Q.Choose the incorrect statement from the following:
Concept understanding — Human Reproduction
Human Reproduction: A First Look
Think about what makes you you. You have your mother's eyes, your father's laugh, a mix of traits from two people you may never have met — your grandparents. That chain of life, stretching back thousands of years, runs through one process: human reproduction. It is not a topic for biology students alone. It is the story of how every single person on this planet came to be here.
The Big Picture: Why Does Reproduction Exist?
Every living thing has one fundamental drive: to continue its kind. A mango tree grows fruit so its seeds can sprout elsewhere. A bacterium splits in two. For humans, reproduction is more complex — and more personal. It is the reason families exist, why you have siblings or cousins, and why populations grow or shrink.
At its simplest, human reproduction is the biological process by which a new human individual is created. It requires two parents — a male and a female — each contributing a special cell that fuses to form a single, new cell. That single cell then grows, divides, and develops into a baby over about nine months.
Reproduction is not the same as sex. Sex is an act; reproduction is the entire sequence from cell fusion to birth. Not every act of sex leads to reproduction, and reproduction can sometimes happen with medical help (like IVF) without sex.
The Two Key Players: Male and Female Reproductive Systems
Your body, whether male or female, has a set of organs designed specifically for reproduction. These are not the same as the organs that keep you alive — they are the "spare set" dedicated to creating the next generation.
The Male System: Production and Delivery
The male reproductive system has one main job: to produce male sex cells (sperm) and deliver them to the female body. The key parts are:
- Testes (two oval organs in a pouch called the scrotum): These are the factories. They produce sperm continuously from puberty onwards — millions every day. They also produce testosterone, the hormone that drives male physical changes at puberty.
- Duct system (a series of tubes): Sperm travel from the testes through a long coiled tube (epididymis) where they mature, then through a muscular tube (vas deferens) that carries them toward the urethra.
- Accessory glands (seminal vesicles, prostate gland, bulbourethral glands): These add fluids to the sperm to nourish them and help them swim. The mixture of sperm and these fluids is called semen.
- Penis: The organ that delivers semen into the female reproductive tract.
The Female System: Production, Reception, and Nurturing
The female system has a bigger job: it produces female sex cells (eggs), receives sperm, and if fertilization occurs, houses and nourishes the developing baby for nine months. The key parts are:
- Ovaries (two almond-sized organs): These produce eggs — but unlike sperm, eggs are not made continuously. A female is born with all the eggs she will ever have (about 1–2 million at birth, reducing to around 300,000–400,000 by puberty). Each month, one egg matures and is released.
- Fallopian tubes (also called oviducts): These are not connected directly to the ovaries. When an egg is released, the finger-like ends of the tube sweep it inside. Fertilization — the meeting of sperm and egg — happens here, in the tube.
- Uterus (womb): A hollow, pear-shaped muscular organ. If fertilization happens, the embryo implants in the lining of the uterus and grows here. If not, the lining is shed — that is menstruation.
- Cervix: The lower, narrow part of the uterus that opens into the vagina. It produces mucus that changes consistency during the month to help or hinder sperm.
- Vagina: A muscular canal that receives the penis during intercourse and serves as the birth canal during delivery.
The female reproductive system has a monthly cycle (the menstrual cycle) that prepares the body for a possible pregnancy. This cycle is controlled by hormones and typically lasts about 28 days. The release of the egg (ovulation) happens around day 14. If no pregnancy occurs, the uterine lining is shed as menstrual blood — this is a normal, healthy process, not a "curse" or something to be ashamed of.
The Moment of Creation: Fertilization
When sperm from the male meet the egg from the female inside a fallopian tube, one sperm may penetrate the egg's outer layer. That single moment — fertilization — creates a new cell called a zygote. This zygote contains 23 chromosomes from the mother and 23 from the father, making 46 in total. That is the complete genetic blueprint for a new human being.
The zygote immediately begins to divide as it travels down the fallopian tube toward the uterus. By the time it reaches the uterus (about 5–7 days later), it has become a ball of about 100 cells called a blastocyst. This blastocyst burrows into the soft, thick lining of the uterus — a process called implantation. That is when pregnancy truly begins.
