A cell that is 98% water is placed in 50% salt water. This cell will
A. shrink.
B. swell.
C. shrink and then swell.
D. remain the same size.
A. shrink.
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A number of systems for pumping ions across membranes are powered by ATP. Such ATP-powered pumps are often called ATPases, although they do not often hydrolyze ATP unless they are simultaneously transporting ions
Because small increases in calcium ions in the cytosol can trigger a number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a resting muscle cell's cytosol has a free calcium ion concentration of 10-7 while the concentration in the SR is 10-2, then how is the ATPase acting? A) ATPase activity must be powering an inflow of calcium from the outside of the cell into the SR. B) ATPase activity must be transferring i to the SR to enable this to occur. C) ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient. D) ATPase activity must be opening a channel for the calcium ions to diffuse back into the SR along the concentration gradient. E) ATPase activity must be routing calcium ions from the SR to the cytosol, and then to the cell's environment.
When two excitatory postsynaptic potentials (EPSPs) occur at a single synapse so rapidly in succession that the postsynaptic neuron's membrane potential has not returned to the resting potential before the second EPSP arrives,
the EPSPs add together producing _____. A) temporal summation B) spatial summation C) tetanus D) the refractory state E) an action potential with an abnormally high peak of depolarization
Gene targeting:a
usually results in mice homozygous for the knock-out gene in every cell. b. is used to study orthologous genes. c. measures gene expression activity. d. is a rapid process. e. is a technique typically performed in humans.
Ammonia, which is a byproduct of protein metabolism, is converted to __________ primarily in the __________.
a. ketones? liver b. ketones? kidney c. urea? kidney d. urea? liver