REPRODUCTION IN ORGANISMS

REPRODUCTION IN ORGANISMS:

Ø LIFE SPAN: Period from birth to a natural death of an organism. Eg. Parrot- 140 years, Crow- 15 years.

Ø REPRODUCTION: Biological Process where an organism give rise to young ones of its own kind.

Ø ASEXUAL Reproduction:  Process in which Offspring (CLONES) is produced by only ONE individual; No involvement of Gametes.

Ø SEXUAL Reproduction: Process in which Offspring (Hybrids) is produced by TWO Parents; Fusion of male female gametes occur.

Ø CLONES: Morphologically & genetically similar individuals. Eg. Mostly Unicellular organisms. sometimes multi cellular too. (Technically any organism produced from single parent cell, remember DOLLY)

Ø Binary Fission: mode of asexual reproduction where an individual divides into two equal halves. Eg. Amoeba.

Ø Budding: Asexual reproduction where an individual divides into two Unequal halves (small buds). Eg. Yeast.

Ø Spores: Special structures for asexual reproduction in FUNGUS: - mostly Zoospores (microscopic motile spores) others include Conidia (non motile exospores eg. Penicillium), some animals also have special structures like Exogenous & Endogenous Buds in Hydra & GEMMULES (mostly for Perrination/ passing adverse conditions) in Sponges.

Ø  VEGITATIVE PROPAGATION-

 Rhizomes (Ginger), eye (potato), bulbils (agave), leaf bud (Bryophillum).

(Rhizome of Ginger)

(Eye in Potato Tuber)

(Bulbils of Agave)

(Leaf of Bryophyllum)

Ø WATER HYACINTH (Terror of Bengal):- Most invasive weed in India (in Standing Water) due to Vegetative Propagation (Stem OFFSETS).was introduced for beautiful flower & shapes of leaves, now a Problem.

(Offsets in Water Hyacinth)

Ø Sexual Reproduction is favoured during Adverse conditions:- As it is a complex & slow process as compared to asexual reproduction, hence needs less energy (which is a point during adverse conditions). 

Moreover, it produces Variations (Hybrids) which provides better suitability & adaptability of genes in the environment.

Ø The form of growth & maturation prior to sexual phase is called JUVINILE/Vegetative Phase.eg. Annuals /biennials. In Perennials inter - flowering period is present. Eg. Bamboo flowers only once in lifetime. Strobilanthus kunthiana (Neelkuranji of famous Nilgiri Hills in South) flowers once in 12 years. (Last in Sept-Oct. 2018).

(Bamboo Flower)

(Neelkuranji in Munnar valley Kerala)

Ø Females of Placental Mammals undergo cyclic changes in Ovarian activities as well as Hormones during reproduction:- OESTRUS CYCLE (Non Primate Mammals/ seasonal breeders) eg.. Cow, sheep, rat. Deer, dog etc.. MENSTRUAL CYCLE (Primate Mammals/ continuous breeders)eg. Human, apes, monkeys.

Ø GAMETOGENESIS: process of formation of reproductive cells (male/female).

(a) Isogametes /Homogametes (when gametes are same. eg. Chlymadomonas, cladophora); 

(b) & (c) Anisogametes/Heterogametes (male gamete is small and motile sperm/antherozoid & female gamete is large and non motile Ovum/Egg).

Ø SEXUALITY IN ORGANISMS: Animals with both sexes are HERMAPHRODITE (earthworm, leech, Tapeworm). Plants are bisexual (Homothallic or Monoecious) & Unisexual (Heterothallic or Dioecious:-Stamenate/Pistillate)

Ø GAMETIC MEIOSIS in Diploids (2n) as Meiocytes (gamete mother cell or Gametogonia) undergoes meiosis. But Haploid parents (n) produce gametes by Mitosis and undergo ZYGOTIC MEIOSIS to produce haploid body.

Ø Chromosomes in MEIOCYTES = 2 X Chromosomes in Gametes; eg. Human meiocyte (46) & Gamete (23).

Ø GAMETE TRANSFER: In simple plants (algae, Bryophytes, Pteridophyta) Water is the medium. Number of male gametes is high to increase the chance factor of fertilization. In Angiosperms (seed Plants) Pollen Grain carry the male gamete & Ovule carry the Female Gamete/Egg.

Ø SYNGAMY (fusion of gametes) results in a diploid Zygote (2n). Fertilization & Syngamy are synonamus.

Ø PARTHENOGENESIS: Formation of organisms without Syngamy/ Fertilization. Eg. Rotifers, Honeybee, Turkey.

