12th Zoology / Bio Zoology Important 2, 3, 5 Mark Questions 2026

Chapter 2 : Human Reproduction

Most Repeated Questions

Number next to question tells how many times the question has been repeated in the past few years

TWO MARKS

1.Expand the acronyms.(2)

  • a) FSH – Follicular stimulating Hormone
  • b) LH – Lutenizing Hormone
  • c) hCG – Human Chrionic Gonadotropin
  • d) HPL – Human Placental Lactogen

2.What is inhibin? State its functions?(2)

Inhibin is a hormone secreted by Sertoli cells in the seminiferous tubules.

Function: It regulates sperm production by negative feedback control, inhibiting excess spermatogenesis.

3.What is Ectopic pregnancy?(2)

  • Ectopic pregnancy is a condition in which the fertilized ovum implants outside the uterus.
  • Most commonly occurs in the fallopian tube and may lead to internal bleeding and serious complications.

THREE MARKS

1.Differentiate Spermiogenesis and Spermatogenesis?(3)

SpermiogenesisSpermatogenesis
Formation of sperms from spermatogonia through mitosis and meiosisTransformation of spermatids into mature spermatozoa
Includes mitotic and meiotic divisionsNo cell division, only differentiation
Produces primary spermatocytes → secondary spermatocytes → spermatidsConverts spermatids → spermatozoa
Complete process of sperm formationFinal stage of spermatogenesis
Formation of haploid spermatidsFormation of mature motile sperms

2.What is Colostrum? Write its significance?(2)

Definition

  • Colostrum is a yellowish, nutrient-rich fluid secreted by the mammary glands during the first few days after childbirth.

Significance

  • Easily digestible and essential for newborn growth
  • Rich in proteins, vitamin A, minerals and IgA antibodies
  • Provides immunity and protects against infections
  • Acts as a natural antimicrobial agent
  • Helps in maturation of the infant’s immune system

3.Draw a schematic representation of spermatogenesis and  oogenesis in humans. (2)

schematic representation of spermatogenesis and  oogenesis

4.How does the body organs develop from the primary germ layers? (2)

Development of Body Organs from Primary Germ Layers (3 Marks)

  • The primary germ layers (ectoderm, mesoderm, endoderm) give rise to all body organs.

1. Ectoderm

  • Forms:
    • Central nervous system (brain, spinal cord)
    • Peripheral nervous system
    • Epidermis and its derivatives
    • Mammary glands

2. Mesoderm

  • Forms:
    • Connective tissues, cartilage, bone
    • Muscles
    • Urinogenital organs (kidney, ureter, gonads)

3. Endoderm

  • Forms:
    • Epithelium of digestive and respiratory tracts
    • Liver, pancreas
    • Thyroid and parathyroid glands

FIVE MARKS

1.What is menstrual cycle? Explain the various phases of the menstrual cycle. (6)

Definition

  • The menstrual cycle is a series of cyclic changes in the ovary and uterus occurring every 28–29 days during the reproductive life of females (from menarche to menopause).
  • It involves periodic changes in the endometrium and indicates normal reproductive function.

Phases of Menstrual Cycle

1. Menstrual Phase (3–5 days)

  • Shedding of endometrial lining with blood flow
  • Caused by decrease in progesterone and oestrogen
  • Occurs if fertilization does not take place

2. Follicular / Proliferative Phase (Day 5–14)

  • A primary follicle develops and matures into a Graafian follicle.
  • Endometrium regenerates and thickens
  • Controlled by FSH and LH
  • Increased oestrogen secretion

3. Ovulatory Phase (Around Day 14)

  • LH surge causes rupture of Graafian follicle
  • Release of ovum (ovulation)

4. Luteal / Secretory Phase (Day 15–28)

  • Formation of corpus luteum
  • Secretes progesterone to maintain endometrium
  • Prepares uterus for implantation
  • If fertilization occurs:
    • Endometrium maintained → pregnancy
  • If no fertilization:
    • Corpus luteum → corpus albicans
    • Endometrium breaks down → next menstruation

Conclusion

  • Cycle repeats every 28 days
  • Controlled by hormones (FSH, LH, oestrogen, progesterone)

2.Define Oogenesis, Explain the structure of Ovum with diagram.(3)

Definition

  • Oogenesis is the process of formation and development of the female gamete (ovum) in the ovaries.

Process of Oogenesis (Brief)

  • During foetal development, oogonia are formed by mitosis
  • Oogonia develop into primary oocytes and get arrested in Prophase I
  • Each primary oocyte is surrounded by granulosa cells to form a primary follicle
  • Many follicles degenerate; only few remain at puberty

Structure of Ovum

  • Human ovum is:
    • Non-cleidoic (without shell)
    • Alecithal (very little yolk)
    • Microscopic

Parts:

  • Ooplasm → Cytoplasm of ovum
  • Germinal vesicle → Nucleus

Coverings (3 layers):

  1. Vitelline membrane
    • Inner thin, transparent layer
  2. Zona pellucida
    • Middle thick layer
  3. Corona radiata
    • Outer layer of follicular cells
  • Perivitelline space:
    • Space between vitelline membrane and zona pellucida

3.List the various menstrual disorders.(2) Nill (Not for Biology)

1. Amenorrhoea

  • Absence of menstruation
  • Primary amenorrhoea → Menarche not attained till 18 years
  • Secondary amenorrhoea → Absence of menstruation for more than 3 months

2. Polymenorrhoea

  • Short menstrual cycle (< 21 days)
  • Causes:
    • Hormonal imbalance (pituitary hyperactivity)
    • Psychological stress, malnutrition
    • Infections (e.g., STDs)

3. Dysmenorrhoea

  • Painful menstruation
  • Types:
    • Primary → Due to prostaglandins (no disease)
    • Secondary → Due to disorders (endometriosis, fibroids)

4. Menorrhagia

  • Heavy and prolonged menstrual bleeding
  • Causes:
    • Hormonal imbalance
    • Uterine fibroids
    • Ovarian dysfunction
    • Sometimes cancers (uterus, ovary, cervix)

5. Oligomenorrhoea

  • Infrequent menstruation (> 35 days gap)
  • Occurs in women of reproductive age
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