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DEVELOPMENT OF FROG
β’ Breeding:
Table 1: Breeding in Frog
Point | Detail |
|---|---|
Season | Rainy season β June to September |
Place | Water |
Male mating call | Croaking sound by vocal sacs |
Amplexus | Sexual embrace of male + female frog / false copulation |
Purpose of amplexus | Simultaneous discharge of male + female gametes at same place in water |
β’ Ovulation:
- β’Release of eggs from ovary into body cavity
- β’Eggs released as secondary oocytes
- β’Occurs by rupture of ovary
β’ Spawning:
Table 1: Spawning
Term | Meaning |
|---|---|
Spawning | Laying of eggs by female frog; stimulated by male during amplexus |
Spawn | Cluster / mass of eggs laid by female |
β Egg Covering:
- β’Thin vitelline membrane
- β’3 jelly coats made of gelatin
- β’Gelatin β protects egg from predators
- β’Gelatin β insulation / warmth
β’ Structure of Frog Egg:
Table 1: Frog Egg
Feature | Point |
|---|---|
Yolk amount | Mesolecithal |
Yolk distribution | Telolecithal |
Animal hemisphere | Upper pigmented part |
Vegetal hemisphere | Lower unpigmented part |
Animal pole | Cytoplasm concentrated |
Vegetal pole | Yolk-rich; directed downward |
β Developmental Sequence:
- Fertilization
- Cleavage
- Morula
- Blastula
- Gastrula
- Neurula
- Tadpole
- Adult frog
β’ Fertilization:
β Type: External fertilization in water
β Key Points:
- β’Sperms released on egg mass before it reaches water
- β’Second meiotic division occurs after sperm entry
- β’Sperm enters through animal hemisphere
β Grey Crescent:
Table 1: Grey Crescent
Feature | Point |
|---|---|
Position | Equatorial zone opposite to sperm entry |
Importance | Marks dorsal side of future embryo |
β Sperm Entry Point:
- β’Marks anterior side of future embryo
- β’Establishes bilateral organization
- β’Region called reception cone
β’ Cleavage:
β Definition: Early mitotic divisions of zygote up to blastula stage
β Nature:
- β’Holoblastic
- β’Unequal after 3rd cleavage
- β’Indeterminate / regulative development
β Stages:
Table 1: Cleavage in Frog
Cleavage | Plane / Type | Result |
|---|---|---|
1st cleavage | Meridional, holoblastic, equal | 2 blastomeres β right + left |
2nd cleavage | Meridional, holoblastic, equal | 4 blastomeres; grey crescent in 2 dorsal blastomeres |
3rd cleavage | Horizontal / latitudinal; above equator; holoblastic unequal | 8 blastomeres β 4 micromeres + 4 macromeres |
4th cleavage | Two synchronous meridional divisions | 16 blastomeres |
5th cleavage | Two simultaneous latitudinal divisions | 32 blastomeres |
6th cleavage | Irregular + asynchronous | Micromeres divide faster than macromeres |
7th cleavage | Irregular divisions | Morula |
β Blastomeres after 3rd Cleavage:
Table 1: Micromeres vs Macromeres
Blastomere | Position | Features |
|---|---|---|
Micromeres | Upper 4 cells | Smaller, pigmented, no yolk |
Macromeres | Lower 4 cells | Larger, non-pigmented, yolk-laden |
β Morula: Solid mulberry-shaped ball of cells
β Blastula:
- β’Blastocoel appears toward animal hemisphere
- β’Frog blastula = coeloblastula
- β’Blastocoel contains albuminous fluid secreted by surrounding cells
β’ Gastrulation:
β Definition: Conversion of blastula into 3-layered gastrula with archenteron
β Germ Layers:
- β’Ectoderm
- β’Mesoderm
- β’Endoderm
β Gastrulation Movements:
Table 1: Movements in Frog Gastrulation
Movement | Meaning / Event |
|---|---|
Epiboly | Migration + spreading of micromeres over embryo |
Invagination | Infolding below equator under grey crescent midpoint β slit + blastopore |
Involution | Chordamesoderm cells sink inward + move anteriorly along blastocoel roof |
Ingression | Individual vegetal cells migrate into embryo interior |
β Involution Importance: Failure of involution β gastrulation stops β development halts
β Cavities / Openings:
Table 1: Gastrula Structures
Structure | Meaning / Fate |
|---|---|
Archenteron | Future gut cavity |
Blastopore | Opens into archenteron; gives rise to anus in frog |
Yolk plug | Endodermal plug closing blastopore |
β End of Gastrulation:
- β’Blastocoel reduces
- β’Yolk plug closes blastopore
- β’Yolk plug side β posterior side of future tadpole
β’ Neurula:
Table 1: Neurulation
Process / Formation | Point |
|---|---|
Neurulation | Occurs after gastrulation |
Neural tube | Formed from ectoderm |
Notochord / Notogenesis | Notochord formation |
Gut | Formed from archenteron / endodermal region |
β’ Metamorphosis:
β Hormone: Thyroxine from thyroid gland initiates metamorphosis
β Tadpole Nature: Herbivorous
β Influencing Factors:
Table 1: Factors Affecting Metamorphosis
Factor | Effect |
|---|---|
Food abundance | Delays metamorphosis |
Food deficiency | Favours metamorphosis |
β Changes:
- Feeding stops; tail stores provide nutrition
- Tail shortens
- Larval epidermis lost
- Horny jaws lost
- Skin glands develop
- Lungs become functional
- Gill clefts close
- Blood vascular system modified
- True jaws formed
- Eyes move to top + bulge
- Tongue enlarges
- Intestine shortens
- Stomach + liver enlarge
- Forelimbs develop
- Young frog leaves water
- Feeds + grows
- Remaining tail disappears
β’ High-Yield Recall:
Table 1: Frog Development One-Liners
Fact | Answer |
|---|---|
Frog breeding season | Rainy season / JuneβSeptember |
Mating call | Croaking by vocal sacs |
False copulation | Amplexus |
Amplexus purpose | Simultaneous gamete discharge |
Ovulation | Egg release from ovary into body cavity |
Spawning | Egg laying by female frog |
Spawn | Cluster / mass of eggs |
Frog egg yolk amount | Mesolecithal |
Frog egg yolk distribution | Telolecithal |
Animal hemisphere | Upper pigmented part |
Vegetal hemisphere | Lower unpigmented yolk-rich part |
Fertilization in frog | External in water |
Sperm entry | Animal hemisphere |
Grey crescent | Opposite sperm entry; future dorsal side |
Sperm entry point | Future anterior side |
Reception cone | Sperm entry region |
1st cleavage | Meridional, holoblastic, equal |
2nd cleavage | Meridional, holoblastic, equal |
3rd cleavage | Horizontal / latitudinal, unequal |
32-cell stage | After 5th cleavage |
Morula | Solid mulberry-like ball |
Frog blastula | Coeloblastula |
Blastocoel position | Toward animal hemisphere |
Gastrulation | 3 germ-layer formation |
Archenteron | Future gut cavity |
Blastopore fate in frog | Anus |
Yolk plug | Endodermal; closes blastopore |
Yolk plug side | Future posterior side |
Neurulation | Neural tube formation |
Metamorphosis hormone | Thyroxine |
Tadpole diet | Herbivorous |