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🌱 Chapter 1 Introduction — Reproduction in Plants
DefinitionReproduction is the biological process by which living organisms produce offspring of their own kind. It ensures continuity of species and transfer of genetic material from one generation to the next.
- Asexual reproduction — single parent, no gametes, offspring genetically identical (clones)
- Sexual reproduction — two parents, involves gametes (male + female), genetic variation in offspring
- Plants show both types — lower plants mainly asexual, higher plants mainly sexual
- Reproduction involves juvenile → reproductive phase → senescence
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🔄 Asexual Reproduction in Plants
DefinitionReproduction without formation of gametes or fusion. Offspring are genetically identical to parent — called clones.
Fission
Single cell divides into two equal cells. e.g. Amoeba, Chlamydomonas
Budding
Small outgrowth (bud) forms and detaches. e.g. Yeast, Hydra
Fragmentation
Body breaks into fragments, each grows into new organism. e.g. Spirogyra
Spore Formation
Spores (zoospores/conidia) produced, germinate to form new plant. e.g. Rhizopus, Fern
Vegetative Propagation
New plant from vegetative parts — root, stem, leaf. e.g. Potato, Ginger
Regeneration
From body fragments. e.g. Planaria, Bryophyllum leaves
⭐ Vegetative propagation types: Natural (runners, rhizomes, bulbs, tubers) | Artificial (cutting, grafting, layering, tissue culture)
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🌸 Structure of a Flower — Reproductive Organ
Flower is the reproductive organ of angiosperms. A complete flower has 4 whorls:
🟢 Calyx (Sepals)
Outermost whorl. Protects flower bud. Usually green.
🌸 Corolla (Petals)
Colourful to attract pollinators. Inside calyx.
🟡 Androecium (Stamens)
Male reproductive organ. Filament + Anther. Produces pollen.
🟤 Gynoecium (Pistil)
Female reproductive organ. Stigma + Style + Ovary. Contains ovules.
⭐ Bisexual flower = has both androecium and gynoecium (e.g. rose, mustard). Unisexual = only one (e.g. papaya, maize).
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🟡 Microsporogenesis — Formation of Pollen Grains
MicrosporogenesisProcess of formation of microspores (pollen grains) from microspore mother cells (MMC) in the anther by meiosis.
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Anther has 4 microsporangia (pollen sacs)
Each microsporangium is surrounded by: Epidermis → Endothecium → Middle layer → Tapetum (innermost, nourishes pollen)
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MMC undergoes Meiosis
2n Microspore Mother Cell → (meiosis) → 4 haploid microspores (tetrad)
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Microspores separate → Pollen grains
Each pollen grain has 2 layers: Exine (outer, sporopollenin — very resistant) and Intine (inner, cellulose + pectin)
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Pollen grain is mature male gametophyte
Has 2 cells: Vegetative cell (large) + Generative cell (small). Generative cell divides to form 2 male gametes.
⭐ Sporopollenin — most resistant organic material known. Pollen grains preserved as fossils for millions of years. Not degraded by enzymes.
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🌿 Megasporogenesis — Formation of Embryo Sac
MegasporogenesisFormation of megaspores from Megaspore Mother Cell (MMC) in the ovule by meiosis. One megaspore develops into embryo sac (female gametophyte).
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Ovule structure
Funicle → Hilum → Integuments (1 or 2) → Nucellus → Embryo sac. Entry point = Micropyle. Opposite end = Chalaza.
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MMC (2n) → 4 megaspores by meiosis
3 degenerate. 1 functional megaspore (chalazal end) survives.
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Functional megaspore → Embryo sac (3 mitotic divisions)
Results in 7-celled, 8-nucleate embryo sac (Polygonum type — most common)
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7-celled embryo sac composition
3 Antipodal cells (chalazal end) + 2 Synergids + 1 Egg cell (micropylar end) + 1 Central cell (2 polar nuclei)
Embryo Sac — 8 nuclei, 7 cells3 Antipodals + 2 Synergids + 1 Egg cell + 1 Central cell (2 polar nuclei)
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🌬️ Pollination
DefinitionTransfer of pollen grains from anther to stigma of a flower. Precondition for fertilisation.
| Type | Definition | Agent | Example |
|---|
| Autogamy | Pollen → same flower's stigma | Self | Wheat, Rice, Pea |
| Geitonogamy | Pollen → different flower on same plant | Self (genetically) | Maize |
| Xenogamy | Pollen → flower of different plant | Cross pollination | Papaya, Vallisneria |
💨 Anemophily (Wind)
Light, non-sticky pollen. Long filaments. e.g. Maize, Wheat
🐝 Entomophily (Insects)
Sticky/scented pollen. Colourful petals. e.g. Rose, Sunflower
💧 Hydrophily (Water)
Aquatic plants. Pollen on water surface. e.g. Vallisneria
🦅 Ornithophily (Birds)
Nectar-rich. Red/orange flowers. e.g. Bignonia |
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⚡ Double Fertilisation — Unique to Angiosperms
Double FertilisationFusion of one male gamete with egg cell (syngamy) AND fusion of second male gamete with central cell (polar nuclei) — triple fusion. Only in angiosperms.
