B/B Reproduction

"Milk is an emulsion of fats, suspended in an aqueous solution. Milk fat is composed of a complex mixture of triglycerides, containing both saturated and unsaturated fatty acids. If fresh milk is allowed to stand undisturbed, the triglycerides form a separate layer on top. The major saturated fatty acid in milk is palmitic acid (31%) and the major unsaturated fatty acid is oleic acid (24%). Whole milk contains fats, proteins, carbohydrates, vitamins, and minerals. These components can be separated by taking advantage of differences in physical and chemical properties." Which of the following best explains the separation of triglycerides from whole milk? A. The triglycerides are denser than the remaining materials. B. The triglycerides are equally as dense as the remaining materials. C. The triglycerides are hydrophobic. D. The triglycerides are hydrophilic.

***triglyceride layer separates from the remaining aqueous solution, and forms a layer on top.* A. The triglycerides are denser than the remaining materials. Show Explanation B. The triglycerides are equally as dense as the remaining materials. Hide Explanation Paragraph 2 tells us that the triglyceride layer separates from the remaining aqueous solution, and forms a layer on top. If this layer is on top, then it must be less dense than the material in the aqueous layer. C.--- correct The triglycerides are hydrophobic. Hide Explanation If the triglycerides are hydrophobic, then they are not soluble in water and will separate from the aqueous layer (like oil and water). D. The triglycerides are hydrophilic. Hide Explanation Because of the long hydrocarbon tails of triglycerides (which are the fatty acids), they are not hydrophilic.

Oxytocin (Pitocin) is routinely administered to pregnant women during difficult labor. However, it can only be given when contractions have progressed to a certain point, or it will be ineffective. Why is this true? I. Oxytocin is normally not the initial stimulus for uterine contractions. II. Exogenous oxytocin reduces production of oxytocin by the pituitary due to negative feedback. III. Oxytocin and progesterone compete for the same receptor binding site.

-I chose Roman numeral 3 because I thought 1 (giving oxytocin) is the inducer of contractions. However for MCAT on the save side just know oxytocin that stimulates uterine contractions not labor. A.---correct I only Hide Explanation Oxytocin perpetuates labor by increasing uterine elasticity, which leads to stimulation of uterine stretch receptors. These positively feed back to the pituitary to increase oxytocin production. However, increasing uterine elasticity has no effect if the uterus is not already in the process of contracting. Interestingly, the initial signal for the induction of labor is still unknown. B.-Wrong III only Hide Explanation Oxytocin is a peptide hormone, while progesterone is a steroid. Even ignoring their completely different actions, it would be impossible for them to bind to the same receptor site (III).

At what time during development does an "embryo" become a "fetus"? A. 6 weeks B. 9 weeks C. 12 weeks D. 24 weeks

A. 6 weeks Hide Explanation An embryo becomes a fetus by definition at the 9th week of development. B. 9 weeks Hide Explanation An embryo becomes a fetus by definition at the 9th week of development. You must know the different developmental stages for an embryo and fetus. C. 12 weeks Hide Explanation An embryo becomes a fetus by definition at the 9th week of development. D. 24 weeks Hide Explanation An embryo becomes a fetus by definition at the 9th week of development.

Following the LH surge, progesterone remains elevated for the latter half of the menstrual cycle. Treatment with which of the following would most likely place a pregnant female in danger of miscarriage? A. A progesterone receptor agonist B. A progesterone receptor antagonist C. A FSH receptor agonist D. A FSH receptor antagonist

A. A progesterone receptor agonist Hide Explanation Progesterone must remain elevated to maintain the uterine endometrium and prevent contractions. A progesterone receptor agonist would support these objectives and would not disrupt the cycle to a degree significant enough to cause miscarriage. B.-- CORRECT A progesterone receptor antagonist Hide Explanation Progesterone must remain elevated to maintain the uterine endometrium and prevent contractions. Antagonizing its receptor would prevent progesterone from binding, likely leading to spontaneous abortion. C. A FSH receptor agonist Hide Explanation FSH remains low during the luteal phase and, therefore, is unlikely to play a significant role in maintaining pregnancy. D. A FSH receptor antagonist Hide Explanation FSH remains low during the luteal phase and, therefore, is unlikely to play a significant role in maintaining pregnancy.

Which reaction type would the researchers use to convert an unsaturated fatty acid into a saturated fatty acid? A. Acetylation B. Hydrogenation C. Elimination D. Substitution

A. Acetylation Hide Explanation Acetylation would result in more C-C bonds. B.--correct Hydrogenation Hide Explanation The passage gives an example of both a saturated and an unsaturated fatty acid, palmitic acid and oleic acid, respectively. The unsaturated fatty acid contains a carbon-carbon double bond, whereas the saturated fatty acid only has carbon-carbon single bonds. Addition of hydrogen to the carbon-carbon double bond would convert the unsaturated fatty acid into a saturated fatty acid, which often lowers the melting point. Hydrogenation is the addition of hydrogen to a carbon-carbon multiple bond. C. Elimination Hide Explanation Elimination would create additional C-C bonds. D. Substitution Hide Explanation Substitution would not alter the saturation of the acid.

