Biology Notes of 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.
• 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 reffered to as being in “heat” at a specific time of Oestrus cycle. They reabsorbs the endometrium if conception does not occur.

Asexual Reproduction

1. Binary Fission (in single celled organism) – eg- amoeba, paramecium
2. In algae, fungi and multicellular lower organisms. (Multiple Fission: e.g. Plasmodium)

   >> Zoospore e.g. Chalamydomonas

   >> Conidia e.g. Penicillium

   >> Bud e.g. Hydra Offset

   >> Gemmules e.g. Sponge

   >> Fragmentation e.g. Spirogyra

   >> Sporulation e.g. Amoeba, Paramoecium

   >> Regeneration e.g. Hydra, Planaria

3. Vegetative propagation

   >> Runner e.g. Oxalis

   >> Rhizome e.g. Ginger

   >> Sucker e.g. Banana

   >> Offset e.g. Water hyacinth

   >> Bulb e.g. Onion

   >> Leaf buds e.g. Bryophyllum

   >> Bulbil e.g. Agave

   >> Eye buds e.g. Potato

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 brust 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

• 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