Biology Practice Questions

Which hormone is most responsible for ovulation? A. Progesterone B. LH C. FSH D. Estrogen

B. Luteinizing Hormone LH and FSH surge during ovulation (LH peak higher), during midcycle

At what stage of the sliding filament cycle is ATP hydrolyzed? A. Resetting the myosin head to bind actin again B. Release of actin C. Binding of the myosin head to actin D. During the power stroke

A ATP is hydrolyzed into ADP & Pi when the myosin-heads are reset to their high-energy conformation (choice A is correct). The myosin heads are now ready to bind actin; ATP has already been hydrolyzed & ADP is bound to myosin (choice C is wrong). The power stroke occurs when myosin (now bound to actin) returns to its low-energy conformation; no ATP is needed to do this (choice D is wrong). ATP binding (but not hydrolysis) is required in order to release actin from the myosin heads and start the cycle over (choice B is wrong).

Which of the following characteristics are true concerning cardiac muscle? I. It is striated. II. It acts as a functional syncytium. III. It is under the control of the autonomic nervous system. A. I, II, and III B. II only C. I only D. II and III only

A Cardiac muscle contains essentially the same organization of actin/myosin myofilaments found in skeletal muscle that give this tissue a striated appearance under the microscope (Item I is true). Although cardiac muscle is not a true syncytium, w/ more than one nucleus per cell, it is a functional syncytium since neighboring cells are linked by gap junctions that communicate action potentials directly from the cytoplasm of one cell to another (Item II is true). Stimulation by the sympathetic system increases the heart rate, while parasympathetic stimulation decreases the heart rate (Item III is true).

A block in prophase II of spermatogenesis would result in: A. limited numbers of spermatids. B. a decreased population of secondary spermatocytes. C. an accumulation of primary spermatocytes. D. increased gamete migration from the seminiferous tubule basement membrane to its lumen.

A. A block in prophase II of spermatogenesis would mean that the secondary spermatocytes could not complete meiosis II & would accumulate (choice B is wrong). This would lead to fewer spermatids (choice A is correct). Since spermatogenesis would be decreased, there would be less gamete migration from the seminiferous tubule basement membrane to its lumen (choice D is wrong). Finally, primary spermatocytes are the cells going through meiosis I, not meiosis II. Since the block is in meiosis II (i.e. after the primary spermatocytes have become secondary spermatocytes), the number of primary spermatocytes should be unaffected (choice C is wrong).

A mother just gave birth to a child and directly experienced the effects of oxytocin. What are the possible effects of oxytocin? I. A decrease in oxytocin causes labor to begin. II. Once labor begins, the posterior pituitary increases secretion of oxytocin which causes increased uterine contractions. III. Oxytocin facilitates milk let-down for breastfeeding. A. II and III only B. I, II, and III C. III only D. I and II only

A. A mother just gave birth to a child & directly experienced the effects of oxytocin. The possible effects of oxytocin are II and III only. I. A decrease in oxytocin causes labor to begin. II. Once labor begins, the posterior pituitary increases secretion of oxytocin which causes increased uterine contractions. III. Oxytocin facilitates milk let-down for breastfeeding. Item I is false: It is a drop in progesterone, not oxytocin, that causes labor to begin (choices with Item I can be eliminated). Since both remaining answer choices include Item III, Item III must be true and you can focus on Item II. Item II is true: Once labor begins, the secretion of oxytocin by the posterior pituitary is increased via a positive feedback mechanism, and this functions to increase the intensity of uterine contractions (choice "III only" can be eliminated). Note that Item III is in fact true: After parturition, oxytocin release (stimulated by suckling) facilitates milk let-down.

Cardiac, skeletal, and smooth muscle cells share all of the the following EXCEPT: A. troponin. B. actin. C. myosin. D. regulation by increased cytoplasmic calcium.

A. All types of muscle cells contain the proteins actin & myosin (choices B & C can be eliminated). Calcium plays a role in the regulation of all muscle types (choice D can be eliminated). Troponin is a regulatory protein in cardiac and skeletal muscle, but not in smooth muscle, which utilizes calmodulin instead (choice A is the correct).

An exercise physiologist looking at Type IIA muscle fibers under the microscope would see: A. white cells with some mitochondria. B. white cells with no mitochondria. C. red cells with many mitochondria. D. red cells with no mitochondria.

A. Type IIA fibers are fast twitch fibers that are moderately fatigue-resistant; so they would have mitochondria (choices B & D can be eliminated). They would not have as many mitochondria as the red (myoglobin filled) slow twitch fibers that very fatigue-resistant, & do not have myoglobin so appear white (C is wrong, A is correct).

Which of the following is an example of passive transport? A. Movement of protons into the mitochondrial matrix in oxidative phosphorylation, w/ the proton influx driving ATP synthesis B. Transport of protons out of the mitochondrial matrix by the ETC C. Movement of a bolus of food through the digestive tract D. Absorption of glucose from the digestive tract

A. An example of passive transport is the movement of protons into the mitochondrial matrix in ox. phosph, w/ the proton influx driving ATP synthesis. In ox. phosph., H+ move down their gradient from the intermembrane space of the mitochondria into the mitochondrial matrix. When a substance moves across a membrane, down its gradient, the process is a form of passive transport. Do not let the fact that the H+ movement is driving ATP formation confuse you; even though the protons are moving through the ATP synthase, they are still moving down their gradient so the process is passive. Note the initial movement of protons out of the matrix & into the intermembrane space requires energy b/c they are moving against their gradient; this is a form of active transport & the energy for this comes from the ETC. Movement of food through the digestive tract requires muscular contraction, so it is not passive; in any case, active & passive transport more correctly refer to the movement of substances across a cell membrane. Absorption of glucose from the digestive tract is coupled to Na+ transport (the Na+/glucose cotransporter). Since the movement of sodium is driven by it's conc. gradient, & the conc. gradient was initially set up via active transport, the movement of glucose is termed secondary active (requires ATP indirectly).

Each of the following is involved in some way with blood filtration EXCEPT: A. the peritubular capillaries. Correct Answer B. the afferent arteriole, branching from the renal artery. C. Bowman's capsule. D. the glomerulus.

A. Each of the listed responses are involved in some way w/ blood filtration EXCEPT the peritubular capillaries. The afferent arteriole (which branches off the renal artery) supplies "dirty" blood to the glomerulus for filtering (the glomerulus & the afferent arteriole, branching from the renal artery are involved in renal blood filtration and can be eliminated). Bowman's capsule collects the filtrate from the glomerulus (Bowman's capsule is involved in filtration & can be eliminated). The peritubular capillaries wind around the nephron tubule & help w/ reclaiming reabsorbed substances & maintaining salt conc. in the medulla. They do not function in blood filtration (peritubular capillaries are not involved in filtration & is correct choice).

All of the following are true statements EXCEPT: A. fraternal twins occur from the fertilization of both oocytes of a double ovulation; one that occurs about midcycle (day 14) and one that occurs about a week later. Correct Answer B. ovulation is triggered by an LH surge that is the result of the positive feedback of estrogen on the anterior pituitary gland. C. LH causes ovulation and the formation of the corpus luteum. Your Answer D. menstruation is triggered by a drop in estrogen and progesterone levels.

A. Fertilization of both oocytes from a double ovulation is in fact what leads to fraternal twins, however the two ovulations must occur within 24 hours of each other, not a week apart (A is not true & is the correct answer choice). The LH surge that causes ovulation is the result of the positive feedback effect that estrogen has at high levels (B is true & can be eliminated), & the LH surge causes both ovulation & the formation of the corpus luteum after ovulation (C is true & can be eliminated). The drop in estrogen & progesterone as the corpus luteum degenerates (around day 27-28) is what triggers menstruation (D is true and can be eliminated).

A mutation leading to a loss of function in which of the following hormones would have the greatest impact on enzyme activation in the stomach? A. Gastrin B. Cholecystokinin C. Erythropoeitin D. Secretin

A. Gastrin is secreted from G cells in the stomach, & stimulates acid & pepsinogen secretion, as well as increases stomach motility. Hydrochloric acid (HCl) cleaves the zymogen pepsinogen to active pepsin; a mutation leading to loss of gastrin function would impair HCl secretion and thus pepsin activation (choice A is correct). CCK triggers release of bile & also works to regulate the flow of chyme through the pyloric sphincter and into the small intestine, but does not impact gastric enzyme activation. Erythropoeitin stimulates RBC production in the bone marrow & is made by the kidneys, thus it is not relevant to this question. Secretin triggers the release of pancreatic exocrine secretions (including digestive enzymes & aqueous bicarbonate) into the small intestine, & is not involved in gastric enzyme activation.

In Kartagener's syndrome, defective dynein is produced causing a paralysis of microtubule-based movement of flagellae and cilia. One could expect to find all of the following outcomes EXCEPT: A. failure to ovulate in women. B. male infertility. C. chronic lung infections. D. ectopic pregnancy in women.

