Question 1

When does the heartbeat of a human fetus starts?

Accepted Answer

Answer reason: In the fourth week of its development. The primitive heart tube begins to beat and circulate blood around day 22–23 after fertilization, which falls in the 4th week of embryonic development. The 1st week is dominated by fertilization/cleavage and implantation, before cardiac morphogenesis. While cardiac activity may be detectable by ultrasound around 5.5–6 weeks of gestational age, the heartbeat itself starts earlier at about week 4 of embryonic age.
Category reason: This question tests timing of early fetal/embryonic cardiac development (onset of heartbeat), which is a core concept in embryology rather than a nursing intervention or care decision.

Question 2

Q.1259 WHEN DOES THE FETAL HEART START BEATING?

Accepted Answer

Answer reason: The primitive heart tube forms and begins contractile activity early in embryogenesis, typically around day 22, which corresponds to the 4th week of gestation. This early rhythmic activity precedes formation of the fully partitioned, four-chambered heart, which develops over subsequent weeks. By about 6 weeks, cardiac activity is often detectable on transvaginal ultrasound, but the onset of beating occurs earlier.
Category reason: This question tests timing of early human developmental milestones (onset of embryonic cardiac activity), which is a core topic in embryology rather than nursing care decision-making.

Question 3

Ost of the nervous system is derived from which germ layer?

Accepted Answer

Answer reason: The central and peripheral nervous systems develop primarily from neuroectoderm, which arises from the ectodermal germ layer. During neurulation, the neural plate forms from ectoderm and folds to create the neural tube (future brain and spinal cord). Neural crest cells, also ectoderm-derived, give rise to many peripheral nervous system structures (e.g., sensory and autonomic ganglia).
Category reason: This question tests germ-layer origin of the nervous system, a core concept in embryologic development rather than clinical nursing decision-making.

Question 4

Identical twins are also called?

Accepted Answer

Answer reason: Identical twins arise when a single fertilized ovum (one zygote) splits into two embryos, resulting in genetically very similar offspring. This contrasts with dizygotic (fraternal) twins, which come from two separate ova fertilized by two separate sperm. “Heterozygous” describes allele variation at a gene locus rather than a type of twinning, and “polyzgotic” is not a standard classification for twins.
Category reason: This item tests the origin and terminology of twins based on zygote formation and early embryonic development, which is primarily an Embryology concept rather than a nursing-care decision.

Question 5

In human muscle is derived from?

Accepted Answer

Answer reason: Skeletal, cardiac, and most smooth muscle tissues originate from the mesoderm during embryonic development. Specifically, paraxial mesoderm (somites) forms most skeletal muscles, while splanchnic mesoderm contributes to cardiac and much of the smooth muscle of viscera and vessels. Endoderm mainly forms epithelial linings of the gastrointestinal and respiratory tracts, and ectoderm primarily forms the nervous system and epidermis, making them incorrect here.
Category reason: This is a question about germ-layer derivatives during development, which is a core Embryology concept rather than patient-care decision-making.

Question 6

Conjoined twins result from division occurring after how many days of fertilization?

Accepted Answer

Answer reason: Monozygotic twinning timing determines chorionicity and amnionicity. When embryonic division happens late—around days 8–12, after formation of the chorion but before completion of the amnion—an incompletely separated embryo may result, leading to conjoined twins (typically from very late splitting around/after day 13). Earlier splitting (e.g., within 72 hours or 4–8 days) produces separate or shared placental structures but not conjoined twins.
Category reason: This question tests timing of embryonic division and its developmental consequences (twinning and conjoining), which is a core concept in Embryology rather than nursing care decision-making.

Question 7

What is the first cell formed after fertilization?

