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Gametogenesis

BiologyHuman ReproductionFor NEET aspirants

Gametogenesis is the formation of gametes: sperms in the testis by spermatogenesis and the ovum in the ovary by oogenesis. This page covers the stages of spermatogenesis and its hormonal control, and the structure of a sperm. It then covers the follicle stages of oogenesis and the phases and hormones of the menstrual cycle, as in the NCERT Class 12 chapter Human Reproduction. NEET often asks chromosome numbers at each stage, the LH surge, the corpus luteum and the differences between the two kinds of gametogenesis.

On this page1Gametogenesis2Spermatogenesis3Hormonal control4Sperm structure5Oogenesis6Comparison7Menstrual cycle8Exam essentials9Quick revision10Solved examples11Practice
Key Points at a Glance
  1. ★ Must learn Spermatogonium (46) → primary spermatocyte (46) → 2 secondary spermatocytes (23) → 4 spermatids (23) → 4 sperms.
  2. Spermiogenesis: spermatids → spermatozoa. Spermiation: release of sperms from the seminiferous tubules.
  3. ★ Must learn GnRH (hypothalamus) → LH and FSH (anterior pituitary). LH → Leydig cells → androgens; FSH → Sertoli cells → factors for spermiogenesis.
  4. Sperm: head (nucleus + acrosome), neck, middle piece (mitochondria), tail; 200-300 million per ejaculation.
  5. Normal fertility: at least 60% sperms of normal shape and size, and at least 40% with vigorous motility.
  6. ★ Must learn Oogenesis starts in fetal life; primary oocytes stay arrested in prophase-I; no oogonia are added after birth.
  7. Follicles: primary → secondary → tertiary (antrum) → Graafian; 60,000-80,000 primary follicles per ovary at puberty.
  8. Meiosis I is unequal: secondary oocyte + first polar body; it is completed in the tertiary follicle.
  9. ★ Must learn Menstrual cycle (about 28/29 days): menstrual (3-5 days) → follicular → ovulatory (about day 14) → luteal phase.
  10. ★ Must learn LH surge at mid-cycle causes ovulation; the corpus luteum secretes progesterone that maintains the endometrium.
  11. Menarche: the first menstruation; menopause: cycles cease at about 50 years.

1. Gametogenesis

  • Gametogenesis: the process by which the primary sex organs produce gametes.
  • The testis in males produces sperms; the ovaries in females produce the ovum.
  • In the testis it is called spermatogenesis; in the ovary it is called oogenesis.
Key idea
Testis → sperms (spermatogenesis); ovary → ovum (oogenesis).

2. Spermatogenesis

  • Spermatogenesis: the production of sperms from the immature male germ cells (spermatogonia).
  • ★ Exam imp Spermatogenesis begins at puberty.
  • Spermatogonia (singular: spermatogonium) lie on the inside wall of the seminiferous tubules.
  • They multiply by mitotic division and increase in number.
  • Each spermatogonium is diploid and contains 46 chromosomes.

Stages of spermatogenesis:

  1. Some spermatogonia differentiate into primary spermatocytes, which periodically undergo meiosis.
  2. A primary spermatocyte completes the first meiotic division (reduction division).
  3. This gives two equal, haploid secondary spermatocytes, each with only 23 chromosomes.
  4. Each secondary spermatocyte undergoes the second meiotic division.
  5. This gives four equal, haploid spermatids, each with 23 chromosomes.
  6. The spermatids are transformed into spermatozoa (sperms) by spermiogenesis.
  7. After spermiogenesis, the sperm heads become embedded in the Sertoli cells.
  8. The sperms are finally released from the seminiferous tubules by spermiation.
Enlarged sectional view of the wall of a seminiferous tubule An enlarged wedge cut from the wall of a seminiferous tubule. A pink band of tubule wall runs along the bottom. Resting on it is a row of large, rounded spermatogonia. Above them, layers of spermatocytes fill the wedge, with a few narrow Sertoli cells among them. At the top, near the lumen, lie spermatids and spermatozoa, their thin tails pointing upwards into the lumen. Spermatozoa Spermatid Secondaryspermatocyte Sertoli cell Primaryspermatocyte Spermatogonium
Figure 1: Enlarged sectional view of a seminiferous tubule. Spermatogonia lie next to the wall, with primary and secondary spermatocytes, spermatids and spermatozoa towards the lumen, and Sertoli cells among them.
Spermiogenesis
  • Spermatids are transformed into spermatozoa
  • A change of form, no division
Spermiation
  • Sperms are released from the seminiferous tubules
  • Happens after the sperm heads were embedded in Sertoli cells
★ Very important Spermiogenesis is the transformation of spermatids into spermatozoa. Spermiation is the release of sperms from the seminiferous tubules. Spermiogenesis comes first.
Memory Trick Order of names: Go, Cyte, Cyte, Tid, Zoa = spermatogonia, primary spermacyte, secondary spermacyte, spermatid, spermatozoa. Then -genesis (making the form) comes before -ation (release): spermiogenesis, then spermiation.
Memory Trick Chromosome numbers: only the first two names carry 46 (spermatogonium, primary spermatocyte). Everything after the first meiotic division carries 23. One primary spermatocyte gives 4 spermatids.
Key idea
46 → 46 → 23 → 23: the first meiotic division halves the chromosome number, and one primary spermatocyte gives four sperms.

