XII
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Chapter 1: Reproduction In
Organisms
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QUESTIONS
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NOTES
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Life Span: Period frm birth to natural death
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Why unicellular org immortal?
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Life span not related to size (e.g. mango – short; peepal
– long)
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Reproduction significance: Continuity of species
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Sexual vs asexual rep
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Factors on which mode of reproduction depends: habitat,
internal physiology etc.
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Y asexual rep progeny k/a clones?
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Cell div mode of rep in unicellular org.
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In favourable condition - Binary fission: In amoeba &
paramecium (two equal halves)
In Unfav conditions: Encystation & Sporulation
(formation of minute Amoeba or Pseudopodiospores)
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Budding: yeast (2 unequal halves)
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Asexual vs vegetative
What are veg. Propagules?
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In Fungi & Algae: Asexual rep through spores:
Types:
Zoospores – motile; zygospores – non motile
Conidia – in Penicillium; Gemmules – in Sponges
Fragmentation – Hydra
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Water Hyacinth (terror of Bengal), high rate of veg
propagation.
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Veg propagules: Potato: Buds (eyes), Banana & Ginger:
Rhizome; Bryophyllum: Adventitious
buds on leaf margins…… Key feature: NODE
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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
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Sexual Rep: Elaborate, Complex & Slow.
Offspring not identical to parents
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Veg, rep & senescent phase in annual, biennial &
Perennials
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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.
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Seasonal Breeders vs Continuous breeders.
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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
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Gametogenesis: Male & Female, haploid, may be homogametes
(isogametes) or heterogametes.
Male: antherozoid or sperm; female: egg or ovum
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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
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Sexuality in animals:
Bisexual (Hermaphrodite): Earthworm, Sponges, tapeworm
& leech
Unisexual: Rest
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Gamete Formation: Haploid
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