The total amount of DNA is measured in various cells, all of which are participating in distinct stages of oogenesis. Amounts are reported as a percentage of values measured for a somatic cell in the G1 phase. Cell %of DNA 1 200 2 99 3 49 4 159 5 47 Which of the following statements is true? A. Cell 2 must be a primary oocyte. B. Cell 1 has yet to undergo any meiotic divisions. C. Cell 4 is a dark polar body. D. Cell 5 must be in an ovum.

A. Cell 2 must be a primary oocyte. Hide Explanation With this amount of DNA, Cell 2 could also be a primordial germ cell that has not yet differentiated into an oocyte. B.-- correct Cell 1 has yet to undergo any meiotic divisions. Hide Explanation The percentages of DNA are based on a comparison to a cell in the G1 phase, which would not yet have undergone replication. In comparison, a cell that has recently experienced replication will have twice the amount of DNA. C. Cell 4 is a dark polar body. Hide Explanation Polar bodies would have a total amount of DNA that is about 50% of a somatic cell in the G1 phase. D. Cell 5 must be in an ovum. Hide Explanation With this amount of DNA, Cell 5 could also be a first or second polar body.

Ciliopathy refers to a group of conditions in which cilia fail to form or function properly. Ciliopathy of motile cilia is a possible cause of dysfunction in which of the following organ systems? A. Digestive Show Explanation B. Reproductive Show Explanation C. Lymphatic Show Explanation D. Auditory

A. Digestive Hide Explanation The digestive system utilizes many different types of ciliated cells, but not motile cilia. B.--Correct Reproductive Hide Explanation The uterus relies on motile cilia in its epithelium to move the embryo from the ovary and Fallopian tubes. Dysfunction of these cilia can result in an ectopic pregnancy. Cilia are present on most cells of the body, but motile cilia that move under their own power are found only in the uterine lining and the trachea. C. Lymphatic Hide Explanation The lymphatic system utilizes cilia in its epithelial cells, but not motile cilia. D. Auditory Hide Explanation The auditory hair cells on the basilar membrane contain cilia, but not motile cilia.

At which time are estrogen levels lowest for a woman? A. During pregnancy B. Prior to ovulation C. During menstruation D. Just after ovulation

A. During pregnancy Hide Explanation Estrogen levels increase during pregnancy. B. Prior to ovulation Hide Explanation Estrogen levels are high just before ovulation. C.---correct During menstruation Hide Explanation Estrogen and progesterone help to build the uterine lining. During menstruation, estrogen and progesterone levels are low. D. Just after ovulation Hide Explanation While estrogen levels do decrease after ovulation, the estrogen levels are not as low as those during menstruation.

It is believed that a variety of factors, both genetic and environmental, interact to cause structural birth defects. These defects, such as spina bifida, oral clefts, and congenital heart defects, result from the complex influences that disrupt embryonic development. Which maternal factor(s) would increase the risk of developmental abnormalities in the embryo? A. Exposure to teratogens only B. Genotype only C. Heart disease only D. All of the above

A. Exposure to teratogens only Hide Explanation Maternal genotype and heart disease would also increase the risk of developmental abnormalities in the embryo. B. Genotype only Hide Explanation Maternal exposure to teratogens and heart disease would also increase the risk of developmental abnormalities in the embryo. C. Heart disease only Hide Explanation Maternal genotype and exposure to teratogens would also increase the risk of developmental abnormalities in the embryo. D.--- correct All of the above Hide Explanation Maternal exposure to teratogens, maternal genotype, and maternal disease all are environmental and genetic factors that could predispose an embryo to developmental abnormalities. Teratogens are chemical agents that may disturb the development of an embryo, such as medications, drugs, or chemicals. More vulnerable maternal genotypes or existing maternal conditions, such as heart disease, may also increase the risk of pathological development.

Which of the following structures are disrupted when a milk protein is placed in the animal bladder as described in the passage? I. Primary II. Secondary III. Tertiary IV. Quaternary

A. I and II only B. III and IV only C.--correct II, III, and IV only Hide Explanation The passage tells us that enzymes in the stomach were able to denature the milk proteins. Denaturation of proteins involves the disruption and destruction of both the secondary and tertiary structures. D. I, II, III and IV Hide Explanation Denaturation reactions are not strong enough to break th

A developing zygote is exposed to a drug that inhibits cell differentiation. Which developmental process is this drug most likely to impede? A. Intercalation B. Pattern formation C. Cell movement D. Organogenesis

A. Intercalation Hide Explanation Intercalation is the process by which cells move to create thin layers. Pattern formation is the organization of cells based on their position, and requires cell movement or migration. All of these options are related to cell position, not cell function. Consequently, they would not be directly affected if differentiation were stalled. B. Pattern formation Hide Explanation Intercalation is the process by which cells move to create thin layers. Pattern formation is the organization of cells based on their position, and requires cell movement or migration. All of these options are related to cell position, not cell function. Consequently, they would not be directly affected if differentiation were stalled. C. Cell movement Hide Explanation Intercalation is the process by which cells move to create thin layers. Pattern formation is the organization of cells based on their position, and requires cell movement or migration. All of these options are related to cell position, not cell function. Consequently, they would not be directly affected if differentiation were stalled. D.--- correct Organogenesis Hide Explanation Inhibiting differentiation would completely prevent organogenesis. Differentiation is the process by which stem cells mature into cells with specific functions. These clusters of differentiated cells give rise to organs and organ systems in organogenesis.