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Pollen tube formation
Pollen germinates on stigma → pollen tube grows through style → reaches ovule through micropyle
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Syngamy (True fertilisation)
1 male gamete (n) + Egg cell (n) → Zygote (2n) → develops into Embryo
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Triple Fusion
1 male gamete (n) + 2 Polar nuclei (n+n) → Primary Endosperm Nucleus (3n) → develops into Endosperm (nutritive tissue)
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After fertilisation
Ovary → Fruit | Ovule → Seed | Zygote → Embryo | PEN → Endosperm | Integuments → Seed coat (testa + tegmen)
🌟 Double Fertilisation SummarySyngamy: ♂ gamete + Egg → Zygote (2n) → Embryo
Triple fusion: ♂ gamete + Polar nuclei → PEN (3n) → Endosperm
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🌱 Embryo Development & Seed Formation
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Zygote → Proembryo
Zygote divides → suspensor (pushes embryo into endosperm) + embryo proper
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Globular → Heart → Torpedo stage
Embryo develops cotyledons (seed leaves), plumule (shoot tip), radicle (root tip)
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Dicot seed structure
Seed coat (testa + tegmen) + 2 Cotyledons + Embryonal axis (plumule + radicle) + Endosperm (in endospermic seeds)
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Monocot seed structure
1 Cotyledon (scutellum) + Coleoptile (covers plumule) + Coleorhiza (covers radicle) + Large endosperm
| Feature | Dicot seed | Monocot seed |
|---|
| Cotyledons | 2 | 1 (scutellum) |
| Endosperm | Present (castor) or absent (pea) | Always present and large |
| Plumule cover | Absent | Coleoptile |
| Radicle cover | Absent | Coleorhiza |
| Example | Pea, Bean, Castor | Maize, Wheat, Rice |
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🧬 Chapter 2 — Reproduction in Animals
IntroductionAnimals reproduce both sexually and asexually. Higher animals (including humans) reproduce sexually. The chapter covers human reproduction — male and female reproductive systems, gametogenesis, fertilisation and development.
Asexual in Animals
Fission (Amoeba), Budding (Hydra), Regeneration (Planaria), Parthenogenesis (bees, ants)
Sexual Reproduction
Involves male & female gametes. Fertilisation forms zygote. Used by most higher animals.
Oviparous
Lay eggs externally — fish, frogs, birds, reptiles. Embryo develops outside mother's body.
Viviparous
Give birth to young ones — mammals including humans. Internal development.
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♂ Male Reproductive System
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Testes (2)
Located in scrotum (outside body — lower temperature needed for sperm). Produce sperms (spermatogenesis) and testosterone hormone. Each testis has 250+ testicular lobules containing seminiferous tubules.
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Accessory ducts
Rete testis → Vasa efferentia → Epididymis (sperm maturation & storage) → Vas deferens → Ejaculatory duct → Urethra
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Accessory glands
Seminal vesicles (60% semen), Prostate gland (30%, activates sperm), Bulbourethral (Cowper's) glands (lubrication)
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Semen
Sperm + secretions of accessory glands. ~200–300 million sperms/ejaculate. pH slightly alkaline (7.2–7.6).
⭐ Seminiferous tubules lined by: Spermatogonia (sperm-producing cells) + Sertoli cells (nourish developing sperms) + Leydig cells (interstitial cells, produce testosterone).
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🔬 Spermatogenesis — Formation of Sperms
SpermatogenesisProcess of formation of spermatids (then spermatozoa) from spermatogonia in the seminiferous tubules. Begins at puberty.
Spermatogenesis StepsSpermatogonia (2n) → [Mitosis] → Primary spermatocyte (2n) → [Meiosis I] → 2 Secondary spermatocytes (n) → [Meiosis II] → 4 Spermatids (n) → [Spermiogenesis] → 4 Spermatozoa (n)
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Sperm structure (Head → Middle piece → Tail)
Head: Nucleus (haploid DNA) + Acrosome (lysosomal enzymes to penetrate egg)
Middle piece: Mitochondria (energy for movement — ATP)
Tail: Flagellum for motility
⭐ Spermiation = release of sperms from Sertoli cells into the lumen. Spermiogenesis = transformation of spermatids into spermatozoa.
⭐ Normal sperm count = 200–300 million/ejaculate. Less than 20 million/mL = oligospermia. Zero sperm = azoospermia.
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♀ Female Reproductive System
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Ovaries (2)
Primary sex organs. Located in pelvic cavity. Produce ova (oogenesis) and female hormones (estrogen, progesterone). Each ovary has ovarian follicles at different stages.
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Fallopian tubes (Oviducts)
Infundibulum (funnel, has fimbriae to collect egg) → Ampulla (widest, fertilisation occurs here) → Isthmus (joins uterus)
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Uterus (Womb)
Pear-shaped. 3 layers: Perimetrium (outer) → Myometrium (muscular, middle) → Endometrium (inner, site of implantation). Cervix connects to vagina.
