FAQS WITH ANSWERS – REPRODUCTION (CLASS 12 BIOLOGY, CHSE)
1. What is reproduction?
Answer:
Reproduction is a biological process by which organisms produce offspring similar to themselves, ensuring continuity of species.
2. What are the two main types of reproduction?
Answer:
Asexual reproduction
Sexual reproduction
3. Why is reproduction important?
Answer:
It ensures continuation of species, maintains population, introduces variation (in sexual reproduction), and enables adaptation.
4. Give two examples of organisms showing asexual reproduction.
Answer:
Hydra (budding), Amoeba (binary fission), Yeast (budding), Spirogyra (fragmentation).
5. What is sexual reproduction?
Answer:
Sexual reproduction involves the fusion of male and female gametes, leading to formation of a zygote.
6. What is gametogenesis?
Answer:
Gametogenesis is the formation of male and female gametes: spermatogenesis and oogenesis.
7. What is fertilization?
Answer:
Fertilization is the fusion of male and female gametes to form a diploid zygote.
8. Where does fertilization occur in humans?
Answer:
In the ampullary–isthmic junction of the fallopian tube.
9. What is ovulation?
Answer:
It is the release of a mature ovum from the ovary, typically on the 14th day of the menstrual cycle.
10. What is the menstrual cycle?
Answer:
A 28-day cyclic change in the female reproductive system that includes menstruation, follicular phase, ovulation, and luteal phase.
11. What are gonads? Give examples.
Answer:
Gonads are reproductive organs producing gametes.
Male – Testes
Female – Ovaries
12. What is placentation?
Answer:
Arrangement of ovules within the ovary of a flower.
Examples: axile, parietal, basal, marginal.
13. What is the difference between self and cross-pollination?
Answer:
Self-pollination: Transfer of pollen within the same flower or plant.
Cross-pollination: Transfer of pollen from one plant to another genetically different plant.
14. Name the male and female reproductive parts of a flower.
Answer:
Male – Stamen (anther + filament)
Female – Carpel/Pistil (stigma + style + ovary)
15. What is double fertilization?
Answer:
Fusion of one male gamete with the egg and another male gamete with the polar nuclei.
Seen only in angiosperms.
16. What is parthenocarpy?
Answer:
Formation of fruit without fertilization.
Example: banana.
17. What is semen?
Answer:
A mixture of spermatozoa and secretions from seminal vesicles, prostate gland, and bulbourethral glands.
18. What is implantation?
Answer:
Attachment of blastocyst to the uterine wall, occurring around 7th day after fertilization.
19. What is parturition?
Answer:
Process of childbirth, triggered by neuro-endocrine signals involving oxytocin.
20. What are the major male accessory glands?
Answer:
Seminal vesicles, prostate gland, and bulbourethral (Cowper's) glands.
21. What is lactation?
Answer:
Production of milk by mammary glands after childbirth under the influence of prolactin.
22. What is vegetative propagation?
Answer:
Asexual reproduction in plants using vegetative parts like stem, root, leaf.
Examples: potato tuber, onion bulb, Bryophyllum leaf.
23. What is a zygote?
Answer:
The diploid cell formed after fusion of male and female gametes.
24. What are hermaphrodites?
Answer:
Organisms having both male and female reproductive organs.
Example: Earthworm.
25. What is foetal ejection reflex?
Answer:
Reflex triggered by full-term fetus and cervix dilation leading to release of oxytocin and childbirth.
26. Define spermatogenesis.
Answer:
Formation of sperm from spermatogonia in seminiferous tubules under the influence of testosterone and FSH.
27. What is oogenesis?
Answer:
Formation of mature ovum from oogonia in ovaries; begins before birth and completes after fertilization.
28. What is colostrum?
Answer:
The first yellowish milk rich in antibodies (IgA) and nutrients, crucial for newborn immunity.
29. What is apomixis?
Answer:
Asexual formation of seeds without fertilization.
30. What is asexual reproduction?
Answer:
Production of offspring without gamete fusion, producing genetically identical offspring.
LONG ANSWER QUESTIONS
1. Describe the structure of the human male reproductive system and explain the process of spermatogenesis.
Answer:
A. Structure of Male Reproductive System
The human male reproductive system consists of:
1. Testes
Paired oval organs located within the scrotum.
Surrounded by tough covering tunica albuginea.
Contains seminiferous tubules where sperms are produced.
Leydig cells secrete testosterone.
