REPRODUCTION IN ORGANISMS: Key Points

Life Span: Period frm birth to natural death

Life span not related to size (e.g. mango – short; peepal – long)

Reproduction significance: Continuity of species

Factors on which mode of reproduction depends:  habitat, internal physiology etc.

Cell div mode of rep in unicellular org.

In favourable condition – Binary fission: In amoeba & paramecium (two equal halves) In Unfav conditions: Encystation & Sporulation (formation of minute Amoeba or Pseudopodiospores)

Budding: yeast (2 unequal halves)

In Fungi & Algae: Asexual rep through spores: Types: Zoospores – motile; zygospores – non motile Conidia – in Penicillium; Gemmules – in Sponges Fragmentation – Hydra

Water Hyacinth (terror of Bengal), high rate of veg propagation.

Veg propagules: Potato: Buds (eyes), Banana & Ginger: Rhizome;  Bryophyllum: Adventitious buds on leaf margins…… Key feature: NODE

In simple org: asexual rep in fav conditions; sexual in unfav (provides variations, enables protection by hard seed coat) In higher org: sexual rep common, asex rare. In animals only sexual

Sexual Rep: Elaborate, Complex & Slow. Offspring not identical to parents

Common pattern of sexual rep: Complete juvenile/vegetative (in plants) phase Beginning of rep phase (flowering in plants) senescent phase Length of the 3 phases variable in different organisms Hormones responsible for transition between 3 phases. Unique: Bamboo perennial but flowering once in lifetime Strobilanthus kunthiana once in 12 yrs.

Animals: e.g. birds seasonal breeders in nature (in captivity; exploited) Placental Mammals: Cyclical changes in ovaries & Hormones Non primate mammals: Oestrous Cycle Primate mammals: Menstrual cycle

Events: Pre-fertilization, Fertilization & Post fertilization

Gametogenesis: Male & Female, haploid, may be homogametes (isogametes) or heterogametes. Male: antherozoid or sperm; female: egg or ovum

Sexuality in plants: Unisexual/Dioecious/Heterothallic e.g. papaya, date palm OR Bisexual/Monoecious/Homothallic Male: staminate; Female: Pistillate If make and female flower on different plants: dioecious If male & female flower on same plant: Monoecious

Sexuality in animals: Bisexual (Hermaphrodite): Earthworm, Sponges, tapeworm & leech Unisexual: Rest

Gamete Formation: Haploid Parents body may be haploid: e.g. fungi, algae, Bryophytes. Produce gametes by mitosis Diploid: e.g. pteridophytes, Gymnosperms, Angiosperms and all animals. Produce gametes by Meiosis

Site of meiosis in diploid organisms: Meiocytes (gamete mother cells)

Gamete Transfer: organisms where both male & female gametes: fungi & Algae To compensate for loss during transfer, male gametes produced in large numbers.

In bisexual flowers – self fertilization In unisexual flowers – cross fertilization, so pollination important.

Fertilisation/ Syngamy: Dev of new organisms without fertilization : Parthenogenesis Seen in Rotifers, Honeybees & some Lizards. Site of Fertilization: Outside (External), Inside mother’s body (Internal) fertilization. Disadvantages of Ext Fertilization: Gametes can be destroyed by predators. Technique to avoid this – large number of gametes released.

Post Fertilization Events: Formed in medium (external fert)/ In Mother’s body (Int Fert) Types of development; Undergoes period of rest- fungi & Algae  (develops thick wall to protect from desiccation and damage) Undergoes Meiosis – Haplontic life cycle – forms haploid spores Forms embryo

Embryogenesis: Zygote                  Cell Division & Cell Differentiation                                                         Embryo Oviparous vs Viviparous Parts of flower after fertilization: Petals: wither & fall Sepals: Wither and Fall (Exception- Brinjal, Tomato) Pistil: Remains attached Stamen: wither & Fall Ovary: Fruit (Wall of fruit – Pericarp)

And now some questions:

1. Why unicellular organisms are considered immortal?
2. Why progeny of asexual reproduction called Clones?
3. What are vegetative Propagules?
4. Characterize: Veg, rep & senescent phase in annual, biennial & Perennials
5. Differentiate: Seasonal & Continuous Breeders