A. In Kartagener's syndrome, defective dynein is produced causing a paralysis of microtubule-based movement of flagellae & cilia. One could expect to find all of the following outcomes EXCEPT failure to ovulate in women. A male with Kartagener's syndrome would be infertile due to immobile sperm, eliminating male infertility. In females, ova would not enter the Fallopian tubes normally, due to the lack of cilia, causing increased risk of ectopic pregnancy, eliminating ectopic pregnancy in women. The lungs also require cilia to remove bacteria & particulates, eliminating lung infections. Ovulation, however, is determined by levels of circulating hormones & will not be affected by lack of dynein.

Which of the following statements about bile is/are true? I. Bile emulsifies lipids for easier digestion. II. The amphipathic nature of bile allows it to digest lipids. III. Bile is produced by the liver and gallbladder. A. I only B. I and III only C. II and III only D. I, II, and III

A. Item I is true: bile is amphipathic (has both polar & non-polar regions); this allows it to interact with both lipids & the hydrophilic intestinal contents. The lipids are emulsified, allowing pancreatic lipases easier access to them for digestion. Bile is sometimes referred to as intestinal soap, because it emulsifies fat in the intestines much like soap emulsifies fat on your hands when you wash them. Item II is false: bile is not an enzyme and does not digest lipids. It only makes it easier for the pancreatic enzymes to digest. Item III is false: bile is made only by the liver. It is stored and concentrated in the gallbladder.

Fully mature bone is composed of all of the following EXCEPT: A. cartilage. B. collagen. C. calcium. D. phosphate.

A. Mature bone is made rigid by the inclusion of hydroxyapatite, a calcium-phosphate crystalline solid (choices C & D are found in bone & can be eliminated). Collagen forms the framework for mature bone & this framework is then hardened by the crystalline solid (choice B is found in bone & can be eliminated). Cartilage is deposited in growing bone, but is replaced w/ solid bone matrix as bone matures (choice A is not found in fully mature bone & is the correct answer choice).

Which of the following is an incorrect matching of developmental phase and characteristics? A. Blastulation - development of the blastocyst, including the trophoblast and the outer cell mass B. Differentiation - the ectoderm develops into neural tissue, while the endoderm develops into epithelial tissue C. Cleavage - cell divisions without an increase in cell volume, resulting in the morula D. Gastrulation - development of the three primary germ layers (ectoderm, endoderm & mesoderm)

A. The ectoderm differentiates to form all nervous system tissue, & most epithelial components are derived from the endoderm (choice B is a correct match and can be eliminated). Cleavage is the development of the morula from the zygote (choice C is a correct match and can be eliminated). Gastrulation is germ layer development (choice D is a correct match and can be eliminated). However, blastulation is the development of the blastocyst, which is composed of the trophoblast & an INNER cell mass (choice A is an incorrect match & the correct answer choice).

The nephrons of the kidney are responsible for filtering blood and modifying the filtrate to produce urine. Which of the following provides the best description of the initial composition of filtrate in a healthy individual? A. Water, glucose, ions B. Water, ions, cells C. Water, cells, proteins D. Water, proteins, glucose

A. The glomerular basement membrane is only permeable to water & small, hydrophilic molecules, such as glucose, amino acids, & ions (choice A is correct). Whole cells/whole proteins should not be able to cross through this filter (choice B, C, & D are wrong). Glucose (& other molecules) will be subsequently reabsorbed, but are still able to pass through to glomerular basement membrane -- note question asks about INITIAL composition.

If tumor suppressor activity was induced exogenously to exceed normal levels by several-fold, which cellular process would most likely be blocked? A. Mitosis B. Transcription C. Meiosis D. Translation

A. Tumor suppressor genes work to prevent deregulated cell growth & division. Turning up their activity level would therefore most likely impact mitosis. Meiosis only occurs in gonads, & both transcription & translation are not the focus of the monitoring by these gene products.

During the production of urine, the nephron controls the composition of urine by all of the following physiological processes EXCEPT: A. filtration to leave Na+ in blood. B. secretion of solutes into urine. C. countercurrent exchange with blood. D. reabsorption of water.

A. During the production of urine, the nephron controls the composition of urine by all of the listed physiological processes EXCEPT filtration to leave Na+ in blood. Only large solutes (proteins) are filtered out. Na+ pass freely into the filtrate & must be reabsorbed later in filtrate processing to make urine.

Which of the following represents the correct sequence of mammalian development? A. Zygote--> morula --> blastocyst --> gastrula --> fetus B.Morula --> blastocyst --> zygote --> gametes --> fetus C.Fetus --> morula --> blastocyst -->zygote --> gastrula D. Zygote --> blastocyst --> morula--> gastrula --> fetus

A. Two gametes (egg & sperm) join to form a zygote, which develops into a morula, then a blastocyst, then a gastrula & eventually a fetus

Why is light-headedness and occasional dizziness a common symptom for women in their second trimester of pregnancy? A. While the maternal circulatory system has expanded to accommodate the needs of the growing fetus, the production of blood itself needs to fill in the new capacity. B. Maternal myoglobin production has increased and stores more oxygen in the mother's muscles to prepare for labor. C. The increased affinity for oxygen demonstrated by fetal hemoglobin removes too much oxygen from the maternal blood supply. D. Pressure from the expanding uterus makes breathing difficult, thus limiting the amount of oxygen exchange with the blood supply.

A. Light-headedness & occasional dizziness is a common symptom for women in their 2nd trimester b/c while maternal circulatory system has expanded to accommodate the needs of the growing fetus, the production of blood itself needs to fill in new capacity. During the 2nd trimester, the capacity to supply blood to the fetus is expanding, but the maternal hematopoietic tissue takes longer to produce enough blood to fill what the new vasculature can hold. This can lead to dizziness until the gap in the capacity closes. Obstruction of breathing by the uterus typically does not take place until the third trimester & though it can impinge on the lung capacity, it does not interfere w/ circulatory exchange. Though fetal hemoglobin has higher affinity for O2 than maternal hemoglobin, it is not so extensive as to actively deprive the mother of oxygen; & by same token, the muscles are not storing so much O2 as to deprive standard circulation

What stage(s) of sexual response is/are mediated by the sympathetic nervous system? A. Orgasm and resolution B. Arousal only C. Arousal and orgasm D. Orgasm only

A. Point and Shoot (Parasympathetic, Sympathetic)

A researcher uses a radioactive label to trace the development of the GI glands in chicken embryos. From what primary germ layer do they come? A. Endoderm B. Ectoderm C. Blastopore D. Mesoderm

A. endoderm = digestive tract/organs (-most external ones) The endoderm gives rise to the epithelial lining of the GI tract (except for the nasal, oral, & anal epithelium), the respiratory tract, & the urogenital organs/ducts. It also gives rise to GI glands & urinary bladder. The ectoderm gives rise to the nervous system, the cornea & lens, the pituitary gland, the adrenal medulla, the epidermis, & the nasal, oral, & anal epithelium. The mesoderm gives rise to all muscle, bone, connective tissue, cardiovascular system, lymphatic system, urogenital organs, & the dermis. The blastopore is not a primary germ layer and will eventually give rise to the anus.

Secreted and membrane-bound proteins must go through the secretory pathway, targeted there by a signal sequence. The signal sequence must be composed of: A. hydrophilic amino acids. B. hydrophobic amino acids. C. basic amino acids. D. acidic amino acids.

B

Which of the following organ(s) is directly involved in the synthesis of substances important in bone remodeling? I. Thyroid II. Parathyroid III. Liver A. II only B. I, II, and III C. II and III only D. I and II only

B Calcitonin (made in the thyroid), parathyroid hormone (made in the four parathyroid glands), & the biologically active form of Vitamin D (which requires hydroxylation reactions in both the liver & kidneys) coordinate bone remodeling by acting on osteoblasts & osteoclasts in the bone. These hormones also act on the intestines & kidneys to regulate levels of calcium & phosphate, the constituents of the inorganic component of bone (hydroxyapatite). All items are correct.

Which of the following statements regarding the microscopic structure of bone is correct? A. Individual osteons are anatomically separated & are not connected. B. Individual osteocytes communicate w/ one another via gap junctions. C. Compact bone is vascular but aneural (does not contain nerves). D. Compact bone is innervated but is avascular (is not supplied by blood vessels).

B Individual osteocytes communicate w/ one another via gap junctions is a correct statement regarding the microscopic structure of bone. Osteoblasts that become entrapped by bone are called osteocytes & maintain cytoplasmic attachments w/ one another via gap junctions. These cytoplasmic extensions traverse tiny channels (canaliculi), which course through the surrounding bone. Central (Haversian) canals contain lymph vessels, blood vessels, & nerves ["compact bone is innervated but is avascular" & "compact bone is vascular but aneural" are wrong]. Individual osteons are physically connected & are also connected via perforating (Volkmann's) canals, which carry vessels ("individual osteons are anatomically separated and are not connected" is wrong).

