Chapter 2: Human Reproduction Application Questions | biology Class 12 CBSE

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Chapter 2: Human Reproduction Application Questions | biology Class 12 CBSE | ByteNotes.in

Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 1

Applied Concept

A couple has been trying to conceive for two years. Tests show the male partner has only 35% of sperms with vigorous motility and 50% sperms of normal shape. With reference to the chapter, explain whether these values indicate normal fertility and what structures in the sperm are responsible for motility.

According to the chapter, for normal fertility, at least 40% of sperms must show vigorous motility and at least 60% must have normal shape and size. The male partner has only 35% motile sperms (below the 40% threshold) and 50% normal shaped sperms (below the 60% threshold), indicating subfertility.
Sperm motility is generated by the tail (flagellum) of the sperm, which performs the whip-like movement that propels the sperm toward the ovum. The energy for tail movement is produced by numerous mitochondria in the middle piece of the sperm through cellular respiration.
Reduced motility means fewer sperms can navigate from the vagina through the cervix and uterus to reach the ampullary region of the fallopian tube where fertilisation must occur, significantly reducing the chance of fertilisation.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 2

Applied Concept

A 48-year-old woman reports that her periods have become irregular and she has not menstruated for the past 8 months. With reference to the menstrual cycle described in the chapter, what is the likely explanation? Also state whether she can still become pregnant.

The chapter states that menstrual cycle ceases around 50 years of age, a stage called menopause. The woman at 48 years is likely experiencing perimenopause — the transition phase leading to menopause — during which cycles become irregular before stopping entirely.
Menopause represents the end of the reproductive phase (the phase between menarche and menopause). As the chapter describes, cyclic menstruation is an indicator of the normal reproductive phase; absence of menstruation signals the end of this phase.
Once menopause is established and ovulation ceases, natural pregnancy is no longer possible, as no ova are released. Since the woman has not menstruated for 8 months, it is highly likely she has entered menopause and can no longer conceive naturally.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 3

Applied Concept

A doctor detects a heartbeat in a uterus using a stethoscope and estimates the patient is in the first month of pregnancy. Using the embryonic development timeline from the chapter, predict what other developmental changes will have occurred by the end of the third month.

The chapter states that by the end of the first month, the embryo's heart is formed and can be detected by a stethoscope. By the end of the second month, the foetus develops limbs and digits.
By the end of 12 weeks (first trimester/end of third month), most major organ systems are formed. Specifically, the limbs and external genital organs are well-developed by this stage, allowing determination of the foetal sex.
This progression from heart formation (1 month) to limb/digit development (2 months) to full organogenesis and external genitalia formation (3 months) represents the critical period of embryonic development when all major body systems are established.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 4

Applied Concept

In a biology practical, a student observes that a tissue section from the testis shows cells arranged in two distinct locations — some inside coiled tubules and some outside them. With reference to the chapter, identify these cell types and describe their specific hormonal roles.

The cells inside the seminiferous tubules include spermatogonia (male germ cells that undergo meiotic divisions to produce sperms) and Sertoli cells (which provide nutrition to developing germ cells and support spermiogenesis under FSH stimulation).
The cells outside the seminiferous tubules, in the interstitial spaces, are Leydig cells (interstitial cells). These cells synthesise and secrete testicular hormones called androgens, which are essential for stimulating spermatogenesis and maintaining male secondary sexual characteristics.
Leydig cells are stimulated by LH from the anterior pituitary, while Sertoli cells are regulated by FSH. This division of location reflects their distinct functional roles: Leydig cells for endocrine (hormonal) function and Sertoli cells for supportive (nutritive) function within the tubule.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 5

Applied Concept

A scientist claims that an embryo at the blastocyst stage has the potential to give rise to all the tissues of the body. With reference to the chapter, explain the cellular basis of this claim and identify which structure in the blastocyst is responsible.

The blastocyst consists of an outer trophoblast and an inner cell mass (ICM). The chapter explicitly states that the inner cell mass contains certain cells called stem cells, which have the potency to give rise to all tissues and organs of the body.
After implantation, the inner cell mass differentiates into three primary germ layers: an outer ectoderm, an inner endoderm and a mesoderm between them. The chapter states that these three layers give rise to all tissues and organs in adults.
The scientist's claim is therefore supported: the inner cell mass of the blastocyst contains pluripotent stem cells that can differentiate into any cell type in the human body, making the blastocyst stage the key window for total developmental potential before differentiation restricts cell fate.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 6

Applied Concept

A couple is informed that their twin babies were born from a single fertilised egg. With reference to the chapter, explain how many ova were released during that menstrual cycle and what type of twins these are. How would your answer change if the twins were fraternal?