Below is a table that documents hormone levels throughout a typical menstrual cycle. Levels are reported as a percentage of the highest concentration observed for each hormone. Which of the four hormones peaks latest in the cycle? A. LH B. FSH C. Estrogen D. Progesterone

A. LH Hide Explanation LH peaks at day 14, earlier than progesterone. B. FSH Hide Explanation FSH peaks at day 7, the earliest of the hormones in the table. C. Estrogen Hide Explanation This answer choice results from comparing the data in the table at day 28 and picking the highest number. However, the question stem states that the table values reflect the percentage of the highest concentration, or peak, of each hormone, which is critical to interpreting the table. D.-- correct Progesterone Hide Explanation Of the four hormones listed, FSH peaks at 7 days, while LH and estrogen peak at 14. The peak for progesterone is not shown, but this hormone exists at low levels throughout the cycle, except for at day 21. Therefore, it can be assumed that the peak is either right before or right after this date. This is the latest peak of the four hormones.

The latter half of the menstrual cycle, shown below, is characterized by endometrial proliferation and vascularization. During the final days of the cycle, assuming implantation has not occurred, uterine contractions facilitate expulsion of the endometrium Which of the following hormones, if administered to a pregnant female, would be most effective in preventing pre-term birth? A. Oxytocin B. Prolactin C. Estrogen D. Progesterone

A. Oxytocin Hide Explanation Oxytocin actually stimulates uterine contractions, making it a poor choice for preventing labor. B. Prolactin Hide Explanation Prolactin levels do not increase until after birth. This implies that this hormone is unnecessary for maintaining pregnancy, and it likely has no effect on the uterine myometrium. C. Estrogen Hide Explanation Estrogen is also elevated during the luteal phase, but not nearly as much as progesterone. On the graph, it is represented by the second-highest line during the final week or so of the cycle. This suggests that progesterone is more instrumental in preventing contractions. D.---Correct Progesterone Hide Explanation D is correct. Progesterone is the dominant hormone during the luteal phase and is represented by the darkest line on the graph. The sudden drop in progesterone at the end of the luteal phase triggers uterine contractions, resulting in menses. In fact, progesterone also drops sharply just before parturition (birth), relieving the inhibition of uterine contractions that permitted the maintenance of pregnancy.

A scientist uses a radioactive label to mark the cells on the outside of a gastrula. The labeled cells are shown below as those drawn with bolded black lines. Following another 8 weeks of development and organogenesis, which of the following tissues would be labeled? A. Red blood cells, cardiac muscle, and gonads B. Lungs, thyroid, glands, mouth, and rectum C. Brain, skin, spinal cord, hair, and nails D. Skin, brain, sweat glands, eyes, and red blood cells

A. Red blood cells, cardiac muscle, and gonads Hide Explanation These tissues are derived from the mesoderm. B. Lungs, thyroid, glands, mouth, and rectum Hide Explanation These internal organs and linings are derived from the endoderm. C.---correct Brain, skin, spinal cord, hair, and nails Hide Explanation This question indicates that the ectoderm has been labeled, so all tissue derived from this layer should be labeled as well. The nervous system, skin, hair, and nails are all derived from the ectoderm. D. Skin, brain, sweat glands, eyes, and red blood cells Hide Explanation Although the skin, brain, and portions of the eye are derived from the ectoderm, erythrocytes arise from mesodermal tissue.

Meiosis typically produces four haploid cells. Why, then, does each primary oocyte give rise only to a single ovum? A. The remaining daughter cells, known as polar bodies, are small enough to allow the ovum to keep the majority of the original DNA. B. The remaining daughter cells, known as polar bodies, are small enough to allow the ovum to keep the majority of the original cytosol and organelles. C. A primary oocyte has already undergone one meiotic division. D. It doesn't; each primary oocyte gives rise to four mature ova.

A. The remaining daughter cells, known as polar bodies, are small enough to allow the ovum to keep the majority of the original DNA. Hide Explanation Oogenesis represents the unequal division of cytoplasm, not DNA. A polar body has no less DNA than an oocyte produced during the same division. B.-correct The remaining daughter cells, known as polar bodies, are small enough to allow the ovum to keep the majority of the original cytosol and organelles. Hide Explanation One round of oogenesis yields one ovum and multiple small, dark polar bodies. These "extra" cells later undergo apoptosis. As a result of this phenomenon, the ovum (which is very demanding of both nutrients and energy) is able to retain most of the original organelles and cytosol. C. A primary oocyte has already undergone one meiotic division. Hide Explanation Primary oocytes are those that have not yet completed meiosis I. D. It doesn't; each primary oocyte gives rise to four mature ova.

