Pregnancy and Embryonic development Questions in English

(D) The $Placenta$ is a structural and functional unit formed between the developing embryo (foetus) and the maternal body.
It facilitates the supply of oxygen and nutrients to the embryo and also helps in the removal of carbon dioxide and waste materials produced by the embryo.
Therefore,the correct option is $D$.

(B) During pregnancy,the placenta acts as an endocrine tissue and produces several hormones.
$1$. Human Chorionic Gonadotropin $(hCG)$
$2$. Human Placental Lactogen $(hPL)$
$3$. Relaxin
Estrogen and Progesterone are produced by the placenta as well,but they are also produced by the ovary in non-pregnant women.
Therefore,only $hCG$,$hPL$,and Relaxin are produced exclusively during pregnancy.
The total count is $3$.

(B) In the standard diagram of a human fetus within the uterus:
$P$ points to the finger-like projections arising from the chorion,known as Chorionic villi.
$Q$ points to the sac-like structure that is vestigial in humans but serves as an early site for blood cell formation,known as the Yolk sac.
Therefore,$P$ is Chorionic villi and $Q$ is Yolk sac.

(D) The placenta acts as an endocrine tissue and produces several hormones essential for pregnancy.
These hormones include:
$1$. Human Chorionic Gonadotropin $(hCG)$
$2$. Human Placental Lactogen $(hPL)$
$3$. Estrogens
$4$. Progesterone
$5$. Relaxin (produced in the later phase of pregnancy)
Since all five listed hormones are produced by the placenta,the correct answer is $5$.

(B) The correct matching is as follows:
$P$. After one month: The first sign of growing fetus is usually noticed by listening to the heart sound carefully. Thus, $P-II$.
$Q$. End of second month: The fetus develops limbs and digits. Thus, $Q-III$.
$R$. End of three months (first trimester): Most of the major organ systems are formed, for example, the limbs and external genital organs are well-developed. Thus, $R-I$.
$S$. During fifth month: The first movements of the fetus and appearance of hair on the head are usually observed during the fifth month. Thus, $S-IV$.
Therefore, the correct sequence is $(P-II), (Q-III), (R-I), (S-IV)$.

(D) By the end of $24$ weeks of gestation (end of the second trimester),several significant changes occur in the fetus:
$1$. The eyelids separate,and eyelashes are formed.
$2$. The body becomes covered with fine hair (lanugo).
Therefore,all the given options are correct.

(C) The average duration of human pregnancy,also known as the gestation period,is approximately $9$ months or $270-280$ days from the last menstrual period.
This period is divided into three trimesters,each lasting about $3$ months.
Therefore,the correct option is $C$.

(D) According to the $NCERT$ textbook on human reproduction:
$A.$ Correct: By the end of $12$ weeks (first trimester),most of the major organ systems are formed.
$B.$ Incorrect: Major organ systems are formed by the end of $12$ weeks,not $8$ weeks.
$C.$ Correct: The first sign of a growing fetus is the heart sound,which can be heard after one month of gestation.
$D.$ Correct: Limbs and digits develop by the end of the second month of pregnancy.
$E.$ Correct: The first movements of the fetus and the appearance of hair on the head are usually observed during the fifth month.
Therefore,statements $A, C, D,$ and $E$ are correct.

(A) In human pregnancy,the development of the foetus follows a specific timeline.
By the end of the first month of pregnancy,the embryo's heart is formed.
By the end of the second month,the foetus develops limbs and digits.
By the end of $12$ weeks (first trimester),most of the major organ systems,such as the limbs and external genital organs,are well-developed.
The first movements of the foetus and the appearance of hair on the head are usually observed during the fifth month.
By the end of $24$ weeks (second trimester),the body is covered with fine hair,eyelids separate,and eyelashes are formed.
Therefore,the correct answer is that most major organ systems are formed by the end of $12$ weeks.

(C) The placenta acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin $(hCG)$,human placental lactogen $(hPL)$,estrogens,and progestogens.
Among these,$hCG$,$hPL$,and relaxin are produced in women $ONLY$ during pregnancy.
Estrogens and progestogens are produced by the ovary as well,even in non-pregnant women.
Therefore,Estrogen is not produced exclusively during pregnancy.

