Modes of Reproduction
Reproduction is the biological process by which living organisms generate offspring of their own kind, ensuring species continuity across generations.
1. Asexual Reproduction:
Involves a single parent without gamete formation or fertilisation. Offspring are genetically identical clones.
- Binary Fission: Parent cell divides into two equal daughter cells (Amoeba divides along any plane; Leishmania divides along a definite longitudinal plane).
- Multiple Fission: Parent cell divides inside a cyst into numerous daughter cells simultaneously (Plasmodium).
- Budding: Outgrowth arises from repeated cell division at one specific site, develops into tiny individual and detaches (Hydra, Yeast).
- Spore Formation: Spores contained in sporangia with thick protective walls germinate upon landing on moist surfaces (Rhizopus bread mold).
- Vegetative Propagation: New plants generated from vegetative parts (roots, stems, leaves):
- By Leaves: Adventitious buds in leaf notches of Bryophyllum.
- Artificial Methods: Cutting (Rose), Layering (Jasmine), Grafting (Mango).
Sexual Reproduction in Flowering Plants (Angiosperms)
A flower is the reproductive unit of an angiosperm plant.
Stamen (Male Organ) ---> Anther (Pollen Grains) + Filament
Carpel (Female Organ) ---> Stigma (Pollen Reception) + Style + Ovary (Ovules / Egg Cell)Pollination & Double Fertilisation:
- Pollination: Transfer of pollen grains from anther to stigma (Self-pollination or Cross-pollination via wind, water, insects).
- Pollen Tube Growth: Pollen grain germinates on stigma, sending a pollen tube through style to the ovule inside ovary.
- Syngamy: One male gamete fuses with female egg cell to form a diploid Zygote ($2n$).
- Triple Fusion: Second male gamete fuses with two polar nuclei to form triploid Endosperm ($3n$) providing nourishment.
- Post-Fertilisation Changes:
- Zygote $\rightarrow$ Embryo
- Ovule $\rightarrow$ Tough seed coat and seed
- Ovary $\rightarrow$ Ripens and enlarges into Fruit
Human Reproductive Systems
Male Reproductive System:
- Testes: Located outside abdominal cavity in scrotum because sperm formation requires a temperature $2 - 2.5^\circ\text{C}$ lower than normal internal body temperature. Produce sperms and testosterone.
- Vas Deferens: Transports mature sperm from epididymis towards urethra.
- Accessory Glands: Seminal Vesicles and Prostate Gland secrete alkaline fluid rich in fructose that provides nutrition and mobility to sperm.
Female Reproductive System:
- Ovaries: Produce female gamete (ovum) and hormones estrogen/progesterone. One egg is released every month by one of the ovaries.
- Fallopian Tube (Oviduct): Site of fertilisation where sperm meets ovum.
- Uterus (Womb): Elastic muscular structure where embryo implants into thickened vascular endometrial wall.
- Placenta: Disc-like vascular organ embedded in uterine wall containing villi on embryo side. Provides large surface area for glucose and oxygen transfer from mother to child and removes embryo metabolic wastes.