A clinical trial for an experimental form of birth control involves injecting patients with progestin, or synthetic progesterone. If a woman receives this injection during the early part of the follicular phase, and if its effects persist for approximately three weeks, what can be expected to occur? A. The woman's menstrual cycle will proceed as usual. B. The woman's blood will contain augmented levels of LH and FSH. C. The woman will not experience ovulation at the usual time. D. The woman will actually face an enhanced probability of becoming pregnant.

A. The woman's menstrual cycle will proceed as usual. Hide Explanation Persistently high progesterone levels near the beginning of the menstrual cycle will prevent this woman from ovulating - at least until the effects wear off. Therefore, her menstrual cycle will not proceed as usual. B. The woman's blood will contain augmented levels of LH and FSH. Hide Explanation LH and FSH levels should be low, not high. Since estrogen and progesterone secretion is promoted by both LH and FSH, a large progesterone concentration is a clear signal for the anterior pituitary to slow its release of these two hormones. C.---Correct The woman will not experience ovulation at the usual time. Hide Explanation Typically, estrogen and progesterone negatively feed back on gonadotropin-releasing hormone (GnRH). As a result, high levels of these steroids lead to reduced release of LH and FSH. As a surge in LH is required to stimulate ovulation, persistently high progesterone levels near the beginning of the menstrual cycle will prevent this woman from ovulating - at least until the effects wear off. D. The woman will actually face an enhanced probability of becoming pregnant. Hide Explanation Progestin is actually a very common and fairly effective form of birth control.

All cells in a developing organism are initially identical. However, during embryogenesis, they are able to differentiate into various cell types and localize using positional information. This phenomenon, known as pattern formation, requires all of the following EXCEPT: A. cell-signaling pathways B. maternal growth factors. C. a morphogen gradient. D. cell-to-cell communication.

A. cell-signaling pathways Hide Explanation Signaling pathways allow a cell to communicate with itself and neighboring cells to coordinate cellular fate. This is critical for pattern formation. B.--Correct maternal growth factors. Hide Explanation In healthy developing organisms, maternal growth factors do not pass through the placenta. Thus, they play no role in pattern formation. C. a morphogen gradient. Hide Explanation A morphogen gradient does form across a developing embryo. This gradient signals cells regarding their relative positions, which is essential for position-based differentiation. D. cell-to-cell communication. Hide Explanation Signaling pathways allow a cell to communicate with itself and neighboring cells to coordinate cellular fate. This is critical for pattern formation.

The single diploid cell formed when an ovum is fertilized by a spermatozoon is known as a(n): A. embryo B. zygote C. morula D. gastrula

A. embryo Hide Explanation An embryo is a multicellular organism with developing organ systems. The question specifies that the answer should be single-celled. B.--- correct zygote Hide Explanation A zygote is formed by the fusion of gametes (one sperm and one ovum). As both gametes are haploid, fusion results in a single, diploid cell. C. morula Hide Explanation Following the formation of the zygote, four cell divisions occur with no significant growth. The resulting ball of cells is known as the morula, which is not unicellular. D. gastrula Hide Explanation A gastrula is a collection of cells containing three germ layers; these will develop and differentiate into organs during organogenesis. The question refers to a much earlier stage of development.

Oxytocin, secreted by the posterior pituitary, increases the contractility and elasticity of the uterine wall. As a result, uterine contractions continue, eventually culminating in parturition (birth). Oxytocin production is most directly induced by: A. progesterone secretion. B. hCG secretion. C. uterine contraction. D. placental detachment.

A. progesterone secretion. Hide Explanation Progesterone secretion drops markedly just prior to the onset of parturition. It does not play a stimulatory role in uterine contractions or oxytocin secretion. B. hCG secretion. Hide Explanation hCG only remains high during the first trimester of pregnancy. It would provide no stimulatory effects during the third trimester. C.--correct uterine contraction. Hide Explanation C is correct. Parturition is one of the rare examples of a positive feedback loop. Stimulation of oxytocin receptors located in the uterine wall increase uterine elasticity, which causes increased uterine stretch during subsequent contractions. This stimulates stretch receptors that feed back to the posterior pituitary gland to trigger more oxytocin production. D. placental detachment. Hide Explanation In a healthy pregnancy, the placenta detaches from the endometrium soon after fetal delivery.

In a healthy intrauterine pregnancy, fertilization occurs in the: A. uterine endometrium Show Explanation B. uterine myometrium. Show Explanation C. Fallopian tube. Show Explanation D. vaginal canal.

A. uterine endometrium Hide Explanation This answer choice is incorrect. B. uterine myometrium. Hide Explanation This answer choice is incorrect. C.---correct Fallopian tube. Hide Explanation C is correct. The sperm and oocyte meet in the Fallopian tube. The zygote continues to travel down the tube until it reaches the uterus. Implantation occurs in the uterine endometrium. D. vaginal canal. Hide Explanation This answer choice is incorrect.

