PLZ WRITE AT LEAST A THREE SENTANCE LOGICAL SUMMARY FOR THIS PIECE OF TEXT Cells share common structural features, including an outer boundary called the cell membrane. The cell membrane encloses the cell and separates the cell interior, called the cytoplasm, from its surroundings. The cell membrane also regulates what enters and leaves a cell—including gases, nutrients, and wastes.
Movement across the cell membrane that does not require energy from the cell is called passive transport. One kind of passive transport, diffusion, is the movement of a substance from an area of high concentration to an area of lower concentration caused by the random motion of particles of the substance. The diffusion of water through a selectively permeable membrane is called osmosis. In facilitated diffusion, a carrier protein transports a substance across the cell membrane down the concentration gradient of the substance.
Active transport is the movement of a substance against the concentration gradient of the substance. Active transport requires cells to use energy. In animal cells, the sodium-potassium pump uses energy supplied by ATP to transport sodium ions out of the cell and potassium ions into the cell. During endocytosis, substances are moved into a cell by a vesicle that pinches off from the cell membrane. During exocytosis, substances inside a vesicle are released from a cell as the vesicle fuses with the cell membrane.