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Unformatted text preview: to the cells and tissues (which are
dehydrated and therefore have a more negative
water potential than the drink). Note: Many sports
drinks are isotonic. Depending on the level of
dehydration involved, these drinks are more
effective when diluted. 7. (a) Water will move into the cells and they will burst
(b) The cells would lose water and the plasma
membrane would crinkle up (crenulate).
(c) Water will move into the cells and they will burst
(lyse). 8. Malarial parasite: Isotonic to blood. Ion Pumps (page 27)
1. ATP (directly or indirectly) supplies the energy to
move substances against their concentration gradient. 2. (a) Cotransport describes coupling the movement of
a molecule (such as sucrose or glucose) against
its concentration gradient to the diffusion of an ion
(e.g. H+ or Na+) down its concentration gradient.
Note: An energy requiring ion exchange pump is
used to establish this concentration gradient.
(b) In the gut, a gradient in sodium ions is used
to drive the transport of glucose across the
epithelium. A Na+/K+ pump (requiring ATP)
establishes an unequal concentration of Na+
across the membrane. A specific membrane
protein then couples the return of Na+ down its
concentration gradient to the transport of glucose
(at a rate that is higher than could occur by
(c) The glucose then diffuses from the epithelial
cells of the gut into the blood stream, where it is
transported away. This maintains a low level in the
intestinal epithelial cells. 3. Extracellular accumulation of Na+ (any two of):
– maintains the gradient that is used to cotransport
useful molecules, such as glucose, into cells.
– maintains cell volume by creating an osmotic
gradient that drives the absorption of water
– establishes and maintains resting potential in
nerve and muscle cells
– provides the driving force for several facilitated
membrane transport proteins (k) Name: Cytoskeleton
Location: Throughout cytoplasm
Function: Provides structure and shape to a cell,
responsible for cell movement (e.g. during muscle
contraction), and provides intracellular transport of
organelles and other structures.
Visible under LM: No Passive Transport Processes (page 25)
1. (a) Large surface area
(b) Thin membrane 2. (a) and (b) any of:
– Molecules always move down a concentration
gradient (from high to low c...
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- Winter '13