Which of the following are functions performed by parietal cells? I. Acid production II. Secretion of pepsinogen III. Secretion of intrinsic factor, required for the absorption of vitamin B12 A. I only B. I and III only C. II and III only D. I, II, and III

B Item I is true: parietal cells are the acid-secretors of the stomach (choice C can be eliminated). Item II is false: pepsinogen is secreted by chief cells (choice D can be eliminated). Item III is true: parietal cells also secrete gastric intrinsic factor (GIF), which is necessary for the absorption of vit. B12

Which of the following types of renal vasculature are NOT responsible for returning components to the circulatory system as part of filtrate adjustment? A. Efferent arterioles B. Afferent arterioles C. Peritubular capillaries D. Vasa recta

B The afferent arterioles carry blood toward the glomerulus, but do not function in returning substances to the circulatory system after filtration (choice B is the correct answer). The efferent arterioles carry blood away from the glomerulus & ultimately branch into the peritubular capillaries. These vessels interlace w/ the nephron and pick up reabsorbed material (choices A & C return components to the circulatory system & can be eliminated). The vasa recta is part of the peritubular capillaries; it runs in parallel w. the renal tubule & is also involved in returning material to the circulatory system

What role does the macula densa (in the distal tubule) play in regulating blood pressure? A. High filtrate osmolarity triggers the macula densa to stimulate the JG cells & dilate the afferent arterioles. B. Low filtrate osmolarity triggers the macula densa to stimulate the JG cells & dilate the afferent arterioles. C. High filtrate osmolarity triggers the macula densa to stimulate the JG cells & constrict the afferent arterioles. D. Low filtrate osmolarity triggers the macula densa to stimulate the JG cells & constrict the afferent arterioles.

B The macula densa on the distal convoluted tubule monitors filtrate osmolarity. If the filtrate osmolarity decreases (choices A & C are wrong), this indicates a drop in filtration rate. The macula densa then stimulates the juxtaglomerular cells (in order to activate the renin-angiotensin axis to increase blood pressure), while also causing the afferent arterioles to dilate (choice D is wrong and choice B is correct). The combination of increased systemic blood pressure and increased blood flow to the glomerulus increases filtration rate.

How are long bones lengthened during the growth characteristic of childhood and adolescence? A. Deposition of hydroxyapatite within the diaphysis B. Deposition of cartilage at the epiphyseal plate C. Deposition of cartilage within the diaphysis D. Deposition of collagen at the epiphyseal plate

B. epiphyseal plate = "growth plate" in epiphysis of long bones, deposition of cartilage allows for growth

Which cells of the skin undergo mitosis in order to replace damaged squamous epithelial skin cells? A. Hypodermis B. Stratum basale C. Dermis D. Melanocytes

B The stratum basale is the deepest layer of the epidermis, & undergoes mitosis to replace squamous epithelial skin cells that are damaged or worn out . The main purpose of the epidermis is to serve as a protective barrier. As the stratum basale produces daughter cells, these cells push the older cells closer to the surface of the skin, where they are eventually sloughed off. The hypodermis is a layer of adipose subcutaneous tissue underlying the dermis; it does not undergo mitosis to replace epithelial cells. The dermis is a layer of connective tissue that lies beneath the epidermis & above the hypodermis. It contains all of the blood vessels, sensory receptors, hair follicles, & sweat glands that allow the skin to release excess heat & convey information about touch, temp., pressure, & pain to the CNS. Melanocytes are specialized epidermal epithelial cells that produce melanin, a pigment that absorbs UV from the sun, preventing damage to underlying tissues.

Which of the following requires hydrolysis of ATP to occur? A. Flow of sodium into skeletal muscle cells B. Removal of calcium from cytoplasm after contraction C. Diffusion of ACh across the synaptic cleft D. Hydrolysis of acetylcholine

B. The removal of calcium from the cytoplasm after contraction works against the calcium concentration gradient & therefore requires energy (ATP hydrolysis). The flow of sodium ions into muscle cells occurs down the sodium concentration gradient and so is passive (choice A is wrong). Diffusion of ACh across the synaptic cleft is also passive and gradient-driven (choice C is wrong). Hydrolysis of ACh is enzymatic and does not require ATP hydrolysis (choice D is wrong).

At birth, females possess the total # of their potential ova. In oogenesis, meiotic division is arrested for a long period at which stage? A. Secondary oocyte B. Primary oocyte C. Oogonium D. Ovum

B. At birth, females possess the total # of their potential ova. In oogenesis, meiotic division is arrested for a long period at the primary oocyte stage. Primary oocytes are arrested in meiotic prophase I in the ovaries from birth until they are stimulated to ovulate sometime during sexual maturity.

Damage to the macula densa in the distal convoluted tubule would have what impact on blood flow to the glomerulus? A. The efferent arterioles would dilate in response to an increase in filtrate osmolarity & pressure at the glomerulus would be increased. B. The afferent arterioles would not dilate in response to a decrease in filtrate osmolarity & pressure at the glomerulus would not be increased. C. The efferent arterioles would not dilate in response to a decrease in filtrate osmolarity & pressure at the glomerulus would not be increased. D. The afferent arterioles would dilate in response to an increase in filtrate osmolarity & pressure at the glomerulus would be increased.

B. Damage to the macula densa would impact blood flow to the kidneys b/c the afferent arterioles would not dilate in response to a decrease in filtrate osmolarity & pressure at the glomerulus would not be increased. As part of the body's blood pressure regulation, the macula densa monitors filtrate osmolarity; if it falls too far, the macula densa causes the afferent arterioles of the kidney to dilate, thus increasing the pressure at the glomerulus & increasing the glomerular filtration rate. The macula densa does not regulate the dilation of the efferent arterioles & afferent arterioles do not dilate in response to increases in filtrate osmolarity.

Albumin, an extracellular protein found in the plasma, is labeled with green fluorescent protein and translated. In which of the following locations would the fluorescent signal be WEAKEST during production? A. trans-Golgi network B. Endosomes C. Secretory vesicles D. Endoplasmic reticulum

B. Fluorescent signal would be weakest in endosomes during albumin production. Fluorescent albumin would begin being detected at the rER following its translation. Next it would travel to the cis-Golgi & progress through the compartments to the trans-Golgi where it would ultimately be shuttled to the cell exterior via a secretory vesicle. Endosomes are formed following endocytosis & is unlikely that a significant quantity of albumin would be in endosomes.

Which of the following situations would NOT stimulate gluconeogenesis? A. High glucagon levels B. High levels of AMP C. High levels of citrate D. High levels of acetyl-CoA

B. Gluconeogenesis will be stimulated when energy charge is high & glycolytic & Krebs cycle intermediates are high. If energy is low, &/or Krebs cycle intermediates are low, then glycolysis will be stimulated. High levels of AMP indicate that energy charge is low & that ATP needs to be made. AMP inhibits the enzyme fructose-1,6-bisphosphatase, keeping levels of fructose-1,6-bisphosphate high & driving the cell towards glycolysis. High levels of citrate & acetyl-CoA indicate that the Krebs cycle is active & does not need more precursors, so will shift the cell away from glycolysis & toward gluconeogenesis. Think of it as taking these biosynthetic precursors & stashing them for future use. They aren't needed if the Krebs cycle is operating at capacity. Glucagon is released when blood glucose levels are low & drives pathways toward gluconeogenesis to keep blood glucose levels stable.

An infant is born in the 6th month of gestation. Which of the following best describes her alveoli as compared to an infant born in the 9th month of gestation? A. Higher amount of surfactant leading to an increase in surface tension B. Lower amount of surfactant leading to an increase in surface tension C. Higher amount of surfactant leading to a decrease in surface tension D. Lower amount of surfactant leading to a decrease in surface tension

B. Increased surfactant = lower surface tension An infant is born in the sixth month of gestation. Her alveoli have a lower amount of surfactant leading to an increase in surface tension, compared to an infant born in the ninth month of gestation. Surfactant is a substance consisting of phospholipids, proteins & ions. It is released by Type II alveolar cells, & its primary function is to reduce the surface tension of the alveoli in order to prevent their collapse & thus, to make breathing easier. Surfactant is not produced until about eight months of gestation, so in a premature infant (an infant born prior to the eighth month of gestation) there is an insufficient amount of surfactant for the child to breathe easily upon birth. A lack of surfactant would lead to an increase in surface tension.

Zollinger-Ellison syndrome is a disease of gastrin over-secretion. Often, it results from a gastrin-secreting tumor residing outside of the stomach. Which of the following would be most likely in a patient with this condition? A. Elevated serum gastrin, decreased gastric pH, elevated serum chloride B. Elevated serum gastrin, decreased gastric pH, low serum chlorider C. Decreased serum gastrin, increased gastric pH, low serum chloride D. Elevated serum gastrin, increased gastric pH, low serum chloride

B. Since the disease is defined by gastrin over-secretion, we would expect to see elevated serum gastrin. Since gastrin stimulates acid secretion in the stomach, we would expect increased gastric acidity (or, a decrease in gastric pH). While high acid levels normally inhibit gastrin secretion, an ectopic gastrin tumor would not respond to this feedback, thus we see highly elevated gastrin in the setting of extreme stomach acidity. Since stomach acid is actually HCl, chloride ions would be pumped into the stomach lumen along w/ the protons, & this will eventually cause its conc. in the blood to decrease (A can be eliminated, B is correct).