3. Hormonal Control of Spermatogenesis

  • Spermatogenesis starts at puberty because the secretion of gonadotropin releasing hormone (GnRH) rises significantly.
  • GnRH is a hypothalamic hormone.
  1. The increased GnRH acts on the anterior pituitary gland.
  2. It stimulates the secretion of two gonadotropins: luteinising hormone (LH) and follicle stimulating hormone (FSH).
  3. LH acts on the Leydig cells and stimulates the synthesis and secretion of androgens.
  4. Androgens, in turn, stimulate the process of spermatogenesis.
  5. FSH acts on the Sertoli cells and stimulates the secretion of some factors that help in spermiogenesis.
Memory Trick L to L, S to S: LH acts on Leydig cells; FSH acts on Sertoli cells (both have an S sound).
NEET Focus Common trap: FSH acts on Sertoli cells, not on Leydig cells; LH acts on Leydig cells. Androgens stimulate spermatogenesis, while the Sertoli-cell factors help spermiogenesis. GnRH comes from the hypothalamus, and LH and FSH come from the anterior pituitary.
Quick Recall: tap to check
How many chromosomes does a spermatid have?
23. It is haploid, formed by the second meiotic division.
Which hormone's rise starts spermatogenesis at puberty?
Gonadotropin releasing hormone (GnRH), a hypothalamic hormone.
On which cells does LH act in the testis?
Leydig cells, which then secrete androgens.
What happens to sperm heads after spermiogenesis?
They become embedded in the Sertoli cells until spermiation releases the sperms.
Key idea
GnRH → LH and FSH; LH → Leydig cells → androgens → spermatogenesis; FSH → Sertoli cells → spermiogenesis.

4. Structure of a Sperm

  • A sperm is a microscopic structure made of a head, neck, middle piece and tail.
  • A plasma membrane envelops the whole body of the sperm.
PartWhat it containsRole
HeadAn elongated haploid nucleus; its anterior portion is covered by a cap-like acrosomeCarries the chromosomes to the ovum
AcrosomeFilled with enzymesHelps fertilisation of the ovum
NeckJoins the head to the middle pieceConnection
Middle pieceNumerous mitochondriaProduce energy for the movement of the tail
TailLong thread-like partMovement; sperm motility essential for fertilisation
Structure of a human sperm A single human sperm drawn upright. The head at the top is pointed above and rounded below, with a pale outer layer that forms a cap, the acrosome, over the tip and encloses a large dark nucleus. A short neck joins the head to a narrow middle piece, in which a row of mitochondria runs along its length. Below this, a long, slender tail curves gently towards the bottom. Head Middle piece Tail Acrosome Plasmamembrane Nucleus containingchromosomal material Neck Mitochondria(energy source for swimming)
Figure 2: Structure of a sperm. The head carries the haploid nucleus capped by the acrosome, the middle piece is packed with mitochondria, and the tail drives swimming.
  • ★ Exam imp A human male ejaculates about 200 to 300 million sperms during a coitus.
  • For normal fertility, at least 60 per cent of sperms must have normal shape and size.
  • At least 40 per cent of them must show vigorous motility.
Memory Trick Sperm parts from front to back: Head, Neck, Middle piece, Tail, like a person: head, neck, waist, legs. Fertility numbers: 60 for shape, 40 for motility; shape needs the higher share.

4.1 Transport of sperms and semen

  • Sperms released from the seminiferous tubules are transported by the accessory ducts.
  • ★ Exam imp Secretions of the epididymis, vas deferens, seminal vesicle and prostate are essential for the maturation and motility of sperms.
  • Semen: the seminal plasma along with the sperms.
  • The functions of the male sex accessory ducts and glands are maintained by the testicular hormones (androgens).
Key idea
Acrosome enzymes help fertilisation; middle-piece mitochondria power the tail; semen = seminal plasma + sperms.