Accepted Answer

Answer reason: Fertilization is the fusion of a sperm and ovum to form a single diploid cell, which is the earliest developmental stage. The blastocyst forms later after multiple mitotic divisions and cavitation, and the term embryo applies after implantation and further differentiation. Therefore, the immediate product of fertilization is the zygote.
Category reason: This question tests knowledge of early human developmental stages following fertilization, which is a core topic in Embryology rather than nursing care decision-making.

Question 8

First Cell of Human Body is...?

Accepted Answer

Answer reason: The first cell of a new human organism is formed at fertilization when the sperm and ovum nuclei fuse, creating a single diploid cell. This cell is totipotent and undergoes cleavage divisions to form the early embryo. Gametes (sperm and egg) are haploid reproductive cells and are not the first cell of the developing individual, and RBCs arise much later during hematopoiesis.
Category reason: This item tests early human development and the cell formed immediately after fertilization, which is a core topic in Embryology.

Question 9

A patient is seen in the clinic. He has an autosomal-recessive disorder that resulted in a deficiency in tyrosinase activity in specific cells. He appears pale, with light blond hair and blue eyes, and notes that he sunburns easily and that his eyes are very sensitive to light. The cells most involved in this condition are derived from which of the following germ layers?

Accepted Answer

Answer reason: Tyrosinase deficiency causing hypopigmentation, easy sunburning, and photophobia is consistent with albinism due to impaired melanin production in melanocytes. Melanocytes arise from neural crest cells, which are derived from neuroectoderm. Therefore, the germ-layer origin of the key affected cells is neuroectoderm via the neural crest lineage. The other germ layers do not give rise to melanocytes.
Category reason: This question tests embryologic origin (germ-layer derivation) of melanocytes rather than nursing interventions, making it a foundational biomedical science question under Embryology.

Question 10

According to the branching pattern the villi may be?

Accepted Answer

Answer reason: C. ramuli chorii : Finer branches – ramuli are attached to the cytotrophoblastic shell. Chorionic villi are classified by their branching into stem villi (truncus), intermediate branches (rami), and terminal/finer branches (ramuli). The terminal villi form the most delicate arborization and are the main sites for maternal–fetal exchange. These finer branches are supported and anchored in relation to the cytotrophoblastic shell, which stabilizes the villous tree within the placenta.
Category reason: This item tests classification of chorionic villi and related placental structures, a foundational concept in early human development and placentation, which falls under Embryology.

Question 11

Tertiary chorionic villi consist of

Accepted Answer

Answer reason: Tertiary chorionic villi are defined by the development of a fetal vascular core within the villus, allowing establishment of fetoplacental circulation. Primary villi contain only trophoblast layers, and secondary villi add extraembryonic mesoderm, but neither has vessels. The appearance of fetal capillaries is the distinguishing feature that makes the villi “tertiary,” enabling maternal–fetal exchange.
Category reason: This tests a developmental sequence and structural components of chorionic villi in placental formation, which is a core topic in Embryology rather than nursing care decisions.

Question 12

Umbilical arteries become:

Accepted Answer

Answer reason: After birth, the distal portions of the umbilical arteries fibrose and persist as medial umbilical ligaments on the inner surface of the anterior abdominal wall. The proximal portions remain patent as branches of the internal iliac arteries (superior vesical arteries). The other listed ligaments derive from different fetal structures (ductus venosus, ductus arteriosus, and umbilical vein).
Category reason: This question tests the postnatal remnants of fetal vessels (fetal circulation derivatives), which is a core topic in embryology rather than nursing care decision-making.

Question 13

Conjoined Twins are more common in?

Accepted Answer

Answer reason: Conjoined twinning results from abnormal events in the splitting of a single fertilized egg, typically due to incomplete separation of the embryonic disc. Because it originates from one zygote, it is a form of monozygotic twinning rather than dizygotic twinning. Dizygotic twins arise from two separate ova and sperm and therefore cannot produce conjoined embryos. This is a foundational concept in early embryologic development and twinning.
Category reason: This question tests the developmental origin of conjoined twins (timing/abnormal splitting of the embryo), which is a core topic in Embryology rather than nursing care decision-making.

