An increase in heart rate, blood pressure, and blood glucose concentration are all associated with stimulation of the:
Answer(s): B
The nervous system is divided into the peripheral nervous system and the central nervous system. The central nervous system consists of the brain and the spinal cord. The peripheral nervous system is divided into the sensory division and the motor division. The sensory division consists of those receptors and neurons that transmit signals to the central nervous system. The motor division transmits signals from the central nervous system to effectors, and is divided into the somatic nervous system and the autonomic nervous system. The somatic system, choice C, innervates skeletal muscle, and its nervous pathways are typically under voluntary control. The autonomic nervous system regulates the internal environment by way of involuntary nervous pathways. The autonomic nervous system innervates smooth muscle in blood vessels and the digestive tract, and innervates the heart, the respiratory system, the endocrine system, the excretory system, and the reproductive system. The autonomic system is further divided into the sympathetic division, choice B, and the parasympathetic division, choice A. The sympathetic division innervates those pathways that prepare the body for immediate action; this is known as the "fight-or-flight" response. Heart rate and blood pressure increase, blood vessels in the skin vasoconstrict and those in the heart vasodilate, pathways innervating the digestive tract are inhibited, and epinephrine, or adrenaline, is secreted by the adrenal medulla, thereby increasing the conversion of glycogen into glucose. Based on this discussion, it's obvious that the correct answer is choice B; activation of the sympathetic nervous system is associated with an increased heart rate, blood pressure, and blood glucose concentration. The parasympathetic system innervates nervous pathways that return the body to homeostatic conditions following exertion. Heart rate, blood pressure, and blood glucose concentration all decrease, blood vessels in the skin vasodilate and those in the heart vasoconstrict, and the digestive process is no longer inhibited.
Which of the following compounds share the same absolute configuration?
This question asks you to compare the absolute configurations of four compounds which are in the form of Fischer projections. There are certain rules which you need to be familiar with in order to decipher the absolute configuration. First, the substituent with the lowest priority must be positioned vertically, that is, either up or down. Remember that in 3-D terms, vertical lines represent bonds going into the page. Second, to move your diagram around on the page you have to remember that interchanging any two pairs of substituents will give you the same compound that is, it will preserve the absolute configuration. Interchanging just ONE pair of substituents will always REVERSE the absolute configuration. Also, you can hold one group steady while rotating the other three clockwise or counterclockwise. The third rule is that once you have the lowest-priority group positioned vertically, you should determine the order of priority among the other three substituents. If that order increases clockwise, that means the chiral carbon has an R configuration, while if it increases counterclockwise, the chiral carbon has an S configuration. If you look at compound I, you can see that the order of increasing priority is hydrogen, methyl, carboxyl, and hydroxyl. In order to get the hydrogen into a vertical position, you can hold the methyl group steady and rotate the others by 90°. The order of increasing priority is clockwise and so the configuration is R, for compound II, the hydrogen is already placed vertically, so you don't have to worry about moving the molecule around the page. The order of increasing priority is hydrogen, methyl, carboxyl and amine, so when you draw arrows between the last three, the direction is counterclockwise and so the configuration is S. Therefore, you can discard choice C since these two molecules have opposite configurations. Compound III may catch you off guard, because if you look at this molecule closely you can see that it is achiral. Although they are written differently, there are two ethyl substituents in this molecule, therefore this molecule is neither R nor S, and so choices A and D can be eliminated. This leaves choice B, but let's just look at compound IV anyway. Again, the hydrogen is positioned vertically and the order of priority is the same as in compound I). However, if you connect the arrows this time, you can see that the direction is counterclockwise and so the configuration is S. This makes compounds II and IV the same, and so choice B is correct.
Which of the following structures plays a role in both the male excretory and male reproductive systems, but in the female excretory system only?
Answer(s): C
This question tests your knowledge of the male and female reproductive and excretory systems, which, as you should know, are NOT identical in structure. The epididymis, choice A, is a group of coiled tubes sitting on top of the seminiferous tubules in the male reproductive tract. Sperm are produced in the seminiferous tubules and mature and acquire motility in the epididymis. Sperm are stored in the epididymis until ejaculation. Hence, the epididymis functions in the male reproductive system only; so choice A is wrong. Choice B, prostate, is one of the glands associated with the male reproductive tract; the prostate gland secretes and alkaline milky fluid that protects the sperm from the acidic conditions in the female reproductive tract. So, choice B also functions only in the male reproductive system, and is therefore incorrect. The urethra, choice C, is a structure found in both men and women. During ejaculation, sperm travels from the epididymis, through the vas deferens, and through the urethra, which opens to the outside from the tip of the penis. The urethra is also directly connected to the bladder. Hence, in males, the urethra functions in both the reproductive and excretory systems. In females, however, the reproductive and excretory systems do NOT share a common pathway. Sperm enter the vagina and travel up through the cervix, uterus, and fallopian tubes, and urine leaves the body through the urethra; the vagina and the urethra never meet they are SEPARATE openings. So, choice C is the right answer. Choice D, ureter, is the duct connecting the kidney to the bladder. Urine is formed in the kidneys, it travels down to the bladder by way of the ureters, and is stored there until it is excreted through the urethrA. This process is the same in both sexes.
The reaction R Br + Br* R Br* + Br is always accompanied by inversion. If this reaction is carried out on an optically pure sample of a chiral compound, which of the following statements will be true? [Note: Br* represents a radioactive isotope of bromine.]
Answer(s): A
This is another chemistry question about SN2 reactions and their effect on optical activity. Here you have to think about exactly what's happening as the stated reaction proceeds. Each time an alkyl halide molecule reacts, incorporating a radioactive bromine atom, it will be optically inverted; that is, it will go from R to S or vice versA. Each molecule thus inverted "cancels out" one of the molecules that still has the old configuration; thus each inversion event leads to the racemization of two molecules of alkyl halide. So the rate of radioactive bromine incorporation is equal to half of the rate of racemization, and so the correct answer is A.
Which of the following cell types does NOT contain the diploid number of chromosomes?
In males, diploid cells called spermatogonia undergo mitosis to produce diploid cells called primary spermatocytes. The primary spermatocytes undergo the first round of meiosis to yield secondary spermatocytes, which are haploid. The secondary spermatocytes undergo the second round of meiosis, resulting in four haploid cells called spermatids. The spermatids then mature into sperm the male gametes.So, choice A is incorrect because a spermatogonium is a diploid cell. And we've already found the correct answer choice B, spermatid, is NOT a diploid cell, it's haploid. Let's look at what happens in females anyway.In females, a diploid cell called a primary oocyte undergoes the first meiotic division to yield two haploid cells a polar body and a secondary oocyte. The secondary oocyte undergoes the second meiotic division to produce two more haploid cells a mature oocyte, or ovum, and another polar body. So, choice D, primary oocyte, is also incorrect because these are diploid cells. During fertilization, an ovum and a sperm fuse; two haploid cells fuse to form a single diploid cell called a zygote. Thus, choice C is also incorrect.
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