5. Oogenesis

  • Oogenesis: the formation of a mature female gamete; it is markedly different from spermatogenesis.

5.1 In the fetal ovary

  • ★ Exam imp Oogenesis is initiated during the embryonic development stage.
  • A couple of million gamete mother cells (oogonia) form within each fetal ovary.
  • No more oogonia are formed and added after birth.
  • The oogonia start division and enter prophase-I of meiosis, where they are temporarily arrested.
  • Primary oocytes: these arrested cells.

5.2 Follicle stages

  1. Primary follicle: a primary oocyte surrounded by a layer of granulosa cells.
  2. Many follicles degenerate from birth to puberty, so only 60,000-80,000 primary follicles are left in each ovary at puberty.
  3. Secondary follicle: the primary follicle gets more layers of granulosa cells and a new theca.
  4. Tertiary follicle: characterised by a fluid-filled cavity called the antrum; the theca organises into an inner theca interna and an outer theca externa.
  5. In the tertiary follicle, the primary oocyte grows and completes the first meiotic division.
  6. This is an unequal division: a large haploid secondary oocyte and a tiny first polar body form.
  7. Graafian follicle: the mature follicle into which the tertiary follicle changes.
  8. The secondary oocyte forms a new membrane, the zona pellucida, around itself.
  9. The Graafian follicle ruptures and releases the secondary oocyte (ovum) from the ovary: this is ovulation.
  • The secondary oocyte retains the bulk of the nutrient-rich cytoplasm of the primary oocyte.
  • Whether the first polar body divides further or degenerates is not yet certain.
Sectional view of an ovary showing follicles at different stages A cut section of an ovary drawn as a thick slab. Red and blue blood vessels enter through a stalk at the upper left and wind through the tissue, with tiny follicles and a small primary follicle among them. Further right are larger follicles with fluid-filled cavities, a tertiary follicle with its antrum and, biggest of all, a mature Graafian follicle. At the lower right a ruptured follicle opens at the surface and releases a secondary oocyte. Two wrinkled corpora lutea lie at the lower centre, with a smaller shrunken body beside them. Blood vessels Primary follicle Tertiary follicleshowing antrum Graafianfollicle Secondary oocyte Corpus luteum
Figure 3: Sectional view of an ovary. Follicles grow from primary follicles to a tertiary follicle with an antrum and a Graafian follicle, which releases the secondary oocyte; the ruptured follicle becomes the corpus luteum.
Memory Trick Follicle order: Please Send The Gift = Primary, Secondary, Tertiary, Graafian. Add the clue words: Primary = 1 layer of granulosa; Secondary = more layers + theca; Tertiary = antrum; Graafian = mature, ruptures.
★ Very important The cell released at ovulation is the secondary oocyte, not a fully formed ovum. Its first meiotic division is completed in the tertiary follicle; its second division is completed only after a sperm enters it.
Tips and Tricks Unequal divisions belong to oogenesis only. If a statement mentions a polar body or an unequal division, it is about oogenesis. Spermatogenesis always gives equal cells: two secondary spermatocytes, then four spermatids.
Schematic representation of spermatogenesis and oogenesis Two panels. (a) Spermatogenesis, starting at puberty: spermatogonia multiply by mitosis and differentiate into primary spermatocytes with 46 chromosomes. The first meiotic division gives two secondary spermatocytes and the second meiotic division gives four spermatids, each with 23 chromosomes. The spermatids differentiate into four spermatozoa. (b) Oogenesis: oogonia formed in fetal life differentiate into primary oocytes with 46 chromosomes, which wait through birth and childhood. After puberty, the first meiotic division, completed before ovulation, gives one large secondary oocyte and a small first polar body with 23 chromosomes. The second division gives the ovum and a small second polar body. One primary oocyte forms a single ovum, while one primary spermatocyte forms four sperms. (a) Spermatogenesis Chromosome number per cell At puberty Spermatogonia Mitosis, differentiation Primary spermatocytes 1st meiotic division Secondary spermatocytes 2nd meiotic division Spermatids Differentiation Spermatozoa 46 23 23 (b) Oogenesis Chromosome number per cell Fetal life Birth Childhood Puberty Adult reproductive life Oogonia Mitosis, differentiation Primary oocyte 1st meiotic division (completed prior to ovulation) Secondary oocyte Ovum First polar body Second polar body 46 23 23
Figure 4: Schematic representation of (a) spermatogenesis and (b) oogenesis. One primary spermatocyte gives four sperms, while one primary oocyte gives one ovum and polar bodies; the first meiotic division reduces the chromosome number from 46 to 23.