Question 14

Fertilized ovum is embedded in the endometrium at about which day after fertilization?

Accepted Answer

Answer reason: Implantation typically begins when the blastocyst reaches the uterine cavity and attaches to the endometrium around day 6 after fertilization. The trophoblast then starts invading the endometrial lining over the next several days. Earlier days (2–4) correspond more to cleavage and morula/early blastocyst transport through the tube, while day 10 is later than the usual onset of embedding.
Category reason: This tests timing of implantation and early human development events after fertilization, which is a core topic in Embryology rather than nursing intervention or prioritization.

Question 15

Which defect shows "banana sign" on prenatal ultrasound?

Accepted Answer

Answer reason: B. Spina bifida The banana sign refers to a curved, “banana-shaped” cerebellum caused by downward displacement of the hindbrain (Chiari II malformation). This finding is classically associated with open neural tube defects, most commonly myelomeningocele, which is a form of spina bifida. It is often accompanied by other prenatal ultrasound markers such as the lemon sign and ventriculomegaly.
Category reason: This question tests recognition of a prenatal ultrasound marker linked to a congenital neural tube defect and its developmental mechanism, which is best categorized under Embryology.

Question 16

Encephalocele most commonly occurs at:

Accepted Answer

Answer reason: Encephalocele is a neural tube defect due to failure of midline cranial closure, producing herniation of meninges with or without brain tissue through a skull defect. The most frequent location is the occipital region (posterior skull), especially in many Western populations. Other sites (frontal, parietal, temporal) occur less commonly. This distribution reflects typical patterns of cranial dysraphism during embryologic development.
Category reason: This question tests the most common anatomic site of a congenital neural tube defect, which is primarily an embryology/developmental anatomy concept rather than a nursing intervention decision.

Question 17

Which defect involves herniation of brain tissue through a skull defect?

Accepted Answer

Answer reason: B. Encephalocele Encephalocele is a neural tube defect characterized by herniation of intracranial contents (often brain tissue and meninges) through a congenital defect in the skull, commonly in the occipital region. Spina bifida involves vertebral arch defects with potential spinal cord/meningeal protrusion, not brain tissue through the skull. Anencephaly is absence of a major portion of the brain and skull, and holoprosencephaly is a forebrain cleavage defect rather than a herniation through a bony defect.
Category reason: This is a congenital malformation/neural tube defect identification question focused on embryologic development and structural anomalies rather than nursing interventions, fitting Embryology within NursingScience.

Question 18

The portion of the placenta contributed by the embryo is the?

Accepted Answer

Answer reason: The fetal (embryonic) part of the placenta develops from the chorion, specifically the chorion frondosum, which forms the chorionic villi that interface with maternal blood. The maternal contribution is the decidua basalis from the endometrium. The amnion primarily forms the amniotic sac, while the yolk sac and allantois are important in early development (e.g., early hematopoiesis and umbilical structures) but are not the principal embryonic placental component.
Category reason: This question tests which embryonic membrane contributes to placental formation, a core concept in early human development and placentation, which falls under Embryology.

Question 19

Umbilical cord contains

Accepted Answer

Answer reason: In normal fetal circulation, the umbilical cord has two umbilical arteries that carry deoxygenated blood from the fetus to the placenta and one umbilical vein that returns oxygenated blood from the placenta to the fetus. This “2 arteries, 1 vein” pattern is a key anatomic fact used in newborn assessment. A single umbilical artery is an abnormal variant and can be associated with congenital anomalies, which is why correct baseline anatomy matters.
Category reason: This is a foundational question about normal fetal/placental anatomy and circulation, which is primarily studied under Embryology rather than nursing care decision-making.

Question 20

Neural tube closes completely by which day of embryonic life?

