In an atom that is NOT an ion, which of the following must be true?
A. The number of electrons equals the number of protons.
B. The number of electrons equals the number of neutrons.
C. The number of protons equals the number of neutrons.
Answer: A
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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.
As summer comes to the tundra, what will
occur?
a. A long growing season will begin. b. The surface layer will thaw and pools of water will form. c. The permafrost thaws out. d. Birds will begin their southerly migration. e. more than one of these
When membrane lipids are extracted from cells and used to prepare artificial lipid bilayers, cholesterol and sphingolipids tend to self-assemble into ________ that are more gelated and highly ordered than surrounding regions consisting primarily of _________.
a) microdomains, integral proteins b) microdomains, phosphoglycerides c) liquid crystals, microdomains d) liquid crystals, phosphoglycerides e) macrodomains, phosphoglycerides
How would you test to see whether a particular influenza vaccine protects elderly people from influenza?
A. Conclude that elderly people are less likely to be hospitalized or die following vaccination. B. Follow tens of thousands of people over the age of 65 during flu seasons and record illnesses and vaccination status. C. Notice the rise in vaccination rates among the elderly over a period of years. D. Speculate that elderly people who were immunized will have fewer hospital stays and deaths during the winter after vaccination.