(C) The first sign of a growing foetus can be noticed by listening to the heart sound carefully through the stethoscope.
During pregnancy,the heart of the foetus starts beating early,and by the end of the first month of pregnancy,the foetus's heart is formed.
However,the heartbeat becomes audible through a stethoscope as the pregnancy progresses,serving as a primary clinical indicator of a healthy,growing foetus.

(B) During pregnancy,the mammary glands of the female undergo differentiation.
This process involves the development of alveoli and ducts,which are stimulated by hormones such as estrogen,progesterone,and prolactin.
This differentiation prepares the mammary glands for the production and secretion of milk (lactation) after childbirth.

(C) temporary endocrine gland is one that functions as an endocrine organ only for a specific period during the life cycle of an organism.
In humans,the $Placenta$ acts as a temporary endocrine gland during pregnancy.
It produces several hormones essential for maintaining pregnancy,such as human chorionic gonadotropin $(hCG)$,human placental lactogen $(hPL)$,estrogens,and progestogens.
Once the pregnancy ends and the placenta is delivered,it ceases to function as an endocrine gland.
In contrast,the pineal gland,pancreas,and parathyroid glands are permanent endocrine glands that function throughout the life of an individual.

(D) The developmental milestones of a human foetus are as follows:
$1$. After $1^{st}$ month of pregnancy,the embryo's heart is formed. Thus,$A-iii$.
$2$. By the end of the $2^{nd}$ month,the foetus develops limbs and digits. Thus,$B-iv$.
$3$. By the end of the $3^{rd}$ month (first trimester),most of the major organ systems are formed. Thus,$C-ii$.
$4$. During the $5^{th}$ month,the first movements of the foetus and appearance of hair on the head are usually observed. Thus,$D-i$.
Therefore,the correct matching is $A-iii, B-iv, C-ii, D-i$.

(C) The process of formation of the three germinal layers (ectoderm,mesoderm,and endoderm) from the blastula is known as gastrulation.
This process occurs during the gastrula stage of embryonic development.
During gastrulation,the cells of the blastula undergo extensive rearrangement and migration to form these distinct layers,which eventually give rise to all the tissues and organs of the body.

(A) After ovulation,the ruptured Graafian follicle is converted into a temporary endocrine structure called the corpus luteum.
This process is known as luteinization.
The primary function of the corpus luteum is to secrete large amounts of progesterone,which is essential for the maintenance of the endometrium for potential implantation of the embryo.
Since the formation of the corpus luteum directly leads to the secretion of progesterone,the Reason is a correct explanation of the Assertion.

(A) During pregnancy,the placenta produces several hormones essential for maintaining the pregnancy and supporting fetal development.
$1$. Progesterone and Estrogen levels increase significantly to maintain the endometrium and support the growing fetus.
$2$. Cortisol levels also increase in maternal blood during pregnancy.
$3$. Thyroxine levels increase to support the increased metabolic rate of the mother.
$4$. $FSH$ and $LH$ levels decrease significantly during pregnancy due to the negative feedback effect of high levels of estrogen and progesterone on the anterior pituitary gland.
Therefore,the hormones that show increased levels are Progesterone $(b)$,Thyroxine $(c)$,Cortisol $(d)$,and Estrogen $(f)$.

(B) The human placenta is classified as 'haemochorial' because the maternal blood comes into direct contact with the foetal chorionic villi.
In this type of placenta,the maternal blood vessels are eroded,allowing the maternal blood to bathe the chorionic villi directly.
This facilitates the efficient exchange of nutrients,gases,and waste products between the maternal and foetal circulation.

(A) After fertilization, the zygote undergoes successive mitotic divisions called cleavage as it moves through the isthmus of the oviduct towards the uterus.
By the end of the $4^{\text{th}}$ day after fertilization, the embryo consists of $16-32$ cells.
This solid ball of cells is known as the morula, which resembles a mulberry in appearance.

(D) During the process of gastrulation,the inner cell mass differentiates into two layers: the hypoblast and the epiblast.
The epiblast is a layer of columnar cells that gives rise to the three primary germ layers: ectoderm,mesoderm,and endoderm.
Therefore,the primary ectoderm develops from the epiblast cells.

