Question 1 (1998)- Cells transport substances across their membranes. Choose THREE of the following four types of cellular transport. Osmosis Active transport Facilitated diffusion Endocytosis/exocytosis For each of the three transport types you choose, a) describe the transport process and explain how the organization of cell membranes functions in the movement of specific molecules across the membrane; and b) explain the significance of each type of transport to a specific cell (you may use different cell types as examples.) Osmosis (Max 4) a) DESCRIPTION OF PROCESS •movement of water from: high to low water concentration a) STRUCTURE/FUNCTION •high to low water potential •Aquaporins •high to low osmotic potential •phospholipid bilayer allowspassage of small/ uncharged/polar molecules allow passage b) EXAMPLE/specific cell type • Any legitimate link of water passage to cell function Animal cells: • can cause lysis • can cause shriveling to high solute concentration • in •low Plant cells: •low to high osmotic pressure • diffusion of water · passive and/or not require cellular energy kidney (nephron) cells: allows for osmoregulation · provides water for photosynthesis · can create turgor · can cause plasmolysis · in guard cells: allows control of stomatal opening · in root hairs: allows water uptake Active Transport (Max 4) a) DESCRIPTION OF PROCESS · movement of molecules/ions against their gradient · cellular energy required i.e. ATP; NADH; NADPH a) STRUCTURE/FUNCTION · proteins act as carriers and/or pumps · protein conformation changes b) EXAMPLE/specific cell type · Any legitimate link of passage to cell function Animal cell examples: · Na+/K+ pumps: establish polarity assist in repolarization · assist in glucose transport · Ca++ pumps allow uptake for muscle contraction · allow uptake for neurotransmitter release Plant cell examples: · K+ pumps regulate turgor establish polarity · H+ pumps permit sucrose loading in phloem · Any specific cell example: generate H+ gradient Facilitated Diffusion (Max 4) a) DESCRIPTION OF PROCESS · mediated movement of molecules/ solutes/ ions/ substances along their gradient · passive transport/ does not require cellular energy a) STRUCTURE/FUNCTION · proteins act as carriers of large and/or charged molecules · ion channels transport ions · protein conformation changes b) EXAMPLE/specific cell type · Any legitimate link of passage to cell function Animal cell examples: · Cl- ion channels assist cardiac repolarization · Ca++ ion channels assist neurotransmitter release assist muscle fiber contraction Bacterial cells/ mitochondria/ chloroplasts Any specific cell examples: · porins create permeability to small molecules · Na+; K+; (ion) channels help establish polarity · carrier proteins assist amino acid transport assist sugar transport ENDOCYTOSIS/EXOCYTOSIS (Max 4) a) DESCRIPTION OF a) STRUCTURE/FUNCTION PROCESS Endocytosis (including · Membrane fluidity/ phagocytosis and pinocytosis) solubility/fusion allows vesicles to join membrane · transport of substance into cell via vesicle formation · clathrin and non-clathrin and/or membrane folding coated pits allow specificity e.g.: engulf/ invaginate/ · external/internal envelope/ pinch in monolayers ("sidedness") · transport of substance into allow fusion cell via vesicle formation may · cytoskeleton is involved be receptor-mediated EXOCYTOSIS · transport of substance out of cell via vesicle fusion · Both require energy b) EXAMPLE/specific cell type · Any legitimate link of passage to cell function Examples: · protists: for nutrition · mast cells: for secretion of histamines · liver cells: for LDL/cholesterol uptake · Golgi & ER form vesicles for · export of cell products secretion · uptake of specific substances · growth [addition of cell membrane] Scoring: · Bulleted items earn points · Each mode of transport earns a maximum of 4 points. There is an internal maximum of one point per category (a1, a2,b). · One additional point may be earned from any one category for discussion of a second bulleted item or an elegant elaboration.