Membrane Transport Worksheet (Answers)

Membrane Transport Types of Transport Outline the two key qualities of plasma membranes Semi-permeability (some things can cross the membrane, other things can’t cross) 1. …………………………………………………………………………………………………………………………………………………... Selectivity (cells can control the passage of certain materials across the membrane) 2. …………………………………………………………………………………………………………………………………………………... Distinguish between passive transport and active transport Passive Transport Active Transport Movement from a region of high concentration to a ………………………………………………………………………… Movement from a region of low concentration to a ………………………………………………………………………… region of lower concentration (along a gradient) ………………………………………………………………………… region of higher concentration (against a gradient) ………………………………………………………………………… Does not require the expenditure of ATP ………………………………………………………………………… Requires the expenditure of ATP ………………………………………………………………………… E.g. simple diffusion, facilitated diffusion, osmosis ………………………………………………………………………… Also requires membrane proteins (protein pumps) ………………………………………………………………………… Passive Transport Define simple diffusion The net movement of particles from a region of high concentration to a region of low concentration ………………………………………………………………………………………………………………………………………………….......... (until equilibrium is reached) ………………………………………………………………………………………………………………………………………………….......... Describe the process of facilitated diffusion • Facilitated diffusion is a passive transport mechanism ……………………………………………………………………………… for materials that cannot freely cross the membrane ……………………………………………………………………………… ……………………………………………………………………………… • Large and charged substances cannot freely cross the ……………………………………………………………………………… hydrophobic bilayer (e.g. ions, macromolecules) ……………………………………………………………………………… ……………………………………………………………………………… • Membrane proteins may include: ……………………………………………………………………………… - Channel proteins (form a hydrophilic pore) ……………………………………………………………………………… - Carrier proteins (translocate substances) ……………………………………………………………………………… List three molecules that are transported by simple diffusion and facilitated diffusion oxygen, carbon dioxide, lipophilic substances (e.g. steroids) Simple Diffusion: ……...……………………………………………………………………………………………………………….......... Ions (e.g. sodium, potassium, etc.), macromolecules (glucose, starch, etc.) Facilitated Diffusion: …………………...…………………………………………………………………………………………….......... Describe how the structure of the potassium channel facilitates diffusion in nerve cells Integral proteins with a hydrophilic inner pore via which potassium ions may be transported ………………………………………………………………………………………………………………………………………………….......... Inner pore contains a selectivity filter in order to restrict the passage of alternative ions ………………………………………………………………………………………………………………………………………………….......... Channels adopt an open / closed conformation based on: ………………………………………………………………………………………………………………………………………………….......... • Membrane polarity (voltage-gated) ………………………………………………………………………………………………………………………………………………….......... • Binding of neurotransmitter (ligand-gated) ………………………………………………………………………………………………………………………………………………….......... Osmosis Describe the relationship between solutes and solvents in a solution A solute is a substance that is dissolved in a solvent ………………………………………………………………………………………………………………………………………………….......... Due to it’s polarity, water is often termed the ‘universal solvent’ (but won’t dissolve non-polar molecules) ………………………………………………………………………………………………………………………………………………….......... Define osmosis The net movement of free water molecules across a semi-permeable membrane from a region of low solute ………………………………………………………………………………………………………………………………………………….......... concentration to a region of high solute concentration, until equilibrium is reached ………………………………………………………………………………………………………………………………………………….......... Differentiate between hypertonic, hypotonic and isotonic solutions Solute Concentration Effect on Cell Hypertonic Higher solute concentration (relatively) Water flows out of cell (into hypertonic) Hypotonic Lower solute concentration (relatively) Water flows into cell (from hypotonic) Isotonic Equal solute concentration (relatively) No net water movement Define osmolarity Osmolarity is a measure of solute concentration, as defined by osmol/L ………………………………………………………………………………………………………………………………………………….......... Explain why the osmolarity of a solution affects animal cells and plant cells differently • Plant cells have a rigid cell wall which prevents uncontrolled osmosis ………………………………………………………………………………………………………………………………………………….......... • Plant cells may swell (become turgid), but they cannot