(C) The correct pairs are as follows:
$a$. Mesoderm: Forms all types of muscles of the body (except iris and ciliary muscles).
$b$. Ectoderm: Forms the iris and ciliary muscles of the eye.
$c$. Endoderm: Forms the lining of the middle ear.
$d$. Ectoderm: Forms the adrenal medulla,while the adrenal cortex is mesodermal in origin.
$e$. Mesoderm: Forms the sclera and choroid layer of the eye.
Therefore,the correct statements are $a, b, c,$ and $e$. However,based on the provided options,the most accurate selection is $b, c,$ and $e$ (Option $C$). Note: While $a$ is technically correct,it is often excluded in specific contexts where iris/ciliary muscles are highlighted as ectodermal exceptions.

(C) The first trimester of pregnancy covers the first $3$ months. During this period,the heart is formed and the heartbeat can be heard. Progesterone levels remain high to maintain the pregnancy,and the menstrual cycle is suspended. However,eyebrows and eyelashes appear during the second trimester (around the $5^{th}$ month) of pregnancy.

(A) The stages of human embryonic development occur as follows:
$a$. Fully formed morula: The morula stage is reached by the end of the $4^{\text{th}}$ day after fertilization $(a-iii)$.
$b$. Fully formed blastocyst: The blastocyst is fully formed by the end of the $7^{\text{th}}$ day after fertilization $(b-i)$.
$c$. Completion of implantation process: Implantation is generally completed by the end of the $10^{\text{th}}$ day after fertilization $(c-iv)$.
$d$. Fully formed gastrula: Gastrulation begins and proceeds,with the formation of the three germ layers typically becoming distinct around $15$ days after fertilization $(d-ii)$.
Therefore,the correct matching is $A-III, B-I, C-IV, D-II$.

$(D)$ $Statement-I$ is incorrect because the amniogenic cells line the roof of the amniotic cavity and divide to form the amnion, not the chorion.
$Statement-II$ is correct because the chorion is an extra-embryonic membrane that plays a crucial role in the development of the embryo by contributing to the formation of the placenta.

(D) During the early stages of pregnancy, the $Corpus \text{ } Luteum$ is essential for the secretion of progesterone, which maintains the endometrium and supports the developing foetus.
In the third week of pregnancy, the placenta is not yet fully functional to take over the production of progesterone.
If the $Corpus \text{ } Luteum$ regresses at this stage, the source of progesterone is lost.
As a result, the progesterone level in the blood drops significantly, leading to the shedding of the endometrium.
Consequently, the pregnancy cannot be maintained, and the foetus is aborted.

(B) In the provided graph,curve '$A$' represents the levels of estrogens during the menstrual cycle,which peaks before ovulation (around day $14$).
Curve '$B$' shows a sharp rise after day $28$,which is characteristic of human chorionic gonadotropin $(hCG)$ in a pregnant female.
$hCG$ is produced by the placenta after implantation to maintain the corpus luteum,which in turn continues to secrete progesterone to support pregnancy.
Therefore,'$A$' corresponds to estrogens and '$B$' corresponds to $hCG$.

(D) During human embryonic development,the process of gastrulation involves the formation of the three primary germ layers. The first germinal layer to differentiate from the inner cell mass is the endoderm. This occurs as cells from the epiblast migrate through the primitive streak to form the endoderm,followed by the mesoderm,and finally the ectoderm.

(C) The germinal layers in humans give rise to specific organs and tissues during embryonic development.
$1$. The $Ectoderm$ gives rise to structures like the epidermis, sweat glands, mammary glands, salivary glands, and the pineal gland.
$2$. The $Endoderm$ gives rise to the epithelial lining of the digestive tract, respiratory tract, and endocrine glands such as the thyroid gland, parathyroid gland, and thymus.
Therefore, among the given options, the thyroid gland is a derivative of the $Endoderm$.

(D) The diagram represents a blastocyst,which is an early stage of human embryonic development.
In this structure,the outer layer of cells is called the trophoblast.
The inner group of cells attached to the trophoblast is known as the inner cell mass (indicated by $A$).
The fluid-filled cavity present inside the blastocyst is called the blastocoel (indicated by $B$).
Therefore,$A$ represents the inner cell mass and $B$ represents the blastocoel.

(A) The average gestation period in humans is approximately $266$ days from the time of fertilization.
However,when calculated from the beginning of the Last Menstrual Cycle $(LMC)$,it is approximately $280$ days ($266$ days of development + $14$ days of the follicular phase before ovulation).