2. Epididymis
Long coiled tube attached to each testis.
Stores and matures sperms.
3. Vas deferens
Long muscular tube carrying sperms from epididymis to urethra.
4. Accessory Glands
Seminal vesicles – secrete fructose-rich fluid.
Prostate gland – secretes alkaline fluid.
Bulbourethral (Cowper’s) glands – secrete mucus for lubrication.
5. Penis
Organ for copulation and ejaculation.
B. Spermatogenesis (Formation of Sperm)
Spermatogenesis occurs in seminiferous tubules.
Multiplication Phase
Spermatogonia (2n) undergo repeated mitosis.
Growth Phase
Some spermatogonia become primary spermatocytes (2n).
Maturation Phase
Primary spermatocyte → Meiosis I → Secondary spermatocytes (n)
Secondary spermatocytes → Meiosis II → Spermatids (n)
Spermiogenesis
Spermatids → mature spermatozoa.
Spermiation
Release of sperm into the lumen of seminiferous tubules.
Hormonal control:
FSH – stimulates spermatogenesis
LH – stimulates Leydig cells to secrete testosterone
Testosterone – growth and differentiation of sperm.
2. Describe the human female reproductive system. Explain the menstrual cycle.
Answer:
A. Structure of Female Reproductive System
Includes:
1. Ovaries
Paired structures producing ova and hormones estrogen, progesterone.
Each ovary contains ovarian follicles.
2. Fallopian Tubes (Oviducts)
Funnel-shaped infundibulum, ampulla, isthmus.
Fertilization occurs in ampullary–isthmic junction.
3. Uterus
Thick-walled muscular organ (womb).
Lining is endometrium, which undergoes cyclic changes.
4. Cervix
Narrow lower part of uterus opening into vagina.
5. Vagina
Birth canal.
B. Menstrual Cycle (28 days)
Divided into four phases:
1. Menstrual Phase (Days 1–5)
Shedding of endometrium.
Fall in estrogen and progesterone.
2. Follicular Phase (Days 6–13)
FSH stimulates follicle development.
Estrogen level increases.
Regeneration of endometrium.
3. Ovulation (Day 14)
LH surge causes release of ovum.
Most fertile period.
4. Luteal Phase (Days 15–28)
Ruptured follicle becomes corpus luteum.
Secretes progesterone → thickens endometrium for implantation.
If fertilization does not occur, corpus luteum degenerates → next menstruation begins.
3. Explain the process of fertilization, implantation, and pregnancy.
Answer:
A. Fertilization
Occurs in ampullary–isthmic junction of fallopian tube.
Sperm reaches ovum and undergoes capacitation.
Sperm penetrates zona pellucida.
Fusion of gamete nuclei → zygote formation.
B. Implantation
Zygote → cleavage → morula → blastocyst.
Blastocyst reaches uterus on 5th–6th day.
Implantation: attachment of blastocyst to endometrium around 7th day.
Trophoblast becomes chorion and forms placenta.
C. Pregnancy
Placenta secretes hCG, estrogen, progesterone.
Supports embryo and fetus:
Provides nutrients
Removes wastes
Gas exchange
Produces hormones
Duration: 9 months (40 weeks).
4. Explain double fertilization in angiosperms.
Answer:
Double fertilization is a unique process in angiosperms.
Steps:
Pollen grain germinates on stigma.
Pollen tube enters embryo sac.
Two male gametes are released.
First fertilization (syngamy):
Male gamete + egg → zygote (2n)
Second fertilization (triple fusion):
Male gamete + two polar nuclei → endosperm (3n).
Products:
Zygote → embryo
Endosperm → nutritive tissue
5. Discuss vegetative reproduction in plants. Explain any four methods with examples.
Answer:
Vegetative reproduction is asexual reproduction using vegetative parts of plants.
Methods:
1. Stem Tubers
Example: Potato
Buds (“eyes”) develop into new plants.
2. Rhizomes
Example: Ginger
Underground stems producing new shoots.
3. Bulbs
Example: Onion, Garlic
Swollen leaf bases act as storage and reproductive organs.
4. Leaf Buds
Example: Bryophyllum
Plantlets grow from leaf margins and detach to form new plants.
5. Stolons/Runners
Example: Strawberry
Horizontal stems that form new plants at nodes.
6. Explain the hormonal regulation of reproductive processes in males and females.
Answer:
A. In Males
Hypothalamus releases GnRH.