Spermatogenesis occurs: A. throughout the male adult life, due to the ability of spermatogonia to perform binary fission. B. in the seminiferous tubules, starting near the basement membrane & finishing near the lumen. C. via 2 rounds of meiosis, & generates 4 reproductively mature spermatids. D. in a testosterone & GnRH-dependent manner, during some phases of male adulthood.

B. Spermatogenesis occurs throughout male adulthood (D is wrong) b/c spermatogonia can undergo mitosis (to regenerate) & meiosis (to make primary spermatocytes). Note that only bacterial cells perform binary fission (A is wrong). Spermatogenesis involves 2 rounds of division during meiosis, not 2 rounds of meiosis, & generates 4 spermatids, but these cells are not mature (C is wrong). Choice B is true & is correct.

Which of the following would increase the force of contraction generated by a skeletal muscle? A. Increase the voltage of depolarization in each skeletal muscle action potential B. Increase the frequency of somatic motor neuron action potentials C. Increase the number of neurons stimulating the muscle to contract D. Increase the activity of the Na+/K+ ATPase

B. Tension develops in a muscle cell after depolarization occurs. If the next depolarization occurs before the muscle has had a chance to return to its fully relaxed state, then the next twitch will build on the first, resulting in a combined, greater tension. This process is known as summation, & is the way skeletal muscles typically operate. The voltage of depolarization is fixed in an action potential & cannot be increased (choice A is wrong). Increasing the # of neurons stimulating the muscle will only make it more likely to contract, it will not generate a greater force (choice C is wrong). Increasing the activity of the Na+/K+ ATPase will return the muscle ion gradients to resting level faster, but will not affect the generation of force (choice D is wrong).

Advertising and public health campaigns have long been trying to minimize drug & alcohol use in pregnant women. It is most important to limit the ingestion of these substances during the: A. second trimester, since this is when the fetus undergoes the most extensive growth. B. first trimester, since this is when all major organ systems develop. C. second trimester, since this is when organ systems finish development. D. third trimester, since this is when the mother is most uncomfortable & therefore most prone to taking pain-relieving drugs.

B. The basic development of all major organ systems is done in the first trimester of pregnancy, which is why drug or toxin exposure during this time can have major negative effects (choice B is correct). While drug exposure can harm a fetus at any point in development, the first trimester is crucial in development (choice B is better than choices A, C, & D). Most of these developmental pathways near completion in the second trimester, & the fetus increases drastically in size in the third trimester.

In which of the following locations would you LEAST expect to find red marrow? A. Spongy bone of flat bones B. Diaphyses of long bones C. Epiphyses of long bones D. Spongy bone of long bones

B. The location in which you would least expect to find red marrow is the diaphyses of long bones. The diaphyses (shafts) of long bones consist of a tube composed ONLY of compact bone. The shafts are filled w/ yellow, or fatty marrow that is not hematopoietically active (i.e., involved in the synthesis of red blood cells). Red, or hematopoietic, marrow, is found w/in spongy bone in both flat & long bones; in long bones, it is found w/in the epiphyses, covered by an outer shell of compact bone.

Which of the following describes the correct sequence of stomach layers through which an untreated gastric ulcer would erode? A. Epithelium, smooth muscle, submucosa, serosa B. Epithelium, submucosa, smooth muscle, serosa C. Submucosa, epithelium, smooth muscle, serosa D. Epithelium, submucosa, serosa, smooth muscle

B. This question requires an understanding of the anatomical structure of the alimentary canal. The epithelial layer is directly in contact w/ the lumen of the alimentary canal. The epithelial layer is also referred to as the "mucosa"; the layer directly outside the mucosa is the submucosa. Outside the submucosa is a double layer of smooth muscle, & the most external layer is the serosa (choice B reflects the proper sequence of layers moving from the inside of the GI tract lumen to the outside).

The pH inside the stomach is very closely regulated. Which of the following is a major function for the pH in the stomach? A. Neutralizing the acidity of the chyme entering it B. Denaturing proteins to allow for digestive processes C. Activating trypsinogen into the active form D. Establishing a proton gradient for ATP production

B. This question tests your knowledge of the physiological functions that result from the low pH within the stomach cavity. While the acid environment serves several functions, one important one is denaturing the tertiary structure of proteins in food. This lets proteases break up protein into smaller peptides. A. Chyme is the substance that leaves the stomach, not enters it. B. Correct C. Trypsinogen is found in the small intestine, not the stomach. D. A proton gradient is used for ATP production in the mitochondria, not the lumen of the stomach.

How do troponin and tropomyosin work to regulate skeletal muscle contraction? A. Globular troponin binds calcium, a conformational change in protein pulls filamentous tropomyosin, and actin binding sites on myosin are exposed. B. Globular troponin binds calcium, a conformational change in protein pulls filamentous tropomyosin, and myosin binding sites on actin are exposed C. Filamentous tropomyosin binds calcium, a conformational change in protein pulls globular troponin, and actin binding sites on myosin are exposed. D. Filamentous tropomyosin binds calcium, a conformational change in protein pulls globular troponin, and myosin binding sites on actin are exposed.

B. Troponin is the regulatory protein that binds calcium (choices C and D are wrong). This induces a conformational change in troponin that pulls on tropomyosin in order to expose the myosin binding sites on actin. This allows interaction of actin and myosin, and contraction, to occur (choice A is wrong and choice B is correct).

Why are women who wish to breastfeed counseled against taking birth control pills that combine estrogen & progestins as the means to block ovulation? A. High levels of estrogen & progesterone inhibit FSH as well as ovulation. B. High levels of estrogen & progesterone inhibit prolactin as well as ovulation. C. High levels of estrogen & progesterone inhibit relaxin as well as ovulation. D. High levels of estrogen & progesterone inhibit oxytocin as well as ovulation.

B. Women who wish to breastfeed are counseled against taking birth control pills that combine estrogen & progestins as means to block ovulation b/c high levels of estrogen & progesterone inhibit prolactin (hormone responsible for milk production @ mammary glands). This is beneficial during pregnancy when there may not be a baby . to feed, but needs to not occur during times of active lactation. These hormones do not inhibit oxytocin & while they do inhibit FSH, FSH is not involved in lactation. Similarly, relaxin (hormone of pregnancy that loosens joints) is not inhibited by these hormones.

In males: A. the Wolffian duct develops into male external genitalia, and spermatogonia regenerate via mitosis throughout adult life. B. the Wolffian duct develops into male internal genitalia, and spermatogonia regenerate via mitosis throughout adult life. C. the Wolffian duct develops into male external genitalia, and spermatogonia regenerate via meiosis throughout adult life. D. the Wolffian duct develops into male internal genitalia, and spermatogonia regenerate via meiosis throughout adult life.

B. All fetuses begin with both Mullerian ducts & Wolffian ducts. The Mullerian ducts regress in males, & the Wolffian ducts develop into male internal genitalia (A & C are wrong). Spermatogonia regenerate through the male adult life, by performing MITOSIS (choice B is correct and choice D is wrong).

Which of the following proteins is LEAST like a Na+/K+ ATPase? A. Hexokinase B. Sodium-glucose cotransporter C. Kinesin motor proteins D. Myosin

B. The Na+/K+ ATPase hydrolyzes ATP to move Na+ & K+ across the cell membrane. Hexokinase hydrolyzes ATP to phosphorylate glucose in the 1st step of glycolysis (A is like a Na+/K+ ATPase & can be eliminated). Kinesins hydrolyze ATP to "walk" along microtubules (C is like a Na+/K+ ATPase and can be eliminated). Myosin hydrolyzes ATP to reset to a high-energy conformation during muscle contraction (D is like a Na+/K+ ATPase & can be eliminated). However sodium-glucose cotransporters rely on a Na+ gradient to move glucose across the cell membrane. While the Na+ gradient is established by the Na+/K+ ATPase, the cotransporter itself does not hydrolyze ATP (choice B is least like a Na+/K+ ATPase & is correct).

At what stage of embryonic development are all three germ layers established? A. Blastula B. Gastrula C. Embryo D. Zygote

B. Gastrula An embryo at the stage following the blastula, when it is a hollow cup-shaped structure having all three layers of cells

What hormone directly stimulates osteoblasts? A. Calcitriol B. Calcitonin C. Parathyroid hormone D. Thyroid stimulating hormone

B. calcitonin = "tones down calcium" PTH = increase calcium concentration in blood osteoblasts = build bone osteoclasts = cut down bone

Which of the following correctly orders the steps of apoptosis? A. Break down nuclear membrane, break down genome, disassemble cytoskeleton, phagocytic digestion B. Disassemble cytoskeleton, break down nuclear membrane, phagocytic digestion, break down genome C. Disassemble cytoskeleton, break down nuclear membrane, break down genome, phagocytic digestion D. Break down genome, disassemble cytoskeleton, break down nuclear membrane, phagocytic digestion

C

During normal inspiration: A. the thoracic volume decreases. B. pressure in the alveoli is slightly greater than atmospheric pressure. C. intercostal muscles contract. D. the diaphragm is relaxed

C Contraction of the diaphragm & the intercostal muscles drives inspiration (choice C is correct & D is wrong). When the diaphragm contracts, the size of the chest cavity increases, so thoracic volume increases (choice A is wrong). B/c of the increase in thoracic volume, the pressure in the alveoli decreases below atmospheric pressure. This is what allows air to enter the respiratory system; if the pressure in the alveoli were higher than atmospheric pressure, air would exit the respiratory system (choice B is wrong)

Which of the following is/are functions of the placenta? I. To maintain the corpus luteum by secreting hCG II. Providing a site for blastocyst implantation III. To secrete estrogen during pregnancy A. I only B. III only C. I and III only D. II and III only

C Item I is true: the trophoblast is the early precursor (months 0-3) of the placenta. It secretes hCG which acts in a manner similar to LH to maintain the corpus luteum (choices B & D can be eliminated). Since neither of the remaining choices includes Item II, it must be false: the blastocyst implants in the uterine lining (endometrium). Statement III is true: once the placenta is mature (months 4-9) it secretes estrogen & progesterone (A can be eliminated, so C is correct).