6. Spermatogenesis and Oogenesis Compared

FeatureSpermatogenesisOogenesis
SiteSeminiferous tubules of the testisOvary
StartsAt pubertyDuring embryonic (fetal) development
Mother cellsSpermatogonia keep multiplying by mitosisOogonia form only in the fetal ovary; none are added after birth
First meiotic divisionEqual: two secondary spermatocytesUnequal: secondary oocyte and first polar body
Second meiotic divisionEqual: four spermatidsUnequal: ovum (ootid) and second polar body
Output of one primary spermatocyte or primary oocyteFour spermsOne ovum and polar bodies
ArrestNo arrestPrimary oocyte arrested in prophase-I from fetal life
With ageContinues even in old menCeases around 50 years (menopause)
Quick Recall: tap to check
How many oogonia are added to the ovary after birth?
None. All oogonia form in the fetal ovary.
At which follicle stage does the primary oocyte complete the first meiotic division?
The tertiary follicle.
What is the fluid-filled cavity of the tertiary follicle called?
The antrum.
Why does the secondary oocyte keep most of the cytoplasm?
The nutrient-rich cytoplasm stays with the one cell that becomes the ovum, which supports the early zygote.
Key idea
Spermatogenesis: from puberty, equal divisions, four sperms. Oogenesis: from fetal life, unequal divisions, one ovum.

7. Menstrual Cycle

  • Menstrual cycle: the reproductive cycle in female primates (monkeys, apes and human beings).
  • ★ Exam imp Menarche: the first menstruation, which begins at puberty.
  • In human females, menstruation repeats at an average interval of about 28/29 days.
  • The cycle of events from one menstruation to the next is the menstrual cycle.
  • One ovum is released (ovulation) during the middle of each menstrual cycle.

7.1 Phases of the cycle

  1. Menstrual phase: menstrual flow occurs and lasts 3-5 days. The endometrial lining of the uterus and its blood vessels break down and form a liquid that comes out through the vagina.
  2. Follicular phase (proliferative phase): primary follicles grow into a fully mature Graafian follicle; at the same time, the endometrium regenerates through proliferation.
  3. During the follicular phase, LH and FSH rise gradually; they stimulate follicular development and the secretion of estrogens by the growing follicles.
  4. Ovulatory phase: LH and FSH both peak in the middle of the cycle (about the 14th day). The rapid rise of LH to its maximum, the LH surge, induces rupture of the Graafian follicle and release of the ovum.
  5. Luteal phase (secretory phase): the remaining parts of the Graafian follicle transform into the corpus luteum, which secretes large amounts of progesterone.
  • Progesterone is essential for the maintenance of the endometrium.
  • Such an endometrium is necessary for implantation of the fertilised ovum and other events of pregnancy.
  • The changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones.
Changes in hormone levels, the ovary and the uterine lining over a 28-day menstrual cycle A menstrual cycle chart drawn over numbered day boxes from day 1 to day 28, with a dashed line marking ovulation at day 14. A pink band over the first half and an orange band over the second half mark the two phases. The hormone graph has four coloured curves: LH and FSH stay low, then rise to a sharp peak around day 14, LH much higher; estrogen climbs to a peak just before day 14 and rises again in the luteal phase; progesterone rises after ovulation to a peak around day 21. Below, follicles grow from small to mature, one ruptures to release the ovum, then a corpus luteum forms and shrinks. At the bottom, the endometrium is shed in days 1 to 5 and then thickens. Hormone levels Ovarian events Uterine events 12345678910111213141516171819202122232425262728 Menstruation Follicular phase (Proliferative phase) Luteal phase (Secretory phase) Estrogen LH Progesterone FSH Developing follicle Mature follicle Ovulation Developingcorpus luteum Regressingcorpus luteum Menses
Figure 5: Events during a menstrual cycle. FSH and LH peak around day 14 and the LH surge causes ovulation; estrogen peaks before ovulation, progesterone from the corpus luteum rises in the luteal phase, and the endometrium thickens until it breaks down at menses.

