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Sexual reproduction involves the fusion of motile (male) and stationary (female) gametes. Asexual reproduction involves reproduction of organisms from

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Sexual reproduction involves the fusion of motile (male) and stationary (female) gametes.Asexual reproduction involves reproduction of organisms from parts or the whole parent body form

Advantages and disadvantages of metamorphosis

Advantages include: less competition between young and parents (more food, shelter, etc. is available); young raised in a more hospitable environment; young face different predator pressures than adults; protected even if one habitat become inhospitable; adults unable to cannibalize young; and greater specialization for each life stage.

Disadvantages include: little parental protection for young; difficulty in finding appropriate, unpolluted, adjacent habitats; and possibility of accidentally mating with close relative.


COURTSHIPDefinition :Rituals and actions performed to attract the mate.Courtship rituals include the following actions; Displaying beauty e.g. male peacock feathersFighting skills, e.g. lions, elephants Performing intricate dances, touching or vocalisation e.g. fiddler crabBringing food e.g. Pels fishing owl

Performing intricate dances

Displaying beauty e.g. male peacock feathers

Courtship rituals

Courtship rituals INTERNAL FERTILISATION The sperm cell from the male is transferred into the female by copulation (sexual intercourse).The sperm cell then fuses with the egg cell inside the body of the female. Examples : terrestrial mammals, birds, and insects.Advantages :Ensures that the sperm cell comes into contact with the egg Protected from predatorsRemoved from harsh environmentsDisadvantages : Fewer eggs are produced .The animal must have an organ to insert the sperm cells.

Internal FertilizationTerrestrial vertebrates clasp each other tightly during copulation, the act by which the male deposits his sperm into the females reproductive tract. For the giant Galpagos tortoises pictured here, mating may take hours and is initiated by the male, who bangs his shell against that of the female to get her attention. These animals mate in the spring.

EXTERNAL FERTILISATIONThe sperm cell fuses with the egg cell outside the body of the female.The sperm cells are discharged (released) directly into water.Examples are aquatic animals like frogs, sponges, jellyfish, worms and fishAdvantages :No additional energy is needed for parental care or formation of a protective layer.No need for a male to have a special organ to insert the sperm into the females body.Chances of fertilisation are enhanced by courtship display by fish.Does not need much energy.Disadvantages :Chances are very slim for a sperm cell to meet the egg of same species.

A mass of amphibian eggs, appearing as small black spots, is contained within a gelatinous mass while they incubate in a freshwater pond. Eggs deposited in this fashion receive little or no parental protection and will soon hatch into small, wriggling tadpoles.

Shark Egg Case with Embryos These two dogfish egg cases show the developing embryos inside. Each egg case contains enough yolk to sustain the nutritional needs of the embryo until it hatches. The outer covering of the egg case is a tough, horny material. Each of the corners of the egg case is drawn out into a long coiled filament, or tendril, that wraps around rocks, kelps, or other materials on the sea floor, preventing the egg case from being carried away by currents and exposed to possible predation TYPES OF REPRODUCTIONOVIPARITY /EGG-LAYINGRefers to egg laying animalsEggs are protected by a hard shell , while others are protected by a jelly like layer after fertilisation.Development does not occur inside the bodyThe development of an organism is completed inside the egg after it has been laidExamples: Frogs, insects, birds, and marine mammalsAdvantages :Eggs and sperm cells are produced in large numbers to increase chances of survival to adulthood.Much energy is invested for parental care.Parental care ensures survival to adulthood. Disadvantages:Mortality rate is high.

OVOVIVIPARITYRefers to animals that do not lay eggs , but keep them in their bodies until they hatch.The body temperature is necessary for them to hatch.There is no connection between the embryo and the mother.Examples : Sharks , lizards cockroaches and some snakesADVANTAGES :The young one is protected from cold and predators to ensure survivalThe young one can develop to a fairly large size before birth

Common LizardThe common lizard is the most northerly occurring lizard and can be found within the Arctic circle. It does not lay eggs but gives birth to fully formed youngVIVIPARITYRefers to animals that give birth to live young ones.There is a connection between the developing foetus and the mother.Examples : Human beings, whales and kangaroos.Advantages :The temperature is regulated by the motherThe mother provides nutrition for the young oneMortality rate is lowerDisadvantages :Number of off springs produced is few. More energy is used to provide parental care.

