A scientist measuring the rate of uptake of radiolabeled alanine by cultured cells finds that rates are faster when the experiments are carried out in a buffered, balanced salts solution than when the experiments are carried out in a complete (containing all nutrients required for survival and growth) medium. The most likely explanation for this observation is
a. the concentration gradient for alanine is steeper in the former case than the latter.
b. the crenation (shrinkage of cells) in the salts solution increases the surface area-to-volume ratio for the cells increasing the rate of diffusion.
c. the absence of amino acids in the balanced salts solution decreases the abundance of molecules competing for transport, and therefore increases the apparent transport rate.
d. the temperature of the balanced salt solution is higher, so rates of transport are greater.
e. no response provides a valid answer.
C
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The evolution of a true brain (superganglion) occurred in
a. animals with radial symmetry. b. animals with bilateral symmetry c. cnidarians. d. echinoderms. e. all animals having symmetry.
Regarding the set point of a negative feedback loop, which of the following statements is false?
It is determined by the activity of effectors. Regulatory mechanisms are activated when there are deviations from the set point. Sensors are activated by deviations from the set point. Internal conditions vary around the set point.
The main ligament supporting the lateral aspect of the elbow is the
A. annular ligament. B. ulnar collateral ligament. C. radial collateral ligament. D. ulnar condylar ligament. E. lateral cruciate ligament.
The iliopubic tract is the thickened inferior margin of which of the following structures?
(A) inguinal ligament (B) transversalis fascia (C) conjoined tendon (D) falciform ligament (E) round ligament