7.2 With and without fertilisation

If fertilisation occurs
  • Pregnancy follows
  • All events of the menstrual cycle stop
  • There is no menstruation
If fertilisation does not occur
  • The corpus luteum degenerates
  • The endometrium disintegrates
  • Menstruation follows, marking a new cycle
  • ★ Exam imp Menstruation occurs only if the released ovum is not fertilised.
  • Lack of menstruation may indicate pregnancy; it may also be caused by stress, poor health and other underlying causes.
  • Menopause: menstrual cycles cease at around 50 years of age.
  • Cyclic menstruation indicates the normal reproductive phase, which extends from menarche to menopause.
HormoneSourceRole in the cycle
FSHPituitaryRises gradually in the follicular phase; stimulates follicular development; peaks at mid-cycle
LHPituitaryRises gradually; the LH surge at about day 14 induces ovulation
EstrogensGrowing folliclesSecreted during the follicular phase; peak before ovulation
ProgesteroneCorpus luteumMaintains the endometrium for implantation
★ Very important The LH surge induces rupture of the Graafian follicle and ovulation. The corpus luteum then secretes large amounts of progesterone, which maintains the endometrium for implantation.
Memory Trick Phases in order: My Friend Owns Land = Menstrual (3-5 days), Follicular, Ovulatory (about day 14), Luteal. Second names: the follicle grows while the endometrium proliferates (follicular = proliferative); the corpus luteum secretes progesterone (luteal = secretory).
NEET Focus Statement traps: menstruation happens only when the ovum is not fertilised; during pregnancy all events of the cycle stop. The corpus luteum secretes progesterone, not LH or FSH. The phase that regenerates the endometrium is the follicular (proliferative) phase.

7.3 Menstrual hygiene

  • Maintaining hygiene and sanitation during menstruation is very important.
  • Take a bath and clean yourself regularly.
  • Use sanitary napkins or clean homemade pads, and change them after every 4-5 hours as required.
  • Dispose of used sanitary napkins properly, wrapped in used paper.
  • Do not throw used napkins into the drainpipes of toilets or in open areas.
  • Wash hands with soap after handling the napkin.
Quick Recall: tap to check
What is menarche?
The first menstruation, which begins at puberty.
What induces ovulation?
The LH surge: the rapid rise of LH to its maximum at mid-cycle, about day 14.
Which structure secretes progesterone after ovulation?
The corpus luteum, formed from the remaining parts of the Graafian follicle.
Why does menstruation not occur during pregnancy?
During pregnancy all events of the menstrual cycle stop, so the endometrium is not shed.
Key idea
FSH and LH grow the follicle; the LH surge releases the ovum; the corpus luteum's progesterone holds the endometrium until it degenerates.

8. Exam Essentials

Pairs to Match

TermMeaning or role
SpermiogenesisTransformation of spermatids into spermatozoa
SpermiationRelease of sperms from the seminiferous tubules
GnRHHypothalamic hormone; acts on the anterior pituitary
LH (male)Acts on Leydig cells; androgen secretion
FSH (male)Acts on Sertoli cells; factors for spermiogenesis
AcrosomeCap of enzymes that help fertilisation
Middle pieceMitochondria; energy for tail movement
Primary folliclePrimary oocyte with one layer of granulosa cells
Secondary follicleMore granulosa layers and a new theca
Tertiary follicleAntrum; theca interna and theca externa
Zona pellucidaNew membrane formed by the secondary oocyte
MenarcheFirst menstruation, at puberty
LH surgeRupture of the Graafian follicle; ovulation
Corpus luteumProgesterone; maintains the endometrium
MenopauseMenstrual cycles cease, around 50 years
Exceptions
  • Spermatogenesis begins at puberty, but oogenesis begins during embryonic development.
  • No oogonia are formed or added after birth.
  • Both meiotic divisions in oogenesis are unequal; in spermatogenesis both are equal.
  • The cell released at ovulation is the secondary oocyte, not a mature ovum (ootid).
  • FSH acts on Sertoli cells, not on Leydig cells.
  • Menstruation occurs only if the released ovum is not fertilised.
  • Lack of menstruation does not always mean pregnancy; stress or poor health can also cause it.
  • During pregnancy, all events of the menstrual cycle stop.

Numbers to Remember

  • Chromosomes: spermatogonium and primary spermatocyte 46; secondary spermatocyte and spermatid 23.
  • Spermatids from one primary spermatocyte: 4.
  • Sperms per ejaculation: about 200-300 million.
  • Normal fertility: at least 60% normal shape and size; at least 40% vigorous motility.
  • Oogonia in each fetal ovary: a couple of million.
  • Primary follicles per ovary at puberty: 60,000-80,000.
  • Menstrual cycle: about 28/29 days; menstrual flow 3-5 days; LH and FSH peak at about day 14.
  • Menopause: around 50 years. Change sanitary napkins every 4-5 hours.