A placental mammal, the female cat gives birth to young that have developed inside its body. Nine weeks after fertilization, hormones stimulate the cats uterus to contract and expel the kittens. Here, one kitten has already been born. The next can be seen emerging from the birth canal of the mother, shrouded in the amniotic sac that encloses each developing kitten in the womb. When the membrane breaks, the young animal takes its first breath of air. The mother licks the newborn kitten clean and dry and chews through the umbilical cord still connecting it to the placenta. Another kitten is born within half an hour, by which time the first two, blind but not helpless, have smelled and felt their way to their mothers belly to begin feeding. The placenta, or afterbirth, follows the last kitten.

AMNIOTIC EGGThis is the egg laid by reptiles, birds and some mammals.The embryo develops inside the amnion and is protected by many membranes and hard shell.Amniotic fluid protects the embryo from drying out. It feeds from the yolk.The allantois removes metabolic wastes.The chorion supplies oxygen, food and water.Advantages :They are resistant to drynessOviporous mammals can move to environmentsIs protected by a number of membranes.This complicated structure can allow animals to evolve into bigger forms, and better protect themselves.

Amniotic EggA critical evolutionary development for terrestrial animals is the reptilian amniotic egg, now also characteristic of birds and some mammals. The developing embryo, protected from drying out, can survive out of water and in a variety of habitats. The yolk provides it with food, and the albumen supplies water and nutrients. Wastes are released to the allantois, an extension of the embryonic gut. Oxygen diffuses easily through the thin outer shell of the egg; its passage to the embryo is regulated by the chorion.TYPES OF DEVELOPMENTSPRECOCIAL DEVELOPMENTYoung ones are relatively mature and are able to move around after they are born or hatch.

Their eyes are open, and have good eyesightThey can go out to search food for themselves. Have strong skeleton, and their body is either covered by feathers (birds) or hair(mammals).Birds need their parents to keep them warm, but this lasts for a short period.Mammals can regulate their body temperature. Examples : birds, cattle, sheep, antelopes, buffalo, elephants, hippos and giraffe.

Snake Giving BirthMost snakes hatch from eggs that have been laid outside the mother's body, but among some snake species, females bear live young, as shown here. This method of reproduction may be beneficial to snakes that live in cold climates, because the pregnant female can bask in the sun to keep her developing offspring warm.ALTRICIAL DEVELOPMENTYoung ones are unable to move after birth and are helpless.They do not have feathers (birds) and blind.They need to be fed and kept warm.

Helpless at BirthAlthough this two-month-old parma wallaby joey successfully completed a blind journey from its mothers birth canal to her pouch without help, it would not survive without her.

PARENTAL CARERefers to looking after young ones through feeding, keeping them warm, protecting them from the predators.Such animals give rise to few offsprings

Metamorphosisbiological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's form or structure through cell growth and differentiation.Metamorphosis usually proceeds in distinct stages, starting with larva or nymph, optionally passing through pupa, and ending as adult

Because development is not the same in all insects, it is convenient to group them into major categories according to the pattern of structural changes: complete and incomplete metamorphosis

Complete metamorphosis is characteristic of beetles, butterflies and moths, flies, and wasps. Their life cycle includes four stages: egg, larva, pupa , and adult. The larva differs greatly from the adult. It is wingless, and its form and habits are suited for growth and development rather than reproduction


In insects (e.g., grasshoppers, termites, true bugs) there is a incomplete metamorphosis that consists of an egg, nymph, and adult. The nymph, or immature insect, resembles the adult in form and eating habits, differing in size, body proportions, and colour pattern

.Advantages and disadvantages of metamorphosis Advantages include: less competition between young and parents (more food, shelter, etc. is available); young raised in a more hospitable environment; young face different predator pressures than adults; protected even if one habitat become inhospitable; adults unable to cannibalize young; and greater specializat

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