Accepted Answer

Answer reason: Neurulation occurs early in embryogenesis, with closure of the cranial neuropore around day 25 and the caudal neuropore around day 27–28. Completion of closure by the end of the 4th week is a key developmental milestone. Failure of closure during this window is associated with neural tube defects such as spina bifida and anencephaly, which is why folate is critical before and during early pregnancy.
Category reason: This is a timing question about a key developmental event (neural tube closure) during early embryogenesis, which is primarily tested under Embryology rather than nursing intervention or patient-care decision-making.

Question 21

Which condition shows “frog eye” appearance on antenatal scan?

Accepted Answer

Answer reason: B. Anencephaly On prenatal ultrasound, anencephaly (a neural tube defect due to failed closure of the cranial neuropore) results in absence of the cranial vault with protruding orbital structures. This produces the characteristic “frog-eye” appearance because the orbits are prominent without overlying frontal bones. The other listed conditions primarily involve cerebral malformations or CSF space enlargement without the typical absent calvarium finding that creates this sign.
Category reason: This question tests recognition of a congenital malformation identified on antenatal imaging and its developmental basis (neural tube closure), which is best classified under Embryology rather than nursing interventions or prioritization.

Question 22

Which of the following is a closed type of spinal dysraphism?

Accepted Answer

Answer reason: Closed spinal dysraphism refers to neural tube defects covered by intact skin, often termed occult dysraphism. Lipomeningocele is a skin-covered lesion with a subcutaneous lipoma that is contiguous with the meninges and may tether the spinal cord. In contrast, meningocele and myelomeningocele are typically open defects with exposed sac/neural elements, and encephalocele involves cranial rather than spinal herniation.
Category reason: This question tests classification of congenital neural tube defects (spinal dysraphism types) based on embryologic development and anatomic presentation, which most directly fits Embryology.

Question 23

Which of the following is not a risk factor for NTD?

Accepted Answer

Answer reason: Neural tube defects are strongly associated with impaired neural tube closure early in embryogenesis, particularly with inadequate folate availability. Teratogenic exposures such as valproic acid and maternal hyperglycemia (e.g., pregestational diabetes) increase the risk of congenital malformations including NTDs. Vitamin K deficiency is classically linked to bleeding tendencies (e.g., hemorrhagic disease) rather than failure of neural tube closure.
Category reason: This question tests embryologic risk factors for congenital neural tube defects rather than nursing interventions or prioritization, so it fits Embryology within NursingScience.

Question 24

Most sensitive time period for folic acid supplementation to prevent NTDs is?

Accepted Answer

Answer reason: B. Preconception to 28 days post-conception Neural tube closure occurs very early in embryonic development (around the 3rd–4th week after conception), often before pregnancy is recognized. Adequate folate must be present during this narrow window to reduce the risk of neural tube defects such as spina bifida and anencephaly. Supplementation started after this period (later first trimester or beyond) is less effective for primary prevention because the critical morphogenetic event has already occurred.
Category reason: This tests timing of a key early developmental event (neural tube closure) and prevention of congenital malformations, which is primarily an Embryology concept rather than a nursing-intervention prioritization scenario.

Question 25

Holoprosencephaly is a failure of?

Accepted Answer

Answer reason: C. Cerebral hemispheres to divide Holoprosencephaly results from failed or incomplete cleavage of the embryonic forebrain (prosencephalon) into two distinct cerebral hemispheres and ventricles. This early midline developmental defect often leads to associated facial anomalies due to disrupted midline patterning. Neural tube closure defects are a different category (e.g., spina bifida, anencephaly), and skull ossification defects do not explain the defining brain malformation. Brainstem development is not the primary embryologic failure in holoprosencephaly.
Category reason: This question tests an embryologic mechanism of a congenital brain malformation (forebrain cleavage), which is primarily studied in Embryology rather than nursing care decision-making.

Question 26

Which of the following is not a neural tube defect?

