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Transcript
BIOLOGY Ch 4 Cells and their Environment Concentration of substances __________________ __________ Organisms maintain homeostasis by the movement of substances across the cell membrane. Cells may or may not use energy to move substances across the membrane. PASSIVE TRANSPORT It is the movement across the membrane that does not need energy Concentration gradient – is the difference in the concentration of a substance across space e.g. Two rooms with a door in between and balls being released from one room to the other Equilibrium – is the condition in which the concentration of a substance is the same across the space Diffusion – is the movement of a substance from a higher to lower concentration e.g. many molecules or ions dissolved in the cytoplasm or in the fluid outside cells enter or leave cells by diffusing across the cell membrane Types of membranes Permeable membranes – allow substances to pass through Impermeable membranes – do not allow substances to pass through Semi permeable membranes – allow only some substances to pass through Osmosis – is the diffusion of water through a semi permeable membrane Types of solutions Hypertonic Hypotonic Isotonic (Refer to picture at end of packet) CROSSING THE CELL MEMBRANE Transport proteins called channels provide polar passageways through which ions and polar molecules can move across the cell membrane. Diffusion through ion channels (Refer to picture at end of packet) Ion channels allow certain ions to pass through the cell membrane. They have gates which may open or close in response to some stimuli e.g. stretching of cell membrane, change in electrical charge, or binding of specific molecules to the ion channel e.g. Na +, Cl – Electrical charge and ion transport The inside of a cell is typically ______________________. Opposite charges ________________, Like charges ____________________. Facilitated diffusion (Refer to picture at end of packet) It is a type of passive transport Cell membrane has some _________________________ in channels that allow certain substances to be carried inside cell e..g _____________, _______________ ACTIVE TRANSPORT Cell moves materials in opposite direction against the concentration gradient and needs energy (i.e. from an area of low concentration to an area of higher concentration) Some carrier proteins are involved in active transport and they act as ____________ that move substances against their concentration gradients. e.g. Movement of Ca, K, Na ions Sodium Potassium Pump (Refer to picture at end of packet) Usually uses ATP to transports 3 sodium ions out of a cell and 2 potassium ions into a cell Why is the pump useful? Movement in Vesicles (Refer to picture at end of packet) Endocytosis – taking material into cells by means of infoldings or pockets of cell membrane e.g. proteins, polysaccharides Phagocytosis – Pinocytosis – Exocytosis- membrane surrounds material, fuses with the cell and forces content out of cell e.g. some proteins modified by golgi apparatus are exported in this way Membrane receptor proteins A Receptor protein is a protein that binds to a specific signal molecule and controls the opening and closing of ion channels Second messengers When they are activated, they act as signal molecules in the cytoplasm; they amplify the signal of the original signal molecule and also change the functioning of the cell in different ways e.g. activating enzymes, triggering some biochemical reactions in cell etc.