The Nine-Month Journey: Development
Once implanted, the developing human is called an embryo for the first eight weeks, and then a fetus from the ninth week until birth. During these months:
- A special organ called the placenta develops, connecting the mother's blood supply to the fetus. It delivers oxygen and nutrients and removes waste — without the mother's and baby's blood ever mixing directly.
- The umbilical cord links the baby to the placenta.
- The baby is protected by a fluid-filled sac (amniotic sac) that cushions it.
- All major organs form in the first three months (first trimester). The next three months (second trimester) are about growth and refinement. The final three months (third trimester) are about rapid weight gain and preparation for life outside the womb.
The mother's body undergoes enormous changes during pregnancy — hormonal shifts, weight gain, increased blood volume, and physical discomfort. This is not a "condition" or an illness; it is a normal physiological state.
Birth: The Final Act
After about 40 weeks from the last menstrual period (or 38 weeks from fertilization), the baby is ready. Hormones trigger strong, rhythmic contractions of the uterus — labour. The cervix softens and opens (dilates), and the baby is pushed through the birth canal (vagina) into the world. The umbilical cord is clamped and cut — that stump becomes the belly button.
The mother's body then expels the placenta (the "afterbirth"). Breastfeeding soon after birth helps the uterus contract back to its normal size and provides the baby with colostrum, a nutrient-rich first milk.
Why This Matters to You
You do not need to be a doctor to understand human reproduction. This knowledge helps you:
- Understand your own body — why periods happen, what puberty changes mean, how fertility works.
- Make informed decisions — about relationships, contraception, family planning, and health.
- Recognize what is normal — and what might need medical attention.
- Appreciate the miracle — every person you know, including yourself, is the result of this precise, coordinated process.
Reproduction is not just biology. It is deeply connected to culture, law, ethics, and personal identity. Understanding the science gives you a solid foundation to think clearly about issues like abortion, surrogacy, IVF, contraception, and reproductive rights — topics you will encounter in news, policy, and everyday life.
A Final Thought
Human reproduction is not a "dirty" or "embarrassing" topic. It is the most ordinary miracle in the world — so ordinary that it happens millions of times every year, and so miraculous that scientists still cannot fully replicate it in a lab. You are here because it worked, exactly as it was meant to, for every one of your ancestors going back to the beginning of our species. That is worth understanding.
This is a topic students often look up online as "Human Reproduction class 12 biology", "Human Reproduction important questions", or "Human Reproduction NEET questions". This concept is directly part of the Human Reproduction chapter in the NCERT/CBSE Class 12 Biology syllabus, and it is also an important topic for NEET and state medical/CET entrance exams, making it worth mastering for both board and competitive-exam preparation.
Let’s go through each statement one by one.
(A) is correct — birds and mammals do have internal fertilisation.
(B) is correct — colostrum is rich in antibodies and nutrients.
(D) is correct — implantation in humans begins around day 7 after fertilisation.
Now (C) says: "Polyspermy in mammals is prevented by the chemical changes in the egg surface." This is where the NCERT text draws a careful distinction. In mammals, the block to polyspermy is primarily due to electrical changes in the egg plasma membrane (fast block), followed by cortical reaction that modifies the zona pellucida (slow block). The statement mentions only "chemical changes in the egg surface," which is incomplete and misleading — the fast block is electrical, not chemical. Hence, (C) is the incorrect statement.
The incorrect statement is (C), because in mammals the fast block to polyspermy is electrical, not chemical.
The incorrect statement is (C): Polyspermy in mammals is prevented by the electrical changes in the egg surface, not chemical changes — that mechanism belongs to other animals like frogs.
Let’s walk through each option carefully, because this question tests a subtle but important distinction in how different organisms prevent more than one sperm from entering the egg.
Option (A): “In birds and mammals internal fertilisation takes place.” This is correct. Both birds and mammals are amniotes that have evolved internal fertilisation, where the male deposits sperm inside the female’s reproductive tract. This is a key adaptation for life on land, protecting the gametes from drying out. NCERT clearly states this for both groups.
Option (B): “Colostrum contains antibodies and nutrients.” Absolutely correct. Colostrum is the first milk secreted by the mammary glands after childbirth. It is rich in immunoglobulins (especially IgA) that provide passive immunity to the newborn, along with essential nutrients. This is a standard NCERT point in the chapter on reproductive health.