Which of the following hormones is LEAST likely to significantly affect a lactating woman's production of milk? A. Epinephrine B. Progesterone C. Estrogen D. Oxytocin

A.--- correct Epinephrine Hide Explanation We are looking for the hormone that does not affect milk production. Epinephrine, or adrenaline, is a fight or flight hormone released by the adrenal gland, which does not significantly affect milk production. B. Progesterone Hide Explanation High levels of estrogen and progesterone inhibit the production of milk. Estrogen and progesterone levels drop after birth, helping stimulate the production of milk. C. Estrogen Hide Explanation High levels of estrogen and progesterone inhibit the production of milk. Estrogen and progesterone levels drop after birth, helping stimulate the production of milk. D. Oxytocin Hide Explanation Oxytocin causes the contraction of smooth muscles in the uterus during labor and is essential for the release of milk.

Activin is a small signaling protein with a number of biological roles. One of its functions involves the increase of FSH binding to the FSH receptor in the developing follicle. In males, an activin receptor agonist is most likely to cause: A. increased spermatogenesis B. decreased spermatogenesis. C. desensitization of Leydig cells. D. desensitization of Sertoli cells.

A.--- correct increased spermatogenesis Hide Explanation A is correct. Activin essentially magnifies the effects of FSH on its target cells. In males, FSH acts on Sertoli cells to stimulate spermatogenesis. An activin receptor agonist is a molecule that stimulates the activin receptor, exactly like endogenous activin. B. decreased spermatogenesis. Hide Explanation This answer choice is incorrect. C. desensitization of Leydig cells. Hide Explanation According to the question, activin has a sensitizing effect. In other words, the normal effects of FSH are increased in the presence of activin. D. desensitization of Sertoli cells. Hide Explanation According to the question, activin has a sensitizing effect. In other words, the normal effects of FSH are increased in the presence of activin.

Which of the following enzymes is involved in the in vivohydrolysis of peptide bonds? A. Pepsin B. Amylase C. Hexokinase D. Lactase

A.----Correct Pepsin Hide Explanation Pepsin is an enzyme released in the stomach that catabolizes proteins to smaller peptides and amino acids, which is the reaction of interest in this question. B. Amylase Hide Explanation Amylase is an enzyme that catalyzes the hydrolysis of starches to sugars and is produced by the salivary glands and pancreas. C. Hexokinase Hide Explanation Hexokinase is an enzyme that catalyzes the phosphorylation of sugars. D. Lactase Hide Explanation Lactase is an enzyme that catalyzes the hydrolysis of lactose to glucose and galactose.

What path does sperm take from production to ejaculation? A. Seminiferous tubules → epididymis → vas deferens → ejaculatory duct → urethra → penis B. Seminiferous tubules → ejaculatory duct → vas deferens → epididymis → urethra → penis C. Epididymis → seminiferous tubules → vas deferens → ejaculatory duct → urethra → penis D. Vas deferens → seminiferous tubules → epididymis → ejaculatory duct → urethra → penis

A.---correct Seminiferous tubules → epididymis → vas deferens → ejaculatory duct → urethra → penis Hide Explanation Make sure to know this pathway for the MCAT. B. Seminiferous tubules → ejaculatory duct → vas deferens → epididymis → urethra → penis Hide Explanation This answer choice mixes up the sperm pathway. C. Epididymis → seminiferous tubules → vas deferens → ejaculatory duct → urethra → penis Hide Explanation This answer choice mixes up the sperm pathway. D. Vas deferens → seminiferous tubules → epididymis → ejaculatory duct → urethra → penis Hide Explanation This answer choice mixes up the sperm pathway.

Which of the following hormone levels peaks just prior to ovulation? A. LH B. FSH C. Progesterone D. Estrogen

A.--correct LH Hide Explanation This peak, known as the LH surge, triggers ovulation. Note that LH refers to luteinizing hormone, while FSH refers to follicle-stimulating hormone. B. FSH Hide Explanation While there is a slight increase in follicle stimulating hormone (FSH) just prior to ovulation, it is not what triggers ovulation and it is very small in comparison to the peak in luteinizing hormone (LH). C. Progesterone Hide Explanation Progesterone is produced by the corpus luteum and its levels are highest during the luteal phase after ovulation. D. Estrogen Hide Explanation While estrogen levels are high just prior to ovulation, this is not what triggers ovulation; estrogen levels are lower in comparison to the peak in luteinizing hormone (LH).

After numerous unsuccessful attempts to breed a male rabbit, a researcher decides to examine its sperm under a microscope. He finds that the sperm cells have normal tails and healthy motility. What is the most likely issue? A. The digestive enzymes in the acrosomes have been modified and are no longer functional. B. The sperm are no longer able to release toxins that kill the other sperm and allow for fertilization. C. The sperm do not have enough mitochondria to remain warm outside of the body. D. The sperm are unable to produce enough ATP to remain properly mobile.

A.--correct The digestive enzymes in the acrosomes have been modified and are no longer functional. Hide Explanation The digestive enzymes in the acrosome are used to dissolve the protective coating on the ovum, allowing the sperm cell to enter and fertilize. Of the options given, this is the only reasonable choice. B. The sperm are no longer able to release toxins that kill the other sperm and allow for fertilization. Hide Explanation Toxins that kill other sperm only reduce the rate of fertilization, so the absence of this toxin would not likely lead to unsuccessful attempts at fertilization. C. The sperm do not have enough mitochondria to remain warm outside of the body. Hide Explanation Reduced mitochondria in the sperm cells would also lead to low motility, as the energy generated by mitochondria is what drives flagellum action for sperm motility. However, the question stem states that the sperm cells have healthy motility, so they must have normal levels of mitochondria. D. The sperm are unable to produce enough ATP to remain properly mobile. Hide Explanation The question stem states that the sperm cells have healthy motility.

