CLASS 12TH BIOLOGY CHAPTER- 1 REPRODUCTION IN ORGANISMS NCERT QUICK REVISION NOTES FOR NEET AND CBSE EXAM
CHAPTER 1: REPRODUCTION IN ORGANISMS
Clone : Morphologically and genetically similar individuals. Juvenile Phase: It is the period of growth and maturity before an organism can reproduce sexually.
Reproduction - a characteristic feature of all organisms for continuation of species: modes of reproduction-asexual and sexual reproduction; asexual reproduction binary fission, sporulation, budding, gemmule formation, fragmentation; vegetative propagation in plants.
Meiocytes: These are specialized cells of diploid organisms which undergo meiosis to produce gametes.
Pericarp: It is the protective coverning of fruit, may be divided into epicarp. mesocarp and endocarp.
Parthenogenesis: Development of an egg into an embryo without fertilisation. e.g. in rotifers, honeybees, turkey and some lizards.
Monoecious Plants: Plants having both male and female flowers on same plant. e.g. cucurbits and coconut. The term 'homothallic" is used in Fungi for same condition.
Dioecious Plants: Plants having male and female flowers on separate plant. e.g. Papaya and date palm. The term "heterothallic" is used in fungi for the same condition.
Oestrus Cycle: The reproductive cycle in non-primate mammals like cows. sheep, rats, deer, dogs and tigers etc;. The sexually active females referred to as being in "heat' at a specific time of Oestrus cycle. They reabsorb the endometrium if conception does not occur.
ASEXUAL REPRODUCTION
¶ In single celled organisms:
• Binary fission
e.g. Amoeba, Paramecium
• Multiple fission
e.g. Plasmodium
¶ In algac, fungi and multicellular lower animals
• Zoospores in Chlamydomonas
• Conidia in Penicillium
• Budding in Hydra
• Gemmules in Sponges
• Fragmentation in Spirogyra
• Sporulation in Amoeba
• Regeneration in Hydra and Planaria
¶ Vegetative Propagation
• Runner in Oxalis
• Rhizome in Ginger
• Sucker in Mint
• Bulb in Onion
• Bulbil in Agave
• Leaf buds in Bryophyllum
• Buds in Eye of Potato
• Offset in Water hyacinth
GAMETE TRANSFER
1. In Algae, Bryophytes and Pteridophytes: The male and female gametes are flagellated and motile, need a medium (water) to reach to egg.
2. In seeded plants: Pollen grains are transferred to stigma of flower of same species by various agents, like wind, water, insects, birds and ants etc.
3. In animals:
(a) By Copulation: e.g., Reptiles, Birds and Mammals.
(b) By External medium: e.g., Fishes and Amphibians.
Sporulation : During unfavourable conditions organisms like Amoeba surrounded by resistant coat (three layered-hard covering) or cyst. This is called encystation. Within cyst a number of spores are formed. On returning favourable conditions, the cyst burst and spores are liberated and gradually grows in adults. This process is known as sporulation (multiple fission).
Fragmentation : It is a type of asexual reproduction where an organism splits into fragments. Their fragments develops into fully grown individual. e.g. spirogyra, fungi and some annelids.
Regeneration : It is a process of renewal, restoration and growth. It can occur at the level of the cell, tissue and organ. It is common in Hydra, Planaria and echinoderms.
echinoderms
¶ In human, liver has power of regeneration, if it is partially damaged.
¶ During danger a lizard discard a part of its tail which can regenerate later.
EVENTS IN SEXUAL REPRODUCTION
¶ Pre-fertilisation
Events Gametogenesis Gamete Transfer
¶ Fertilisation
External Fertilisation Internal Fertilisation
¶ Post Fertilisation
Events The zygote formation Embryogenesis
ASEXUAL REPRODUCTION
(i) Fusion of gametes is not involved.
(ii) Single parent involved, so mating not required.
(iii) Offspring produced are genetically similar, so no variation occurs.
SEXUAL REPRODUCTION
(i) Fusion of gamates in involved.
(ii) Two parents involved (biparental). so mating is required.
(iii) Offsrping produced are genetically different, so variation occurs.
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