STUDY NOTES

CHAPTER – REPRODUCTION (CHSE BIOLOGY)

CLASS 12 BIOLOGY

 

1. Definition

Reproduction = process by which living organisms produce offspring → continuity of species.

2. Types of Reproduction

(1) Asexual – one parent, no gametes (2) Sexual – two parents, gamete fusion, variation

ASEXUAL REPRODUCTION

Binary fission → Amoeba

Budding → Hydra, Yeast

Fragmentation → Spirogyra

Vegetative propagation:

Stem tuber → Potato

Rhizome → Ginger

Bulb → Onion

Leaf buds → Bryophyllum

Features: Fast ✔ No variation ✘ Single parent ✔

SEXUAL REPRODUCTION

Involves male + female gametes

Three stages:

Pre-fertilization (gametogenesis + gamete transfer)

Fertilization (syngamy)

Post-fertilization (zygote → embryo)

FLOWERING PLANTS (ANGIOSPERMS)

Parts of Flower

Stamen (male) Carpel (female) Anther → pollen Ovary → ovule → embryo sac

Microsporogenesis

MMC (2n) ↓ meiosis Microspores (n) → pollen grains

Megasporogenesis

Megaspore mother cell ↓ meiosis 1 functional megaspore

Embryo Sac (7-celled, 8-nucleate)

(Antipodals) o o o
|
Synergid ○ Egg ○
|
(Polar nuclei)

Egg – 1 Synergids – 2 Polar nuclei – 2 Antipodals – 3

Pollination

Self-pollination – same flower/plant Cross-pollination – different plant

Agents: wind, insect, water

Double Fertilization

Unique to angiosperms ✔

Male gamete + egg → Zygote (2n)

Male gamete + 2 polar nuclei → Endosperm (3n)

RESULT: Zygote → Embryo Endosperm → food storage

Fruit & Seed

Ovary → fruit Ovule → seed Endosperm nourishes embryo

HUMAN REPRODUCTION

Male Reproductive System

Testis: sperm + testosterone Epididymis: storage & maturation Vas deferens: transport Seminal vesicle: fructose Prostate: alkaline secretion Cowper’s gland: lubrication Penis: copulation

Female Reproductive System

Ovary: ovum + hormones Fallopian tube: fertilization site Uterus: implantation Cervix: opening Vagina: birth canal Mammary glands: milk

Gametogenesis

Spermatogenesis (in testes)

Spermatogonia → Primary spermocyte → Spermatids → Spermatozoa Hormones: FSH, LH, Testosterone

Oogenesis (in ovary)

Oogonia → Primary oocyte (arrested in Prophase-I) At puberty: Primary oocyte → Secondary oocyte + polar body Meiosis II completes only after fertilization

Menstrual Cycle (28 Days)

Day 1–5 → Menstruation Day 6–13 → Follicular phase Day 14 → Ovulation (LH surge) Day 15–28 → Luteal phase (Progesterone ↑)

Fertilization → Implantation → Pregnancy

Fertilization

Occurs in ampullary-isthmic junction Sperm + ovum → Zygote

Implantation

On 7th day Blastocyst attaches to uterus

Placenta – Functions

Nutrition Respiration Excretion Hormones → hCG, Progesterone, Estrogen Immunity (IgG)

Lactation

Prolactin → milk production Oxytocin → milk ejection Colostrum → antibodies (IgA)

Parturition

Induced by oxytocin

3 stages:

Dilation

Delivery

Afterbirth

Birth Control Methods

Natural: safe period, withdrawal Barrier: condoms Hormonal: pills Surgical: vasectomy, tubectomy

ART Techniques

IVF (test tube baby) GIFT ZIFT ICSI Artificial insemination