Option (C): “Polyspermy in mammals is prevented by the chemical changes in the egg surface.” This is the trap. Polyspermy — the entry of multiple sperm into one egg — is indeed prevented, but the primary mechanism in mammals is different from what this statement claims. In mammals, the moment a sperm fuses with the egg membrane, an electrical change (depolarisation) occurs within milliseconds, blocking further sperm entry. This is the fast block to polyspermy. A slower, more permanent block involves cortical granules releasing enzymes that alter the zona pellucida (the egg’s outer coat) — that part is chemical. But the statement says “chemical changes in the egg surface” as the sole mechanism, which is misleading. NCERT specifically highlights the electrical change as the immediate block in mammals, while chemical changes (cortical reaction) are more characteristic of species like sea urchins or frogs. So this statement is incorrect as written.
In frogs and many marine invertebrates, the cortical reaction (chemical) is the main block. In mammals, the fast electrical block is crucial — the chemical changes in the zona pellucida come later and are secondary.
Option (D): “In the human female implantation occurs almost seven days after fertilisation.” This is correct. After fertilisation in the ampulla of the fallopian tube, the zygote undergoes cleavage divisions while travelling toward the uterus. By about day 5–6, it becomes a blastocyst. Implantation — the embedding of the blastocyst into the endometrium — begins around day 7 after fertilisation. NCERT gives this timeline clearly.
The key distinction to remember: fast block to polyspermy in mammals is electrical (membrane depolarisation), not chemical. The chemical changes (zona reaction) are a slower, secondary block.
In short, the incorrect statement is (C) because polyspermy in mammals is prevented primarily by an electrical change in the egg membrane, not a chemical change — the chemical alteration of the egg surface is a later, secondary mechanism.
Showing the 12 most recent of 14 on this concept.
- AP EAPCET 2026Set ap-2026-05-19-AN1 markMCQQ.Assertion (A): The placenta of humans is haemochorial type. Reason (R): The maternal blood comes into direct contact with the foetal chorion. (A) Both (A) and (R) are true. (R) is correct explanation for (A) (B) Both (A) and (R) are true. (R) is not correct explanation for (A) (C) (A) is true. But (R) is false (D) (A) is false. But (R) is true
›Reveal solutionSolution
"Haemochorial" placenta is, by definition, one where maternal blood directly bathes the foetal chorion — exactly what humans have, so both statements are true and directly linked.
Concept and Intuition
Placental classification across mammals is based on how many tissue layers separate maternal blood from foetal blood/chorion. In some mammals, additional maternal endometrial layers remain intact, keeping maternal blood vessels separate from foetal tissue (e.g., epitheliochorial or endotheliochorial placentas). In humans (and other haemochorial mammals), the invading trophoblast erodes through the maternal endometrial epithelium and even the endometrial blood vessel walls, so maternal blood pools directly around the chorionic villi within the intervillous space — placing maternal blood in direct physical contact with the foetal chorion. This intimate arrangement maximises efficiency of nutrient, gas, and waste exchange between mother and foetus, and "haemochorial" is literally named for this direct blood-to-chorion contact — so the assertion and reason describe the same fact from two angles, with the reason being the precise anatomical definition explaining the assertion.
Step-by-Step Solution
- Recall placental type classification is based on layers separating maternal blood from foetal chorion.
- Recall that in humans, the placenta is haemochorial — maternal blood directly bathes the chorionic villi.
- Recognise that "maternal blood in direct contact with foetal chorion" is literally the definition of haemochorial — so R is not just true, but is exactly why A is true.
- Conclude: both true, R explains A.
Common Mistakes
- Confusing haemochorial with other placental types (e.g., endotheliochorial, seen in carnivores) that retain a maternal endothelial layer.
- Thinking maternal and foetal blood physically mix in haemochorial placentation — they remain separated by the chorionic membrane itself, even though maternal blood directly bathes it.
✓Final answerThe correct option is (A) — Both (A) and (R) are true, and (R) is the correct explanation for (A).
ANSWER: A
- AP EAPCET 2026Set ap-2026-05-19-AN1 markMCQQ.The following events are observed by the end of 12 weeks during pregnancy (A) Body covered with fine hair (B) First movements of foetus (C) Limbs and external genital organs (D) Limbs and digits
›Reveal solutionSolution
The 12-week (end of first trimester) milestone in human foetal development is well-formed limbs and identifiable external genitalia — later milestones like body hair and first foetal movements occur around months 5–6.
