The movement of large quantities of materials into or out of the cell

Endocytosis Brings large amounts of material into the cell from the extracellular fluid

There are two forms of endocytosis: 1. Phagocytosis – bulk transport of solids into the cell The cell membrane sends out finger-like projections called pseudopods that surround and enclose the particle in a vesicle that is within the cell’s cytoplasm Such a vesicle is called a phagocytotic vesicle Macrophages use this to engulf harmful bacteria 2. Pinocytosis – bulk transport of liquids into the cell Pinocytotic vesicle – a vesicle that is formed when cells engulf extracellular fluid by pinocytosis

Exocytosis The movement of large amounts of material out of a cell by secretory vesicles Secretory vesicles – the membrane sac containing substances that are transported out of a cell The secretory vesicle fuses with the cell membrane and spills its contents into the extracellular fluid Proteins produced in the rough endoplasmic reticulum are packaged into secretory vesicles by the Golgi apparatus and are transported out of the cell by exocytosis

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