Accepted Answer

Answer reason: Neural tube defects result from failure of closure of the neural tube and include anencephaly and open spinal dysraphism (e.g., meningocele) as well as cranial herniation defects like encephalocele. Hydrocephalus is an abnormal accumulation of cerebrospinal fluid due to impaired flow or absorption, most commonly from obstruction (e.g., aqueductal stenosis) or other causes. It can occur secondary to neural tube defects (especially myelomeningocele/Chiari II), but it is not itself classified as a primary neural tube closure defect.
Category reason: This question tests embryologic classification of congenital malformations arising from neural tube closure versus other mechanisms, which is primarily Embryology rather than nursing care decision-making.

Question 27

The “lemon sign” on prenatal ultrasound suggests:

Accepted Answer

Answer reason: The “lemon sign” describes scalloping/concavity of the frontal bones on fetal ultrasound, most classically associated with open spina bifida and Chiari II malformation. It reflects altered intracranial pressure dynamics and posterior fossa abnormalities that accompany these neural tube closure defects. Microcephaly is primarily a reduced head circumference pattern, hydrocephalus is ventriculomegaly, and porencephaly refers to cystic cavities in the brain—none are specifically indicated by the lemon-shaped frontal contour.
Category reason: This question tests recognition of a prenatal ultrasound marker that arises from abnormal neural tube development and fetal morphogenesis, which is most directly covered under Embryology.

Question 28

Which of the following is a closed neural tube defect?

Accepted Answer

Answer reason: Closed neural tube defects are skin-covered spinal dysraphisms without an exposed neural placode. Myelomeningocele and encephalocele are typically open defects with herniation of neural tissue through a bony defect, and anencephaly is an open cranial neural tube defect with absent calvarium. Sacral agenesis (caudal regression spectrum) presents as a closed spinal anomaly with absent or malformed sacral vertebrae and may be grouped with occult/closed dysraphism in exam classifications.
Category reason: This question tests classification of congenital malformations arising from neurulation and caudal development, which is primarily an embryology topic rather than a nursing intervention or patient-care decision.

Question 29

At 5 month gestation, which of the following fetal development would probably be achieved?

Accepted Answer

Answer reason: Quickening is typically perceived by the pregnant client around 16–20 weeks’ gestation, and by 5 months (~20 weeks) fetal movement is commonly felt. Vernix caseosa is present earlier but becomes more prominent later in the second trimester and is not reliably described as covering the entire body at exactly 5 months. Fetal viability is generally not expected at 20 weeks (more commonly ~24 weeks or later). Braxton Hicks contractions can occur during pregnancy but are maternal uterine activity and are more characteristically noticed later, making this less specific than quickening for 5 months.
Category reason: This question tests timing of normal fetal developmental milestones during gestation, which is a foundational concept in prenatal development within Embryology rather than a nursing intervention decision.

Question 30

Which week fetus & placenta weight equal?

Accepted Answer

Answer reason: Around 19 weeks, placental weight has increased rapidly while fetal weight is rising but has not yet markedly exceeded placental mass, making them roughly equal. After this point, the fetus gains weight faster than the placenta, so equality becomes less likely in later weeks such as 21 or 23. Earlier than this (e.g., 17 weeks), the placenta is typically still relatively heavier compared with the fetus, so equality is less consistent.

Question 31

Fetal stage starts at?

Accepted Answer

Answer reason: In standard embryology, the embryonic period spans weeks 3 through 8 post-fertilization. Therefore, the fetal stage starts at the beginning of week 9. Options like 3 or 6 weeks fall within organogenesis, and 12 weeks is later within an already-established fetal period.

Question 32

Cervix develops from :-

Accepted Answer

Answer reason: The cervix specifically forms as part of the fused caudal Müllerian ducts that also contribute to the uterovaginal canal. In contrast, the Wolffian (mesonephric) duct primarily contributes to male reproductive structures under androgen influence and regresses in typical female development. Mesonephron and metanephros are embryologic kidney structures and are not precursors of the cervix.