During the first trimester, a pregnant woman develops an autoimmune disorder in which antibodies to hCG are formed. The result is: I. Continued pregnancy II. Termination of pregnancy III. Regression of the corpus luteum A. I only B. II only C. II and III only D. I and III only

C The purpose of hCG is to act as a substitute for LH. The corpus luteum is formed in the presence of LH, but as the LH levels fall after ovulation, the corpus luteum begins to deteriorate. The corpus luteum is responsible for secreting progesterone, which helps maintain the uterine lining, in case that particular ovulation results in a pregnancy. As the corpus luteum deteriorates, progesterone levels fall, & when they fall low enough, menstruation begins. The role of hCG, then, is to prolong the life of the corpus luteum (much like LH would if it were still present). If the corpus luteum does not deteriorate (as in fertilization), progesterone levels stay high, & menstruation does not occur. An autoimmune disorder in which anti-hCG antibodies were formed would result in destruction of hCG, deterioration of the corpus luteum, a fall in progesterone levels, & the onset of menstruation (termination of the pregnancy).

One of the 1st hormones produced by a developing embryo is hCG, human chorionic gonadotropin, whose function is to prolong the life of the corpus luteum, ensuring that the endometrium is maintained until full development of the placenta by 3 months of gestation. hCG is most like which of the following hormones? A. Estrogen B. Progesterone C. LH D. FSH

C hCG is most like LH. The LH surge in the middle of the menstrual cycle triggers both ovulation & the conversion of follicular remnants into the corpus luteum, which then secretes progesterone & estrogen. However, levels of LH rapidly fall, & in the absence of LH the corpus luteum only survives for about two weeks. At the end of that time period, the corpus luteum degenerates, the levels of progesterone & estrogen fall, & menstruation occurs. In order to maintain the endometrium in the case of pregnancy, levels of progesterone & estrogen must remain elevated, & in order to keep the levels elevated, the corpus luteum must be maintained. hCG takes on the role of LH in this regard. FSH does not affect formation or maintenance of the corpus luteum. Further, it does not make logical sense for hCG to be like progesterone or estrogen, if this was the case, there would be no need to maintain the corpus luteum to secrete these hormones.

Where does most digestion take place? A. Large intestine B. Stomach C. Small intestine D. Mouth

C.

Alkylating agents are highly reactive compounds that can be used as anti-cancer drugs. They covalently link an alkyl group (R-CH2) to a chemical species in nucleic acids; most are bipolar (they contain two groups capable of reacting with DNA). They can thus form cross bridges between a single strand of DNA or between two separate strands. Alkylating agents would most likely interfere with which stage of the cell cycle? A. Anaphase B. Metaphase C. S phase D. Prophase

C. Alkylating agents would most likely interfere with the S phase of the cell cycle. If DNA is being covalently cross-linked, either to itself or to another DNA strand, DNA polymerase will be incapable of replicating the strands. DNA replication occurs in S phase, thus this is the phase that would be inhibited. Replication does not occur in prophase, metaphase, or anaphase.

What type of ion channel is unique to cardiac muscle as opposed to skeletal or smooth muscle? A. Voltage-gated sodium channel B. Voltage-gated potassium channel C. Voltage-gated calcium channel D. Potassium leak channel

C. All types of muscle depend on voltage-gated sodium channels for depolarization (choice A is wrong) & voltage-gated potassium channels for repolarization (choice B is wrong). Potassium leak channels are important in establishing the resting membrane potential in all muscle types (choice D is wrong). However, only cardiac muscle cells have voltage-gated calcium channels; these are used to extend depolarization & create the distinctive plateau phase seen in cardiac muscle action potentials (choice C is correct). (fast and slow calcium channels)

Anatomical dead space is classified as that area of the respiratory pathway where no gas exchange occurs with the blood. Which of the following is part of the anatomical dead space? A. Alveolar duct B. Alveolus C. Terminal bronchioles D. Respiratory bronchioles

C. Anatomical dead space is the portion of the respiratory tree where gas exchange does not take place, also known as the conduction zone. The conduction zone includes the nose, pharynx, larynx, trachea, bronchi, bronchioles, & terminal bronchioles (choice C is correct). The respiratory zone includes the respiratory bronchioles, alveolar ducts, and alveoli (choices A, B & D are wrong).

Semen contains: A. glucose as a primary food source for spermatozoa. B. mucus, secreted from the prostate gland, to help w/ lubrication. C. alkaline secretions to help neutralize the low pH in the male urethra & the female vagina. D. water, secreted from only the seminal vesicles.

C. Besides spermatozoa, semen contains: mucus from the bulbourethral glands for lubrication (choice B is wrong); water (which is secreted from all three accessory glands) to provide the liquid medium (choice D is wrong); alkaline secretions (from the prostate & bulbourethral glands) to neutralize acidic environments (choice C is correct); nutrients (primarily fructose) secreted from the seminal vesicles (choice A is wrong).

Colchicine is a compound that interferes w/ formation of microtubules. Which of the following would be affected LEAST by the administration of colchicine? A. Organelle movement B. Flagellae C. Amoeboid motility of cells D. Mitotic spindles.

C. Colchicine is a compound which interferes with the formation of microtubules. Amoeboid motility of cells would be affected LEAST by the administration of colchicines. Actin microfilaments (not microtubules) are responsible for amoeboid movement of cells. The other choices are wrong b/c microtubules are a key component of mitotic spindles, flagella, & the scaffold that organelles interact w/ to move w/in the cytoplasm.

During the menstrual cycle, the corpus luteum degrades, but if a fertilized ovum implants in the uterus, the corpus luteum persists. Which of the following hormones supports the corpus luteum during pregnancy? A. Progesterone B. Lutenizing hormone C. Human chorionic gonadotropin D. Estrogen

C. During the menstrual cycle, the corpus luteum degrades, but if a fertilized ovum implants in the uterus, the corpus luteum persists. Human chorionic gonadotropin supports the corpus luteum during pregnancy. Human chorionic gonadotropin (hCG) is secreted by the trophoblast, beginning at implantation. hCG plays a role similar to that of lutenizing hormone (LH) in maintaining the corpus luteum. In the presence of hCG, the corpus luteum continues to secrete estrogen and progesterone to maintain the uterine lining so that the pregnancy is not lost. The trophoblast ultimately develops into the placenta (by about the 3rd month of gestation), which takes over the endocrine role of the corpus luteum.

How does freezing-point depression work to defy the thermodynamic principle of entropy? A. During freezing, solvent first forms crystals before solutes are organized into an array; thus higher solute conc.'s require lower temps to freeze. B. During freezing, solvent first forms crystals before solutes are organized into an array; thus lower solute conc.'s require lower temps to freeze. C. During freezing, solutes are first organized into an array before the solvent forms crystals; thus higher solute conc.'s require lower temps to freeze. D. During freezing, solutes are first organized into an array before the solvent forms crystals; thus lower solute conc.'s require lower temps to freeze.

C. Freezing point depression works to defy the thermodynamic principle of entropy because during freezing, solutes are first organized into an array before the solvent forms crystals; thus higher solute concentrations require lower temperatures to freeze. In the process of freezing, solutes are arrayed before the solvent freezes. The more solute present in the solution, the more energy must be removed from that system to organize those solutes into the requisite array. Thus, even more energy needs to be removed to then freeze the solvent. As a side note, freezing-point depression is calculated in the same way as boiling point depression only the cryogenic constant is negative.

Which of the following is a correct timeline for first trimester fetal development? A. Fetus - morula - blastocyst - trophoblast B. Zygote - trophoblast - morula - embryo C. Fertilization - morula - blastocyst - fetus D. Zygote - morula - placenta - blastocyst

C. Gametes fuse in fertilization to form the zygote, which undergoes cleavage to form the morula. Next the blastocyst forms, which includes the trophoblast (trophoblast = layer of tissue on the outside of the blastula) (choice B can be eliminated). Placental development starts once the blastocyst has implanted in the uterine wall (or endometrium; choice D is wrong). The developing human is called an embryo for the first two months, & is called a fetus after this (choice A is wrong). Choice C presents the correct order of development.