9. Quick Revision

  • Gametogenesis: testis → sperms (spermatogenesis); ovary → ovum (oogenesis).
  • Spermatogenesis begins at puberty; spermatogonia (46) multiply by mitosis.
  • Primary spermatocyte (46) → meiosis I → 2 secondary spermatocytes (23) → meiosis II → 4 spermatids (23).
  • Spermiogenesis: spermatids → sperms; heads embed in Sertoli cells; spermiation releases them.
  • GnRH → LH and FSH; LH → Leydig cells → androgens → spermatogenesis; FSH → Sertoli cells → spermiogenesis.
  • Sperm: head (haploid nucleus, acrosome), neck, middle piece (mitochondria), tail; plasma membrane covers all.
  • 200-300 million sperms per coitus; 60% normal shape and size, 40% vigorous motility for fertility.
  • Secretions of epididymis, vas deferens, seminal vesicle and prostate: sperm maturation and motility.
  • Oogenesis: oogonia form in the fetal ovary; primary oocytes arrested in prophase-I.
  • Primary → secondary → tertiary (antrum) → Graafian follicle; 60,000-80,000 primary follicles per ovary at puberty.
  • Meiosis I (tertiary follicle): secondary oocyte + first polar body; zona pellucida forms; ovulation releases it.
  • Menstrual cycle in primates; menarche at puberty; about 28/29 days; one ovum per cycle.
  • Menstrual (3-5 days) → follicular/proliferative → ovulatory (LH surge, day 14) → luteal/secretory.
  • Corpus luteum: progesterone, maintains the endometrium; degenerates without fertilisation.
  • Menopause at about 50; cyclic menstruation marks the reproductive phase between menarche and menopause.

10. Solved Examples

Solved Example 1
Match List I with List II.
List I: A. LH, B. FSH, C. GnRH, D. Androgens
List II: I. Acts on Sertoli cells, II. Secreted by the hypothalamus, III. Stimulate spermatogenesis, IV. Acts on Leydig cells
Choose the correct answer:
(A) A-I, B-IV, C-II, D-III
(B) A-IV, B-I, C-III, D-II
(C) A-IV, B-I, C-II, D-III
(D) A-II, B-I, C-IV, D-III
Solution:

Answer: (C). LH acts on Leydig cells (IV); FSH acts on Sertoli cells (I); GnRH is a hypothalamic hormone (II); androgens stimulate spermatogenesis (III).

Solved Example 2
Read the statements about oogenesis.
A. Oogenesis is initiated during embryonic development.
B. New oogonia keep forming in the ovary after puberty.
C. The primary oocyte completes the first meiotic division in the tertiary follicle.
D. The first meiotic division gives a large secondary oocyte and a tiny first polar body.
E. The Graafian follicle releases a primary oocyte at ovulation.
Choose the correct answer:
(A) A, C and D only
(B) A, B and C only
(C) B, D and E only
(D) A, C, D and E only
Solution:

Answer: (A). B is wrong: no oogonia are added after birth. E is wrong: the Graafian follicle releases the secondary oocyte. A, C and D are correct.

Solved Example 3
Arrange the following in the order in which they appear in the ovary.
A. Graafian follicle
B. Secondary follicle
C. Primary follicle
D. Tertiary follicle
E. Corpus luteum
Choose the correct answer:
(A) C, D, B, A, E
(B) C, B, D, A, E
(C) B, C, D, A, E
(D) C, B, A, D, E
Solution:

Answer: (B). Primary (C) → secondary (B) → tertiary with antrum (D) → Graafian (A); after ovulation the remaining parts form the corpus luteum (E).

Solved Example 4
Which of the following is NOT correct about the menstrual cycle?
(A) It occurs in female primates
(B) The LH surge induces ovulation
(C) The corpus luteum secretes large amounts of FSH
(D) Menstruation occurs only if the ovum is not fertilised
Solution:

Answer: (C). The corpus luteum secretes large amounts of progesterone, which maintains the endometrium.