Concept and Intuition
Human prenatal development is conventionally tracked by trimester milestones. By the end of the first trimester (roughly 12 weeks), the embryo has completed the bulk of organogenesis — the major organ systems (heart, limbs, and external genitalia among them) are formed and identifiable, even though the foetus is still tiny and not yet capable of independent movement felt by the mother. Later trimester milestones follow a well-known sequence: around the fifth month, the mother typically first perceives foetal movements (quickening), and fine hair (lanugo) begins appearing on the head; by around the sixth month, the body becomes covered with fine lanugo hair and eyelids/eyelashes fully separate and form. By the ninth month, the foetus is fully developed and positioned for birth. Distinguishing these staged milestones (12 weeks vs. 5th/6th month vs. 9th month) is a commonly tested detail in human reproduction.
Step-by-Step Solution
- Identify the developmental stage in question: end of 12 weeks = end of the first trimester.
- Recall the defining milestone at this stage: limbs and external genital organs are well developed (sex can be visually distinguished).
- Eliminate "body covered with fine hair" and "eyelids separate" type milestones — these belong to the 5th–6th month.
- Eliminate "first foetal movements" — this is typically noted around the 5th month, not 12 weeks.
- Select "Limbs and external genital organs" as the correct 12-week milestone.
Common Mistakes
- Assuming limb/digit formation and "first movements" happen together — digit/limb formation is earlier (by 12 weeks) while movements perceptible to the mother come later (~5th month).
- Mixing up first-trimester organogenesis milestones with second-trimester surface/integument milestones (lanugo, eyelids).
✓Final answerThe correct option is (C) — Limbs and external genital organs.
ANSWER: C
- AP EAPCET 2025Set ap-2025-05-19-AN1 markMCQQ.Assertion(A): Placenta of human beings is called haemochorial type. Reason (R) : Chorianic villi of the foetus comes into direct contact with the maternal blood. Identify the correct option from the following (A) Both (A) and (R) are true, and (R) is correct explanation of (A) (B) Both (A) and (R) are true, but (R) is not the correct explanation of (A) (C) (A) is true, but (R) is false (D) (A) is false, but (R) is true
›Reveal solutionSolution
This tests the definition of haemochorial placentation in humans. The answer is (A): both statements are true and R correctly explains A.
Concept and Intuition
Placentas are classified by how many maternal tissue layers separate maternal blood from foetal chorionic tissue. In the human (and most primate) placenta, the erosive action of the trophoblast destroys the maternal endometrial lining so thoroughly that chorionic villi of the foetus float directly in pools of maternal blood (the intervillous space) — this is the literal meaning of "haemo-chorial" (blood-chorion contact). This maximizes the surface area and efficiency for gas, nutrient, and waste exchange between mother and foetus.
Step-by-Step Solution
- Assertion: Human placenta is haemochorial — this is an established embryological fact.
- Reason: Chorionic villi contact maternal blood directly — this is exactly what "haemochorial" means.
- Since the Reason is the literal definitional basis for the Assertion, R correctly explains A.
- Both statements are independently verifiable as true.
Common Mistakes
- Assuming every true Assertion-Reason pair with true statements must be independent (not explanatory) — here the Reason is literally the definition of the term used in the Assertion.
✓Final answerThe correct option is (A) — Both (A) and (R) are true, and (R) is the correct explanation of (A).
ANSWER: A
- AP EAPCET 2024Set ap-2024-05-16-AN1 markMCQQ.Identify incorrect combinations among the following. List-1 / List-2 / List-3: I. Hyaluronidase / Released by acrosome / Dissolves zona pellucida. II. Placenta / Somatomammotropin / Increased availability of glucose and amino acids to foetus. III. Hypomere / Somatic mesoderm and splanchnic mesoderm / Gives rise to pericardial cavity. IV. Secondary spermatocyte / Meiosis-II / Large spermatid and small polar body (A) I, III (B) II, III (C) II, IV (D) I, IV
›Reveal solutionSolution
Two combinations are wrong: hyaluronidase actually dissolves the corona radiata (not the zona pellucida) (I), and secondary-spermatocyte meiosis-II gives two equal spermatids with no polar body — polar bodies are an oogenesis-only concept (IV).
