Transport mechanisms of the cell

The cell does not allow everything to come in and out making it selectively permeable. A concentration gradient are molecules moving from high to low concentration until equilibrium is reached. When we reach that equilibrium molecules still move at a constant rate in and out of the cell. Diffusion and osmosis are both types of passive transport; Passive transport is movement of molecules without energy. In passive transport, we have no energy use, molecules just move from high to low. Simple diffusion it is just diffusion across the cell membrane. Osmosis is the movement of water from high to low concentration. In Isotonic, the cell is isolated, it does not change its shape and it stays the same size, water moves in and out of the cell at the same rate. The cell shrinks in a hypertonic solution and the cell grows in a hypotonic solution. Cytolysis is the bursting of a cell. During plasmolysis the cell shrinks. During facilitated diffusion, molecules are transported with the help of carrier proteins. Molecules come into a carrier protein and once it binds to it, it changes its shape and it moves the other side. Ion channels are pores that allow ions to pass; Ions open when an electrical current tells it to or when a chemical signal happens. Energy is required during active transport because we need to move the molecules from an area of low to high concentration and it uses energy in the form of ATP. ATP is the fuel that makes the engine go inside the cell. One active pump known as the sodium potassium pump creates a high concentration of both sodium and potassium inside and outside the cell, which makes the cell charged (Na+, K+). Nerve cells move through an electrical current so they need that charge in order for it to happen. In our sodium-potassium pump, three sodium ions bind from inside the cell onto a carrier protein. An ATP comes in and binds to the to the carrier protein to provide energy and as a result the shape of the carrier protein changes causing the 3 NA+ ions to be released out of the cell. This creates a situation of high affinity where potassium wants to bind to the carrier protein as well. Two K+ come in and bind causing the shape of the carrier protein to change again allowing K+ inside the cell. Endocytosis needs energy (ATP) to function properly (substances, usually a molecule, enters the cell via a vesicle. In phagocytosis (cell devourer) and pinocytosis, molecules come in, bind to the cell membrane, the membrane pinches around it, and the food particle then gets sent wherever it needs to go. Same thing in pinocytosis, which is liquid, it requires energy and it is a way to transport things in and out of the cell. White blood cells are known to engulf bacteria through these vesicles. In exocytosis, we have substances exit the cell via vesicles.