Pituitary releases FSH & LH.
FSH → stimulates spermatogenesis.
LH → stimulates Leydig cells → testosterone.
Testosterone – development of male features & sperm maturation.
B. In Females
GnRH → FSH + LH.
FSH → follicle development.
Estrogen → growth of endometrium.
LH surge → ovulation.
Corpus luteum secretes progesterone → prepares uterus for implantation.
If pregnancy occurs → hCG maintains corpus luteum.
7. Describe the structure of a typical angiosperm embryo sac.
Answer:
The embryo sac is the female gametophyte in flowering plants.
7-celled, 8-nucleate structure:
1. Egg Apparatus (at micropylar end)
1 egg cell
2 synergids
2. Central Cell
Contains two polar nuclei.
3. Antipodal Cells (at chalazal end)
Three small cells with unknown function.
The embryo sac develops from megaspore through megagametogenesis.
8.Describe the process of oogenesis. Add a labelled diagram of a mature ovum (description only).
Answer:
Oogenesis is the process of formation of a mature female gamete (ovum) in the ovaries.
A. Stages of Oogenesis
1. Multiplication Phase
Begins during foetal development.
Oogonia (2n) divide by mitosis and form primary oocytes (2n).
Around 2 million primary oocytes are present at birth.
2. Growth Phase
Primary oocytes enlarge and enter prophase I of meiosis, but remain arrested till puberty.
Surrounded by granulosa cells → primary follicle.
3. Maturation Phase
At puberty, under FSH:
(i) Meiosis I
Primary oocyte (2n) →
Secondary oocyte (n)
First polar body (n)
(ii) Meiosis II
Secondary oocyte begins meiosis II and is arrested in metaphase II.
Meiosis II completes only after fertilization, forming:
Mature ovum (n)
Second polar body
B. Diagram Description (Labelled Features)
A mature ovum shows:
Plasma membrane
Zona pellucida
Corona radiata
Cytoplasm
Nucleus (female pronucleus)
(If you want, I can draw this diagram in ASCII or provide a clean image-based description.)
9.Explain the structure and functions of the placenta.
Answer:
Placenta is a temporary, intimate connection between fetus and mother formed during pregnancy.
A. Structure of Placenta
Fetal part – formed from chorionic villi.
Maternal part – formed from endometrium (decidua basalis).
Together they form interdigitating villi.
Placental structures include:
Chorionic villi – finger-like projections with fetal blood vessels
Intervillous space – contains maternal blood
Umbilical cord – 2 arteries & 1 vein
Placental membranes – act as a barrier
B. Functions of the Placenta
1. Nutrition
Glucose, amino acids, lipids → from mother to fetus.
2. Respiration
O₂ diffuses from mother; CO₂ from fetus.
3. Excretion
Urea and uric acid from fetus → maternal blood.
4. Hormone Secretion
Placenta acts as a temporary endocrine gland. It secretes:
hCG (maintains corpus luteum)
hPL
Estrogen
Progesterone
Relaxin
5. Protection
Provides antibodies (IgG) → passive immunity to fetus.
6. Barrier Function
Prevents some harmful substances, but viruses and alcohol can cross.
10.Describe the events of human parturition. How is labor regulated by hormones?
Answer:
Parturition is the process of childbirth, usually after 9 months of pregnancy.
A. Stages of Parturition
1. Dilation Stage
Uterine contractions begin.
Cervix softens and widens (dilates up to 10 cm).
Amniotic sac may rupture.
2. Expulsion Stage
Strong contractions push the fetus through the cervix and vagina.
Baby is delivered head first.
3. Afterbirth Stage
Placenta and membranes are expelled after the baby.
B. Hormonal Regulation of Labour
Parturition is a neuro-endocrine reflex:
1. Stretch Reflex
Fully grown fetus stretches the uterus.
Stretching of cervix sends signals to the hypothalamus.
2. Oxytocin Release
Hypothalamus → posterior pituitary releases oxytocin.
Oxytocin → strong uterine contractions.
Positive Feedback Loop
More contractions → more cervical stretching → more oxytocin release.
3. Estrogen and Progesterone Balance
Near term:
Progesterone decreases (relaxes smooth muscles)
Estrogen increases (stimulates contraction)
4. Relaxin
Secreted by placenta.
Softens cervix and relaxes pelvic ligaments.
Outcome:
Coordinated contractions, dilation, and hormone actions → birth of the baby.