Concept and Intuition
Fertilization requires the sperm's acrosome to release a set of hydrolytic enzymes in sequence: hyaluronidase disperses the hyaluronic-acid-rich matrix binding the corona radiata (cumulus) cells around the oocyte, while a separate, more specific protease (acrosin) then digests the zona pellucida to let the sperm reach the oocyte membrane — so pairing hyaluronidase specifically with 'dissolves zona pellucida' overstates/misattributes its target. Separately, spermatogenesis and oogenesis diverge sharply at meiosis: a secondary spermatocyte's meiosis-II division is symmetric, producing two equal-sized spermatids each time (four total from one primary spermatocyte), with no polar bodies at all — the unequal division producing a large gamete plus a tiny polar body is a purely oogenesis phenomenon (secondary oocyte → ootid + second polar body). The placental somatomammotropin (hPL) statement (II) and the hypomere/coelom-derived pericardial cavity statement (III) are both standard, correctly stated facts.
Step-by-Step Solution
- Evaluate I: hyaluronidase's true target is the corona radiata's hyaluronic acid matrix, not the zona pellucida (that's acrosin's job) — INCORRECT combination.
- Evaluate II: placental somatomammotropin (hPL) raises maternal insulin resistance, sparing glucose/amino acids for the fetus — CORRECT.
- Evaluate III: hypomere (lateral plate mesoderm) splits into somatic and splanchnic layers enclosing the coelom, which gives rise to the pericardial (and other serous) cavities — CORRECT.
- Evaluate IV: secondary spermatocyte meiosis-II gives two equal spermatids, never a 'small polar body' — polar bodies occur only in oogenesis — INCORRECT combination.
- The incorrect combinations are I and IV → option (D).
Common Mistakes
- Accepting the loose simplification that 'acrosomal enzymes dissolve the zona pellucida' without distinguishing hyaluronidase's actual corona-radiata target from acrosin's zona-pellucida target.
- Importing the oogenesis concept of 'polar bodies' into spermatogenesis, where no such unequal division or polar body ever occurs.
✓Final answerThe correct option is (D) — I, IV.
ANSWER: D
- AP EAPCET 2024Set ap-2024-05-16-FN1 markMCQQ.Human chorionic gonadotropic hormone resembles this hormone in its function (A) Oxytocin (B) Vasopressin (C) Somatotropin (D) Luteinizing hormone
›Reveal solutionSolution
hCG, secreted by the early embryo/placenta, mimics LH's action of maintaining the corpus luteum so pregnancy can continue.
Concept and Intuition
In a normal menstrual cycle, LH from the pituitary triggers ovulation and briefly sustains the corpus luteum before it degenerates (in the absence of pregnancy). If fertilization occurs, the developing embryo secretes human chorionic gonadotropin (hCG), which takes over LH's role — keeping the corpus luteum alive and progesterone-secreting to support the pregnancy — hence its LH-like function.
Step-by-Step Solution
- Oxytocin causes uterine contractions and milk ejection — unrelated function.
- Vasopressin regulates water balance — unrelated function.
- Somatotropin (growth hormone) regulates growth — unrelated function.
- Luteinizing hormone maintains the corpus luteum, exactly what hCG does — matching function.
Common Mistakes
- Assuming hCG resembles FSH (follicle stimulation) rather than LH (corpus luteum maintenance) — hCG's defining pregnancy-sustaining role is LH-like.
✓Final answerThe correct option is (D) — Luteinizing hormone.
ANSWER: D
- AP EAPCET 2023Set ap-2023-05-22-FN1 markMCQQ.Match the following events during pregnancy with time List I | List II A. End of 4 weeks | i) Developments of limbs & limb digits B. End of 8 weeks | ii) Hair on body & separation of eyelids C. End of 12 weeks | iii) Formation of heart D. End of 24 weeks | iv) Formation of external genital organs (A) A – iii B – i C – ii D – iv (B) A – iii B – i C – iv D – ii (C) A – iii B – ii C – iv D – i (D) A – iii B – iv C – ii D – i
›Reveal solutionSolution
Tests recall of the timeline of key human foetal developmental milestones. Answer: (B) A–iii, B–i, C–iv, D–ii.