Which types of protein are produced by the ribosomes of the rough endoplasmic reticulum? I. Membrane-bound II. Integral III. Secreted A. I and II only B. II and III only C. I, II, and III D. I and III only

C. Protein types I, II & III are produced by the ribosomes of the rER. I. Membrane-bound II. Integral III. Secreted POE is especially effective when dealing w/ a Roman numeral question. Ribosomes on the rER synthesize proteins in the secretory pathway. This includes proteins in the plasma membrane, both membrane-bound & integral proteins. Secreted proteins are also part of the secretory pathway.

Butyl-biguanide inhibits the function of Na+/K+ ATPases in the small intestine. Which of the following would be the most likely effect of butyl-biguanide application to the duodenum? A. Increased chylomicron formation & consequent lipemia B. Elevated K+ levels in the enterocytes C. Decreased absorption of monosaccharides from the intestinal lumen D. Greater sodium concentration gradient between the lumen & the cytoplasm of enterocytes

C. The Na+/K+ ATPases in the small intestine generate a sodium conc. gradient between the lumen & cytoplasm of enterocytes by pumping Na+ out of the cell & K+ in. If the Na+/K+ ATPases were inhibited, K+ levels would not increase inside the enterocytes (B is wrong), & the Na+ concentration gradient would not be generated (D is wrong). The gradient allows AAs & monosaccharides to be transported into the enterocytes via secondary active transport & symport w/ sodium; if the gradient is not generated, monosaccharide (& amino acid) absorption would decrease (choice C is correct). These proteins have no role in the absorption of fats (choice A is wrong).

How does the van't Hoff factor of NaCl compare to that of NH3? A. The i of NaCl is 2 while the i of NH3 is 4. B. The i of both NaCl and NH3 is 1. C. The i of NaCl is 2 while the i of NH3 is 1. D. The i of both NaCl and NH3 is 2.

C. The i of NaCl is 2 while the i of NH3 is 1. The van't Hoff or ionizability factor is determined by the # of ions produced when a single molecule dissolves in soln. Since NaCl is ionic, it breaks into Na+ & Cl- giving an i = 2. Since NH3 is non-ionic, it does not break down, thus i = 1.

At which of the following times in the respiratory cycle is the intrapleural pressure most negative? A. At the beginning of exhalation B. At the beginning of inhalation C. At the end of inhalation D. At the end of exhalation

C. The intrapleural pressure is most negative at the end of inhalation during the respiratory cycle. Negative intrapleural pressure is what drives air into the lungs during inhalation. When the chest cavity increases in size, the intrapleural pressure becomes more negative. The chest wall is moving outward due to muscle contraction,& lung tissue is elastic, thus resisting the outward pull. Hence, while inspiration is happening, the pressure is getting more & more negative; i.e., the expansion of the lungs doesn't quite keep up with the chest wall, & pressure reaches its most negative value when the chest cavity is the most expanded at the end of inhalation. Exhalation involves increasing the intrapleural pressure to push air out ("at the beginning of exhalation" and "at the end of exhalation" are wrong).

How are peptidases activated in the duodenum? A. Trypsinogen from the pancreas is converted to trypsin by stomach acid; trypsin then activates the other pancreatic enzymes. B. Enterokinase converts trypsinogen from the pancreas into trypsin; trypsin then triggers the release of other pancreatic enzymes. C. Enterokinase converts trypsinogen from the pancreas into trypsin; trypsin then activates the other pancreatic enzymes. D. Trypsinogen from the pancreas is converted to trypsin by stomach acid; trypsin then activates the brush border enzyme enterokinase.

C. The majority of peptidases in the duodenum come from the pancreas & are secreted as zymogens. Because they work in the duodenum they must be activated there, so stomach acid can't really play a role (choices A and D are wrong). Enterokinase, a duodenal enzyme, cleaves & activates the pancreatic zymogen trypsinogen; the active enzyme trypsin then cleaves other pancreatic zymogens to activate them (choice C is correct). The release of pancreatic enzymes is triggered primarily by secretin (a duodenal hormone); cholecystokinin (another duodenal hormone) can also help (choice B is wrong).

The medullary cavity of long bones contains marrow that performs which of the following functions? A. Red blood cell production B. White blood cell production C. Fat storage D. None; the medullary cavity of long bones is hollow and does not contain marrow

C. The medullary cavity of long bones contains yellow marrow, which is yellow due to the high fat content. Red bone marrow, which is found in flat bones & the spongy bone section of the epiphyses of some long bones, is responsible for all red blood cell production (erythropoiesis; choice A is incorrect), white blood cell production (leukopoiesis; choice B is incorrect), and platelet production (thrombopoiesis).

Which of the following does NOT participate in gas exchange? A. Alveolus B. Alveolar duct C. Terminal bronchiole D. Respiratory bronchiole

C. The terminal bronchioles do NOT participate in gas exchange. Terminal bronchioles belong to the conduction zone, which is the portion of the respiratory system designed only to move air into & out of the system. Gas exchange occurs in the respiratory zone, which consists of alveoli, alveolar ducts, & respiratory bronchioles

How is the final phenotype of a developing stem cell established? A. Differentiation employs methylation to create the genetic identity of the cell. B. Determination allows for phenotypic expression of alternative genomic splicing. C. Its genetic fate is determined and then it becomes visibly differentiated. D. Its genetic fate is differentiated and then it becomes visibly determined

C. A developing stem cell's genetic fate is determined and then it becomes visibly differentiated to establish its final phenotype. Stem cells need to have their genetic programming fixed first via the process of determination. This genetic programming is then physically manifested through the process of differentiation.

Which of the following structures are derivatives of the ectoderm? I. Epidermis of the skin II. Dermis of the skin III. Sweat glands A. I and II only B. I, II, and III C. I and III only D. II and III only

C. Ectoderm = things that make you attractive (skin, CNS, etc.) The skin's epidermis and its derivatives (which include hair, nails, and sweat glands) are derived from the ectoderm (Items I and III are true). The dermis of the skin is derived from the mesoderm (Item II is false).

Which of the following is not derived from the inner cell mass of a blastocyst? A. Embryo B. Amnion C. Trophoblast D. Allantois

C. The trophoblast is not derived from the inner cell mass of a blastocyst. A blastocyst consists of an outer cell mass and an inner cell mass. The outer cell mass, or trophoblast, develops first into the chorion and ultimately into the placenta. The inner cell mass develops into the embryo, amnion, yolk sac and allantois (leaving these as incorrect answer choices).

Which of the following is NOT a component of the filtrate first produced by the nephron? A. Glucose B. Water C. Lipids D. Amino acids

C. Lipids (lipids are absorbed through the lymphatic system and excreted through the feces)

Which of these proteins binds calcium in smooth muscle cells? A. Myosin B. Troponin C. Actin D. Calmodulin

D Of these proteins, calmodulin binds calcium in smooth muscle cells. Instead of using the troponin-tropomyosin complex to bind calcium & facilitate actin-myosin interaction (as seen in striated muscle), calcium ions bind to calmodulin. This in turn activates myosin light-chain kinase (MLCK) to phosphorylate the myosin & enable it to bind actin. Myosin & actin are found in all muscle types, though their arrangement differs in striated & smooth muscle.

A physiologist observes a dark, dense subcellular structure via electron microscopy that spans the space between 2 adjacent cell membranes & extends to the underlying cytoskeleton. Upon further investigation, she discovers that two cells w/ this structure are electrically isolated but that a tracer dye can travel between the cells through the pericellular space. What is the identity of this structure? A. Communicating junction B. Tight junction C. Gap junction D. Desmosome

D The dark structure spanning the cell membranes is a desmosome. Desmosomes are a type of anchoring junction which connect adjacent cells & extend through the cell membrane to associate w/ components of the cytoskeleton. Unlike gap junctions (aka communicating junctions), desmosomes do not link the cytoplasms of the two cells (the cells are not electrically coupled). Tight junctions form connections w/ adjacent cells but prevent pericellular diffusion of molecules, including that of a tracer dye.

Which of these is the primary source of calcium ions in smooth muscle? A. Intracellular space B. T-tubules C. Sarcoplasmic reticulum (SR) D. Extracellular space

D The primary source of calcium ions in smooth muscle is the extracellular space. The SR is poorly developed in smooth muscle cells. As a result, they rely primarily on extracellular Ca2+ to mediate contraction via Ca2+ binding to calmodulin. There is some calcium stored in the SR that can be released when a smooth myocyte is depolarized, however, this is a significantly smaller amount compared to what enters the cell via Ca2+ channels. The intracellular space is always low in Ca2+. T-tubules do not store calcium; they are responsible for propagating surface depolarization into myocytes.

Which of the following describes an amplification step in the G-protein signaling cascade? A. Activation of multiple receptors by the ligand B. Dissociation of G from the beta and gamma subunits C. Binding of multiple ligands to the receptor D. Activation of multiple G-proteins by bound receptor

D. Activation of multiple G-proteins by the bound receptor is one of multiple amplification steps in the G-protein signaling cascade. The G-protein cascade begins w/ association of ligand w/ its receptor which causes receptor activation & subsequent activation of multiple G-proteins (an amplification step). This causes the dissociation of the alpha subunit from the beta & gamma subunits (which is not an amplification step). The G subunit then activates an effector enzyme which generates a product (another amplification step). Note that binding of multiple ligand molecules to a receptor would not be a form of amplification (should it ever happen) & activation of multiple receptors by a single ligand occurs sequentially (one at a time) & would not be an amplification step.