Question 33

Most of the major organ system are usually developed by the end of weeks ?

Accepted Answer

Answer reason: By about 12 weeks’ gestation, the major organ systems are established structurally, and subsequent fetal development is primarily growth and functional maturation. This is why the highest teratogenic risk is earlier (weeks 3–8), while later exposures more often affect growth and function rather than initial formation. Later time points such as 16 or 24 weeks correspond more to maturation and viability-related milestones, not completion of basic organ system development.

Question 34

Newborn baby is called?

Accepted Answer

Answer reason: Embryo and foetus are prenatal developmental stages, so they do not apply after delivery. Infant is a broader term that generally includes the first year of life, making it less precise for the immediate newborn period. Therefore, the most accurate single term for a newborn is the neonatal designation.

Question 35

Stage of pregnancy: (8 weeks- until birth) pregnancy last for about 40 weeks (280 days)

Accepted Answer

Answer reason: The timeframe given in the stem explicitly starts at 8 weeks and continues until birth, which corresponds to the fetal period. This period is characterized primarily by growth and maturation of organ systems rather than initial organogenesis. The embryonic label would be incorrect because it ends at approximately 8 weeks, not from 8 weeks onward.

Question 36

Mackel's diverticulum arises from?

Accepted Answer

Answer reason: The midgut derivative involved is the distal ileum, so the outpouching classically occurs on the antimesenteric border of the ileum. This also explains why it may contain ectopic gastric or pancreatic mucosa and present with painless lower GI bleeding in children. Foregut structures and large-bowel sites like the cecum or colon do not match the embryologic origin or typical anatomic location.

Question 37

From where lower vacina arises?

Accepted Answer

Answer reason: The urogenital sinus contributes endoderm that forms the vaginal plate, which then canalizes to become the lower vagina. The genital ridge primarily gives rise to the gonads, not the vaginal canal. The mesonephric (Wolffian) duct regresses in typical female development and is not the source of the lower vagina.

Question 38

"Rule of ten" is used for?

Accepted Answer

Answer reason: It indicates surgery is generally considered when the baby is about 10 weeks of age, weighs around 10 pounds, and has a hemoglobin near 10 g/dL, reflecting adequate physiologic reserve and reduced anesthetic risk. This rule is specific to cleft lip (not cleft palate timing, which is later based on speech and palatal growth considerations). TEF, CHD, and imperforate anus have different diagnostic and surgical timing frameworks and are not associated with this “10-10-10” heuristic.

Question 39

What is the first organ to develop in the embryo?

Accepted Answer

Answer reason: The cardiovascular system is the first functional system to develop, with the primitive heart tube forming and beginning to beat around week 3 (about day 22). This early pumping supports placental/embryonic blood flow before organs like lungs become functional. While the brain starts neurulation early, it is not the first organ to become functionally active in the way the developing heart is.

Question 40

From where ovary developed?

Accepted Answer

Answer reason: Primordial germ cells migrate into this ridge and differentiate into oogonia within developing ovarian follicles. The Müllerian (paramesonephric) duct develops the fallopian tubes, uterus, and upper vagina, not the ovary itself. The mesonephric (Wolffian) duct contributes to male internal genital structures, and the genital tubercle forms external genitalia.

Question 41

During activation, which parts of the sperm enter through the fertilization cone?

Accepted Answer

Answer reason: In mammals, the sperm head (containing the nucleus) enters, and the proximal part including the connecting piece/centriole region and midpiece can be incorporated early, whereas the distal flagellum is typically excluded and later degraded. This makes the option specifying nucleus plus middle piece the best match to what passes through the fertilization cone. Options claiming the entire sperm or only one subpart are incomplete or overinclusive relative to the typical entry process.

Question 42

What is term given for browny hair on fetus at?