Concept and Intuition
Human prenatal development follows a well-documented order: the heart is among the first organs to form and start beating (around the end of the first month); limb buds elongate into recognizable limbs with digits by about two months; the external genitalia differentiate enough to identify sex by the end of the first trimester (12 weeks); and secondary surface features like fine body hair (lanugo) and eyelid separation appear around the mid-point of gestation (24 weeks).
Step-by-Step Solution
- End of 4 weeks → heart formed → (iii).
- End of 8 weeks → limb & limb digit development → (i).
- End of 12 weeks → external genital organs formed → (iv).
- End of 24 weeks → body hair and eyelid separation → (ii).
- Assemble: A–iii, B–i, C–iv, D–ii, matching option (B).
Common Mistakes
- Assuming genital differentiation happens before or with limb development, rather than after (12 weeks vs 8 weeks).
- Placing hair/eyelid development too early — it is a second-trimester (24-week) milestone, not first-trimester.
✓Final answerThe correct option is (B) — A – iii, B – i, C – iv, D – ii.
ANSWER: B
- AP EAPCET 2023Set ap-2023-05-23-FN1 markMCQQ.Assertion (A): The placenta is connected to the embryo through an umbilical cord. Reason (R): Somatomammotropin released from placenta has anti-insulin effect on mother. (A) Both A and R are true and R is the correct explanation of A. (B) Both A and R are true but R is not the correct explanation of A. (C) A is true and R is false. (D) A is wrong and R is true.
›Reveal solutionSolution
Both statements are factually correct — the umbilical cord does connect placenta and embryo, and placental somatomammotropin does have an anti-insulin effect on the mother — but the hormonal fact in R does not explain the anatomical connection described in A.
Concept and Intuition
The placenta is a specialised organ of pregnancy that serves both structural and endocrine roles. Structurally, it connects to the developing embryo/fetus via the umbilical cord, which carries the umbilical arteries and vein for nutrient/gas exchange (A — true, a purely anatomical fact). Endocrinologically, the placenta also secretes hormones such as human placental lactogen (also called human chorionic somatomammotropin), which has a well-documented anti-insulin (insulin-antagonistic) effect on the mother, increasing maternal blood glucose availability that can be shunted to the fetus (R — true, a physiological/hormonal fact). While both are true statements about the placenta, they describe entirely different aspects (structural connection vs. hormonal action) — R does not explain why or how the umbilical cord connects placenta to embryo.
Step-by-Step Solution
- Confirm A: umbilical cord anatomically links placenta and embryo — true.
- Confirm R: somatomammotropin from the placenta has an anti-insulin effect on the mother — true.
- Check the causal link: R's hormonal effect has no explanatory bearing on the anatomical existence of the umbilical cord connection in A.
- Both true, R not the explanation of A — option (B).
Common Mistakes
- Assuming any two true statements about the placenta must be causally linked, when here they describe unrelated (structural vs. endocrine) roles of the same organ.
✓Final answerThe correct option is (B) — Both A and R are true but R is not the correct explanation of A.
ANSWER: B
- AP EAPCET 2022Set ap-2022-07-12-AN1 markMCQQ.Which is the correct sequence of human reproduction? (A) Gametogenesis, Implantation, Fertilization, Gestation, Parturition (B) Gametogenesis, Gestation, Implantation, Fertilization, Parturition (C) Gametogenesis, Fertilization, Gestation, Implantation, Parturition (D) Gametogenesis, Fertilization, Implantation, Gestation, Parturition
›Reveal solutionSolution
Human reproduction proceeds logically as gametogenesis, then fertilization, then implantation, then gestation, and finally parturition — matching option (D).
Concept and Intuition
Each stage of human reproduction is a logical prerequisite for the next:
- Gametogenesis: sperm are produced in the testes (spermatogenesis) and ova in the ovaries (oogenesis) — gametes must exist before anything else can happen.
- Fertilization: a sperm fuses with a secondary oocyte (typically in the fallopian tube) forming a zygote — this requires gametes to already exist.
- Implantation: the developing blastocyst travels to the uterus and embeds into the endometrial lining — this must follow fertilization, since there must be an embryo to implant.
- Gestation: the ongoing process of embryonic and fetal growth and development within the uterus, spanning roughly 9 months, follows successful implantation.
- Parturition: childbirth, the delivery of the fully developed fetus, is the final event, occurring at the end of gestation.
Step-by-Step Solution
- Gametogenesis must be first — gametes are the raw material for fertilization.