Cartilage can play roles in support, flexibility, or a combination of the two. The strongest cartilage is fibrous, the most flexible is elastic, and hyaline cartilage is in between, both strong and somewhat flexible. Which of the following structures is most likely made of elastic cartilage? A. Articular (joint) cartilage B. Intervertebral disks C. Pubic symphysis D. Epiglottis

D. The epiglottis is found in the respiratory tract, above the opening to the trachea. When swallowing, the epiglottis must fold downward to seal off the trachea thus preventing food & liquid from entering. This requirement for flexibility makes the epiglottis most likely to be made of elastic cartilage. Articular cartilage needs to be strong but somewhat flexible & is made of hyaline cartilage, & both the intervertebral disks & the pubic symphysis must be very strong & are made of fibrous cartilage.

All of the following are true regarding the innervation of skin by the autonomic nervous system EXCEPT: A. the sympathetic nervous system causes increased sweating. B. postganglionic sympathetic neurons that innervate sweat glands release acetylcholine. C. the skin does not receive parasympathetic innervation. D. the sympathetic nervous system causes dilation of blood vessels in the skin

D. All of the listed responses are true regarding the innervation of skin by the autonomic nervous system EXCEPT the sympathetic nervous system causes dilation of blood vessels in the skin. The sympathetic NS mediates the "fight or flight" response & causes increased sweating (to accommodate increased heat production from muscle activity, "the sympathetic nervous system causes increased sweating" is true) & constriction of blood vessels in the skin (so that blood is shunted to the skeletal muscles, which are working overtime, "the sympathetic nervous system causes dilation of blood vessels in the skin" is false & the correct answer choice). The skin only receives sympathetic innervation. Answer "postganglionic sympathetic neurons that innervate sweat glands release ACh" is actually true: The innervation of sweat glands is one exception to the rule that postganglionic sympathetic neurons only secrete NEpi.

As the molality of a solution increases, how are its boiling point & vapor pressure affected? A. Both boiling point & vapor pressure decrease. B. BP decreases & vapor pressure increases C. Both boiling point & vapor pressure increase. D. BP increases & vapor pressure decreases.

D. Boiling point increases w/ an increasing concentration of solutes b/c more energy is required to separate the water from those solutes. Vapor pressure decreases w/ an increasing conc. of solutes; since it takes more energy to trigger evaporation, there will be less solvent evaporating, & thus less pressure due to those evaporated solvent molecules. As a side note, remember that BP elevation is proportional to the van't Hoff value for the solutes involved.

A student becomes anxious during his final exam and begins hyperventilating. Which of the following is/are true? I. Blood pH increases II. Blood CO2 levels decrease III. O2 saturation of hemoglobin increases A. I only B. I and II only C. II and III only D. I, II, and III

D. Items I & II are true: hyperventilation causes the loss of excess CO2, which shifts the equilibrium of the respiratory equation to the left. As H+ and HCO3- combine to form H2CO3, blood pH increases (choices A and C can be eliminated). Item III is true: as blood pH increases, the oxygen saturation curve of hemoglobin shifts to the left. A left-shifted curve means that hemoglobin's affinity for oxygen is increased, and it will be more saturated (choice B can be eliminated and choice D is correct).

All of the following are functions of the liver EXCEPT: A. glycogen storage. B. synthesis of blood proteins. C. bile production. D. secretion of digestive enzymes.

D. The liver has a number of functions in the body, including synthesis of bile (choice C can be eliminated (bile is produced by the liver, & is stored & concentrated in the gallbladder), glycogen storage & metabolism (choice A can be eliminated), synthesis of blood proteins (such as albumin, fibrinogen, angiotensinogen, lipoproteins, etc., choice B can be eliminated), amino acid metabolism, urea production, vitamin storage, detox, etc. However, the liver does not secrete digestive enzymes (choice D is not a function of the liver & is correct).

Various disorders of the liver can lead to jaundice (yellowing of the skin and eyes), a darkened urine color ("Coca-Cola" urine), and feces that is very light in color. Why would liver problems cause this change in excretory products? A. Antibodies created to fight infection in the liver also have an impact on the function of the large intestine & kidneys. B. Inflammation of the liver leads to an increase in damaged erythrocytes which then show up in the urine, creating its darkened color. C. Liver problems cause changes in the flora of the gut, thus altering the appearance of the body's solid waste. D. When the liver is adversely impacted, bilirubin may not be properly routed to the gut & instead may end up being filtered by the kidneys.

D. Liver problems cause the described changes in excretory products b/c when the liver is adversely impacted, bilirubin may not be properly routed to the gut & instead may end up being filtered by the kidneys. The liver is responsible for recycling the components of worn out erythrocytes, & the waste product produced from the breakdown of heme is bilirubin. Normally, it is routed to the gut for elimination, thus creating the typically dark color of solid waste, but problems w/ the liver can leave bilirubin circulating, causing it to collect in the skin (leading to jaundice) & end up in the urine (leading to the dark urine color). Damaged erythrocytes should not show up in the urine unless the glomerular basement membrane is also damaged. There is no inherent connection between the functioning of the liver & the state of intestinal flora. Antibodies would be specific to an infection of the liver and would not impact other organs unless the same organism was also infecting those other organs.

A patient with bulimia begins to develop lethargy which is believed to be related to metabolic alkalosis. Which of the following best explains this finding? A. A decrease in the cooperativity of oxygen binding to hemoglobin B. An increase in oxygen delivery due to hemoglobin's decreased oxygen affinity C. A right-shift in the oxygen saturation curve for hemoglobin D. A left-shift in the oxygen saturation curve for hemoglobin

D. Repeated vomiting can raise blood pH (metabolic alkalosis) & increase hemoglobin's affinity for oxygen (B is wrong). This is seen as a left-shift in the oxygen saturation curve for hemoglobin (D is correct & C is wrong). Note that answer choices B & C describe decreased oxygen affinity which may be due to situations such as acidosis, increased temperature, or increased CO2. Cooperativity does not change significantly w/ the shift described by Bohr effect; the curve would still be sigmoidal (choice A is wrong).

Why is the first step of apoptosis to disassemble the cytoskeleton? A. Disassembling the cytoskeleton provides a channel for cytokines to enter the cell. B. Disassembling the cytoskeleton allows for the filaments to be recycled as part of programmed cell death. C. Disassembling the cytoskeleton provides a source of ATP to power the process of programmed cell death. D. Disassembling the cytoskeleton allows the cell to shrink, thus minimizing damage to neighboring cells as it is destroyed.

D. The breakdown of the cytoskeleton makes the cell smaller, pulls it away from neighboring cells & thus reduces the risk of damage to other cells as its phagocytic destruction continues. The filaments do not need to be recycled as part of apoptosis nor do they provide energy. Cytokines trigger apoptosis as opposed to entering the cell as part of the process.

The effects of aldosterone on sudoriferous (sweat) glands of the skin are analogous to this hormone's effects on nephrons within the kidney. Which of the following is correct regarding how aldosterone influences the salt content of sweat? A. Aldosterone increases the secretion of sodium, making sweat more concentrated. B. Aldosterone decreases the secretion of sodium, making sweat more concentrated. C. Aldosterone increases the secretion of sodium, making sweat more dilute. D. Aldosterone decreases the secretion of sodium, making sweat more dilute

D. The effects of aldosterone on sudoriferous (sweat) glands of the skin are analogous to this hormone's effects on nephrons w/in the kidney. Aldosterone decreases the secretion of sodium, making sweat more dilute is correct regarding how aldosterone influences the salt content of sweat. Aldosterone increases blood pressure. Aldosterone increases renal sodium reabsorption, returning more sodium to the blood. In the skin, this hormone also acts to conserve sodium by decreasing this ion's secretion. Sweat with less sodium (salt) will be more dilute, not more concentrated ("aldosterone decreases the secretion of sodium, making sweat more dilute" is correct and "aldosterone decreases the secretion of sodium, making sweat more concentrated" is wrong).

The liver has all of the following functions EXCEPT: A. the storage of glycogen. B. deamination of amino acids. C. the conversion of carbohydrates to fats. D. synthesis of red blood cells.

D. The liver plays a key metabolic role in many ways. One thing the liver does is store carbs as glycogen during periods in which carbs & energy are abundant (eliminates "storage of glycogen"). The liver is also involved in fat metabolism. If glycogen stores are at max levels, glucose is converted to fatty acids & stored as TGs (eliminates "conversion of carbohydrates to fats"). The deamination of amino acids can be performed in the liver to allow AAs to enter metabolic pathways, providing energy (eliminates "deamination of amino acids"). The synthesis of RBCs occurs in the bone marrow & is not associated with the liver.