(C) The hormone $Relaxin$ is secreted by the $Corpus \ luteum$ during the later stages of pregnancy.
It helps in the relaxation of the pelvic ligaments and the widening of the birth canal,which facilitates the easy birth of the baby (parturition).
Therefore,the correct option is $C$.

(A) Cleavage is a series of rapid mitotic divisions of the zygote that converts the single-celled zygote into a multicellular structure called a blastula.
In each cleavage division,the number of cells (blastomeres) doubles.
- After the $1^{st}$ cleavage,the number of blastomeres = $2^1 = 2$.
- After the $2^{nd}$ cleavage,the number of blastomeres = $2^2 = 4$.
- After the $3^{rd}$ cleavage,the number of blastomeres = $2^3 = 8$.
Therefore,after the third cleavage,$8$ blastomeres are formed.

(C) During pregnancy,the placenta produces several hormones essential for maintaining the pregnancy,such as human chorionic gonadotropin $(hCG)$,human placental lactogen $(hPL)$,estrogens,and progestogens.
$hCG$ is produced by the syncytiotrophoblast of the placenta shortly after implantation to maintain the corpus luteum.
Its levels rise rapidly during the first trimester to ensure the production of progesterone.
By the second trimester,the placenta itself becomes fully capable of producing sufficient progesterone and estrogens to maintain the pregnancy,leading to a significant decline in the levels of $hCG$.

(D) Human Chorionic Gonadotropin $(hCG)$ is a hormone produced by the syncytiotrophoblast cells of the placenta during pregnancy.
It plays a crucial role in maintaining the corpus luteum,which in turn continues to secrete progesterone to support the pregnancy until the placenta takes over this function fully.
Therefore,the correct answer is $D$ (Placenta).

(C) Gastrulation is the morphogenetic process during embryonic development in which the blastula is reorganized into a multi-layered structure known as the gastrula.
This process involves the movement and rearrangement of cells to form the three primary germinal layers: ectoderm,mesoderm,and endoderm.
Blastulation is the formation of the blastula,cleavage is the series of mitotic divisions of the zygote,and implantation is the attachment of the blastocyst to the uterine wall.

(D) The provided image represents a blastocyst stage of human embryonic development.
$I$ points to the outer layer of cells,known as the Trophoblast,which attaches to the endometrium.
$II$ points to the fluid-filled cavity inside the blastocyst,known as the Blastocoel.
$III$ points to the group of cells clustered at one end,known as the Inner cell mass (or embryoblast),which gives rise to the embryo proper.
Therefore,the correct labelling is $I$ - Trophoblast,$II$ - Blastocoel,$III$ - Inner mass cells.

(B) The corpus luteum is a temporary endocrine structure in the ovary that plays a vital role in the menstrual cycle and early pregnancy.
It primarily secretes progesterone,which is essential for maintaining the endometrium.
It also secretes moderate amounts of estrogen,inhibin,and relaxin (especially during pregnancy).
However,$hCG$ (human Chorionic Gonadotropin) is secreted by the syncytiotrophoblast cells of the developing placenta,not by the corpus luteum.
Therefore,the correct answer is $hCG$.

(B) During pregnancy,the placenta acts as an endocrine tissue and produces several hormones which are essential for maintaining pregnancy.
Specifically,human Chorionic Gonadotropin $(hCG)$,human Placental Lactogen $(hPL)$,and relaxin are hormones that are produced in women $ONLY$ during pregnancy.
While estrogens and progestogens are also produced by the placenta during pregnancy,they are also produced by the ovaries in non-pregnant women.
Therefore,the correct option is $B$.

(D) The correct sequence of embryonic development is as follows:
$(III)$ The embryo's heart is formed: This is the first sign of organ development,usually observed by the end of the first month.
$(II)$ The foetus develops limbs and digits: This occurs by the end of the second month of pregnancy.
$(I)$ The first movements of the foetus: These are observed during the fifth month of pregnancy.
$(IV)$ The body is covered with fine hairs: This occurs by the end of the second trimester (around the sixth month).
Therefore,the correct sequence is $(III), (II), (I), (IV)$,which corresponds to option $D$.