- Fertilization must follow gametogenesis and precede implantation, since only a fertilized zygote (developing into a blastocyst) can implant.
- Implantation must precede gestation, as gestation describes the intrauterine developmental period that begins once the embryo is implanted and continues to grow.
- Parturition, the birth event, necessarily comes last, at the end of the gestational period.
- This full logical order — Gametogenesis, Fertilization, Implantation, Gestation, Parturition — matches option (D).
Common Mistakes
- Placing gestation before implantation (as in some distractor options) — gestation is the whole developmental period that follows implantation, not a separate step before it.
- Reversing fertilization and implantation order.
✓Final answerThe correct option is (D) — Gametogenesis, Fertilization, Implantation, Gestation, Parturition.
ANSWER: D
- AP EAPCET 2022Set ap-2022-07-12-AN1 markMCQQ.How many foetal membranes are formed during the development of human embryo? (A) 3 (B) 4 (C) 2 (D) 1
›Reveal solutionSolution
Four extraembryonic membranes — amnion, chorion, yolk sac, and allantois — develop during human embryo development.
Concept and Intuition
As an amniote, the human embryo develops surrounded by four extraembryonic membranes, each with a specific role:
- Amnion: encloses the embryo in amniotic fluid, providing a cushioning, shock-absorbing environment and preventing desiccation.
- Chorion: the outermost membrane, contributing to placenta formation and facilitating gas/nutrient exchange with the maternal blood supply.
- Yolk sac: though vestigial in humans (since nutrition comes from the placenta, not yolk), it is still formed and contributes early blood cell formation and primordial germ cells.
- Allantois: also largely vestigial in humans, contributing to umbilical cord blood vessel formation and (in other amniotes) waste storage/gas exchange.
Step-by-Step Solution
- List the standard four extraembryonic membranes taught in human embryology: amnion, chorion, yolk sac, allantois.
- Confirm none of these four membranes are absent in human development, even if some (yolk sac, allantois) are functionally reduced/vestigial compared to other vertebrates.
- This gives a total count of 4 foetal membranes, matching option (B).
Common Mistakes
- Undercounting by omitting the vestigial yolk sac or allantois, since their function in humans is much reduced compared to birds/reptiles — but they are still present as membranes during development.
✓Final answerThe correct option is (B) — 4.
ANSWER: B
- AP EAPCET 2022Set ap-2022-07-12-FN1 markMCQQ.Human placenta is not of the following type (A) Chorioallantoic (B) Discoidal (C) Haemochorial (D) Non-deciduate
›Reveal solutionSolution
The human placenta is chorioallantoic, discoidal, and haemochorial, but it IS deciduate (not non-deciduate) — so "non-deciduate" is the type it is NOT.
Concept and Intuition
Placentae are classified by several criteria: by embryonic membranes involved (chorioallantoic vs choriovitelline), by shape (discoidal, zonary, cotyledonary, diffuse), by the intimacy of maternal-fetal blood contact (haemochorial, endotheliochorial, epitheliochorial), and by whether maternal tissue is shed at parturition (deciduate vs non-deciduate). The human placenta falls into specific categories across these classifications, and the question tests knowing which one it does NOT belong to.
Step-by-Step Solution
- Chorioallantoic (A): The human placenta forms from the chorion and the vascularised allantois — this is a correct classification, so it IS this type (not the answer).
- Discoidal (B): Human placenta is disc-shaped — correct, so it IS this type.
- Haemochorial (C): In humans, maternal blood directly bathes the chorionic villi (no intervening maternal endothelium) — correct, so it IS this type.
- Non-deciduate (D): At parturition, part of the maternal decidua (endometrial lining) is shed along with the placenta in humans — meaning the human placenta is actually deciduate, not non-deciduate. So this is the type the human placenta is NOT.
- Therefore, the correct answer to "human placenta is NOT of the following type" is (D) Non-deciduate.
Common Mistakes
- Forgetting that "deciduate" refers to whether maternal tissue sheds with the placenta at birth — humans lose part of the endometrium (deciduate), unlike non-deciduate placentae (e.g., in pigs/horses) where no maternal tissue is shed.
✓Final answerThe correct option is (D) — Non-deciduate.