A researcher discovers that a molecule of interest can travel across the cell membrane. To characterize how this happens, he increases the external concentration & records rate of entry into the cell. He discovers that there appears to be no limit (w/in physiological conditions) to how quickly the compound can enter the cell. How is the molecule entering the cell? A. Facilitated diffusion B. Secondary active transport C. Primary active transport D. Simple diffusion

D. The molecule that can enter the cell membrane w/ no effective upper limit to its rate is undergoing simple diffusion. The rate of diffusion of a solute across a membrane is proportional to its conc. & does not saturate. If the molecule was moving by facilitated diffusion, we would observe a max rate of transport b/c the protein carrier/channel becomes saturated & no greater rate of transport is possible. Active transport (primary & secondary) requires energy & also saturates. Note primary active transport relies upon ATP hydrolysis, while secondary active transport utilizes a conc. gradient (established by a primary active transporter) to drive a diff. molecule against its conc. gradient.

The renal medulla is made up primarily of: A. glomeruli. B. nephrons. C. proximal tubules. D. collecting ducts.

D. The renal medulla is divided into regions called pyramids, which are composed of collecting ducts (choice D is correct). Glomeruli are the beginning of the nephron, where filtration occurs, & proximal tubules are found directly after glomeruli; both are located in the renal cortex (A & C are wrong). While portions of the nephron are found in the renal medulla, "nephron" is a broad term and not the best answer choice here (choice D is better than choice B).

What effect does growth hormone have on the epiphyseal plate during childhood development? A. Collagen is deposited at the epiphyseal plate, extending the length of the bone & becoming part of its infrastructure. B. Collagen is deposited at the epiphyseal plate, extending the length of the bone before being replaced by cartilage & hydroxyapatite. C. Cartilage is deposited at the epiphyseal plate, extending the length of the bone & becoming part of its infrastructure. D. Cartilage is deposited at the epiphyseal plate, extending the length of the bone before being replaced by collagen & hydroxyapatite.

D. During the primary bone growth & development of childhood, GH causes the deposition of cartilage at the epiphyseal plate to lengthen the bone (choices A and B are wrong). This cartilage is soon replaced with the long-term bone components of collagen & hydroxyapatite (a calcium-phosphate crystalline solid) (C is wrong & D is correct).

Low blood pressure and low blood volume trigger which of the following? A. An increase in ADH followed by a subsequent decrease in aldosterone B. An increase in ADH followed by a subsequent increase in aldosterone C. An increase in aldosterone followed by a subsequent decrease in ADH D. An increase in aldosterone followed by a subsequent increase in ADH

D. First, aldosterone levels increase (choices A and B are wrong). This allows sodium reabsorption from the distal nephron. The resulting increase in plasma osmolarity triggers antidiuretic hormone (ADH, or vasopressin) release (choice C is wrong and choice D is correct). This induces expression of water channels on the cells of the distal tubule and collecting duct, allowing water reabsorption.

If a baby is born with both male and female genitalia, which of the following is a possible explanation? A. The baby is genetically female and there was a mutation in the gene for Wolffian inhibiting factor. B. The baby is genetically male and there was a mutation in the gene for Wolffian inhibiting factor. C. The baby is genetically XXY and the extra X chromosome caused a surge in estrogen leading to development of both genitalia. D. The baby is genetically male and there was a mutation in the gene for Mullerian inhibiting factor

D. If a baby is born with both male & female genitalia, a possible explanation for this is that the baby is genetically male & there was a mutation in the gene for Mullerian inhibiting factor. The Y chromosome must be present for male genitalia to develop, and Mullerian inhibiting factor (MIF) must be present to prevent female genitalia from developing. If the Y chromosome is present, and MIF is absent or mutant (non-functional), then both sets of genitalia will develop. There is no such thing as Wolffian inhibiting factor. An extra X chromosome would not lead to increased estrogen, & even if it did, as long as MIF was present, no female genitalia would develop.

The inheritable disease myoclonic epilepsy & ragged red fiber disease (MERRF) is caused by a mutation in one of the mitochondrial transfer RNA genes. The disease is characterized by a decrease in synthesis of the mitochondrial proteins required for electron transport and&ATP production. A cell containing many mitochondria afflicted by MERRF would demonstrate: I. decreased intracellular Na+ concentrations. II. decreased negativity of the interior of the cell. III. decreased activity of secondary active transport proteins. A. II only B. III only Your Answer C. I and II only D. II and III only

D. Item I is false: since MERRF leads to a decrease in ATP production, the Na+/K+ ATPase function, which depends on ATP, will be inhibited. This means that not as much Na+ will be pumped out of the cell, and&intracellular Na+ would increase, not decrease (choice C can be eliminated). Item II is true: normally 3 Na+ ions are pumped out the cell while 2 K+ ions are pumped in. W/ inhibition of the pump, MERRF would lead to less positive charge leaving the cell & more remaining inside. Thus, the cell would become less negative on the inside (choice B can be eliminated). Item III is true: since not as much Na+ is pumped out of the cell, secondary active transporters will have less of a Na+ gradient to work with, & thus will decrease in activity (A can be eliminated & D is correct).

If the production of surfactant were reduced, which of the following effects would be most likely to occur? A. Surface tension in the alveoli would decrease B. Surface tension in the bronchioles would decrease C. Surface tension in the bronchioles would increase D. Surface tension in the alveoli would increase

D. Surface tension in the alveoli would INCREASE if the production of surfactant were reduced. Surfactant is produced in the alveoli so it primarily affects surface tension in that region. It may have some small effect on the respiratory bronchioles (which contain alveoli in their walls) due to the leakage of surfactant from these alveoli into the respiratory bronchiole tube. However, it would not have any effect on the terminal bronchioles, nor on any structure higher in the respiratory tree. Since the question asks for the most likely effect, & since it does not differentiate between the respiratory & terminal bronchioles, "surface tension in the bronchioles would decrease" & "surface tension in the bronchioles would increase" can be eliminated. Normally, the presence of surfactant REDUCES surface tension in the alveoli, so if the production of surfactant were decreased, we would expect to see an increase in alveolar surface tension.

Which of the following is made up of pluripotent cells? A. The mesoderm B. The zygote C. The morula D. The inner cell mass

D. The cells of the inner cell mass differentiate into the three primary germ layers & have the ability to become any cell in the body; they are considered to be pluripotent cells (choice D is correct). The mesoderm is one of the three primary germ layers & can become many, but not all cell types in the body; it is considered to be multipotent (choice A is wrong). The zygote & morula are totipotent; they can become any of the cells in the body & can also form the trophoblast (choices B and C are wrong).

When is meiosis II of oogenesis considered complete? A. After 1st polar body is secreted & disintegrates B. After the primary oocyte completes cytokinesis C. After the secondary oocyte is fertilized D. When 4 ootids are generated from 1 oogonium

D. The secondary oocyte starts meiosis II before ovulation but freezes in metaphase II. Meiosis II is completed (& the 2nd polar body is secreted) only if fertilization occurs (choice C is correct). Note, only one ootid is generated from a oogonium, b/c of polar body secretion (D is wrong). The disintegration of the 1st polar body is not part of meiosis II (A is wrong), & division of the primary oocyte is part of meiosis I (choice B is wrong)

Human chorionic gonadotropin (hCG) is secreted from which structure to help maintain pregnancy? A. Inner cell mass B. Morula C. Zygote D. Trophoblast

D. hCG is secreted from the trophoblast to help maintain pregnancy. hCG is secreted from the trophoblast (which ultimately becomes the placenta) during early development to keep the corpus luteum from degenerating. This keep progesterone high in order to maintain the uterine lining. The inner cell mass ultimately becomes the embryo and does not secrete hCg, the zygote is the initial cell formed when the sperm and egg fuse, and the morula is a solid ball of cells formed after many cell divisions of the zygote.

Angiotensin II acts as a vasoconstrictor to increase blood pressure in the short term, but it also triggers the release of what hormone to perpetuate this effect? A. Antidiuretic hormone B. Erythropoietin C. Oxytocin D. Aldosterone

D. RAAS system = Renin Angiotensin Aldosterone System

The epidermis of the skin is embryologically derived from the same germ layer that gives rise to which of the following? A. Skeletal muscle B. Liver C. Stomach D. Spinal cord

D. The epidermis of the skin is embryologically derived from the same germ layer that gives rise to the spinal cord. (things that make you attractive = ectoderm) You must memorize which adult tissues are derived from each of the 3 primary germ layers. The endoderm give rise to the stomach, the colon, the liver, the pancreas, the urinary bladder, the lining of the urethra, & the epithelial parts of the trachea, lungs, pharynx, thyroid, parathyroid, & intestines. The mesoderm gives rise to skeletal muscle, the skeleton, the dermis of the skin, connective tissue, the urogenital system, all parts of the cardiovascular system, the blood, & the spleen. The ectoderm gives rise to the CNS (brain & spinal cord), lens of the eye, ganglia & nerves, head connective tissue (pharyngeal cartilages, hyoid bone, auditory ossicles, etc.), the epidermis, hair, sweat glands, & mammary glands. This content is important to know for the MCAT.