Accepted Answer

Answer reason: This is termed lanugo and can be seen on the shoulders, back, and forehead. By contrast, vernix caseosa is a greasy, white protective coating on fetal skin rather than hair. Amnion and chorion are fetal membranes involved in gestation and placental formation, not hair growth.

Question 43

Embryonic stage in known as?

Accepted Answer

Answer reason: After week 8, development is referred to as the fetal period, characterized mainly by growth and maturation of already formed organs. The other choices are all time ranges within the fetal period (second/third trimester time frames), not the embryonic stage. This is why the 8-week cutoff is the key defining boundary for the embryonic stage.

Question 44

During which week does the fetal heart begin pumping it's own blood?

Accepted Answer

Answer reason: This initial pumping starts before the heart is fully formed into chambers, but it is sufficient to circulate embryonic blood through the developing vasculature. Weeks 5–6 are better associated with further septation and structural maturation rather than the onset of pumping. By week 9, the heart is far beyond the initial functional start point, making that timing too late for the first pumping activity.

Question 45

A neonate has an imperforate anus, tracheoesophageal fistula, and a single umbilical artery. A nurse suspects that the neonate might have which congenital disorder?

Accepted Answer

Answer reason: VATER/VACTERL includes vertebral defects, anal atresia (imperforate anus), cardiac defects, tracheoesophageal fistula with esophageal atresia, renal anomalies, and limb abnormalities; a single umbilical artery is a common associated finding suggesting multisystem malformations. The findings given directly match the A and TE components, making this association the best fit. Beckwith-Wiedemann is classically associated with macroglossia, organomegaly, and omphalocele, not this GI/airway combination. Turner’s syndrome primarily causes gonadal dysgenesis and characteristic features (e.g., webbed neck, coarctation), which do not explain these defects.

Question 46

How many germ layers are present in the developing embryo?

Accepted Answer

Answer reason: The ectoderm differentiates into structures like the nervous system and epidermis, the mesoderm into muscle, bone, blood, and connective tissues, and the endoderm into the epithelial linings of the GI and respiratory tracts and associated organs. A count of two would describe the earlier bilaminar disc stage (epiblast/hypoblast) before gastrulation is complete. Four or five layers are not part of the standard developmental model taught for human embryogenesis.

Question 47

Fertilization activates —?

Accepted Answer

Answer reason: These early divisions are the defining feature of cleavage and occur while the conceptus is traveling through the fallopian tube toward the uterus. Ovulation precedes fertilization, and implantation occurs later at the blastocyst stage after several cleavage divisions. Although metabolic activation of the oocyte also occurs, the classic single best “activated” event tested after fertilization is the onset of cleavage.

Question 48

Fertilization is important for—?

Accepted Answer

Answer reason: It also restores the species-specific chromosome number by combining maternal and paternal chromosomal sets. Genetic sex is determined at fertilization because the sperm contributes either an X or a Y chromosome, establishing XX or XY at the moment the zygote forms. Since all three listed outcomes occur as direct consequences of fertilization, the combined choice is the most accurate.

Question 49

The fertilised egg is called?

Accepted Answer

Answer reason: That one-cell stage is termed a zygote and represents the earliest point of a new organism’s development. “Embryo” refers to later stages after cell divisions and implantation have progressed, and “foetus” is a still later stage in pregnancy. “Ovum” is the unfertilized female gamete, so it does not apply after fertilization.

Question 50

Placental barrier initially has how many layers?

Accepted Answer

Answer reason: Classically, the initial placental barrier includes syncytiotrophoblast and cytotrophoblast, trophoblastic basement membrane, villous connective tissue (mesenchyme), fetal capillary endothelium plus its basement membrane(s), totaling seven layers. As gestation advances, cytotrophoblast largely disappears and the connective tissue thins, reducing the number of effective layers and facilitating diffusion. Lower numbers like 2 or 4 correspond to later, thinned placental membranes rather than the initial configuration.

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