The chapter states that one ovum is released per menstrual cycle during ovulation. If identical twins were born from a single fertilised egg (zygote), only one ovum would have been released and fertilised; the single zygote subsequently divided to form two separate embryos.
These are identical (monozygotic) twins. Since only one ovum was fertilised, only one ovum was released during that cycle.
If the twins were fraternal (dizygotic), two separate ova would have been released and fertilised by two different sperms. This would require two ovulation events in the same cycle — an exception to the usual single-ovum release — resulting in two genetically distinct embryos.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 7

Applied Concept

A pregnant woman's blood test shows elevated levels of hCG and hPL. With reference to the chapter, identify the source of these hormones and explain their significance in maintaining pregnancy.

The chapter states that hCG (human chorionic gonadotropin) and hPL (human placental lactogen) are produced by the placenta. These hormones are produced in women only during pregnancy, making them markers of pregnancy.
The placenta also produces estrogens, progestogens and, in later pregnancy, relaxin. The increased production of these hormones is essential for supporting fetal growth, inducing metabolic changes in the mother and maintaining pregnancy.
Elevated hCG in the early stages of pregnancy prevents degeneration of the corpus luteum, maintaining progesterone production and endometrial integrity. These test results therefore confirm an active, ongoing pregnancy and indicate normal placental function.

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Application Question

Medium difficulty • Concept in a practical situation

Medium

Question 8

Applied Concept

A young girl's guardian claims that a medical examination can determine whether she is sexually experienced based on the condition of her hymen. With reference to the chapter, evaluate this claim scientifically.

The chapter explicitly states that the presence or absence of hymen is not a reliable indicator of virginity or sexual experience. This directly refutes the claim.
The hymen can be broken by causes unrelated to sexual intercourse, including a sudden fall, jolt, insertion of a vaginal tampon, or active participation in sports such as horseback riding or cycling.
Furthermore, in some women the hymen persists even after coitus. Given these variations, drawing any conclusion about sexual experience from the state of the hymen is scientifically unsound and biologically incorrect.

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Application Question

Easy difficulty • Concept in a practical situation

Easy

Question 9

Applied Concept

A mother whose newborn has frequent infections is advised by the doctor to exclusively breastfeed for at least the first few months. With reference to the chapter, explain the biological basis of this advice.

The chapter explains that the milk produced during the initial few days of lactation is called colostrum, which contains several antibodies absolutely essential for developing resistance in newborn babies.
These maternal antibodies in colostrum provide passive immunity to the newborn, who has an immature immune system and is highly vulnerable to infections in the early weeks of life.
The chapter specifically states that breast-feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby — directly supporting the physician's advice to this mother.

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Application Question

Hard difficulty • Concept in a practical situation

Hard

Question 10

Applied Concept

During an IVF (in vitro fertilisation) procedure, scientists need to ensure that only one sperm fertilises each collected ovum. With reference to the mechanism described in the chapter, explain how the ovum naturally prevents fertilisation by more than one sperm.

The chapter describes that when a sperm comes in contact with the zona pellucida layer of the ovum, it induces changes in the membrane of the zona pellucida that block the entry of additional sperms.
This change is triggered by the first successful sperm contact and acts as a fast block to polyspermy, ensuring that only one sperm can fertilise a given ovum under normal physiological conditions.
In IVF, replicating this block is critical: if multiple sperms fertilise one ovum (polyspermy), the resulting embryo would have an abnormal chromosome number and would not develop normally.

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Chapter 2: Human Reproduction | Application Questions

A 48-year-old woman reports that her periods have become irregular and she has not menstruated for the past 8 months. With reference to the menstrual cycle described in the chapter, what is the likely explanation? Also state whether she can still become pregnant.

A doctor detects a heartbeat in a uterus using a stethoscope and estimates the patient is in the first month of pregnancy. Using the embryonic development timeline from the chapter, predict what other developmental changes will have occurred by the end of the third month.

In a biology practical, a student observes that a tissue section from the testis shows cells arranged in two distinct locations — some inside coiled tubules and some outside them. With reference to the chapter, identify these cell types and describe their specific hormonal roles.

A scientist claims that an embryo at the blastocyst stage has the potential to give rise to all the tissues of the body. With reference to the chapter, explain the cellular basis of this claim and identify which structure in the blastocyst is responsible.

A couple is informed that their twin babies were born from a single fertilised egg. With reference to the chapter, explain how many ova were released during that menstrual cycle and what type of twins these are. How would your answer change if the twins were fraternal?

A pregnant woman's blood test shows elevated levels of hCG and hPL. With reference to the chapter, identify the source of these hormones and explain their significance in maintaining pregnancy.

A young girl's guardian claims that a medical examination can determine whether she is sexually experienced based on the condition of her hymen. With reference to the chapter, evaluate this claim scientifically.

A mother whose newborn has frequent infections is advised by the doctor to exclusively breastfeed for at least the first few months. With reference to the chapter, explain the biological basis of this advice.

During an IVF (in vitro fertilisation) procedure, scientists need to ensure that only one sperm fertilises each collected ovum. With reference to the mechanism described in the chapter, explain how the ovum naturally prevents fertilisation by more than one sperm.

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