The hormone levels of a 31-year-old female patient were tracked during the course of a typical menstrual cycle. The table below graphs this data; note that hormone concentrations are given in standardized units per milliliter of blood. Assuming that this patient is healthy, what most directly triggered the peak in progesterone around day 21? A. High levels of estrogen Show Explanation B. High levels of LH Show Explanation C. Fertilization of the ovum and resulting pregnancy Show Explanation D. Formation of the corpus luteum after ovulation

Assuming that this patient is healthy, what most directly triggered the peak in progesterone around day 21? A. High levels of estrogen Hide Explanation This choice is too indirect. High estrogen levels briefly take part in a positive feedback mechanism, promoting the surge in LH that stimulates ovulation. But it is the formation of the corpus luteum that directly affects progesterone levels. B. High levels of LH Hide Explanation This offers a roundabout explanation. High levels of LH play a role in the initiation of ovulation, but not as directly as the formation of the corpus luteum after ovulation. C. Fertilization of the ovum and resulting pregnancy Hide Explanation If this patient were pregnant, her progesterone levels would remain high through day 28 and beyond. D.----Correct Formation of the corpus luteum after ovulation Hide Explanation The table shows that progesterone concentrations are low throughout the cycle, with the exception of a peak around day 21. This increase is promoted by ovulation, in which a follicle bursts and releases a secondary oocyte. The remainder of the follicle gives rise to the corpus luteum, which directly releases progesterone and estradiol. Once the egg is released, the corpus luteum forms and begins producing progesterone. Progesterone helps to prepare the body for pregnancy by stimulating glandular development and the development of new blood vessels. This provides a good environment for implantation by a fertilized egg.

Below is a table that documents hormone levels throughout a typical menstrual cycle. Levels are reported as a percentage of the highest concentration observed for each hormone. How would the results change if fertilization and implantation had occurred? A. Estrogen levels would have remained high. B. Progesterone levels would have remained high. C. FSH levels would have remained high. D. Both A and B are correct.

Basically what hormones willl be high after fertilization and implantation. A. Estrogen levels would have remained high. B. Progesterone levels would have remained high. C. FSH levels would have remained high. D. Both A and B are correct. Hide Explanation Following implantation of the fertilized egg, hCG is released. This hormone mimics LH to stimulate high levels of estrogen and progesterone. Similarly, it is the drop in estrogen and progesterone which triggers a new cycle to begin.

"Cottage cheese can be prepared by adding vinegar to milk, which denatures the protein casein (pI = 4.6). The coagulation of casein traps some of the milk fat and aqueous soluble components, like lactose, within the curd. The resulting whey contains lactose and additional proteins, like lactalbumin, as well as minerals that remain soluble in the mildly acidic aqueous solution. Neutralizing and heating the whey denatures any remaining proteins, which can be filtered after cooling the solution. The lactose in the remaining aqueous solution can be separated from the minerals by evaporating the water to produce a super-saturated solution of lactose." If the lactose solution produced during cottage cheese production is poured into a beaker and then a glass rod is inserted into the beaker and swirled slowly, which of the following will occur? A. Dissolution of lactose B. Crystallization of lactose C. Precipitation of casein D. Dissolution of casein

Cryystallization=Supersaturation A. Dissolution of lactose Hide Explanation Though swirling and mixing can help speed up dissolution of solutes in a solvent, the lactose is already dissolved in the solution when the glass rod is inserted and swirled. B.---correct Crystallization of lactose Hide Explanation The last paragraph tells us that the lactose solution is supersaturated. Supersaturation is a state where a solution contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. If a supersaturated system is perturbed, the excess solute will crystallize (i.e. precipitate) out of solution and onto the glass rod. C. Precipitation of casein Hide Explanation Casein is not a part of this solution. According to the passage, it was denatured by the addition of vinegar early in the process, trapping it in the curds and removing it from the solution. D. Dissolution of casein Hide Explanation Casein is not a part of this solution. According to the passage, it was denatured by the addition of vinegar early in the process, trapping it in the curds and removing it from the solution.

During human embryogenesis, limbs develop from limb buds. A scientist has discovered that he can specify which limb (arm or leg) that a bud differentiates into by: A. expressing different limb-specific transcription factors. B. changing the anterior-posterior patterning. C. changing the dorsal-ventral patterning. D. Dissecting and reattaching limb buds

DONT SECOND GUESS YOURSELF A.--- CORRECT expressing different limb-specific transcription factors. Hide Explanation The scientist has exploited pattern formation to specify which limb arises from a particular bud. While cells in the limb buds receive the same signals, they are interpreted differently to specify the limb that actually forms. This requires limb-specific transcription factors, which activate the transcription of specific genes to initiate differentiation. B. changing the anterior-posterior patterning. Hide Explanation Although changing the poles or zone of polarizing activity may seem sufficient at first, there is no indication that it will directly affect the cell's interpretation of the signals. Similarly, dissecting and reattaching the limb buds may not change the preexisting signaling pathways occurring in the developing embryo. C. changing the dorsal-ventral patterning. Hide Explanation Although changing the poles or zone of polarizing activity may seem sufficient at first, there is no indication that it will directly affect the cell's interpretation of the signals. Similarly, dissecting and reattaching the limb buds may not change the preexisting signaling pathways occurring in the developing embryo. D. Dissecting and reattaching limb buds Hide Explanation Although changing the poles or zone of polarizing activity may seem sufficient at first, there is no indication that it will directly affect the cell's interpretation of the signals. Similarly, dissecting and reattaching the limb buds may not change the preexisting signaling pathways occurring in the developing embryo.