Ø ZYGOTE (Fertilized egg) is the first stage of an embryo. Development may be outside the body eg.. egg jelly in water like fish, frog or in Hard calcareous shells (reptiles, birds)- OVIPAROUS DEVELOPMENT (due to External Fertilization) OR development inside the body of females and females give birth to young ones .eg. mammals like human beings (Due to Internal Fertilization) [VIVIPARY]

Iin Angiosperms Zygote is formed inside the ovule. After fertilization Sepals, Petals, Stamens wither and fall while Pistil remains attached to plant (generally). Zygote develops into embryo, Ovules develop into seed, Ovary develops into Fruit with a thick protective wall PERICARP.

REVISION & ADDITIONAL TIPS

ASEXUAL REPRODUCTION

·       LIFE SPAN:- life expectancy eg. Tortoise – 150 yrs.

·       Unicellular organisms – IMMORTAL.

·       May Fly – One Day.

·       ASEXUAL REPRODUCTION (TYPES):-

v  FISSION:-

(1) BINARY=

(a) SIMPLE/ASYMMETRICAL eg. Amoeba

(b) LONGITUDINAL /VERTICAL eg. Euglena; Trypanosoma

 (c) TRANSVERSE/ HORIZONTAL eg. Paramecium, Planaria, Diatoms, Bacteria

 (d) OBLIQUE eg. Dinoflagellata (ceratium)

(2) MULTIPLE= ENCYSTMENT and SPORULATION ( eg. Amoeba); SCHIZOGONY of Merozoites & SPOROGONY of Oocyst (eg. plasmodium)

(3) PLASMOTOMY eg. Multinucleate protozoa like Opalina & Pelomyxa. [In Paramecium, nuclear division: Meganucleus- Amitosis; Micronucleus - Mitosis ]

v  BUDDING(TORULATION):-

(A) INTERNAL BUD:- Gemmules eg. All freshwater & few marine Sponges

(B) EXTERNAL BUD:- Yeast, some Bacteria & Protozoan, Metazoa (some Sponges & Cnidarians)

v  FRAGMENTATION:-

SIMPLE (eg. Spirogyra), GEMMA (eg. Liverworts), FISSIPARITY (eg. Echinodermata)

v  REGENERATION:-

Amoeba (if nuclear material undamaged considerably); Sponges, Planarians.

v  SPORE FORMATION:-  Fungi produces two class of spores (a) SPORANGIOSPORE (ENDOSPORE) eg. Naked, wall less non absorbent, Motile ZOOSPORES  & Non Motile Aplanospore. (b) CONIDIA: (EXOGENOUS) eg. Ascomycetes & Basidiomycetes. Two main types:- Thallic Conidia (at Tip or Intercalary, develop by Septation & Fragmentation of Hyphae); Blastic Conidia (develop as a chain or single spore by Budding/ Swelling process)

v  VEGETATIVE PROPAGATION:-

(A) NATURAL:- 

(1) Roots (Dahlia, Sweet Potato);

(2) Stem-Tuber (eg. Potato), Stem- Bulbs ( eg. Garlic, Daffodils, Onion), Stem-Corms (like Rhizomes eg. Colocasia, Crocus, Freesia), Rhizome (eg. Banana, Ginger, Turmeric), Suckers (eg. Mint, Chrysanthemum), (3) Subaerial/Creeping Stem (RUNNER:- Lawn Grass, Centella; STOLONS:- Straw-Berry, Vallisneria; OFFSETS:- Water Hyacinth, Water Lettuce) [Hyacinth (Eichhornia crassipes )called “Terror of Bengal” derive oxygen from water hence killing aquatic life, it reproduce through offsets, runners, stolons];

(4) Aerial Stems:- Phylloclades of Opuntia

(5) Leaves (Begonia, Bryophyllum,Kalanchoe)

(6) Bulbils (Oxalis, Agave, Pineapple,Yam, Lilly, Chlorophytum)

(7) Turion (overwintering bud in some aquatic plants eg. Utricularia, Potamogeton)

 (B) ARTIFICIAL/Horticultural METHOD:-

(1) CUTTING :- Stem (eg. Rose, Sugarcane, Coleus, Bougainvillea) Root (eg. Dahlia)

(2) LAYERING (eg. Jasmine, Rhododendron, Magnolia):- [The branch developing adventitious roots is called LAYER] Mound Layering (Apple; Gooseberries) Air Layering/ Gootee (Mango)

(3) GRAFTING:- Cutting of plant (scion) attached to rooted plant (stock) eg. Mango

(4) BUD GRAFTING ( T-shaped cut; spring season) eg.  Pear, Peach, Plum, Citrus, rose

 (5) TISSUE CULTURE/MICROPROPAGATION:- in vitro; explants, Callus; eg. Asparagus, Orchids, Chrysanthemum [STEPS:- Selection; Aseptic Culture; Callus Multiplication; Shoot Elongation; Acclimatization]

(Courtesy Google Images for all the images used here)