Solved Example 5
Statement I: A primary spermatocyte forms four spermatids, while a primary oocyte forms only one ovum.
Statement II: Both meiotic divisions of oogenesis are unequal.
(A) Both Statement I and Statement II are correct
(B) Statement I is correct but Statement II is incorrect
(C) Statement I is incorrect but Statement II is correct
(D) Both Statement I and Statement II are incorrect
Solution:

Answer: (A). The first division gives the secondary oocyte and the first polar body; the second gives the ovum (ootid) and the second polar body. Both are unequal, so only one ovum forms.

Solved Example 6
How many chromosomes are present in a human secondary spermatocyte and a spermatid, respectively?
(A) 46 and 23
(B) 23 and 23
(C) 46 and 46
(D) 23 and 46
Solution:

Answer: (B). The first meiotic division (reduction division) gives haploid secondary spermatocytes with 23 chromosomes; the second division keeps 23 in each spermatid.

11. Practice Questions

Practice Questions
  1. Match List I with List II.
    List I: A. Acrosome, B. Middle piece, C. Antrum, D. Zona pellucida
    List II: I. Fluid-filled cavity of the tertiary follicle, II. Enzymes that help fertilisation, III. Membrane formed by the secondary oocyte, IV. Mitochondria
    Choose the correct answer:
    (A) A-II, B-IV, C-I, D-III
    (B) A-IV, B-II, C-I, D-III
    (C) A-II, B-IV, C-III, D-I
    (D) A-II, B-I, C-IV, D-IIIAnswer: (A). Acrosome-II, middle piece-IV, antrum-I, zona pellucida-III.
  2. Read the statements.
    A. Menarche is the first menstruation at puberty.
    B. The menstrual flow lasts 3-5 days.
    C. The endometrium regenerates during the luteal phase.
    D. Both LH and FSH peak at about the 14th day.
    E. Lack of menstruation always means pregnancy.
    Choose the correct answer:
    (A) A, B and C only
    (B) A, B and D only
    (C) B, D and E only
    (D) A, C and D onlyAnswer: (B). The endometrium regenerates in the follicular (proliferative) phase (C wrong); stress or poor health can also stop menstruation (E wrong).
  3. Arrange the events of spermatogenesis in order: A. Spermiation, B. Second meiotic division, C. Spermiogenesis, D. First meiotic division, E. Mitotic multiplication of spermatogonia.
    (A) E, D, B, C, A
    (B) E, B, D, C, A
    (C) D, E, B, C, A
    (D) E, D, B, A, CAnswer: (A). Mitosis → meiosis I → meiosis II → spermiogenesis → spermiation.
  4. Which statement about human sperms is NOT correct?
    (A) About 200-300 million sperms are ejaculated during a coitus
    (B) For normal fertility, at least 60% must have normal shape and size
    (C) For normal fertility, at least 40% must show vigorous motility
    (D) For normal fertility, at least 90% must show vigorous motilityAnswer: (D). The requirement is at least 40% with vigorous motility; the other three are correct.
  5. Fill in the blanks: (a) Male and female gametes are ____ (diploid/haploid). (b) The release of the ovum from a mature follicle is called ____. (c) Ovulation is induced by a hormone called ____.Answer: (a) Haploid. (b) Ovulation. (c) Luteinising hormone (LH), through the LH surge.
  6. What is spermatogenesis? Briefly describe the process.Answer: Formation of sperms from spermatogonia in the seminiferous tubules, starting at puberty. Spermatogonia multiply by mitosis; primary spermatocytes (46) undergo meiosis I to form two secondary spermatocytes (23), which undergo meiosis II to form four spermatids (23); spermiogenesis turns them into sperms, which spermiation releases.
  7. Name the hormones involved in the regulation of spermatogenesis.Answer: GnRH (hypothalamus), LH and FSH (anterior pituitary), and androgens (Leydig cells).
  8. Define spermiogenesis and spermiation.Answer: Spermiogenesis: transformation of spermatids into spermatozoa. Spermiation: release of sperms from the seminiferous tubules.
  9. Draw a labelled diagram of a sperm.Answer: Label the plasma membrane, acrosome, nucleus containing chromosomal material, head, neck, middle piece, mitochondria (energy source for swimming) and tail (Figure 2).
  10. What is oogenesis? Give a brief account of it.Answer: Formation of a mature female gamete. Oogonia form in the fetal ovary and enter prophase-I, arresting as primary oocytes. Each becomes a primary follicle (granulosa layer), then a secondary follicle (more layers, theca) and a tertiary follicle (antrum), where meiosis I gives a secondary oocyte and the first polar body. The Graafian follicle releases the secondary oocyte at ovulation.
  11. Draw a labelled diagram of a section through the ovary. Which stage is the Graafian follicle?Answer: Label the blood vessels, primary follicles, tertiary follicle showing the antrum, Graafian follicle, secondary oocyte and corpus luteum (Figure 3). The Graafian follicle is the mature follicle that ruptures at ovulation.
  12. Name the functions of (a) the corpus luteum, (b) the acrosome and (c) the sperm tail.Answer: (a) Secretes progesterone, which maintains the endometrium. (b) Its enzymes help fertilisation of the ovum. (c) Its movement gives the sperm motility, essential for fertilisation.
  13. True or false? Correct the false one. (a) Oogenesis takes place in the corpus luteum. (b) The menstrual cycle ceases during pregnancy.Answer: (a) False: oogenesis takes place in the ovary, in the follicles. (b) True.
  14. What is the menstrual cycle? Which hormones regulate it?Answer: The reproductive cycle of female primates, from one menstruation to the next (about 28/29 days). It is regulated by the pituitary hormones LH and FSH and the ovarian hormones estrogens and progesterone.

