Free Test Prep MCAT Exam Questions

Which of the following cell types does NOT contain the diploid number of chromosomes?Section: Biological Sciences  

All of the following are true regarding the function of neurons EXCEPT:Section: Biological Sciences 

Nitric oxide, NO, has recently been found to have widespread physiological effects, acting as a major regulatorin the nervous, cardiovascular, and immune systems. The production of NO in the body is regulated by specificNOS enzymes which exist in at least three different isoforms – bNOS, eNOS, and macNOS. Each of theseisoforms differ in location and function and serve to mediate different physiological responses to NO. Somephysiological roles of NO have been demonstrated as follows:I. In the central nervous system, NO production is regulated by bNOS. Calcium ion concentrations of 200-400nM in the central nervous system activate bNOS to catalyze the formation of NO. NO exerts definite effects onbrain function although its specific roles are not well established. bNOS inhibitors have been found to block therelease of neurotransmitter from presynaptic neurons. Excess levels of NO are also thought to contribute toneurodegenerative disorders such as Alzheimer’s disease.II. In the blood vessels, NO is produced by eNOS which is activated by Ca2+ concentrations of 200-400 nM. NOacts as the major endogenous vasodilator in blood vessels. It diffuses into smooth muscle cells and leads tomuscle relaxation by stimulating cGMP formation through activation of guanylyl cyclase. In addition, NOregulates the vascular system by inhibiting platelet aggregation and adhesion.III. The role of NO in the immune system is regulated by macNOS through a pathway that is not Ca2+dependent. Rather, exposure to cytokines, including interleukin-1 and interferon- γ, leads to synthesis of largeamounts of NO by activation of macNOS in response to inflammatory stimuli. The NO produced plays adefinitive role in the mediation of the activities of macrophages and neutrophils. NO also acts to inhibit themechanism of viral replication.A “knock out” mouse with a mutant bNOS protein was generated by recombination techniques. The mutantprotein was identical to the wild-type protein except for the identity of amino acid 675; the mutated bNOS hasTryptophan instead of Cysteine at position 675. Which of the following is responsible for the mutant protein?Section: Biological Sciences 

The amount of lactic acid in muscles rises when they start lacking: Section: Biological Sciences 

For the last two decades many earth scientists have supported the notion that the Mediterranean was once ahuge, dry desert, lying 3,000 meters below sea level. This “death valley” was thought to have existed at the endof Miocene time, about 6 to 5.5 million years ago……From a geological point of view, the Mediterranean is a tectonically mobile land-enclosed depression – small(about 3,000,000 square kilometers) in comparison to the major world oceans…Immediately obvious on allcharts is the highly variable topography and relief of both the seafloor and adjacent borderland. The coastline ishighly irregular and continental shelves, though generally narrow, are well developed off the major river deltas(Nile, Rhone, Po, and Ebro). Moreover, the deep-sea basins and trenches have distinctive relief, with basinplains ranging in depth from less than 1,000 meters to more than 4,000…Observation that rocks dredgedoffshore are similar to those on land raised a fundamental concept – the key to understanding Mediterraneanhistory lies in the adjacent emerged land masses, and vice-versa……Early paleographic reconstructions showed that the once-open communication with the Atlantic deterioratedduring the upper Miocene. Water-mass exchange continued for a while in the Rif Strait, but then ceasedcompletely prior to the beginning of the Pliocene……High relief near what is now the Strait of Gibraltar served as a barrier to the exchange of waters with theAtlantic. Exposed to a hot and dry climate, water evaporated and the then-dry basin elicited comparison with agigantic Death Valley…Microfossil studies suggested that the depth of the Mediterranean basin at these timeshad been “deep.” Estimates suggested a dry seafloor as far as 2,000 meters below ocean level… As aresponse to suddenly lowered sea level, rivers feeding the Mediterranean and canyons on the now-dry seafloorbegan a geologically dramatic phase of erosion. Deep, Grand Canyon-like gorges of the Nile and Rhone rivers,presently buried on land, were apparently cut during a great drawdown of water – when the Mediterranean floorlay exposed 1,000 meters or more below its present level…The sudden flooding through a gigantic waterfall atGibraltar drowned the exposed basin floor. These falls would have been 1,000 times bigger than NiagaraFalls…This flooding event is recorded by the Miocene Pliocene boundary, a time when open marine faunalassemblages were suddenly reintroduced from the Atlantic……Geological theories usually fall at a glacial pace into a sea of controversy, and this one is no exception. Today– charging that proof for the theory is lacking – many scientists believe that the Med always contained saltwater,with only the depth of the seafloor and the water being in question… Some of the tenets on which the theorywas formulated are, if not defective, very seriously in question. To interpret their findings, a respectable numberof geologists studying the surrounding emerged borderland as well as subsea sections indicate that alternative,more comprehensive concepts must be envisioned……It is not realistic to envision the Mediterranean seafloor of about 5 million years ago as a desert at 3,000meters below present ocean level. Several years ago…the Mediterranean [was compared] to a complexpicture-puzzle that comprises numerous intricate pieces, many of which are already in place. A general imageis emerging, although gaps in some areas of the picture remain fuzzy and indistinct.All of the following are features of the “desert theory” EXCEPT: