Which of the following statements is true?
(a) Amoebae have transporter proteins that actively pump water molecules from the cytoplasm to the cell exterior.
(b) Bacteria and animal cells rely on the Na+-K+ pump in the plasma membrane to prevent lysis resulting from osmotic imbalances.
(c) The Na+-K+ pump allows animal cells to thrive under conditions of very low ionic strength.
(d) The Na+-K+ pump helps to keep both Na+ and Cl– ions out of the cell.
(d) The Na+-K+ pump keeps Na+out directly by pumping it out and keeps Cl–out indirectly by helping to maintain the negative membrane potential. Cells do not have pumps for moving water molecules across the membrane [choice (a)], since the lipid bilayer is permeable to water. Bacteria do not have Na+-K+ pumps in their plasma membranes [choice (b)]. The Na+-K+ pump cannot directly remove water molecules from the cell; it helps maintain osmotic balance by pumping out the Na+ that leaks in, which would not help if the cell were in a solution of very low ionic strength [choice (c)].
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a. 25 b. 50 c. 75 d. 100
A change in a population that is NOT related
strictly to the size of the population is best described as
a. density-dependent. b. density-independent. c. biotic. d. logistic. e. exponential
The following drawing represents simultaneous transcription and translation in E. coli
Answer the questions below the drawing. The arrow gives the direction of the RNA polymerase. (a) Is the letter A nearer the 5' or the 3' end of the molecule? (b) Is the letter B nearer the 5' or the 3' end of the molecule? (c) Is the letter C nearer the 5' or the 3' end of the tRNA molecule? (d) What is the "S" value for the large rRNA that is closest to the letter D? (e) Which terminus (N or C) of the growing polypeptide chain is nearer to the letter E?
Which of the following is a hominin?
A. Chimpanzee B. Australopithecus C. Baboon D. Bonobo E. Gorilla