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External genitalia
Mons pubis, Labia majora, Labia minora, Clitoris, Hymen, Bartholin's glands (lubrication)
⭐ Fertilisation site = Ampulla of fallopian tube. Implantation site = Endometrium of uterus.
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🔬 Oogenesis — Formation of Ovum
OogenesisProcess of formation of a mature ovum (egg) from oogonia in the ovary. Begins before birth, completes after fertilisation.
Oogenesis StepsOogonia (2n) → [Mitosis] → Primary oocyte (2n) → [Meiosis I] → Secondary oocyte (n) + 1st polar body → [Meiosis II, if fertilised] → Ovum (n) + 2nd polar body
| Feature | Spermatogenesis | Oogenesis |
|---|
| Site | Seminiferous tubules (testis) | Ovarian follicles (ovary) |
| Start | Puberty onwards | Before birth (foetal life) |
| Products | 4 functional sperms | 1 ovum + 3 polar bodies |
| Size of gamete | Small, motile | Large, non-motile |
| Meiosis II completion | Before release | After fertilisation |
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📅 Menstrual Cycle
Menstrual CycleCyclic changes in the female reproductive system occurring approximately every 28 days. Controlled by hormones — GnRH, FSH, LH, Estrogen, Progesterone.
| Phase | Days | Events | Hormones |
|---|
| Menstrual | 1–5 | Shedding of endometrium (bleeding) | Estrogen & Progesterone fall |
| Follicular | 6–13 | Follicle matures, endometrium thickens | FSH → Estrogen rises |
| Ovulation | 14 | LH surge → egg released from ovary | LH peak |
| Luteal | 15–28 | Corpus luteum forms, endometrium prepares for implantation | Progesterone dominant |
⭐ If fertilisation occurs → corpus luteum persists → progesterone maintains pregnancy → no menstruation (amenorrhoea). If no fertilisation → corpus luteum degenerates → menstruation occurs.
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⚡ Fertilisation & Implantation in Humans
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Fertilisation (in ampulla)
Sperm reaches egg. Acrosome reaction releases enzymes to penetrate zona pellucida. Cortical reaction prevents polyspermy. Sperm nucleus + egg nucleus → zygote (2n)
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Cleavage (rapid mitosis)
Zygote → 2 cells (blastomeres) → 4 → 8 → morula (16+ cells, solid ball) → all while moving through fallopian tube
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Blastocyst formation
Morula → Blastocyst (hollow ball): Trophoblast (outer layer) + Inner Cell Mass (embryoblast, becomes embryo) + Blastocoel (fluid-filled cavity)
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Implantation (day 6–7)
Blastocyst attaches to endometrium (uterine wall). Trophoblast invades endometrium. Marks beginning of pregnancy.
TimelineFertilisation (Day 0) → Morula (Day 3) → Blastocyst (Day 5) → Implantation (Day 6–7) → Gastrulation → Organogenesis → Birth (Day ~280)
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🤰 Pregnancy, Placenta & Parturition
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Gastrulation
ICM → 3 germ layers: Ectoderm (skin, nervous system) + Mesoderm (muscles, bones, blood) + Endoderm (gut, lungs, liver)
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Placenta
Disc-shaped organ formed by trophoblast + uterine tissue. Functions: nutrition, respiration, excretion, hormone secretion (hCG, estrogen, progesterone). Connected to foetus by umbilical cord.
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Gestation period
9 months (280 days / 40 weeks) in humans. 1st trimester (1–3 months): organogenesis. 2nd (4–6): rapid growth. 3rd (7–9): full development.
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Parturition (Childbirth)
Triggered by oxytocin (from posterior pituitary). Uterine contractions increase. Foetus expelled. Placenta expelled as afterbirth.
⭐ hCG (human Chorionic Gonadotropin) — secreted by trophoblast → maintains corpus luteum → pregnancy test detects hCG in urine.
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🎯 Exam Important Questions — Ch 1 & 2 Biology
- What is double fertilisation? Why is it unique to angiosperms? Explain its significance. 3 marks
- Draw a labelled diagram of a mature angiosperm embryo sac and describe its formation. 5 marks
- Explain the structure of a pollen grain. What is sporopollenin and why is it significant? 3 marks
- Distinguish between autogamy, geitonogamy and xenogamy with examples. 3 marks
- Describe the process of microsporogenesis with a labelled diagram of T.S. of anther. 5 marks
- Compare dicot and monocot seeds with labelled diagrams. 4 marks
- Describe spermatogenesis. Draw a labelled diagram of human sperm and explain its structure. 5 marks
- Describe oogenesis. How does it differ from spermatogenesis? 4 marks
- Explain the female reproductive system with a labelled diagram. 5 marks
- Describe the menstrual cycle with reference to hormonal regulation. 4 marks
- Explain the process of fertilisation in humans. How is polyspermy prevented? 3 marks
- What is implantation? Describe blastocyst formation and implantation process. 3 marks
- Write the functions of placenta. What is hCG and what is its role? 3 marks
- What is parturition? What role does oxytocin play? 2 marks
- Define: (i) Sporopollenin (ii) Tapetum (iii) Corpus luteum (iv) Acrosome (v) Coleorhiza 5 marks