ANSWER: D
- AP EAPCET 2021Set ap-2021-09-03-AN1 markMCQQ.LH and FSH are collectively called ________ (A) Luteotropic hormones (B) Oxytocin (C) Somatotropins (D) Gonadotropins
›Reveal solutionSolution
This tests the classification of pituitary hormones by their target organ; LH and FSH both target the gonads, so together they are called gonadotropins.
Concept and Intuition
The anterior pituitary secretes several tropic hormones, each named for the gland/organ it stimulates: thyrotropins act on thyroid, adrenotropins (ACTH) on adrenal cortex, and gonadotropins act on the gonads (testes in males, ovaries in females). LH and FSH both regulate gonadal function — spermatogenesis and Leydig-cell testosterone secretion in males, folliculogenesis, ovulation, and estrogen/progesterone secretion in females — so they are grouped under the umbrella term 'gonadotropins'.
Step-by-Step Solution
- Identify the target organ of LH and FSH: both act on the gonads.
- Hormones classified by their target gland are named accordingly: 'gonadotropins' = hormones acting on gonads.
- Luteotropic hormone (prolactin) is a different pituitary hormone (mammary gland action), oxytocin is a posterior pituitary hormone for parturition/milk ejection, and somatotropin is growth hormone — none of these match.
- Hence LH and FSH together are the gonadotropins.
Common Mistakes
- Confusing 'luteotropic hormone' (which refers to prolactin) with LH.
- Forgetting that oxytocin and growth hormone are unrelated to gonadal stimulation.
✓Final answerThe correct option is (D) — Gonadotropins.
ANSWER: D
- AP EAPCET 2021Set ap-2021-09-03-FN1 markMCQQ.Assertion (A): During the formation of placenta some layers of uterus are eroded and during parturition extensive hemorrhage occurs. Reason (R): Placenta of man is described as haemo endothelial placenta. (A) Both A and R are correct and R is the correct explanation of A (B) Both A and R are correct and R is not the correct explanation of A (C) A is correct but R is wrong (D) A is wrong but R is correct
›Reveal solutionSolution
The Assertion about placental erosion and parturition bleeding is correct, but the Reason mis-names the human placenta type — it is haemochorial, not haemoendothelial — so R is wrong.
Concept and Intuition
Placentas are classified (Grosser's classification) by how many maternal tissue layers separate maternal and foetal blood:
- Epitheliochorial: all layers intact (e.g., pig, horse).
- Syndesmochorial: uterine epithelium eroded (e.g., ruminants).
- Endotheliochorial: uterine epithelium and connective tissue eroded, chorion touches maternal capillary endothelium (e.g., carnivores).
- Haemochorial: uterine epithelium, connective tissue, and maternal capillary endothelium all eroded, so chorionic villi are bathed directly in maternal blood — this is the human placenta type.
- Haemoendothelial: an even more eroded type where even the foetal connective tissue is lost, leaving only foetal capillary endothelium separating the two blood supplies (seen in some rodents, e.g., guinea pig), NOT in humans.
Because several maternal tissue layers are eroded during placenta formation in humans (to allow direct contact between chorionic villi and maternal blood), some maternal blood vessels are indeed disrupted, and at parturition, when the placenta separates from the uterine wall, this causes a degree of haemorrhage — both real physiological facts described in the Assertion.
Step-by-Step Solution
- Evaluate Assertion A: uterine layer erosion during placenta formation, and haemorrhage at parturition due to placental separation — both are accurate descriptions of human placentation and delivery physiology. A is TRUE.
- Evaluate Reason R: it claims the human placenta is "haemoendothelial." By the standard classification, the human placenta is actually haemochorial (maternal blood bathes the chorion directly, but the foetal capillary still retains its own endothelium and connective tissue) — haemoendothelial is a distinct, more extreme category applicable to certain rodents, not humans.
- Since R misidentifies the placental type, R is FALSE as stated (even though it correctly implies "a lot of erosion happens," the specific classification name given is wrong for humans).
- Therefore: A is correct, but R is wrong.
Common Mistakes
- Assuming any statement about extensive tissue erosion during placentation must be describing the haemoendothelial type — the correct term specifically for humans is haemochorial.
- Marking both A and R as correct just because R "sounds plausible" without checking the precise classification term against the actual human placenta type.
✓Final answerThe correct option is (C) — A is correct but R is wrong.
ANSWER: C
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