burst or rupture (lyse) like animal cells ………………………………………………………………………………………………………………………………………………….......... • Equally, the cell membrane may shrink from the cell wall (plasmolysis), but overall structure remains intact ………………………………………………………………………………………………………………………………………………….......... Active Transport Distinguish between primary (direct) active transport and secondary (indirect) active transport Direct Active Transport (Primary): ATP hydrolysis is used to mediate transport by causing a conformational ………………………………………………………………………………………………………………………………………………….......... change in the protein pump (thereby translocating the molecule against the gradient) ………………………………………………………………………………………………………………………………………………….......... Indirect Active Transport (Secondary): Transport is coupled to another molecule moving along an ………………………………………………………………………………………………………………………………………………….......... electrochemical gradient (cotransport) ………………………………………………………………………………………………………………………………………………….......... Describe how the structure of the sodium-potassium pump enables active transport in nerve cells Three sodium ions attach to intracellular binding sites on the protein pump ………………………………………………………………………………………………………………………………………………….......... ATP hydrolysis phosphorylates the pump and changes its conformation ………………………………………………………………………………………………………………………………………………….......... Sodium ions are translocated and released from the cell, exposing extracellular binding sites for potassium ………………………………………………………………………………………………………………………………………………….......... Two potassium ions attach to these sites and the pump is dephosphorylated ………………………………………………………………………………………………………………………………………………….......... This returns the pump to its original conformation, internalising the potassium ions ………………………………………………………………………………………………………………………………………………….......... Vesicular / Bulk Transport Outline the role of vesicles in the transport of materials between organelles Polypeptides destined for secretion are synthesised by ribosomes on rough ER ………………………………………………………………………………………………………………………………………………….......... They are transported to the Golgi body via vesicles (formed from the ER membrane) ………………………………………………………………………………………………………………………………………………….......... The Golgi body will potentially sort, store and modify these secretory products ………………………………………………………………………………………………………………………………………………….......... The proteins are then transported by another vesicle to the cell membrane for secretion (exocytosis) ………………………………………………………………………………………………………………………………………………….......... External materials can be internalised into cellular vesicles via endocytosis (for digestion by lysosomes) ………………………………………………………………………………………………………………………………………………….......... Use the diagram below to explain the process of endocytosis Endocytosis is the process by which large substances (or bulk amounts of smaller substances) enter the cell ………………………………………………………………………………………………………………………………………………….......... without crossing the membrane ………………………………………………………………………………………………………………………………………………….......... An invagination of the membrane forms a flask-like depression which envelopes the extracellular material ………………………………………………………………………………………………………………………………………………….......... The invagination is then sealed off to form an intracellular vesicle containing the material ………………………………………………………………………………………………………………………………………………….......... Differentiate between phagocytosis and pinocytosis Phagocytosis: The process by which solid substances (e.g. food particles, foreign pathogens) are ingested ………………………………………………………………………………………………………………………………………………….......... (usually to be transported to the lysosome for break down) ………………………………………………………………………………………………………………………………………………….......... Pinocytosis: The process by which liquids / solutions (e.g. dissolved substances) are ingested by the cell ………………………………………………………………………………………………………………………………………………….......... (allows quick entry for large amounts of substance) ………………………………………………………………………………………………………………………………………………….......... ………………………………………………………………………………………………………………………………………………….......... Use the diagram below to explain the process of exocytosis The process by which large substances (or bulk amounts of small substances) exit the cell without crossing ………………………………………………………………………………………………………………………………………………….......... the membrane ………………………………………………………………………………………………………………………………………………….......... Vesicles fuse with the plasma membrane, expelling their contents into the extracellular environment ………………………………………………………………………………………………………………………………………………….......... Exocytosis adds vesicular phospholipids to the cell membrane, replacing those lost via endocytosis …………………………………………………………………………………………………………………………………………………..........