(B) During human embryonic development,the heart is formed after one month of pregnancy. By the end of the second month (eight weeks) of pregnancy,the foetus develops limbs and digits. By the end of the first trimester (twelve weeks),most of the major organ systems are formed.

(B) The placenta acts as an endocrine tissue and produces several hormones essential for pregnancy,such as human Chorionic Gonadotropin $(hCG)$,human Placental Lactogen $(hPL)$,estrogens,and progestogens.
Relaxin is also produced during the later stages of pregnancy,but it is primarily secreted by the ovary (corpus luteum) and not the placenta.
Therefore,the correct option is $B$.

(B) The correct answer is $B$.
In the process of human development,the blastocyst consists of an outer layer called the trophoblast and an inner group of cells known as the inner cell mass $(ICM)$.
The trophoblast layer attaches to the endometrium and eventually forms the extraembryonic membranes and the fetal part of the placenta.
The inner cell mass differentiates into the embryo proper,which includes the three germ layers (ectoderm,mesoderm,and endoderm) that give rise to all the tissues and organs of the developing fetus.

(A) The correct answer is $A$.
During the process of gastrulation,the embryo forms a structure called the gastrula.
The gastrula contains an opening or pore known as the $Blastopore$.
$Blastopore$ is the first opening formed in the early embryo,which later develops into either the mouth or the anus depending on the organism (protostomes or deuterostomes).

(C) The correct matches are as follows:
$1$. $hCG$ (human Chorionic Gonadotropin) and $hPL$ (human Placental Lactogen) are produced by the placenta during pregnancy.
$2$. Progesterone is primarily secreted by the corpus luteum in the ovary after ovulation.
$3$. Androgens (mainly testosterone) are synthesized and secreted by the Leydig cells (interstitial cells) of the testes.
$4$. Relaxin is produced by the ovary (specifically the corpus luteum) during the later stages of pregnancy.
Therefore,the correct matching is $A-ii, B-iii, C-iv, D-i$.

(B) The correct answer is $B$. The pair "Second month of pregnancy - Movement of foetus" is mismatched.
According to human development milestones:
$1$. During the first month, the heart is formed.
$2$. During the second month, the foetus develops limbs and digits.
$3$. By the end of the third month (first trimester), most major organ systems are formed.
$4$. During the fifth month, the first movements of the foetus and appearance of hair on the head are observed.
$5$. By the end of the sixth month (second trimester), the body is covered with fine hair, eye-lids separate, and eye-lashes are formed.

(D) The correct answer is $D$.
$LH$ (Luteinizing Hormone) is secreted by the anterior pituitary gland,not the placenta.
The human placenta acts as an endocrine tissue and produces several hormones such as Human Chorionic Gonadotropin $(HCG)$,Human Placental Lactogen $(HPL)$,estrogens,and progestogens to maintain pregnancy.

(C) is the correct answer.
Follicle-stimulating hormone $(FSH)$ is secreted by the anterior lobe of the pituitary gland.
It stimulates the growth and maturation of ovarian follicles in the ovary.
Progestogens,human chorionic gonadotropin $(hCG)$,and relaxin are hormones secreted by the human placenta during pregnancy.

(A) The correct answer is $A$.
During the human pregnancy period (gestation),the first movements of the fetus and the appearance of hair on the head are observed during the $5^{\text{th}}$ month of pregnancy.
By the end of the first month,the heart is formed.
By the end of the second month,limbs and digits develop.
By the end of the first trimester,most major organ systems are formed.
During the $5^{\text{th}}$ month,the fetus shows movement and hair appears on the head.

(A) The correct matching is as follows:
$(A)$ First month: The first sign of growing foetus is usually noticed by listening to the heart sound carefully through the stethoscope. Thus,$(A-iii)$.
$(B)$ Second month: By the end of the second month of pregnancy,the foetus develops limbs and digits. Thus,$(B-iv)$.
$(C)$ Fifth month: The first movements of the foetus and appearance of hair on the head are usually observed during the fifth month. Thus,$(C-ii)$.
$(D)$ Sixth month: By the end of $24$ weeks (second trimester),the body is covered with fine hair,eye-lids separate,and eyelashes are formed. Thus,$(D-i)$.
Therefore,the correct sequence is $A-iii, B-iv, C-ii, D-i$.