Common Mistakes to Avoid

Watch out
  • Writing 46 chromosomes for a secondary spermatocyte. Correct: secondary spermatocytes and spermatids have 23.
  • Swapping spermiogenesis and spermiation. Correct: spermiogenesis transforms spermatids into sperms; spermiation releases them.
  • Saying FSH acts on Leydig cells. Correct: FSH acts on Sertoli cells; LH acts on Leydig cells.
  • Saying oogenesis begins at puberty. Correct: it begins during embryonic development; no oogonia are added after birth.
  • Calling the released cell a mature ovum. Correct: the Graafian follicle releases the secondary oocyte.
  • Placing the antrum in the secondary follicle. Correct: the antrum characterises the tertiary follicle.
  • Saying the corpus luteum secretes LH. Correct: it secretes progesterone; LH comes from the pituitary.
  • Linking endometrial regeneration to the luteal phase. Correct: the endometrium regenerates by proliferation in the follicular phase.

Frequently Asked Questions

What is the difference between spermiogenesis and spermiation?

Spermiogenesis is the transformation of spermatids into spermatozoa. After it, the sperm heads become embedded in the Sertoli cells. Spermiation is the later release of these sperms from the seminiferous tubules. So spermiogenesis changes the shape of the cell, and spermiation releases it.

How many chromosomes are present at each stage of spermatogenesis?

The spermatogonium and the primary spermatocyte are diploid with 46 chromosomes. The first meiotic division gives two haploid secondary spermatocytes with 23 chromosomes each. The second meiotic division gives four spermatids, also with 23 chromosomes. Spermatozoa formed from them carry 23 chromosomes.

Which hormones control spermatogenesis?

At puberty, the hypothalamus increases the secretion of GnRH. GnRH stimulates the anterior pituitary to secrete LH and FSH. LH acts on Leydig cells to secrete androgens, which stimulate spermatogenesis. FSH acts on Sertoli cells, which secrete factors that help spermiogenesis.

What are the parts of a human sperm?

A sperm has a head, neck, middle piece and tail, all covered by a plasma membrane. The head has an elongated haploid nucleus capped by the acrosome, whose enzymes help fertilisation. The middle piece has many mitochondria that provide energy for the movement of the tail.

What are the stages of follicle development in the ovary?

A primary oocyte with one layer of granulosa cells forms a primary follicle. More granulosa layers and a new theca make a secondary follicle. A fluid-filled antrum marks the tertiary follicle, which becomes the mature Graafian follicle. It ruptures at ovulation and leaves the corpus luteum.

Why is only one ovum formed from one primary oocyte?

Both meiotic divisions in oogenesis are unequal. The first gives a large secondary oocyte and a tiny first polar body. The second, completed after a sperm enters, gives the ovum and a second polar body. The bulk of the nutrient-rich cytoplasm stays in the single ovum.

What causes ovulation in the menstrual cycle?

LH and FSH rise gradually during the follicular phase and both peak at mid-cycle, about the 14th day. The rapid rise of LH to its maximum, called the LH surge, induces the rupture of the Graafian follicle. The secondary oocyte is then released from the ovary.

What is the role of the corpus luteum?

After ovulation, the remaining parts of the Graafian follicle form the corpus luteum in the luteal phase. It secretes large amounts of progesterone, which maintains the endometrium for implantation. Without fertilisation it degenerates, the endometrium breaks down and menstruation begins a new cycle.

Previous year questions on Gametogenesis

8 questions from past papers, each with a step-by-step solution.

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