What is the net charge of casein at a pH of 4.6? A. -4.6 B. -1 C. 0 D. +1

GOOD ONE- When PH=isoelectric point NO NET CHARGE A. -4.6 Hide Explanation Casein will have no overall charge when the pH of the environment is 4.6. B. -1 Hide Explanation Casein will have no overall charge when the pH of the environment is 4.6. C.- correct 0 Hide Explanation We are told in the passage that the pI for casein is 4.6. The isoelectric point is the pH at which a protein or amino acid has no net charge (it is a neutral zwitterion). Thus, casein will have no overall charge when the pH of the environment is 4.6. D. +1 Hide Explanation Casein will have no overall charge when the pH of the environment is 4.6.

The structure of Bisphenol A (BPA) is shown below. Controversy still exists regarding the endocrine effects of this molecule. Many believe that it causes precocious puberty in females, which is defined as the development of secondary sexual characteristics before the age of 8. Assuming these claims are true, the structure and function of BPA most closely resemble: A. luteinizing hormone. B. follicle-stimulating hormone. C. human chorionic gonadotropin. D. estrogen

Google BPA cause I thought secondary characteristics was the keywords for estrogen, could be though so keep it in mind!! A. luteinizing hormone. Hide Explanation This answer choice is incorrect. B. follicle-stimulating hormone. Hide Explanation This answer choice is incorrect. C. human chorionic gonadotropin. Hide Explanation hCG does have effects similar to LH, but it is also a peptide hormone. D.-correct estrogen Hide Explanation D is correct. Although FSH and LH both increase dramatically during the onset of puberty, they are both peptide hormones and do not at all resemble the structure of BPA. BPA is a small molecule with multiple six-membered rings, so it is reasonable to assume that it could mimic estrogen in vivo.

During the first weeks after fertilization, hCG levels can increase by a factor of over 10,000. However, excessively high hCG has been associated with multiple complications. Endometrial cells treated with high concentrations of the hormone display excessive apoptosis of CD8+ T cells. Pregnant females with abnormally high hCG are most likely at risk for the development of: A. placenta percreta, a condition in which the placenta invades the uterine myometrium. Show Explanation B. spontaneous abortion during the first trimester, caused by inadequate trophoblast implantation. Show Explanation C. eclampsia, a seizure disorder that has been linked to exposure to novel paternal antigens. Show Explanation D. endometriosis, the growth of normal uterine endometrial tissue in abnormal locations such as the Fallopian tubes.

I chose C because I seen "excessive apoptosis of CD8+ T cells." so my thought process was CD8+ = helper T cells. However I should be thinking what is the purpose of HCG- helps maintain the corpus luteum, which secretes progesterone until the placenta takes over. The only answer that states placenta is A. However if I need to eliminate A.---Correct placenta percreta, a condition in which the placenta invades the uterine myometrium. Hide Explanation A is correct. The question informs us that hCG has a suppressive effect on T cells, which are responsible for controlling the presence of foreign cells. A substantial portion of the placenta develops from embryonic tissue, which is immunologically foreign to the maternal immune system. Although a complex mechanism exists to facilitate immunological tolerance of the fetus during pregnancy, it requires proper CD8+ T cell activity. Inactivation of the maternal immune system could result in unchecked placental infiltration through the myometrium. Normally, the placenta does not contact the myometrium at all and is restricted to the endometrial layer. B. spontaneous abortion during the first trimester, caused by inadequate trophoblast implantation. Hide Explanation Inadequate trophoblast implantation has a number of causes. However, excessive hCG is more likely to facilitate implantation. C. eclampsia, a seizure disorder that has been linked to exposure to novel paternal antigens. Hide Explanation Inappropriate reactions to harmless antigens occur due to an overactive immune system. If anything, hCG-mediated suppression of T cell activity would decrease the likelihood of eclampsia developing. D. endometriosis, the growth of normal uterine endometrial tissue in abnormal locations such as the Fallopian tubes. Hide Explanation This choice mentions that the overgrown tissue is "normal," implying that T cells are not responsible for controlling its activity. T cells only recognize foreign cells, and normally would never respond to cells displaying a "self" antigenic profile.

Although in utero conditions can dramatically alter the course of fetal development, the rate of spontaneous DNA damage that occurs within the haploid oocyte is remarkably low. Which of the following, if true, constitutes a possible explanation for this finding? I. The oocyte travels along the tube encased in a layer of metabolically-active maternal cells derived from the ovarian follicle. II. The oocyte contains sufficient nutrients to nurture the embryo during the first zygotic divisions. III. Oocyte chromatin displays a higher degree of supercoiling than that of most other known mammalian cell types.

I chose Roman numeral 2 but basically nutrients isn't strong enough to hell with DNA loss. So MCAT w/o outside knowledge is asking what would help this cell's DNA to be protected. A. I only Hide Explanation This answer choice is incorrect. B. II only Hide Explanation II: Available nutrients do not reduce the risk involved in the extremely active process of zygotic division. C. I and III Hide Explanation C is correct. DNA damage can result from free radical activity generated by normal cellular reactions. This is why rapidly dividing cells often become cancerous. Any options that mitigate the metabolic load on the oocyte will help to preserve the integrity of its DNA. The oocyte is, in fact, surrounded by maternal follicular cells, which synthesize most of its required proteins and other molecules. These cells are expendable and gradually disintegrate as the oocyte travels down the tube. Supercoiling reduces base pair exposure to the nuclear environment, lowering the chances of damage. D. I, II, and III Hide Explanation II: Available nutrients do not reduce the risk involved in the extremely active process of zygotic division.

Along with many other effects, surgical lesion of the anterior pituitary in an adult male would likely cause which of the following? A. Increased serum testosterone B. Increased GnRH production C. Increased spermatogenesis D. Increased osteogenesis

Remember GnRh is secreted by the hypothalamus and it signals the anterior pituitary to secrete FSH and LH to perform its functions. This is all regulated by negative feedback so if lesion there..... A. Increased serum testosterone Hide Explanation Testosterone production is stimulated by LH action on Leydig cells in the testes. Without LH production, synthesis of testosterone is likely to drop dramatically. B.--- correct Increased GnRH production Hide Explanation B is correct. Like most hormone axes in the body, the hypothalamic-pituitary axis is subject to negative feedback. A pituitary lesion will reduce or eliminate the secretion of FSH and LH. GnRH-secreting neurons in the hypothalamus will respond to this drop in serum hormone levels by increasing GnRH secretion. C. Increased spermatogenesis Hide Explanation Spermatogenesis is promoted by the action of FSH on the testes' Sertoli cells. When FSH production is limited, spermatogenesis is likely to decrease. D. Increased osteogenesis Hide Explanation This answer choice is incorrect.

Seminal vesicle dysfunction in males will most likely result in: A. reduced fertility. Show Explanation B. increased susceptibility to urinary tract infections. Show Explanation C. decreased spermatogenesis. Show Explanation D. malformation of spermatozoa.

Seminal vesicle(accessory gland; aids in producing seminal fluid) dysfunction in males will most likely result in: A.---Correct reduced fertility. Hide Explanation A is correct. Sperm require relatively alkaline conditions to survive, but the vaginal tract is generally acidic. The seminal vesicles produce a basic solution to neutralize the vaginal pH and permit the survival of sperm. Dysfunctional seminal vesicles will reduce the chances of fertilization. B. increased susceptibility to urinary tract infections. Hide Explanation Seminal fluid is released only during ejaculation, and does not play any part in establishing the baseline genitourinary environment. Males are less susceptible to urinary tract infections simply because the male urethra is longer. C. decreased spermatogenesis. Hide Explanation Sperm production and maturation occur in the testes and epididymis, respectively. These structures are anatomically and functionally separate from the seminal vesicles. D. malformation of spermatozoa. Hide Explanation Sperm production and maturation occur in the testes and epididymis, respectively. These structures are anatomically and functionally separate from the seminal vesicles.

Spina bifida, or cleft spine, is a birth defect caused by incomplete neurulation and resulting in nerve damage. This condition is the product of the improper development of the: A. ectodermal germ layer. B. endodermal germ layer. C. mesodermal germ layer. D. diploblasmal germ layer.

Spina bifida, or cleft spine, is a birth defect caused by incomplete neurulation and resulting in nerve damage. This condition is the product of the improper development of the: A.--correct ectodermal germ layer. Hide Explanation The question states that spina bifida is a result of improper neurulation. Nervous tissue is derived from the ectoderm. B. endodermal germ layer. Hide Explanation The endoderm is the most internal layer; it forms the linings of many organs but does not relate to neurulation. C. mesodermal germ layer. Hide Explanation The mesoderm is the middle germ layer. Blood, muscle, and kidney cells, among others, are derived from the mesoderm. D. diploblasmal germ layer.

Order the stages of development from fertilization to organogenesis. A. Blastula, zygote, morula, gastrula B. Zygote, blastula, morula, gastrula C. Morula, blastula, gastrula, zygote D. Zygote, morula, blastula, gastrula

Stupid mistake what is the fertilized diploid cell called? When the egg meets sperm D. Zygote, morula, blastula, gastrula Hide Explanation The diploid cell produced by fertilization is known as a zygote. Following multiple divisions with no cell growth, the ball of cells becomes known as the morula. Further division results in the blastula, a compact, hollow collection of cells. Finally, an invagination into this structure results in three tissues layers, and the developing organism is now called the gastrula.